Just checked the compression on my '91 300CE with 80K miles - a little history. We overheated the car last year when the radiator neck broke and spewed coolant all over the place - didn't run it long after that but it seems like I have had numerous running problems since. I replaced the radiator, new water pump, belt and tensioner, etc. Car does not run hot now and doesn't smoke, but I've had a variety of starting issues and it won't run in closed loop.

Results were from a stone cold engine - car hasn't run for a while as I have pulled the fuel distributor etc.

Cylinder 1 - 160-170 psi
Cylinder 2 - 160-170 psi
Cylinder 3 - 125-135 psi (adding oil brought it up to 160 psi and after numerous test #3 steadied around 145-150 psi)
Cylinder 4 - 160-170 psi
Cylinder 5 - 150-160 psi
Cylinder 6 - 160-170 psi

Was going to just run a leakdown test on Cylinder 3 but I did it on all and results were "low" (20-30%) on cylinders 1,2,4,5, and 6 and "moderate" (45% - 60%) on #3 - adding some oil reduced the % to the upper 30% range. This was done using a rather cheap Milton tester and I couldn't really hear air escaping anywhere (coolant cap and oil filler cap removed, listening at adjacent cylinders, exhaust pipe...)

Clearly, #3 is low but should I be worried? All 6 spark plugs look great (I thought the car was running rich, but you wouldn't know it looking at the plugs).

Any advice or suggestions?

Thanks,
Ryan

__________________
RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE