560SEL Water Pump Failure? Head gaskget?
 

Symptoms:

1) System would release water out the overflow tube on the expansion bottle when filled to the full mark. It would then trip the low coolant sensor and we'd refill. Process would repeat. This started about 2 weeks ago.

The Incident:

Noticed 100C op temp yesterday, so kicked on defroster (but no heat came out), sped up on freeway, dropped into neutral tried to cool. Gauge kept climbing near 120, car was turned off then coasted. When engine was back to 110, started back up to get off freeway. Pulled off, let it cool down to 80C, then finished journey. Parked, opened hood, steam was coming from the engine, the coolant bottle was bubbling. All during this the water pump was making screeching sounds.

Car didnt actually hit/sit at 120. It was turned off before it got there and was coated back to normal temp. It NEVER went over/reached 120.

What are you thoughts?
How often do water pumps go bad on these m117s?
How often do head gaskgets go?

Prior to this event there was no evidence of mixing fluids. The bottle/oil were both clean.

Just prior to this event, the owner had purchased a new camshaft and rockers for the passenger side head as it had rounded out two lobes. Parts havent arrived or been installed yet.

Its going in for a leak-down/compression test Friday. So we'll get the official word then, but in the mean time I was hoping for some speculation/experience?

-Kris

Should the car fail to pass the leak-down/compression test it will be parted out.

I think your HG's should be OK, especially if it never reached 120C. Hopefully the compression check comes back OK, and all it needs is a new WP.

i've only replaced water pumps on these because they leak, not because of overheating. bmws, yes, because the impellers fall off, not so with mb. and mb pumps will leak while cold and not hot.

the no heat with defrost on means it was already low on coolant, could be just a weak radiator cap. get the cooling system pressure tested, without, then with the engine running. a stuck thermostat will impede flow to the radiator and also cause overheating.

if it did blow a head gasket, be prepared to timesert the block threads for the head bolts, they like to strip when heated badly enough. good luck, chuck.