DrugDealr

Howdy guys, well its been about 3 months or so since I bought the car, put about 1.5K miles on it. about a month into it I got a top off coolant warning, put in some coolant, all was fine. then tonight I was about to go a for a spirited drive and the warning came on again. Each time I've put in about 1/3rd gallon of coolant in to top it off. I don't seem to have a leak anywhere that I can see the dried blue crust build up from the coolant. I'm going to replace my outside temp sensor tomorrow, so I can inspect it better from the bottom looking up. I'm concerned this might be the dreaded head bolt problem, car has 95K on it. Pulls like a dream, last weekend cruised around the highways doing some pulls, no hesitation from the engine what so ever. Oil looks oily, not milky, hasn't seem to gone up on volume. Any input?

Benzaddict32

If it’s the M156 engine, it could be the head bolts. If it is, be careful and have it fixed. If you don’t, you could hydrolock the engine.
If it’s the M113K, I’d start by looking at the intercooler first. Good luck

tw2

Burning coolant doesn't need to involve the oil. I would inpect and ideally replace the headbolts before major carnage.

Saurabh914

I’d get a compression test done. For me it was my head bolts. If I were you, I wouldn’t drive it much until you can confirm where the coolant is going.

DrugDealr

working on getting some quotes done tomorrow for the head bolts. Is this a 5K repair?

Saurabh914

From the dealer probably, I paid around 1.5k for mine, I’d suggest finding a trustworthy shop who actually knows about this engine and going from there. Shop around and get some quotes.

DrugDealr

I’ll have to get local shop quotes then, I have an appointment with the dealer tomorrow for an estimate. Nobody really wants to touch these cars to begin with, my sunroofs motor is going out and no Mercedes mechanic wants to touch it...

bbirdwell

FWIW, check the coolant reservoir. My 2005's reservoir was literally falling apart due to old age and I was losing coolant out of a fitting that was bad (errata: my '99 E55 was just diagnosed with the same issue last week). $40 and an hour of my time to repair. Mine did not have obvious signs of coolant leaking; I literally found it by inspecting the reservoir and realized it when I went to lift the reservoir and pieces pulled off in my hands....

Yuille36

A few winters ago, I took a trip up to PA, and as such conducted a PTI (Pre Trip inspection).
What is most likely happening is that you have a small crack in your radiator, that's causing your coolant leak.
When my engine was cold, barely any leaks, but once the engine was hot....leaks. (Contraction and Expansion)
So in my case it took weeks before the coolant light appeared. This might be the same in your case.
Get the engine hot then check you radiator, coolant hoses, expansion tank and hose, thermostat housing for leaks.

bbirdwell

Excellent suggestions by Yuille36. I once found a minor leak from an old o-ring on the heater valve on the side under the wiper cowling. Would drip at the back of the front fender when hot and pressurized. Be advised that if that is where the leak is located that you might as well buy a new cowling at the base of the windshield as the old one will break when you remove it.

Yuille36

During that winter, I didn’t see any leaks as the belly pans captured any and all fluids. But, I figured that I had a leak somewhere, as I was checking and topping off coolant on that long road trip. We check coolant expansion tank for leaks, coolant hoses then my tech spotted a leak at the bottom right side of the radiator.
That radiator was 12 yrs old, I was just lucky it didn’t leave me stranded on the side of the road 🙏🏽 But a new OEM one set me back $385.

But, I will say this. Get your car diagnosed and fixed before this leave you stranded somewhere. 😩

DrugDealr

Well called around for some quotes... nobody seems to be equipped to do/want to do the head bolts. Only quote so far came from Eurocharged for right around 3.4K including parts. Listed 14 hour of work for an engine out job. Was a little concerned as they just listed the FCPEuro kit to change out the bolts and not the comprehensive kit that includes the spark plugs, oil, coolant, and gaskets and such. I assume they wanted to replace one by one without changing the head gaskets.

machild

While head bolts are a possibility, that is not the only possible issue causing a loss of coolant. Some of the suggestions here you can do to confirm whether an external small coolant leak is occurring. If you can't find it then you should have the car towed (not driven) to the best tech in your area and have the issue sorted out. Then you can come up with a plan to get whatever the repairs need to be completed by someone qualified.

Yuille36

If you were to have broken head bolts, and coolant was leaking inside the combustion chambers, you would have received a check engine light.
To rule this out of the equation, have your mechanic borescope your cylinders.
I believe your coolant issue, if coming from elsewhere. I would start by having the car diagnosed.

Saurabh914

I wouldn’t go for the head bolt repair right away without a diagnosis. Like I said try to get a compression test done. That will show where the leak is as the coolant would be spilling out from such area. Just like the others said, try to observe if your radiator or any hoses are broken.

Yuille36

Agreed, a compression test will definitely reveal the leak.