it's an LS6 shortblock, milled LQ4 heads, cam, etc. The car sits in a 70 deg. garage year round and is NEVER started in temps under 55 deg F. For about 15 years I've been running 15w-50 w/o any issues (oil temp/pressure wise). I used to drag race the car about 400 passes a year but It mostly just sits now and i rarely get over 4K anymore (I must be getting old!). I have a ton of equipment that requires 20w50 and 5w30. I know the factory spec is 5W\w30 but long ago when I used to run 5w30 I never did like the hot oil pressure at idle (Even w/ the stock short block) which is why I went to 15w50. I'd rather not go back to 5w30).. I know the 15-20psi hot idle pressure is w/in spec and acceptable but I just didn't like it so I switched to a thicker oil. With that said given the price of oil (and ease of stocking) I'd like to move up to 20w50 from 15w50. Given the car is always started at 70 deg ambient I don't see an issue going from a 15w to 20w but curious what you guys have to say.

Thanks
Dave

 

You're not going to see any difference. The first number is an index number based on how cold the oil can be poured. They are both 50weight oil at 70°.

That said, your bearing clearance should determine oil weight. I wouldnt use anything more than 40weight in a stock clearance bottom end. Especially it all it sees is street driving.

 

The bottom end of this thing has stock bearing clearances. I don't know what that is on the LSX but I think maybe .003? I've not had any issues in the many years I've run 15w50 and I've never starved the engine so the return galleys clearly can handle the 50 weight and oil temps have always been manageable. I do know that the winter number isn't going to apply to me but I just want to make sure it wasn't missing anything. In my case 15w50 should be no different than 20w50 but decided to come here for sanity check. I'm not really here to argue if a 50 weight is good or bad, as it's worked for me for many years and street and race applications through probably thousands of quarter mile passes.

ThanksDave

 

I agree. I've run 0w-40 oil for 17 years now in my 427 LS. Good stuff. The thicker the oil, the hotter the oil. If you have 20-25 lbs pressure at idle, and 50lbs at 6k, you're doing just fine. Too many people think they need 75lbs oil pressure at redline, and 40lbs at idle. Not necessary, and robs power....

 

10-30?
Less viscosity improver's than a 5-30, or even a 15-50.
Just a thought...
There is a few petrochemical engineers that hang out here:
https://bobistheoilguy.com/forums/
Beware of unknown clowns.
I've spent many evenings on those boards (oil). Who would have thought...

 

Good guess but half that. .0015.

 

IIRC, .002-.0025"? .003" would be on the upper end of the scale.

 

I doubt anyone here is going to change OP's mind, but 50W is too thick for stock bearing clearances in his application. Even when you drag race, you just don't stay in it long enough to get the oil hot enough. Mine mostly sits lately, but it has a fill of 0W30 and the only way I'll go thicker is if I take it back to the road course. Thin oil flows much better, flow removes heat faster than molasses that just sits there. Flow is what lubes the far ends of the oil circuits too. There is absolutely ZERO justification for 50W in a street car other than making the factory oil pressure gauge read higher, which probably can't be trusted all that much to begin with.

 

Since you've ignored the advice of the GM engineers who made the engine all these years, why now ask a bunch of random people on the internet if your overly heavy choice of oil is OK?

Why 20W50, own a lot of old diesels? Nothing else but big clearance race engines require that kind of oil.

 

Let me preface this with this.. I'm certainly not trying to be argumentative/combative here. People seem to be super passionate about their oil choices, i get it. I'm not disagreeing that given the bearing clearances of the LSx that a 50 weight oil is quite thick. I didn't really want to get into a debate about 5w30 vs.15w50. Just wanted to make sure I wasn't missing anything in regard to the cold viscosity side of things. At my ambient temp a 15w20 and a 20w50 SHOULD be nearly identical which is all I was inquiring about. Just wanted to see if anyone diagreed with that.

As far as my opinion/experience using 15W50 for all the years I'm just basing this on what i have experienced/tried and documented throughout many years with this particular engine. When I was serious into racing I always was data logging and monitoring not only oil pressure and temp but also many other PIDS in relation to operating temps of fluids vs. performance, DA, etc.. I also always had my wideband integrated into my HPT logs so i had a pretty firm grasp of what was going on. Even though I do run a bit less capacity (I use a C6 oil pan) I've never seen a situation where the oil didn't return to the pan fast enough. That was actually my biggest concern but it proved to be a non issue.. The only thing on this engine I did not monitor were EGTs given it was a NA engine I didn't deem it necessary. I never did see any notable issues when going from 5w-30 to 15w-50 in my case. Full discloser I do rev this engine to 7k (T56 car) based on the cam/head setup and dyno sheet. Well I did, I brought it down to 6,800 in subsequent years just because I didn't want to be that hard on the valve springs. One day I'll pull the main/rod caps and see how everything looks but given the history this engine owes me nothing and I bet they still look like new.

20w50 is required for the engine/transmissions in my zero turn mower and that is about 9qts there. Add in the 6 qts for the C5 and that'd put me at exactly 3 five qt containers. Going from 15w-50 to 20w50 in my case would make no difference (as far as I can tell) so it makes sense to me to make the change. Most of my other cars require 5w30. Then I have my RV and it's generator, my portable generator, pressure washer, motorcycle, snow thrower, etc. I'm just trying to find oils that are within spec given their use case and make as many oils the same as I can.

