GM 5.0 noticeably louder on 5 or 15w40

[JT1]

I purchased my caprice in mid december of last year with 40k on the engine. I changed what the owner claimed to be QS HP 5w30 out for RT6 5w40, which netted me an audible clicking noise at cold & hot idle(I even swapped the filter with a new and gained nothing from it). I ran the RT6 for about 3 mo. and then swapped for MC5k 5w30 which caused for a noticeably quieter ,though still lightly audible, ticking. I've since finished a 4.5k oci with the MC5k and swapped over to ST 15w40, and the idle tick has returned with a vengeance.

Does anyone else find it strange that a thicker oil would cause more noise at idle?

What do you think would cause this?

Stuck lifter? I've done a run of .75qt MMO but it hardly helped.

 

[mechtech2]

Sounds like your engine likes the thinner oil, which I'll bet is recommended.
But Why? When really good and hot, I am surprised that there is more noise. Is this part true? Are we talking about cold engine ticks?
Your engine must like flow over higher pressure and lower flow.

 

[JimPghPA]

Why not try the QS HP 5w30 ?

 

[daman]

Why not stay with the 5w30 like supposed to be in there?

 

[tig1]

5-40 or 15-40 anything oil will not make your engine last longer, so why use it? Use what GM says to use and your engine will like you for it.

 

[mechanicx]

Maybe the Rotella cleaned a deposit into a lifter? Usually a thicker oil is quiter. I'm kind of surprised MMO didn't seem to help much. If you mixed MMO with 5W40 it'd seem the oil viscosity wouldn't be much thicker than 5W30. It sounds like you have a lifter ticking issue and it might clear up over time. It does seem strange to me that thicker oil makes it tick louder.

 

[addyguy]

MC5K has high moly in it, I'd bet that is 'cushioning' whatever is causing the noise in your engine. The other oils you listed do not have as high a moly count as the MC5K.

 

[JT1]

Mechanicx, I forgot to mention that even with the original fill when I purchased it that there was a lightly audible tick, and that the RT6 IMMEDIATLY caused for the tick to get louder.

I'm going to drain a qt of the 15w40 out and replace with MMO and run it about a 1000 miles. If the tick does not get better i will refill with a 5w30 and never look back.

 

[Thermo1223]

Are you sure it's not a leaking exhaust header gasket. I owned 305 wagon many moons ago and I always had a tick at idle & accel because of a leaky gasket.

Oil wise on that I used PYB(5w30) at the time with a quart of MMO. That was the first change and after I used just regular PYB(5w30) the next round there was really no difference in noise that I could tell. I don't know why I did MMO since it was rebuilt not to long ago, just because lol.

The only other thing could be a stuck pushrod but I was told by a mechanic when I was concerned that it would be much louder and audibly mechanical regardless of oil.

 

[mechanicx]

It might be possible that a rocker arm is loose. I'm guessing it is a sticky/cloggy lifter though.