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Coolant Loss

9K views 35 replies 6 participants last post by  Tylerman 
#1 ·
This on my daughters 96 C280, 245,000 miles. It has had a persistent coolant loss over the last few months, although I didn't realize it until just recently. My daughter finally mentioned that every couple of weeks the coolant warning light comes on, so she pours in a bottle of 50/50 and goes on her way. I topped up the reservoir and have been watching it all weekend, but there aren't any puddles in any obvious locations. I also checked all the hoses, the pump, t-stat and reservoir and cannot find any wet spots. All the hoses and belts were replaced about two years/30,000 miles ago. The oil is clean.
I did notice, however, there is a stain on the driveway behind the rear passenger tire (she parks in this spot regularly) and it is slightly damp there now. Is there some reason why coolant would be leaking out of the car way back there?
 
#4 ·
Head Gasket Leak with Moisture being Expelled via the Tail Pipe??

Any "White Smoke" while Driving?

Have you checked the "Diaper" (Plastic Underguard) for any signs of Concentrated Coolant? (Remember, a sloooow leak in the engine bay will cause the water to Evaporate in the Hot environ.) so the leak may not be readily visible.

"My" first Diagnostic Step would be to Pressure Test the System, to see if you can locate the Leak

Second step would be to do a Cylinder Head Leak (CO2) Check.

Third step would be a Dye Examination.

Here is how "I" tracked my leak down (W210):

http://www.benzworld.org/forums/w210-e-class/1625614-photo-diy-coolant-leak-now-problem.html
 
#5 ·
Fascinating, I had no idea the washer fluid reservoir was warmed by the coolant system, are you sure this system is extant on a W202?. Given that, though, and given that my daughter had four empty me gallon bottles of 50/50 in her car, shouldn't the washer fluid res be overflowing?
 
#6 ·
More information.
First off, my washer fluid reservoir is not connected to the coolant system, but thank you G-AMG for the idea.
I filled the coolant reservoir on Saturday and let the car idle for about 45 minutes. No drop in the coolant level. I decided since I have a long highway commute (>40 miles) i would take it to work this morning. Halfway through and the coolant level warning light came on. Unfortunately it was raining so by the time I got to work there were wet surface all over the undercarriage and I couldn't see the leak. My guess is then that this leak manifests itself at higher rpms. When the weather dries up at least I can take another stab at this in the driveway running the car up to 2500 - 3000 rpms and see if it starts the flow.
Any likely potential spots to look for? Any thoughts are helpful.
 
#7 ·
Dunno where Cypress is, but if you are anywhere "South", you are more than welcome to drop by, and we could check it out.

"Personally" I find it safer to Pressure test. Engine off, no standing in front of a car which is winding out at 3,000 RPM... ;-)

Check you local "Wally-World" Auto parts store. They may have a Pressure Testing set you can "Borrow"/Loan.

When you pressurize the system, have a good look at the Coolant Hose Connections, the Heater Core near the firewall, and the "Weep-Hole" of the Water Pump.
 
#8 ·
The puddle behind the RR wheel could only be fuel IMO, fuel pump and filler neck are right there, so make sure you check that. There shouldn't be anything coolant related anywhere near there.

For the coolant leak, go to oreillys or alternative, and rent a radiator pressure tester. Make sure its full, then pressure test the system. You will see coolant running out somewhere if there is an external leak. If internal, you want to be careful, as the water could make its way into a cylinder and cause hydraulic lock. To avoid this, I would suggest that if you pressure test it, and you don't see any signs of fluid leaks, but the pressure goes down considerably, before you try to start it remove all plugs and turn motor over a few times with starter. If water got in a cylinder this will blow the water out the spark plug hole and prevent you from bending a rod if you try to start it without taking this step. If it has water in a cylinder, then obviously you have a leaking head gasket. BTW, I think this is common for the 280's.
 
#9 ·
Sounds like a large leak and I would guess (hope) more to do with a hose or water pump than with a head gasket leaking and going out the tailpipe.

This is the M104 inline 6 and hopefully the stronger updated gasket is in there. Failure in older cars showed as oil floating in coolant reservoir or chocolately foamy scum in the oil cap.

As others have suggested, rent a pressure tester. Its like a bicycle pump you fit to your system to pressurize it and the leak should be obvious. Trick here is to get a kit with the right fitting for your car and to get it to seal right so you can pressurize. More definitive and easier than crawling around a hot idling car.
 
#10 ·
I guess the pressure tester is my next step. In driving to and from work this morning, just over eighty miles, it ran through the bottle of coolant I put in it on Saturday as well as another full gallon I put in this morning once I got to work. I ran it in the driveway (parking brake on, with the wife keeping the revs up with a foot on the brake pedal) and I still cannot see anywhere the coolant is going. The engine bay is dry, the oil is clean, hell if it had two gallons of coolant in the cylinders one would think that would manifest itself in some measure of driveability problems.
 
#16 · (Edited)
What about the undercar shield, the plastic part under the engine? Is it there? Is the drain clogged? Is it bent?

Does coolant leak at the duovalve, then run into the under car shield, into the door sill and then leak out by the rear right tire?

Have you taken the car for a drive enough to get the a/c working, thereby circulating coolant throughout the duovalve and heater core, and then let the car sit and run while warmed up in order to make an observation? This is the only way you'll be able to diagnose your leak, I think.
 
