Best engine oil for the RX8 231?

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Re: Best engine oil for the RX8 231?

Post by 13Black »

Regarding taking 10w40 on faith:

5w30 was specified (for allegedly dodgy reasons) and used en mass.
We experienced loads of bearing failures.
... you'd have to try really hard to convince me that this was because the oil was too thick.
Seems only logical that a step in the 10w40 direct can't make it worse.

What kind of hugely expensive, thorough testing does one need to be absolutely bet-your-house-sure that it's better? It's not going to happen either way, so it's a decision you're going to need a little faith with - no different to taking Mazda's 'default' recommendation really.


Edit: o dam I appear to have just missed out Pete's post and may have just been reciting roughly what he's saying, unknowingly.
Now I look like a copy&paste merchant.

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Re: Best engine oil for the RX8 231?

Post by bigpete8 »

PeteH wrote:
Wed Sep 26, 2018 1:49 pm
bigpete8 wrote:
Wed Sep 26, 2018 1:30 pm
Yet everyone seems happy to take it on faith that a 10w does less harm than the manufacturer specified 5w??
Nope. I'm saying nobody knows. But we all have to put something in our engines....

Manufacturers will almost always specify 5W or 0W if the engine is used in very cold climates. I don't use my engine in arctic conditions, and I'm not bothered about fuel consumption. So I make my decision on whether to follow Mazda's recommendations based on my specific usage (note I'm not advocating anything, and I haven't said what I use).
I would imagine that dedicated track usage has its own specific requirements. :)

I suspect that the low temperate grading of the oil is not specifically limited to how viscous it is at the lowest end of its recommended range but also to how viscous it is at all cold starting temperatures.

Nick - I'm not arguing against going 10W40 my point is that it has also increased further the viscosity at low temperature. (so why not 5w40?)
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Re: Best engine oil for the RX8 231?

Post by RobinPZ72 »

Hey all good!
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Re: Best engine oil for the RX8 231?

Post by 13Black »

Correcc - and like Pete says, we mere single entity mortals without the millions of R&D budgets that companies have (that still clearly get it wrong) cannot give any good answer.

5w40
10w40
15w40

Any of them, probably quite dandy. No one knows. No all brands are created equally either. Minefield.

Is the wear because of the 5 or the 30? Or both? Or neither? Nooooobody truly knows.

Does 10w40 generally seem to work well? Seems to.

Is it worth debating 10w40 vs 15w40? Not with current information. It will probably make such little difference that other factors are more worth worrying about, like regular changes whatever you use.
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Re: Best engine oil for the RX8 231?

Post by Ainmhidh »

13Black wrote:
Wed Sep 26, 2018 2:21 pm
...I have some of my own ideas I promise.
Like butter and jam are not friends on toast. You use one or the other you heathen. Why not just go mad and add BBQ sauce as well and fully appease your wayward taste buds.
Next you'll be telling me butter doesn't go on a cream tea either! :roll:
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Re: Best engine oil for the RX8 231?

Post by 13Black »

I fear I'm too working class to understand the question.
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Re: Best engine oil for the RX8 231?

Post by RobinPZ72 »

Very sorry for bringing up the W factor everyone!

Been playing with engines since I was 5yrs and remember my dad with his Ro80 in bits as if it was yesterday!

Dan don't worry about the knewbie bashing comment it was a bit of fun!

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Re: Best engine oil for the RX8 231?

Post by RenesisRaceBuggy »

PeteH wrote:
Wed Sep 26, 2018 1:08 pm
0 is better than 10 isn't a logical argument. Nobody knows if 0W oil provides enough protection to a cold rex engine.

Your argument simply says that all car manufacturers should use 0W-60 oil because that's always got the "best" cold and hot performance. That's just not how oils work. Putting 0W oil in a rex could be far too thin for when the engine internals are cold, and the bearings are at their cold clearances. And it may not. Nobody knows.
Not a chance, 0w is still massively thicker cold than even a 50 or 60 weight oil is when hot - and compared to the changes in bearing clearances vs operating temperature the change is orders of magnitude more - and you'll be up against pumping restrictions, cavitation and the relief valve popping before that was even anywhere near an issue.
You can't even get engine oil thin enough that it would be a cause of bearing wear when cold. You can get it thick enough that it is though.

