Gearhead Jim

We've had lots of speculation and personal opinion about minimum oil temp before going full throttle/full rpm in the LS3. One engineer posted that the numbers for generic 5W-30 in a generic engine would be for oil between 190'F and 260'F. But he was quick to point out that Mobil1 5W-30 in a Corvette engine could have significantly different numbers.

Friday I was at Bloomington Gold and asked one of the guys in the GM display what the minimum oil temp should be before going full throttle/full rpm in a wet sump LS3.

He didn't know, but phoned another fellow from GM who was there with his personal Corvette(s). The answer was that neither of them knew of an official GM number, but buried in the archives of powertrain development there was probably an accurate answer. Too bad we can't find it.

As a personal standard, the GM guy with his own vette at the show said he uses 150'F as his personal minimum.

Random84

I'm sure its a spectrum of temp vs wear rates... So any number will be N approximation at best. 150 seems to be as good a number as any.


Interestingly, our Z's rarely get over 180* on the street, even in the summer.

LDB

I’m a retired oil company chemical engineer, but I’ve spent plenty of time around engine design mechanical engineers. Upper end viscosity numbers (ie, lower end temperature numbers) I’ve heard from them have ranged from 15 to 20 centistokes. With 5W-30 oil, 15 centistokes is about 190 degrees and 20 centistokes is about 170 degrees. The OP didn’t say whether the GM guy he referred to is a mechanical engineer, but for my part, I’ve never heard an engine design mechanical engineer say they would be comfortable with full throttle operation at 25 centistokes, which would be 150 degrees. This is why I sometimes warn about 160 thermostats and extra oil coolers. You don’t want really hot oil, but you don’t want cold oil either. I think basis the numbers above, coupled with my contacts with mechanical engineers, that for 5W-30 oil, 180 is the lower end of the “clearly safe for full throttle” zone, 160 is clearly too cold for full throttle, and the 160-180 range is gray zone.

rayk

I don't know of any GS with the dry sump engine that runs over 155 without getting pushed hard. Cruising with the A/C on, I have trouble getting to 150.

JCtx

There has to be a safe compromise, and I think it's between 150 and 160º, at least with 5/30 oil. After all, many demo cars are redlined with cold engines. I live in hot TX, and sometimes I don't even see 180º after 20 miles, before I get to my destination. With that rule, I'd NEVER be able to do WOT. In addition, WOT is misleading by itself, since it's not the same doing WOT at 4K rpm than at 6.5K. Similarly, you can go to redline without WOT. I think rpm is more important than throttle opening, since lubrication is based on the former, not the latter.

As a final note, my M3 V8 had an increasing redline as engine heats up; it allowed full rpm at 140ºF. And that was with 10/60 oil . The great majority of cars do NOT have an oil temperature gauge, so owners go by the coolant temperature. When that first reaches normal operating temperature, oil is only at 100ºF or so, as most of you know. So 150 to 160 is perfecty accepetable IMO. And that probably makes us the most conservative drivers in the world . Friends with exotics romp on them way before that .

3LZZ06

All ZR1's along with '11+ Z's get to 190* after about 10-15 minutes at idle due to their external oil cooler/heater system.

Random84

My understanding is that the 2011 Zs have an oil cooler integrated into the radiator, just like standard coupes and other vehicles - likely for this very reason. Whatever the case, the early model Zs clearly stay too cold during typical street use.

LDB

Don’t know what to tell you. I admit that I’ve never talked to a design engineer for Vette engines, but my comments remain unchanged about the many that I have talked to. On one hand, one would think that the Vette engineers must know that most GS dry sumps will be driven on the street, and they must know what temps they run on the street, so they must think it’s ok for that engine. On the other hand, it’s not inconceivable that marketing guys over-ruled engineers by saying gosh, gee, wouldn’t it be neatsy-keen to offer dry sump on a street engine, and thus drowned out the objections of engineers that it’s overkill and actually results in oil that is cooler than optimum for the street. All I can tell you with certainty is that 150 degree 5W-30 is about 25 centistokes, which is thicker than I’ve ever heard a mechanical engineer tell me is ok for full throttle. I guess if the worst case scenario is true, with marketing over-ruling engineers, you at least have the lengthy powertrain warranty to protect you.

HOXXOH

Nothing official, but I kinda sorta think I remember reading something about during the LS development that 190 was the engineering standard for both oil and coolant. It was most likely not WOT minimums. Of course, that design phase happened nearly 20 years ago and I've slept a few times since then.

I personally run 0W-30 and try to get and keep the oil over 200 before making a 1/4 mile pass.

3LZZ06

That's the one...

Random84

Although I agree this is a consideration,

There are around 4 years of Z06's and 2+ years of Grand Sports running colder oil temps for tens of thousands of miles, with really no related failures one would expect: bearings, shattered pistons, etc.

And before someone mentions the LS7 valve issue, many believe that to be either a specific parts/supply issue or heat-related (too much heat at 7K RPM).