#18 · (Edited)
Man I'm in Houston Texas, the only time the AC doesn't run is when the car isn't running. But yes, I have run the car from cold up to operating temps, and right after having parked it while it is still hot.
Someone else mentioned the under car shield. The plastic shield directly beneath the engine has been gone for some time (my dad bought this car new, I bought it from him for my daughter two years ago) which has made it easier to do oil changes. Unless there is another shield along the side of the engine compartment. Again though, there is only the small damp spot beneath the rear passenger tire and of course condensate water from the air conditioning. The condensate is clean water, not coolant, and the other spot is too small/not growing fast enough to correspond to the rate of fluid loss I am experiencing. What are you referring to when you mention the duovalve? Where would I find it?
 
#19 ·
For this to work, it would have to be running beneath the doors inside the sill, then accumulating somewhere because while idling in the driveway it is not dripping onto the ground. There is a stain as I mentioned behind the rear passenger tire though, so maybe there is something to this. Are you saying the overflow tube attached to the neck of the filler is bubbling over? Isn't it supposed to do that? At some point, the level in the reservoir would be low enough that it wouldn't drain the system almost completely empty which is what is happening to me.

Is there something that could be "boiling" the coolant out? Normal engine temps are just above the 180 degree mark, middle of the gauge, nothing unusual.
 
#21 ·
Replace the cap. Don't bother with a Stant, go to the dealer to get one. It is not expensive. You need the dealer item because the pressure rating needs to be absolutely correct. Those caps don't last forever.

The coolant could be escaping as vapor, mixing with the air that is circulating in the engine compartment (no under shield) and therefore just disappearing.

The coolant is never meant to boil or freeze, and the system on a Mercedes (and BMW) is different from other cars. The reservoir is meant to be filled along with the radiator, fill it to the black top of the bottle.
 
#22 ·
Well I stopped by the local MB dealer and got a new cap. I'll give it a day or two to see if that did it.
Something I noticed about the cap. The old cap had a tight metal screen on the underside which I could push in approx 3/16", the new cap has a slotted plastic underside, no screen, which cannot be pushed in. I gave the dealer my VIN just to be certain it was the right part, one can only assume the part changed somewhere.
 
#26 ·
Man, I have to say after reading your thread chasing down your coolant leak (ultimately through your washer res) and now this, I have the utmost respect for the effort you put into your car. However, I am lazy and will simply replace this part every five years or so.
 
#27 ·
Well I got a cryptic text from my daughter last night that indicated the coolant level warning light is back on. She did not mention if she looked under the hood to check the fluid level directly. Odd, when I drove it prior to replacing the cap, the light would come on within 10 miles from home. When I replaced the cap and topped up the reservoir the car made it over 80 miles with no light and the level appear unchanged.
 
#28 ·
You're system may be "burping"- circulating and releasing air bubbles. With very frequent shortages, you probably got a lot of air in the system. Have her continue filling it with 50/50.

Fill it to just barely under the black top of the coolant bottle.
 
#32 ·
At last, I think I have it. To tell you though, I have to make something of an admission. Years back when bought this from my dad (who bought the car new) the A/C didn't work correctly. It would blow cold, then after twenty or thirty seconds it would blow hot. He got a quote to fix it of $2k or something and figured it was just as easy to sell it. The temp control panel on the dash was blank, so figured replacing that would set things to right. One replacement panel from a junkyard and viola, I had a working temp panel, but the same problem persisted. At this point, my family and I were still reeling from the depths of the financial meltdown and I had to come up with a cheap solution. I took it to a local shop who identified a vacuum problem in the, well I cannot recall the part but it regulates air flow from either the compressor or the heater coil. It defaulted to the heater coil. Rather than spend the $1500 to replace the faulty vacuum switching module, I had them bypass the heater coil so it would never produce hot air, no matter what. Ok so it was a bodge and I am not proud of it but I live in south Texas and I need heat about four days out of the year, and A/C all year round so I made a tough decision and I have to look myself in the mirror every morning knowing what I've done.
Anyway, turns out the rubber cap they installed on the port on the drivers side of the engine (what I assume is where the heated coolant is pushed to the heater coil) had deteriorated, and given its well hidden location beneath the air intake shroud and a bundle of wires i couldn't see the water leaking by. It also had to be pressurized before it would leak, causing the numerous cracks in the rubber cap to become porous. So rather than repair the system properly, I just put another rubber cap on it, and will fix it again in three years when it cracks again. Maybe I will be in a better financial place to really fix it correctly. Who knows?
 
#33 ·
I am familiar with those rubber caps, and the problem with them is that there is no reinforcement webbing in them. A better solution would be to take a piece of heater hose and connect one end where your rubber cap is now, and the other end to where they installed the other rubber cap. This way you at least have a good quality hose that won't burst on you.


Sent from AutoGuide.com App
 
#35 ·
The "vacuum elements" are behind the dash. This guy actually took the time to fix his-

With this post

Since our cars have dual zone temperature selectors, we have two elements dedicated to making the mix of heated/cooled air, one for each side. Autohausaz has them listed in the electrical and vacuum section, sold as the left and right tempering flap actuators. If you take of the under dash panels, you can look up under the dash and see where some of these actuators are. If your lucky, you can reach the actuators by hand.

If not, fixing your problem would be time consuming, but not beyond your abilities and much cheaper than $1500. Problem is it would take about 5-8 hours of your time.
 
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