1990 300e 3.0l with 285K goes through lots of water. Ran coolant pressure test but showed now leakage. Radiator is good and no visible leaks. Is the L6 motor prone to head gasket leakage and what is the best way to determine source of usage?

 

Does the oil look "milky?"

Exhaust give off any smoke?

 

The factory testing in ALLDATAdiy.com also recommends pulling your plugs to check for coolant contamination in the Cylinder Head of your Mercedes. With the plugs pulled on your 300e crank the engine and check to see if coolant is expelled. (Stand back BTW)

You may have a leak at the intake maifold as well.

 

Yes, this motor is prone to head gasket leakage. It's one of the most common problems in the MB w124 series. If you want to test for oil in the coolant, buy a block tester from NAPA. If you want to test for coolant in the oil, don't rely on visual examination alone, get an oil test from a lab. Most of the six's leak oil into the coolant, but that's not a hard and fast rule. If you even think there's a remote possibility of coolant in your engine oil, don't run the car until you have the oil tested. Antifreeze/coolant mix will trash mineral based oil and ruin your engine's bearing surfaces in short order.

Kevin

 

If it "goes through lots of water", I would first look for leaks in the coolant system, not the head gasket. The water pumps can go every 60-80k and the leaks can be hard to see at first. With 285k, it is hard to imagine that the head gasket wasn't already done and the replacement gasket was improved. I've read that it can be a once and done replacement because of the improved gasket.

 

He can put butcher paper or sheet cardboard under the car after a long run to see where coolant leaks are. However, sometimes the systems will leak only significantly under pressure. Never assume anything. If the car has never been significantly overheated, it may not have developed head gasket problems as of yet. Not all 3 & 3.2 liter engines develop head gasket leaks, but are prone to. Agreed on the water pump going out, but not at the continued frequency you mention.

And there are other scenarios as well; could be the head was given a valve job, new head gasket and then the owner overheated the car sometime after that. Doesn't matter how well the head job was done, if the aluminum head was overheated. The new head gaskets are better designed, but they won't compensate for abuse. Pretty much it's life with an aluminum head-baby it.

Kevin

 

Dark exhaust smoke under acceleration. The head has never been off for I am the second owner and know the history since 113K. I had new valve seals installed at about 195K. Temperature fluctuation last year and replaced the aux fan. Temp is more stable now after the aux fan repand not prone to overheating. There is a fair amount of oil leakage as well. I suspect that it is more than a valve cover gasket, but I will replace that first to try and improve the oils issues. I am more concernerned with the water usage. 1/2 gallon every 100 miles or so. Nor Cal climate is warm and heading for summer, so I anticipate more water/coolant usage.

 

Water pump was also changed at 195K.

 

Aside from an oil analysis or water analysis, how else could I verify a bad head gasket? cylinder leak down? cylinder compression? Is there a link that I can go to for a DIY on cylinder head gasket replacement?

 

No, cylinder leak down tests won't do it...tired that with rosy results. That particular head gasket design as I said in another thread, expands and seals only while the engine is running and at normal temps. You shouldn't be looking for shortcuts or easy fixes. This is one of the more serious engine internal events of the 3.0L. The rubber valve seals are only a band-aid approach, a head job should have been done at that point. The valve seals will fail again, because the valve stems and valve guides weren't addressed. You should be considering a complete head job and head gasket, intake gasket and exhaust gasket repair. However, the 'book' will tell you to remove the intake manifold (with all its attached fuel injection components) and head as a unit. This is 'padding' money in the Service Book vernacular. Leave all that alone and disconnect the intake manifold at the head. Other than that, follow the MB CD. You'll need long extensions for the exhaust manifold and some patience to get all the intake manifold bolts off. Expect to have a reasonable supply of good metric wrenches and good metric sockets in 3/8" drive-except for the cylinder head bolts. Since you have to take the distributor off anyway, it's a good time for plug wires, new distributor & rotor.

The good news is, I had a German MB engineer tell me, on paper, the w124 series were designed for a million miles with proper maintenance. It's one of the few gas series that can make that claim-no big deal to MB diesel fans. Since it's built like a tank and the precursor to the total 'fly by wire' models, I have to believe it. First of all, I never had a car or truck make it past 200K without wanting to trade it and secondly, the ones that made it to that milestone looked like it. My wagon is still svelte and a beauty, some 17yrs later with 222K. The accolades will continue with this car series as all the generic CAD bubbles keep coming off the assembly line. These cars are actually historically significant for MB......maybe even as much as the 300SL was. My only fear is that mine will get wrecked before its time.

MB CD:
http://www.ps2cho.net/downloads/MB%20CD/W124/Main.html

Kevin