My 280E, with 286,000km on the clock, is idling a little rough when the car is at standstill in Drive. As soon as the revs pick up, they smooth out and the engine pulls fine.

The M110 engine was reputedly rebuilt at 210,000 by a previous owner, but a mechanic has now diagnosed uneven compression. A compression test revealed that #6 cylinder is down to 115lbs compared to the rest at 175/180lbs. On doing a cylinder leakage test, compression appears to be leaking past the rings.

What is my best course of action here? Can I keep driving the car for a while? Or am I looking at a full rebuild of the engine, with new pistons and rings and so on?

Or could there be a simpler, less expensive solution to this impending problem?

The car is not using massive amounts of oil, but has started to steadily lose a little coolant. I don't know if this is a related problem.

Any advice will be gratefully received!

Chris

The coolant loss may be a dead give away for a failing head gasket. If you can't explain the loss any other way, (leakage, etc), then that would be my bet. In which case your low compression, etc would be due to the leakage from the head gasket. Does your cooling system show any signs of excessive pressure buildup? Did you try shooting a little oil into the bad cylinder. If you did and there was no change, then you're problem is the head gasket. At least I hope so for your sake.

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Jeff L
1987 300e
1989 300e
1987 BMW 325

Thanks. That's an interesting thought, and I hope you're right ... I'll get it checked out by my independent MB mechanic.

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1977 MB 280E auto
285,000km

It was the head gasket. In fact, shortly after my post, the gasket blew completely!

The mechanic checked out the head while replacing the gasket and found that the seals and one of the valves were worn. The blown gasket was caused by corrosion around no.6 cylinder on the head, so the head was resurfaced too.

With a new gasket, new seals and a new valve, the engine is now idling smoothly with only a hint of roughness - which I think may be a vacuum issue. The compression is also back on par.

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1977 W123 280E
286,000km

[This message has been edited by AucklandGuy (edited 08-31-2000).]

Nice to hear a happy ending. Don't get too carried away on the idle - I spent a bunch of money for almost no improvement - that's just the way they are.

Chuck