So even if it is less than ideal (I agree that mainstream oil under 200* F is not an ideal lubricant), it seems that the LS_ motors continue to do well with this setup. Naturally, the obvious can point out that - as stated above - all Z's and Grand Sports were later changed, resulting in oil temps that essentially run at coolant temps by default on the street (190+*).

ETA: I'm just saying that any increased wear from "cold" oil in a street application must be minimal to the point where we're not seeing it yet; and we are not getting really any LS3 dry sump failures at ALL - and we're talking tens of thousands of cars and countless millions of miles through current C6 production - so unless we're all super retentive and dutifully warm the cars up before topping 3,000 RPM, our concern might be slightly overblown.

Gearhead Jim

You guys make me glad I started this thread, it's an interesting discussion.
And so far, it's still informative and courteous.
Thanks!

Gearhead Jim

That's two very different answers.
Is it possible that a good synthetic like Mobile1, could somehow provide adequate lubrication despite being "too thick" by normal standards?
I'm groping in the dark here...

rayk

My GS ranges from 146-155 for street use. On the track after a 25 minute session, it's at 230-240 using 5w-30 Mobil 1. That's too high IMO for 5w-30 as the oil pressure goes down with the heat rise. The coolant temp is normal between 192-200 and the oil temp is at 240 with hard driving. High rpms will bring the oil temp up fast.

I warm up my car by driving slow on the street and on the track taking it easy for the first lap to get the fluids up to temp.

As long as the oil gets hot enough to burn off any moisture, that's my concern.

There's an interesting thread over on the Duramax forum about oil and coolant temps. Even with the coolant temp under control, the oil temp can go into the high 200's. Going to put a larger cooler on the duramax.

Gearhead Jim

Oil pressure does go down as the oil heats up, but the big issue is how low is too low. On a warm day, cruising 75 mph on the Interstate, our 2009 coupe will stabilize around 220-230 oil temp, so I think your 240' is just fine. Our car doesn't turn the radiator fan to High until the oil gets to 302', and I think LDB said that 260' was the generally accepted upper limit for generic 5W-30 min a generic engine.

rayk

Well, Mobil is concerned about shearing at high rpm with 5w-30, so I don't use it for the track.

LDB

I’ve said a few times in other threads, and a few others have said it in this thread, that you don’t fall off a cliff if you go a few degrees one way or the other from optimum. Most would agree that 180-250 is fully safe for 5W-30, and the gray zone extends 20 or 30 degrees on either side. Chevy has to know that GS dry sump engines run fairly cool on oil, and even if this thread’s worst case scenario were true (ie, the marketers trumped the engineers to put overkill dry sump into a street engine), if those temps were truly dangerous for the Vette engine, you can be sure the engineers would not have let the marketers trump them. It would be too expensive for Chevy from a warranty standpoint. The main thing I would advise is that those without dry sump should not use the cool dry sump oil temps as justification to get their engines down to those oil temps by adding oil coolers and/or 160 thermostats. Virtually all experts would agree that at best, 150 oil is on the cool side of optimum, and most would say it is actually too cool.

On shear, I see comments on the Forum now and then about Mobil 1 being poor in that regard. I don’t know exactly where they are coming from, but it sounds odd to me. Shear refers to VI improver degradation by shearing, not by the oil itself shearing, and synthetics with a 25 vis spread (ie 5W-30 or 15W-40) don’t need much if any VI improver. You normally only have to worry about shear with conventional oils (because they need more VI improver with their lower base oil VI), or wide spread synthetics like 5W-40 (because to get to that wide a spread, even synthetics need VI improver). If somebody has a specific and credible source that says 5W-30 Mobil 1 has shear problems, I’d be interested in looking at it. Incidentally, I’m not trying to defend Mobil 1, they are not the oil company from which I retired. It’s just something that sounds odd to me, so I’d like to look further if there are hard data.

Gearhead Jim

Can you explain more about that?
I was under the impression that any Mobil1 (or other similar oil) would be as good at high rpm as you need, if the temperatures are kept within appropriate limits. Of course, higher weight/viscosity oil would be good to higher temps; but especially your 240' sounds fine for 5W-30.

Looking for an education...

Seadawg

This would be a problem for me, because my dry sump 2011 GS rarely reaches 150 degrees for oil temp. I drive mostly highway, not much stop and go.

I drive about 9 miles to work, and most days my oil temp is only 110 to 120 degrees, unless I really get on it.

I took an infrared heat gun and aimed it at my oil pan (under the car) and it reads within 5 degrees of my oil temp, so I trust my sensor and the car DIC reading.

Only once have I seen mine hit around 180, and that was in stop and go traffic at Tampa for about an hour, with the outside temps near 95 degrees.

EDIT - I did not read the post until now, and saw other GS dry sumps were similar oil temp readings. On coolant temps, mine gets quickly to 195-200, but has only hit 220 once, on that Tampa trip mentioned above.

JCtx

First of all, your oil temperature shouldn't be anywhere near 230º on the interstate, no matter how hot it is outside. And most importantly, you have your numbers wrong on the coolant: redline is 260º, and the fan switches to high speed at 235º. At 302º, you'd be stranded on the side of the road. Maybe you meant some of the numbers for oil, but just in case.