As for the old 30 vs 40 wear arguement - yes, no, it's not as straightforward as 40 = heavier = less wear.
40 weight can cause more wear than 30, it causes more heat buildup in the bearings at high speeds, doesn't flow as well to dissipate that heat, and can cause cavitation issues in the bearings themselves if used at high rpms when cold.

Oil quality is far more important than going to a 40 weight, and I'd guess most of the issues from a 30 is people buying the cheapest 30w 'mineral' oil they can.

People seem to have a believe that 30 and 40 weight oils are somehow quite thin for bearing and gear protection - yet, they're not really much/any thinner than the 75w90 oil you're all using in your gearboxes to take shock loads, shearing from the gears and still protect the teeth faces against the sliding motion even under extreme pressure. And that's oil that's specifically made to be high friction so your synchro's still work.
Oil quality and add packs are more important than 30 vs 40. Far more, given the multitude of jobs the oil needs to do in a Renny.
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Re: Best engine oil for the RX8 231?

Post by PeteH »

RenesisRaceBuggy wrote:
Wed Sep 26, 2018 5:26 pm
PeteH wrote:
Wed Sep 26, 2018 1:08 pm
0 is better than 10 isn't a logical argument. Nobody knows if 0W oil provides enough protection to a cold rex engine.

Your argument simply says that all car manufacturers should use 0W-60 oil because that's always got the "best" cold and hot performance. That's just not how oils work. Putting 0W oil in a rex could be far too thin for when the engine internals are cold, and the bearings are at their cold clearances. And it may not. Nobody knows.
Not a chance, 0w is still massively thicker cold than even a 50 or 60 weight oil is when hot - and compared to the changes in bearing clearances vs operating temperature the change is orders of magnitude more - and you'll be up against pumping restrictions, cavitation and the relief valve popping before that was even anywhere near an issue.
You can't even get engine oil thin enough that it would be a cause of bearing wear when cold. You can get it thick enough that it is though.
I know I'm being argumentative here, but what the hell!!

How do you know? I know that 0W at -30degC (3250cP) is about a hundred times more viscous than 60 weight oil at 100degC (<26.1cSt). But that's not the issue. You may be starting your cold engine in ambient conditions of 30degC, when the oil is getting quite thin, but the engine is still cold, and the bearing clearances may be quite large. And as soon as you start the car the oil in the bearings gets sheared massively, and rapidly heats up (getting even thinner) but the bearings stay cool for much longer. So for the first few seconds it's possible your oil simply doesn't have the load capacity to keep you bearings apart.

I'm guessing all of this. But my point is, the situation is highly complex, and it isn't possible to make simple statements about it. That's why when people go away from manufacturer's recommended settings and products they are taking great risks, because they can never know as much as the manufacturers. Using 0W oil may be very bad. It may be absolutely fine. No body knows. I puzzled by how many people on here think they know.

If Opie Oils come on this thread and tell me I can use 0W-20 in my race car, then I'll accept that advice. Otherwise, I'd rather not guess.

I'm bowing out now, before I get lynched. :lol:
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Re: Best engine oil for the RX8 231?

Post by warpc0il »

PeteH wrote:
Wed Sep 26, 2018 6:34 pm

If Opie Oils come on this thread and tell me I can use 0W-20 in my race car, then I'll accept that advice. Otherwise, I'd rather not guess.
Only if you could claim on their product liability insurance.

Nothing against Opie but their guess is no better than ours, and in many ways worse, as they have no direct rotary experience.

Even the oil manufacturers get it wrong occasionally and, much more rarely, admit it.
This was the case with Fuchs and the GL4, GL4/5 gearbox oil issue.

The specification of GL5 exceeds GL4 so it's "better" and a GL4/5 oil meets all the specifications of both GL4 and GL5, so that would be ideal for our gearboxes that originally specified GL4 oil - right?

Wrong.

GL5 oils are too slippery for the synchromesh cones to operate as designed, since they expect the GL4 level of friction.
The result is that the next gear isn't up-to-speed in time to make a slick change and the teeth get damaged.
A few instances of this and the 'box is damaged beyond economic repair, since bits of broken teeth have now been in circulation and who know what further damage has occurred.

Respect to Fuchs as they paid for strip-down and technical analysis by a respected independent transmission specialists and then hosted the on-site review meeting with myself and Casey (as one of the first victims of their GL4/5 product).

