Purchased a garage queen 2009 CLK550 with 60K miles. Car is in pristine condition, but I realized it suffers from the often hard-to-replicate warm start knock issue that plagues some M272 V6s and M273 V8s.
If the car is up to temp, turned off, and then turned on again around 45 minutes to 2 hours later, it exhibits a 1.5-2 second knock from the bottom end. It does not occur on a cold or very hot start.
My understanding is that MB specced a few bearing clearance(s) too loose and that most folks ignore the issue and live with it. My understanding is that dealerships also tell people to live with it.
The “true” solution is to change the bearings to get a tighter tolerance, but that’s not an option here (ideally). Its not cost effective, and I’m generally averse to opening up a motor. I also do want the motor to last a long time because it’s a cream puff example of the car, and it’s (in my opinion) an underrated vehicle that I’d like to keep for a while.
I’m noticing the issue a bit more often after my first oil change with Castrol Edge 0W40. Would a slightly thicker oil help here? My guess is that the problem rears its head during the time when the oil is still warm (thinner), but the oil has left the bearings/channels and has collected back into the sump.
If helpful, it sounds identical to this:
If the car is up to temp, turned off, and then turned on again around 45 minutes to 2 hours later, it exhibits a 1.5-2 second knock from the bottom end. It does not occur on a cold or very hot start.
My understanding is that MB specced a few bearing clearance(s) too loose and that most folks ignore the issue and live with it. My understanding is that dealerships also tell people to live with it.
The “true” solution is to change the bearings to get a tighter tolerance, but that’s not an option here (ideally). Its not cost effective, and I’m generally averse to opening up a motor. I also do want the motor to last a long time because it’s a cream puff example of the car, and it’s (in my opinion) an underrated vehicle that I’d like to keep for a while.
I’m noticing the issue a bit more often after my first oil change with Castrol Edge 0W40. Would a slightly thicker oil help here? My guess is that the problem rears its head during the time when the oil is still warm (thinner), but the oil has left the bearings/channels and has collected back into the sump.
If helpful, it sounds identical to this: