I have read most of the former posts on this subject and don't see an answer that fits my problem.

I have a 1994 E320 wagon wiht 129,000 miles on it. I recently had a major service (timing chain, head gasket, radiator flush, etc., etc.) Shortle after that service, I noticed that I needed to add about 16 ounces of antifreeze to top-off the coolant tank. I had never needed to do that before. This was about 1,000 miles after the service. On a recent trip of about 250 miles, I noticed the coolant-level-lowwarning light come on and the temperature start to rise. Fortunately I was near home whan that happened. Upon cheching the coolant level, therer was none in the tank. I needed to add almost a gallon to bring it back to normal.

There is no smell of antifreeze anywhere, no aparent leaks or puddles, no steam from my exhaust - it's just disappearing. I've been watching the level daily and it's still SLOWLY going down again.

What could this be (I suspected a possible new head gasket problem) and what could make so much of it go-away so quickly and then almost stop going-away?

I really appreciate the expert opinions and help from the pros on this forum.

Thanks again in advance,

Jack

It is wierd that you had to add that much coolant with no leaks apparent. Check your engine oil level, is it going up?

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

Thanks for the quick reply. The engine oil level remains constant. I have never had to add any oil between changes either. This car has been wonderful in every way.

Could a bad expansion tank cap possibly cause evaporation when it gets hot? It's the only part of the system that I can think of that might not be 'sealed' if it wasn't fitting properly - obviously grasping at straws :-)

Jack

expansion tank cap is one possibility. The hidden leak from the radiator hose is another. It happened to me-no smells or obvious signs of the leak, but needed a gallon of coolant. I found out it was the bottom of the upper radiator hose./ Go figure

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1985 190D 2.2l Sold-to Brother-in-law
1996 Mustang 3.8l -"thinks it's a sports car"
1988 Grand Wagoneer - Sold (good home)
1995 Grand Cherokee Ltd -"What was I thinking??!!"

Thanks for your thoughts Piotr. I have looked at the hoses pretty good, but it's always worth another look. It sure would be great if it were that simple wouldn't it.

The thing that's driving me nuts is the fact that a gallon went away fairly quickly and now it's going away very slowly again.

That leads to a soon and coming question. My experience in life has been that intermitten or very slowly reacting problems are often difficult to find. If I take it in and have it tested with some sort of very slow leak going on somewhere, will any mechanic be able to find the problem?

Thanks again,

Jack

You or a mechanic could pressurize the system (there is a tool made for this) and look for leaks, you can also pressure check the cap on the expansion tank to see If its faulty. A descent mechanic would also have an analyzer to check if exhaust is getting into the coolant, which can cause coolant evaporation do to the high heat of the exhaust.

Hi Jack:

I recently had a similar problem too. The previous owner had a head gasket job done to my car just before I purchased it. Come to find out, he chose to go the cheap route and just clean the head and not take it to the machine shop. His mechanic ended up using two head gaskets to seal the head to the engine block.

I ended up with the same problem as you losing coolant slowly at first then quickly then slowly again. Car ran a bit rough. No apparent white smoke out of the tail pipes. Temp was a bit high too.

My mechanic did a pressure check and found it slowly losing pressure. No apparent leaks under the car. Ran it a week more then I found a little oil in the coolant. Sure enough it was leaking into the cylinder. The edge of the water jacket was corroded enough not have a solid seal even with two head gaskets and started leaking into the cylinder.

I ended up purchasing a refurbished head and now everything runs fine. Temp is fine, coolant level is stable and car has a lot of pep.

Hope this helps.

Aloha,
Eric

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1987 260E Charcoal Grey 157,000 Miles
1987 260E Forest Green 120,000 Miles

Thanks RSH and etsa,

Those synptoms sure are close to mine. A quick follow-up question for etsa - Did you car run rough through the entire process. Mine doesn't run rough at all, the temperature stays normal and I can't see any oil in the expansion tank.

I'm going to replace the expansion tank filler cap today. At least that will take care on one part of the puzzle.

Regarding the expansion tank, could that developed a small pressure leak (I don't see any liquid around it)? It's plastic and almost 9 years old.

Thanks again guys,

Jack

Hi Jack:

The car ran throug the whole ordeal but it did run rough. The more coolant that leaked, the rougher the engine ran. It ran better when it was cold, the hotter it got the worse it got. This was from the pressure that built up from the heat.

I hope this helps.

Aloha,
Eric

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1987 260E Charcoal Grey 157,000 Miles
1987 260E Forest Green 120,000 Miles

Jack,

I've been following this thread and my question would be. Why are you fooling around with this problem. You had all this work done to a tune of a bunch of bucks so why not take it back to the service faclity where the work was done? They should be able to diagnose the problem without much effort. They would probably Sniff the over flow tank to check for hydrocarbons and pressure check the cooling system after the engine has cooled. That would be my recommendation.

Peter

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Auto Zentral Ltd.

I agree with Peter.

FWIW, it might also be a water pump going out. I had a Nissan Quest that was losing coolant, and I had no leak that I tell on my garage floor.

When I had it up in the air for an oil change, after the bottom plastic cover came off underneath the engine, you could see the bottom of the water pump was covered in dried, green coolant. The coolant leaked through the seep hole because the bearing was going out, and It leaked only when the engine was running.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

When my coolant was leaking this is exactly what happened...it seeped out from my failing water pump and was evaporated instantly couldn't find the leak until it got worse by that time the head gaskette went also.

Thanks again for all of the great replys. The reason that I sent this in as a question for the experts on this forum before going to my mechanic is to get some opinions of what the problem could be. You have given me some great ones and I will be asking some questions when I take it in.

Everything considered, I sounds like a possible water pump problem to me. I'll let you know what they find.

BTW - about how long does a water pump last on a 1994 E320 engine?

Thanks again,

Jack

I don't know if there is a specific life of a water pump, but the water pump on my car (see my signature, same engine as yours) went out earlier this year, and in fact, I had forgotten, but that is exactly how it went out.

I was loosing coolant, couldn't find a leak, but I finally noticed it leaking when I let it idle in my driveway. It was the water pump leaking.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

One more thing to consider is that the mechanic did not get the cooling system properly bled. I have seen where the bleed hose becomes plugged and not allow air escape into the expansion tank.

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Scott Diener
89 300E
93 300E
92 Volvo 740 Wagon aka "Mutt mover"