They paid for replacement 'boxes, where a link could be proven, and withdrew their GL4/5 oil from the market.

While I know this thread is meant to be about engine oil, the above shows that "better" isn't always the case.
The RX8 gearbox isn't that different to many gearboxes fitted to other cars, except for the 9K+ rpm input revs.

The Renesis engine has so little in common with a conventional piston engine, that 99.9999% of engine oil are designed for, and none of the significant oil brands test any of their products with rotary engines.
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Re: Best engine oil for the RX8 231?

Post by RobinPZ72 »

Yeah big thanks about the Gl-5 spec thread as I was all set to put it in my gearbox as it was a better! So just getting round to getting the Redline GL-4 and avoid the big whoops!

Robin

I presume folk are using 5w for fuel economy as not sure what other reason! I get between 245-279 miles out of the tank and reading on here that's not bad!
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Re: Best engine oil for the RX8 231?

Post by bigpete8 »

the w figure relates to viscosity only when cold.
Basically the lower the number the more freely it flows
It is always massively thicker than the hot oil regardless.
The debate is whether changing from the Mazda spec of 5w is actually detrimental.
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Re: Best engine oil for the RX8 231?

Post by qwakers »

just read warpcoils breifing on why 5w30 is wrong for this engine.(in the oil faq iirc) good enough for me, all that is written there is bourne out by the facts, and the rx8s habit of eating bearings....
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Re: Best engine oil for the RX8 231?

Post by RobinPZ72 »

This is gonna be a shock to some, but the W = winter, not weight or watt or anything else for that matter) simply means that the oil must have a certain maximum viscosity/flow at low temperature. The lower the “W” number the better the oils cold temperature/(cold start performance with modern piston cars).

Guys I know a little bit about fluids, but I'm thinking out of the box! The RX8 oil cooling system is a bit to good at cooling, so if we can slow it down a touch it might help!

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Re: Best engine oil for the RX8 231?

Post by bigpete8 »

Think that's 'minimum flow' - but yes you are correct that w equates to winter.
from the SAE table several posts back its actually a set minimum flow that must be achieved at -40c + the W no.
so 0w is at -40, 15w is at -25 etc.

If the oil is too thick it doesn't lubricate/protect properly (same with too thin)
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Re: Best engine oil for the RX8 231?

Post by AndyBrad »

Race buggys comment and 13 black make the most sense to me.

The fact that a 5w oil is hundreds of times thicker at cold than a hot 40 oil is the point I was trying to make. Even with expansion factors of the bearings I don’t believe you would get to a point where by the oil was too thick or too thin. In fact if the bearings were too large then you could get oil starvation with a thicker oil if my thinking is right about a hydraulic bearing.

Were not alone with this. Ford speced the 5w20 oil for mustangs. The reason to do this was that if they reduced the emissions by 1/16th of a percent or something daft they then qualified for a government subsidiary. Café or something. The oil achieved this. A statement from the technical guys at ford has said that its too thin!!!!

Over the years tolerances have been designed and tested. Very very rarely are these moved away from I cant imagine that the fluid bearing tolerances are any different in the last r3 to the first s1. (I don’t know) Should we move to a thinner oil? Probably not. Would something like a 0w50 (if it even exists) be better. Most definitely if you were doing a lot of cost starts (like myself).

The fact that 13black states is we don’t really know. That’s the thing we never will. Most cars will die for other reasons first. It makes sense to go with a 10w40 because its cheap, it’s a bit thicker and people that are rebuilding the engines are saying you must use it to keep the warranty.
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Re: Best engine oil for the RX8 231?

Post by bigpete8 »

Graph probably illustrates this ...
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Re: Best engine oil for the RX8 231?

Post by 13Black »

Do remember that R3's have increased oil pressure from standard... which may help overcome whatever it is that made the S1 bearings not agree with their continued existence.
So 5w30 in an R3 is, probably, still okay.
They seem to be lasting better from memory: going off of some higher mileage examples (of which there aren't many, due to their age) and I think from engine builders pulling them apart for rebuilds (either due to side seal failures etc or just because bridge port) at the kind of usage where an S1 bearing would be likely to have failed or be looking quite worn.

