10W-40 for Chevy 350

[Baker11b]

I've been getting a little bit of blue smoke on startup. I'm thinking of going with a thicker oil. I'm running 10w30 conventional now. What's the minimum temperature I should run a 350 with 10w40? We're talking Texas Winters. Think the coldest it ever got here was 11 degress F.

 

[85K304SPD]

Run it year round. I am not sure that will help with your blue smoke problem though. That would probably be oil getting past the seals on the valve guides. How many miles on the engine?

 

[78C10BigTen]

Run it year round. I am not sure that will help with your blue smoke problem though. That would probably be oil getting past the seals on the valve guides. How many miles on the engine?

I agree! I run 10-40 in all my vehicles.

 

[squaredeal91]

Valve guide seals is your blue smoke on startup.

 

[fast 99]

That motor should be cut for PC seals. Should only take an afternoon to fix it.

 

[Baker11b]

Run it year round. I am not sure that will help with your blue smoke problem though. That would probably be oil getting past the seals on the valve guides. How many miles on the engine?

Idk. It was swapped at some point. The heads look new. Probably an early tbi model because I found a matching alternator under by searching under a 1988 K1500. Is there any reason I shouldn't use 10w40, though? Kinda irked about upping the weight.

 

[85K304SPD]

There is no reason that I know of not to run it. I prefer to run 20w50 in my old engines. What is your concern about running 10w40?

 

[Shorty81]

I've always run 10w40. Won't hurt a thing.

 

[Baker11b]

Because Chevy says to use 10w30 lol. It actually smokes a lot less on startup now. There's still some but a lot less.

 

[Trucksareforwork]

Valve seals. I just did mine in my 85 305. Made a world of difference in both smoke at startup and smoke at idle (my guess is vacuum was pulling oil in past the intake seal).

With a spring compressor and an air compressor with a spark plug adapter to pressurize the cylinders, it took me about 5 hours, probably an hour to do the first couple then the balance for the other 14 once I got the hang of it. I posted on this a couple months ago. Well worth the effort and the parts are cheap.

“Thicker oil” still burns.

 

[ChuckN]

I've been getting a little bit of blue smoke on startup. I'm thinking of going with a thicker oil. I'm running 10w30 conventional now. What's the minimum temperature I should run a 350 with 10w40? We're talking Texas Winters. Think the coldest it ever got here was 11 degress F.

My 350 is an almost new rebuild (~1000 miles). I started with 10w-40 with Lucas ZDDP additive during break in and since have gone to Valvoline 20w50 VR1 for the flat tappets for warm weather.

The other day it was 30-40 degrees- it cranked a tiny bit slower, but otherwise I don’t see a downside. It doesn’t irk me at all to run a thicker oil.

 

[Drauka99]

My 4.3 and LS motors all get 15w-40 diesel oil.

 

[Buck69]

10/30 and 10/40 both have the same cold start viscosity rating.
I would not be concerned with increasing the viscosity slightly. Watch your oil pressure. Too high, adds additional strain to the cam gear and pump drive.
Look at a marine 350. Internals are the exact same as what's in an auto with the exception of a milder cam and the head gasket composition. They recommend 20/50 for that application.
Marine engines are under continuous load and do not get above 160 F. I cannot bring myself to paying $20/ltr for the 20/50 though. Have tried 10/30 in them and they tend to burn a little bit. With 15/40, they don't. Have been running it for years without any issues. Lots of boaters do with these engines.

 

[Grit dog]

10/30 and 10/40 both have the same cold start viscosity rating.
I would not be concerned with increasing the viscosity slightly. Watch your oil pressure. Too high, adds additional strain to the cam gear and pump drive.
Look at a marine 350. Internals are the exact same as what's in an auto with the exception of a milder cam and the head gasket composition. They recommend 20/50 for that application.
Marine engines are under continuous load and do not get above 160 F. I cannot bring myself to paying $20/ltr for the 20/50 though. Have tried 10/30 in them and they tend to burn a little bit. With 15/40, they don't. Have been running it for years without any issues. Lots of boaters do with these engines.

Castrol 20-50 is dirt cheap. Has been for a while. Not good or necessary for a tight new engine IMO or anything less than warm weather but it’ll run fine in a small block or a LS.

 

[Grit dog]

My 4.3 and LS motors all get 15w-40 diesel oil.

Virtually all the 4s engines I have or had, from mowers and dirt bikes to small/big blocks, LS and newer Hemis ALL get 15-40 and run just fine.
Except in extreme cold, which isn’t an issue for me except the truck and snowbike occasionally. Bike gets T6 5-40 (wet clutch safe, jaso MA rated) and the truck gets 5-40 or lower when we was in AK or CO mtns.
Although I did see a super sale on 10-30 syn Napa brand a couple months ago and stocked up on it for some of the engines next service.