Coolant leak: Heater core suspect - Mercedes-Benz Forum
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#1 (permalink) Old 05-09-2012, 07:28 PM
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Coolant leak: Heater core suspect

I've been losing coolant for a couple of months now. Never leave home without a jug of anti-freeze in the trunk.

Stopped by my mechanic this morning to get a diagnosis. I've been underneath the car enough to know that the leak comes from above the bellhousing which made me think the leak was in the vicinity of the heater core.

Once the car was on the lift the mechanic said definitely heater core and claimed the leak was coming through a venting tube piped from the core housing. He estimated replacement cost at $1,000. and figured he need three days from start to finish (10 hours total labor).

Okay I wasn't too surprised, but I'm wondering if there is any other explanation. There is no smell of coolant in the cabin. Heat works fine. No moisture or steam anywhere. Is it possible to have a coolant leak in the interior of the car and no signs or symptoms anywhere other than coolant loss?

Any thoughts appreciated. Thanks.
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#2 (permalink) Old 05-09-2012, 11:24 PM
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Have you checked under the wiper cowl? It's possible the rubber hoses there are leaking.

If you really want to check if it's the heater core, get a large length of coolant hosing and bypass the heater core entirely, it's not terribly hard to do. At least that will isolate the leak and make it easier to work on the heater core.

If you have the ability, I'd recommend doing the heater core yourself. It only requires basic tools, a service manual and some patience. I did it myself about a year and a half ago, just need to pull the dash apart. A new OEM heater core was around 95 dollars from parts.com.

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#3 (permalink) Old 05-10-2012, 07:17 PM
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There's a valve that controls how much coolant the heater core gets on the passenger side. If it leaks it will come out kinda behind the rear of the passenger wheel. The heater core is always good to replace (if it hasnt been done recently), but thats more of a 300$ job (with labor) rather than 1000. The replacement valve is like 20$ and takes about 45 minutes to replace.

Leaking coolant . . . . - 190 Revolution
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#4 (permalink) Old 05-10-2012, 08:03 PM
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Pulled the heater control valve out today and put a lenght of straight hose in place. I don't seem to be losing any coolant, but I will need a couple of days to be sure. The valve was damp and the hoses were pretty ratty looking. I'm not sure if this is it, but I'm desperate to avoid ripping out that dash so I will replace the valve as soon as I can get it ordered.
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#5 (permalink) Old 05-11-2012, 03:32 AM
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My recollection about heater cores comes from helping others repair theirs. Remember the car has two engine compartment bulkheads (forward and rear). I have never had to replace my cars' cores yet.

If the heater core is leaking, coolant will flow into the passenger compartment, not the outside of the rear bulkhead down to the ground. In my experience, such leaks come from the hoses that run from the engine compartment's bypass tube through the forward bulkhead to the core. So the $1,000 repair could be for a replacement of one of these hoses.

I suggest carefully removing the rubber trims and the plastic bug screen under the windshield. Carefully inspect the hose arrangement between the two bulkheads found to the rear of the battery. Those items costs pennies to replace and the dealers carry them in stock.

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#6 (permalink) Old 05-12-2012, 07:22 AM
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The dealer in Bridgewater called this morning. Heater valve is in. One day service. He says distribution warehouse in Robbinsville services the entire northeast. Interesting.

The dealer says he doesn't carry bulk heater hose. He suggested selling me the seperate lengths by part number but that is really expensive. Am I ok getting a good brand at NAPA? Do i need to be concerned about metric sizes in hose? Thanks.
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#7 (permalink) Old 05-12-2012, 05:03 PM
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autohauz is super cheap, you can get pretty much all of them for like 20$

Your Parts Search Returned 0 Part(s) %26 Heat - Climate Control&gid=6892@Heater Hose
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#8 (permalink) Old 05-12-2012, 05:55 PM
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NAPA is imported Chinese crap. Stuff from Azautohaus is typically from Germany or the surrounding areas
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#9 (permalink) Old 05-12-2012, 07:07 PM
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I'm really surprised to hear that. I thought it was all american.
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#10 (permalink) Old 05-15-2012, 03:55 PM
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I did my heater core last year, 2011.

Found lots of repairs done wrong in there while I followed the service manual. Thoroughly cleaned everything as I went.

It took a total of 9 hours, over a Saturday and a Sunday.

I had my parts supplier get the OEM hoses for me. Glad I did, as the ones on the car were either hard as a rock, or mushy.

I washed the entire heater box assembly, cleaned the flaps and surfaces. Previous owners were smokers, and it showed.

I'm so glad that I went ahead and did this job. Everything is working properly, and more importantly, there are no rattles in the dash anymore!!
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