It's certainly the case that older 13Bs ran higher oil pressures and didn't seem to have the issues S1s faced. Not that everything else was kept the same to make it a fair test... but like before, fund the testing if you want a satisfactory answer ;)


I do believe RRP have tried various combinations for X miles and torn engines down to inspect parts for what that's worth... they seem to be keeping most of that info to themselves if so, which you can understand given the effort involved. Or they're just busy with other projects, which also seems likely.
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Re: Best engine oil for the RX8 231?

Post by warpc0il »

The S1 stationary bearing failure rate is also skewed by the 192's rear bearing not being designed to cope with the thrust forces from the clutch pressing against the flywheel, as the 4-port was original designed to be automatic only.

The need to re-build a 192 might not initially be determined as "rear bearing failure", it might just be "drop in rear compression", where the autopsy later determines that the cause was E-shaft movement allowing the rotor to tilt and take-out tip and/or side seals.

Just about all re-builders would upgrade the 192 bearing to the 231 part, included in the price.
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Re: Best engine oil for the RX8 231?

Post by 13Black »

While true, 231 bearing failure is certainly still a thing, and 192 front bearings eat themselves as well. So how much the rear bearings skew whatever data there is... who knows!
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Re: Best engine oil for the RX8 231?

Post by Dr. FrankenRex »

How can data be skewed if there is no data? :lol:

Either way, I've had a load of engines shart their pants and I've run all combinations of 5w30, 10w40, premixed, non-premixed - the whole shabang... My thoughts are that if the renny isn't happy, it'll eat seals.

That said, the only thing I never got around to running is a SOHN/COFS.
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Re: Best engine oil for the RX8 231?

Post by RobinPZ72 »

I think we all know how oil works I think!

Fully synthetic and I mean the best ones in race conditions last or is stable for 10hrs max!

good Semi synthetic and the best mineral oils maybe last for 1 to 2hrs before they say feck this in race conditions!I

I do write badly but no badnest is ment!

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Re: Best engine oil for the RX8 231?

Post by RenesisRaceBuggy »

PeteH wrote:
Wed Sep 26, 2018 6:34 pm

How do you know? I know that 0W at -30degC (3250cP) is about a hundred times more viscous than 60 weight oil at 100degC (<26.1cSt). But that's not the issue. You may be starting your cold engine in ambient conditions of 30degC, when the oil is getting quite thin, but the engine is still cold, and the bearing clearances may be quite large. And as soon as you start the car the oil in the bearings gets sheared massively, and rapidly heats up (getting even thinner) but the bearings stay cool for much longer. So for the first few seconds it's possible your oil simply doesn't have the load capacity to keep you bearings apart.

I'm guessing all of this. But my point is, the situation is highly complex, and it isn't possible to make simple statements about it. That's why when people go away from manufacturer's recommended settings and products they are taking great risks, because they can never know as much as the manufacturers. Using 0W oil may be very bad. It may be absolutely fine. No body knows. I puzzled by how many people on here think they know.

If Opie Oils come on this thread and tell me I can use 0W-20 in my race car, then I'll accept that advice. Otherwise, I'd rather not guess.

I'm bowing out now, before I get lynched. :lol:
I know because it's simple mathematics, you can work out the bearing clearances yourself just by checking the thermal expansion ratios - and any dynamic bearing clearance from hot vs cold is a topic that's been researched massively for about 100 years as various parts warm through, you'll find white papers all over on it.
Oil viscosity changes are a very easy thing to work out, even with viscosity modifiers (as an aside, oil with lots of VM's in it = generally bad news for a Renny - but you don't see anybody mention that, more later) in there you can plot the viscosity fairly accurately for any temperature.
If you do you'll see the oil viscosity has a huge increase exponentially as temperatures drop, versus a linear contraction for bearing clearances (which only change tiny amounts) - basically you're never going to get any condition in which the viscosity is too low in the bearing when cold. You're far more concerned about not getting enough flow in there, cavitation damage, and not having the surfaces hot or active enough for the friction/wear additives to work properly (most of them don't work to any decent degree until north of 80-90c)

I would like to know why you think the bearings will stay much cooler than the oil in the first few seconds? The main source of heat in the oil for the first few minutes of warmup is from compression in the bearings, as heat flow through the rotors, etc, is virtually none existant. That plasticises the oil and heat is generated within the oil and on the relevant bearing surfaces.
Basically, there's no way I can see that the oil could be suddenly massively hotter than the bearing.