It's either I'm going 20w50 from the 15w50 I've used for 15+ years or going back to 5w30 and dealing w/ the low hot idle oil pressure I've always seen in the LSx engines. I just don't want to stock a bunch of so many different oils. Years ago i did research on acceptable oil pressures for the LSx and I knew I was w/in spec running 5w30 but I just didn't like the low oil pressure. I certainly could not argue with the results I've had throughout the yeas using 15w-50. The engine always has exceeded expectations on the performance side of things. I put that engine through more than most would and it's never complained. Granted this particular engine has never been forced induction, just a little ole 11:1 NA engine but it has over a thousand passes on it with nothing more than the periodic valve spring change. Oddly upon checking spring rates after probably 600 passes the springs were still within spec! I'm probably thinking of .003 from my ford days as .0015-.0002 sounds about right to me. Been years since I've checked the clearances on an LSx motor.though.

And to the point of engineers recommending an oil, there is much more to recommending an oil for these than just viscosity.. Yes, it's a huge part of it but they will recommend viscosities for other reasons as well For example, a lower viscosity will improve fuel mileage and when trying to reach EPA goals the engineers may go w/a thinner oil as a slight expense to longevity so long as it keeps that longevity beyond a warranty period for example. I'm too lazy to look in my service manuals but I cannot find an ls1/6 viscosity chart on the internet anywhere. I wanted to see the temp vs. viscosity chart they provide for the LSx engine.

Thanks
Dave

 

I'm running Mobil 1 0w-40, have been for years. Good oil. You want protection of a 30 weight, or 40 weight when hot, and you want viscosity of water when cold (yes, an exaggeration on water!). Most engine wear happens during cold/first start of the day. 15w-50 is too thick. You'll never need 50 weight protection unless you're running 1 or 2 mile WOT events in hot weather, or road racing. Years ago, the 'w' in the rating meant the measured viscosity of the oil@0° F. So at 0 degrees, M1 0w-40 would mean a zero viscosity at 0° F, but offer the protection of 40 weight at high temperatures. IF the old formula was correct. My .02, and it IS hard to out-engineer the OEM guys, who have.millions of dollars in test equipment, and computer aided design (CAD). My 2 older sons both work for GM as mechanical engineers. They use a program called Solidworks. 5w-30, or 0w-40 would be my 2 top choices......

 

See, sounds like you've already decided what you're going to do.

I too run 0W40, but I doubt it makes much difference 5W30 or 0W40. I just don't pay much attention to the idle oil pressure and then it doesn't bother me.

 

You'll be fine. Is it 'the best option'? Maybe not. But given how you use it, I don't think its a bad choice either. Back when the c7 was new and they had the tech questions answered from here direct from GM, I found the answer to the question of "can I run 15w50 all the time" interesting (since for the C7 they recommend 5w30 for street and 15w50 for track). Paraphrasing here....but it was more about what they didn't say. The gist was the 5w30 was ideal for all operating conditions on street, extreme temp range and to meet the life requirements of emissions equipment.

I run 0w40 or 5w40 in mine for a similar reason-- I require it in another car and it's nice and easy to just buy the same oil in 5 gal jugs.

 

OK, long story, but has a moral.

I ran 20w-50 in my endurance boat race motors, which operated in ambient temps of 60*-105*. The tolerances were big enough that we went from build, to tune, to race. This was a 1100 hp gasoline supercharged BBC that ran flat out for 20-30 minutes per heat.

Now keeping in mind that the resistance on a boat hull is like driving a car uphill the whole race, even with raw water coolers the oil and engine temps were pushing the edge. The heat soak was incredible by the end of the race..

My engine needed, and was designed for, 50w oil to survive. I suppose it would be OK for a street car, but I don’t believe it is the best choice for a street car. As others have pointed out, rate of flow is an important element of heat transfer. A similar situation with coolant; if it passes through the radiator too quickly, it’s efficiency in transferring heat is diminished. So tolerances play a role in lubrication, but flow plays an important role in heat transfer. Both roles are key.

I’m not an engineer, and I highly recommend that no one takes my advice…lol

 

I’m no oil engineer either but have built and raced my share of engines. Over the years Ive migrated to running as lightweight oils as I can get away with. My theory is the thicker oil really isn’t increasing the pressure it’s just backing it up in the port it’s measured in more because it’s not flowing across the bearing surfaces as much. It seems like it is likely more detrimental than beneficial. It only needs to keep the bearings and friction surfaces lubricated and carry some of the heat away as it moves across the surfaces and in some cases the lifters activated properly. The harder it is to force the oils through the bearings clearances the more heat it will create in the process, not to mention the increased effort required to turn the oil pump. That’s just my take on it.

 

EXACTLY!! I agree with you.There's a reason GM recommends 5w-30. Most engine wear occurs on the first start of the day, in those 2 or 3 seconds of cranking with no oil pressure. So if thick oil is used, the bearings and vital components are without oil pressure just a bit longer. Another reason it's a good idea to fill your oil filter with oil when changing the filter. I use 0w-40 because the cold flow is nearly identical to 5w-30, and it offers a bit more viscosity at high temps.

 

This is a GREAT conversation!
I'll keep my opinion to myself, thank you.
A Celebrity Death Match maybe, in the future??
Kidding, but ... Very interesting.