Is it safe to go from 10w30 to 10w40???

[Carlspike]

There was a technical bulletin for the GM trucks a few years ago that stated the cold start knock is actually due to carbon buildup on the pistons/valves. as the engine warms up the carbon is burned off and it sounds like a normal engine again. I've done fuel induction services on them and had the noise completely go away for up to 10,000 miles until they get dirty again. I know this is the bulliten for the GM V8's but i'd guess that the same thing might be happening to your car's engine. Before you try to run a thicker oil than recommended I would get your fuel system serviced or at least put a cleaner in the tank and see if your problem gets better or even goes away.

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[DanH1081]

I Have tried that. I have used cleaners from STP to redline SI-1 with no change in the knock. The only thing that does effect the knock seems to be the thickness of oil. Thus the reason I want to go with a thicker 10w40.

[geoffinbc]

In my owners manual (95 3.4L) and my moms (94 3100V6) is says not to use 10W 40 or 10W 50. I would live with the few minutes of piston slap if it were me.

[Guest]

A thicker oil won't or shouldn't reduce piston slap, in fact would probably make it worse, or rather hear it a bit longer.

[Carlspike]

I'm not talking about a cleaner in the tank, I'm talking about the whole induction service. You'd have to take your car in to get it done. They used a pressureized system to match the fuel pressure of your pump and then actually run your car on a cleaner for about 10-15 minutes, this cleans the injectors. Then a cleaner is ran through your plenum at elevated rpm's to clean the intakes. Lastly there is a cleaner that is put in the tank. These chemicals are much stronger than you can buy at wal-mart and it works much better, but it also will cost you a lot more cash. It would just be something to try, if you get it done and your car stops making noise at least you have the peace of mind that it's just deposits and not major problems with your engine.

[DanH1081]

A thicker oil won't or shouldn't reduce piston slap, in fact would probably make it worse, or rather hear it a bit longer.

Thats the thing though, I had 10w40 in to flush the engine out after a gasket job, and for the time the 10w40 was in, there was NO Piston Slap. Went back to 10w30 and 5w30, slap was back.

[torq455]

A thicker oil won't or shouldn't reduce piston slap, in fact would probably make it worse, or rather hear it a bit longer.

Thats the thing though, I had 10w40 in to flush the engine out after a gasket job, and for the time the 10w40 was in, there was NO Piston Slap. Went back to 10w30 and 5w30, slap was back.

Yeah, I had piston slap in my worn out 85 cavalier, and I used 20W-50 and the slap was much better. Thicker oil will pad things, but in these motors, I wouldn't go any thicker than 10W30 unless you are in a warm climate.

[3400beretta]

10w40 is fine to use, my dad has been using it in the summer (live in canada) in his 88 beretta with the 2.8 since 48,000 kms. He now has 327,000 kms on the original engine and trans, with no major work been done. We knew it was time to switch to 10w30 in the winter because the lifters would get noisy for the first few minutes untill the car warmed up. but thats just my 2 cents.

[3400beretta]

oh ya, the engine doesnt burn a drop of oil, it passed emissions with flying colours, and the car can still keep up with my brothers 90 gtz, which has a fresh motor.

[DanH1081]

I planned on using a quality oil such as Amsoil, and I alway warm the engine before driving, so being those two things, the 10w40 should work well I hope?