Some people do know a little more because we spent years and years doing materials research ;)
Everything? No.Not even close. But a fair bit more than the average owner. And probably a bit more than the average garage or rebuilder too.

Anyway, coming back to include 13Blacks comment on R3's running more oil pressure that may have helped - all more oil pressure does is flow more oil, so if you were up against the reg before, a 0w will flow a lot more than a 10w or 15w will - so if you concede that the R3 pressure increase was good, you should also be acknowledging that thicker oil when cold is evidently bad. As it will reduce the effectiveness of the pressure bump.

And while I'm here, just to touch on the subject of the fluid bearing tolerances being used for years as mentioned by someone - fluid bearing viscosities depend upon the surface speeds and loading of the bearings as much as the tolerances - in fact film thickness will stay relatively similar over a fairly broad range of tolerances in a well designed journal bearing until you get to the extremes of either end - they have to if you think about it, because the way the journal builds a working wedge of oil is from displacement and wobble which obviously changes a lot over operation.
That means that yes, an engine that does 9000rpm over an engine that does 7000rpm, requires a thinner oil, even with everything else the same, in order to get enough flow and cooling at the higher engine speeds. (another aside there, at full rpm 40 vs 30 weight at the Renesis clearances and loads *should* be worth about 4-5bhp. How that is skewed by the stationary gears though I can't work out easily)
The trick is of course, balancing that out with people lugging around town at 1500rpm.
And the stationary gears trying to chop the oil down to make it thinner and thinner and damage the add-packs.

Which is where you want a damned stout base oil, and lots of zinc and moly to help the gears and bearings, and the base oil to a tightly controlled range so that it doesn't need much in the way of visosity modifiers - or any - to meet specs hot and cold - which means you're looking at top end synthetics.
But then all you get is people pointing at the 'mineral' in the manual.
Everyone is happy to say the manual is wrong suggesting 30 weight oil, but woe betide anyone using synth against Mazda's wishes (even though it's wrong for the UK, as their mineral spec is the same as our decent semi-synths are).

Now, the problem with lots of zinc and moly is they poison catalysts, so most car oils don't have much in as they don't really need them quite as much these days - lets just go back to the 'bearing clearances same for decades' thing - they might have been, but materials technology has come on so far in the last 30-40 years it's probably the human races' greatest feat of progress, steels are stronger, tougher and still more malleable, tyres from the 70's have half the grip, twice the wear and are lethal in the wet compared to even a midrange modern tyres....etc, etc.
A big part of that has been lubrication tech - you can buy, over the counter, today, a 0w-10 ester synthetic race oil that will have more resistance to high temperature, high load shear than a straight 50 weight oil in the 80's did. Basically "RX7's ran 40 and 50 weight oils back in the day and were okay" - is pretty meaningless.

So, okay, we want zinc and moly and good quality base stock - lets go for a race oil, right?
Well, it then has no detergents, so you'll end up changing it every 1000 miles. And they have so much moly and zinc in they'll poison your catalyst and leave ash in the engine when burnt. So no-go. Unless you have a SOHN and no cat, then have at it. I ran 0w and 5w-30's, full esters, FWIW.
And Pete, if your racer has the cat removed, it's definately what I'd recommend -if you don't believe me ask Rotary Revs what condition our old engines were in in terms of bearing and gear wear, as I'd imagine most will give them a bit of weight given the sheer amount of rebuilds they do.

Anyway, back to the oil - so we're worked out standard car oil isn't great, mineral oil needs so many polymer additives to thicken it when hot that it just shears down to a 20 weight when it's gone through the gears after a while anyway - as the gears basically just saw through the polymers chains and your oil reverts to the cheap bright stock that was used to make it - and we can't use fancy race oils, so what is left?

Well, there are 2 common vehicles with similar requirements - one is the classic Mini, which has the gearbox oil shared with the engine - if you look at classic mini oil it's chock full of zinc and they run a 40 and 50w oil on an engine doing half the rpms - but they don't have catalyst poisoning to worry about.
Motorcycles do though.
Modern bikes have catalysts, run very high surface speeds on the pistons and the bearings like a Renny does, and most of them will also burn a little oil because they're using ultra-short skirt pistons, low tension rings, and some are even runing 2 rings instead of three now.
And, even better, the gearbox is in the sump and shares the oil with the engine.

