In a post about a month ago I indicated that my car, a 380SL with new chain/tensioner/rails/etc put in about 2 years ago had developed an occassional chain slap. I also guessed that it may have been related to oil viscosity since the chain tensioner in these cars is hydraulic. To verify the guess, I changed the oil from a very heavy 20w-50 in there (I really didn't need that heavy a viscocity, I had just done it for one oil change) to Mobile One synthetic 10w-30. Since making that oil change, there has never been any indication of chain slap. So if you have a car that has no reason to have chain slap but does, you might consider changing the oil to a lighter weight one and, if you believe in synthetic for your car, maybe a synthetic one. I have come full circle on the use of synthetic oil for the moment and will continue to use it and monitor any significant increase in oil leakage.

Is it possible that it wasn't chain slap but instead one of the hydraulic compensators failing to pump up? Mine does that when it is cold and only at start up. I thought the same thing - just had timing chain, guide rails, tensioner and valve stem seals replaced this summer. Freaked me out to think it was the chain again!

It is possible it was something else but since I've heard what the chain sounds like before (just before it broke a few years ago and before that, though I obviously didn't understand the dangers and misdiagnosed back then) I know what it sounds like, and it really sounded like chain slap. I can't be sure, but I'm really pretty sure.

Steve the moderator had indicated in some other posts in the archives that sometimes it's difficult to get rid of all slap because of the way the tensioner works. I studied that, actually bought a tensioner to look at, etc, and I think I agree but I'm really still guessing. What I definitely can say is that, after changing that oil, the sound went away. Cold starts, whenever starts, I stopped hearing that noise. I'm posting the info here because, if someone has a car that really shouldn't slap because all of the proper things have been done (new rails, new tensioners, etc) then you might consider a lighter weight synthetic oil that works for the weather/season in your area. Also, it seems to me that if I had a car that was say around 80,000 miles or so and coming up on a timing chain change, I might give real thought, based on what I know now, to the visosity of the oil/etc and how that might affect the engine's operation at startup. As I understand it, most of the damage to an engine occurs at cold start and that is certainly the case for a timing chain. And at cold start, that's exactly when a lighter weight oil, and also a synthetic for that matter, provides less friction I think.

Synthetic oil sticks to metal, dino doesn't, so the tensioner won't drain down so fast. Synthetic is also much more viscous at high temps, resists draining for that reason too.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!