- Joined
- Jan 16, 2025
- Messages
- 16
Is there any advantage of using thicker oil in an older engine.
Using thicker oil in an older engine?
- Thread starter Just a guy who likestruck
- Start date
That’s my question as well
- Joined
- Jan 16, 2025
- Messages
- 16
An old 305
Those old chevy engines wanted thicker even when they were new. I run 15w-40 in my 03 and 05 and they love it. With 5w-30 I would hear some valvetrain noise at hot idle but not much but with 15w-40 there's none and oil consumption went down a lot, almost eliminated consumption on my 05 with 341k. Barely burns anything now. I run 5w-40 instead of 0w-20 in my 21 and i'm still under warranty.
A 40 weight would work just fine. Oil pressure will increase slightly, which is a good thing.
How many miles on this engine? What year is it?
- Joined
- Feb 6, 2025
- Messages
- 104
Go for it, it's an older engine. Of course, don't got crazy on it. Go from 0W-20 to 5W-30, sure, or even 5W-40, or anything inbetween. But when you push past or want to use 15W-40 Diesel oil in a gas engine in a cold climate, you might not like the results.
Last edited:
Had to go to 0w30 & 5w30 as the rings are worn and with almost 400,000 k, why not? GDI engines see fuel dilution so it will thin it some. Changing oil sooner is better than later
Might quiet things down or help oil consumption issues with a loose or worn out engine .
If this engine has the original timing chain and gears you would be best to not go beyond a 10W40 in my opinion. Camshaft sprocket has nylon teeth. They will shear off (old set) when the oil pump has to churn thick oil.
You got 400k out of a GM product? I never got more than 190k! What year/model is this?
I run in my 93 5.7l up to 15w40, has 10w40 in it now and what it usually gets year round. I've got around 162k miles on her and she purrs like a kitten. Running thicker will not harm anything.
The real advantage is using thicker oil in a newer engine and slow down the decay rather than band aid it.
10W40 at 0°F, or at 60°F?
Viscosity is determined by 3 factors.
1. Operating oil temp
2. Rod and main bearing clearance
3. The load on those bearings
Unless you've modded the engine significantly, these parameters will not change much, if at all. In a healthy engine, you will likely not wear the bearings enough to warrant an increase in viscosity.
That said, there's no harm in it either. You could run a 5W-40 or 10W-40 in this old 305 that called for 10W-30 and will be just fine. You might lose -0.5% power and fuel economy.
I know a lot of people with these older engines like to use HDMOs like BROtella. I'm not a fan of that in the least. Use an appropriate oil with the foam prevention, oxidation resistance, and ZDDP content the engine needs. Valvoline VR1 synthetic 10W-30 is a good choice. If it's a roller cam or stock flat tappet, a Euro 0W-40 or 5W-40 would work well. Top Shelf options would be Red Line HP 5W-30, Driven LS30 5W-30, Amsoil Premium 10W-30, and HPL Bad Ass 5W-30/40.
1. Operating oil temp
2. Rod and main bearing clearance
3. The load on those bearings
Unless you've modded the engine significantly, these parameters will not change much, if at all. In a healthy engine, you will likely not wear the bearings enough to warrant an increase in viscosity.
That said, there's no harm in it either. You could run a 5W-40 or 10W-40 in this old 305 that called for 10W-30 and will be just fine. You might lose -0.5% power and fuel economy.
I know a lot of people with these older engines like to use HDMOs like BROtella. I'm not a fan of that in the least. Use an appropriate oil with the foam prevention, oxidation resistance, and ZDDP content the engine needs. Valvoline VR1 synthetic 10W-30 is a good choice. If it's a roller cam or stock flat tappet, a Euro 0W-40 or 5W-40 would work well. Top Shelf options would be Red Line HP 5W-30, Driven LS30 5W-30, Amsoil Premium 10W-30, and HPL Bad Ass 5W-30/40.
It's not the journal bearings that I think off when considering oil viscosity, though with autamatic start/stop a higher viscosity wouldn't hurt every time the engine stops or starts, by lowering the rpm at which hydrdynamic lubrication is achieved, and especially turbo engines tend to wear the top conrod bearing shell which indicates to me the oil film isn't quite thick enough.
But there's pistons vs bore, pistong rings, chains and sprockets (more so in dohc designs than old ohv), cam bearings (halve rpm and smaller diameter, often no replaceable bearing shells and highest lubricated point in the engine receiving oil after startup last) which are aften reduced in length on the bottom limiting the oil supply even more, valve guides (quite hot and not much oil should make it there), oil pumps themselves (see unfiltered oil, or filtered oil that has gone through the engine to be more precise), vacuum pump, turbo bearings.... All of these can codemn an engine over time and the car with it, especially considering if one system needs replacing the rest is likely in terrible shape aswell. It doesn't matter one bit if you intend to replace the car at the end of the loan though.
The rod and main bearings are the only parts of the engine that operate solely in full hydrodynamic lubrication. They are also the main "leaks" in the engine. Thus, they dictate viscosity. Cam bearings/journals have an influence on the viscosity but they don't see the loads that the rod and main bearings do. The pistons and rings are splash lubricated, not pressure fed, and while they have an influence, it's always secondary to the bearings. Unlike the bearings, the rings transition through all 3 lubrication regimes on each half stroke. They're in boundary lubrication at TDC and BDC and up to 20° each way from TDC and BDC. As the piston accelerates up and down the bore, the rings transition into EHD and then HD lubrication. Piston speed and hone profile have a big impact on where those transitions occur. In a properly designed and blueprinted engine, the ring thickness and tension, hone profile, and bearing clearance will be sync'd together around the same viscosity, but that viscosity is always determined by the bearings.
The same applies to everything else. The chain and gears operate in boundary and EHD lubrication. The cam lobes, lifters/tappets, and rest of valvetrain are in boundary - EHD lubrication. In all of these areas, the additive package is as much or more of a concern than the viscosity. It doesn't matter if you're using a 0W-16 or 20W-50 as there's no forced oiling to these areas to keep the oil contained in the contact area.
Patman
Staff member
You can’t honestly believe that there aren’t MANY GM vehicles out there with 400k plus? Because there are quite a few.
Similar threads