Now, if you look at a modern, common high performance bike oil - they will invariably be specified at least a decent semi synthetic, if not a full ester, and they have a little bit more zinc and a good chunk more green moly in there than most standard car oils do, to help the gears and bearings out, without having so much that they will contaminate the cat or the combustion chamber.
Speaking of the combustion chamber - normal bike oils still run detergents, so we're good there - and they're generally using high-temperature capable metallic detergents, not the organics found in cheaper oils, ashless 2T's - which as an aside, is also why you shouldn't be using two stroke oil that's designed for mowers, chainsaws, ashless scooter oils or the like - they run organic detergents that don't work correctly at rotary chamber temperatures - use motorcycle or outboard track/race 2T - I've mentioned this before I think.
Anyway, those metallic detergent bases should cope fine with the chamber temperature of a Rotary and keeping it clean, even if you use a full synthetic without a sohn.
The only issue you may get is buildup of the detergents on the plugs (metallic based detergents are great but can form small metal bridges over the spark plugs with extended periods of low-temperature use) if you don't give it a good warm through/full ponies once in a while. But I think that's probably not an issue for most here.

They are a pretty good match to run with a Renesis, and I've recommended them a few times before because of it. Pick your own poison with weight, there are far more issues at hand. 30 vs 40 weight is a tiny part of it. I would have no issues running a 0w30 or 5w-30 - I did.

P.S - this may need an edit later to make it legible, I'm in a rush and there's a few tangents :D
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bigpete8 (Thu Sep 27, 2018 4:32 pm) • AndyBrad (Fri Sep 28, 2018 10:01 am)
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Re: Best engine oil for the RX8 231?

Post by delta0 »

You need to bear in mind our engines are also over-cooled due to the extra oil cooler.
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Re: Best engine oil for the RX8 231?

Post by PeteH »

RenesisRaceBuggy wrote:
Thu Sep 27, 2018 4:07 pm
I would like to know why you think the bearings will stay much cooler than the oil in the first few seconds? The main source of heat in the oil for the first few minutes of warmup is from compression in the bearings, as heat flow through the rotors, etc, is virtually none existant. That plasticises the oil and heat is generated within the oil and on the relevant bearing surfaces.
Basically, there's no way I can see that the oil could be suddenly massively hotter than the bearing.
I said I would bow out, but you asked a question, so it would be rude not to answer.

I agree with most of what you have written. And I agree with the comment above. In fact, it was the reason behind my "bearing stays cooler" comment. The main source of heat for the oil for the first few minutes is indeed the working of the oil within the bearings (I would say oil shear, rather than compression, because oil is nearly incompressible, so does very little compressive work, but the principle is the same). Combustion heat doesn't get anywhere near the bearings or the oil for ages. Almost no work is done directly by the metal of the bearing. All the work is done by the oil between the two bearing surfaces, and it is this thin film of oil that gets really hot really quickly because it has such a small heat capacity (due to its tiny volume). It is the transfer of heat from the oil to the metal bearing that starts to heat the bearing up, but the bearing has a far higher heat capacity than the oil within the bearing, because its volume/mass is orders of magnitude larger than the oil film, so it takes a while to heat up. Now I know that the oil is flowing, and the bearing is being constantly filled with relatively cool oil, but the fact remains that the oil heats the bearing, so the oil in the bearing is hotter than the metal of the bearing. I have no direct knowledge of the local heat generated within the oil in a bearing, but the more viscous (i.e. cold) the oil is the greater the temperature rise must be. Maybe 0W oils are too thin to generate adequate temperature through the shearing process. Maybe 10W oils are too thick to flow properly through cold bearings. I honestly have no idea. I just know it's complex, and anyone that thinks they definitely knows the answer (not aimed at you Mr Buggy) is probably not understanding the question.

(I think you assumed I was referring to the bulk temperature of the oil, but I was actually referring to the local "spot" temperature of the oil in the bearing, which is, of course, what actually matters for engine wear.)

Ps. I'm not doubting your knowledge. Your contribution to this topic is way more informed than some of the "belief, hope and faith in the rotary gods" statements made by others. :thumright: