Very slow Coolant leak. - PeachParts Mercedes-Benz Forum

pberku · #1 08-26-2004, 11:45 PM

My '95 E300 Diesel has had a very slow coolant leak for the last year or so. For the life of me I can't find the source. By a slow coolant leak I mean that I loose about 4 OZ. of coolant every 800 Miles or so.

The car runs fine, no overheating, consistently at 90F with the occasional 100F on very hot days with the AC in traffic. I did change the Expansion cap just incase.

I don't have any symptoms of a blown head-gasket nor a cracked block. No white smoke, no pressure in the upper Radiator hose when cold, no visible oil in the coolant, nor any visible coolant in the oil.

No obvious, or even traces of coolant leaks anywhere, not on the ground, not in the engine compartment, Not in any of the hoses behind the firewall, nor any leaks inside the car.

So far I checked the following:

- Monovalve,
- Auxilaiarry pump
- Water pump
- Radiator
- All hoses,
- Oil cooler lines,
- Winshield washer heater,
- Block Heater,
- Expansion Tank,
- Radiator, and Block Drains.

A pressure test of the cooling system revealed nothing. This is extremely frustrating. Where else can I look?

I would love to hear from anyone else that experienced and solved a coolant leak that was initially hard to diagnose.

Thanks,

Phil

400E_FAN · #2 08-27-2004, 07:56 AM

I had a similar coolant leakage issue for the last year or so and could not
figure out where it was happening. In July I had to make an 800 mile
roundtrip on a hot and humid weekend (92F +) .... My first long trip
in my 400E since I got it.

On the return home I popped the hood (after the engine had cooled) to check
coolant level and noticed (for the first time) that there was a distinct white water mark/residue on that plastic elbow area (literally a spray pattern) on top of the Behr radiator (this elbow has a hose clamped to it that goes to the expansion tank) Found out that that elbow is available for a few bucks at most on-line parts providers....Replaced it alongwith a coolant flush and fill and seems like my coolant level has stablized. The old elbow just crumbled away while I was removing it.

Looking back I always used to notice a couple beads of moisture up on the rubber "pad" on that is attached to the hood. When the hood is closed this is lines up approximately on top of the radiator...but since I could not see any issue with the top of radiator I never connected the moisture on the pad with the coolant loss.

So I think the long trip finally deterioted the elbow to the point it was spouting enough coolant to leave a residue...I am glad that elbow did not go while I was on the road. So my point is that old elbow plastic looked just fine looking it...except that it had "rotted" from the inside out....

Just my 2cents worth.

pberku · #3 08-27-2004, 01:11 PM

Hi Mat, Thanks for your reply. Believe it or not I have been monitoring this "Nipple" on to top of my Radiator tank for the last few weeks. Occasionally I would notice a very small drop (Almost invisible) forming on top of it, I would wipe it off with my hand, but a few Hrs later it may form again. When I say a small drop I do mean it literarily. It was the size of the period at the end of this sentence.

I did not think that such a drop, especially since its not always there can cause me to loose 4 Oz. of antifreeze in 800-Miles, but I did not want to take a chance and sealed the whole area with J-B-Weld.

Based on your comment however, I would like to now change that Nipple. Where did you get it and how do you change this thing.I hope I can still change it inspite of the J-B-Weld that I applied all around it.

Thanks

Phil

400E_FAN · #4 08-30-2004, 10:43 AM

Phil,

A buddy of my ordered the radiator fitting for me with his order from some place in California but I do see it for the 92 400E in FASTLANE under "COOLING".
...somehow I cannot get the link to transplant correctly...so search for it in FASTLANE under your car and model year as "radiator fitting"

As for changing it this is what I did ( these are not meant to be instructions just an outline of the procedure that I used)

With a COLD engine:

1. Drained radiator by opening red drain "stopper" on the bottom left of the radiator
2. Loosened & drained from lower radiator hose (connects to radiator behind the "stopper" area i.e. on the engine side)
3. Loosened & drained hose from waterpump to radiator.
4. Loosened & drained the hose that goes from this radiator fitting (elbow) to
expansion tank
5. Finally VERY VERY gently tried to pry out the fitting...It broke in half at that
point...then used a very small pair of needlenose pliers to pick out the
rest of the remaining piece(s) of the fitting....lost a couple of tiny (a couple
of millimeter square) plastic fragments into the innards of the radiator but there
was no way to retrieve them. Hopefully, they want gung something up inside.
6. The new fitting pops in (make sure it has a rubber gasket on it...the original
had it and so did the replacement)
7. Then went on to take off the t-stat (this sits in the t-stat housing on the
waterpump and will require taking off a rubber hose that has one bolt that is
somewhat hard to get to ...add filtered tap water, sew it up...drive
the thing around for a while...let it cool, drain again and refill with water...
Did that about three times (with heater on FULL to ensure everything diluted out)
over a weekend.
7. Finally, added a new t-stat back in filled with 50/50 coolant/water mix and the
car has been driven about 700 miles since then without any apparent symptoms of coolant loss.

One could save oneself time by skipping step 6 and actually draining the engine
block through drains that are located near the motor mounts on each
side...I looked at that and decided it was too much trouble for me to get at those and
went the longer route as outlined in step 6.

pberku · #5 08-30-2004, 01:58 PM

Thansk for the detailed ouline.

As I mentioned, I used J-B-Weld to seal that fitting, and its still holding well. No leaks from there. If I would have known that its possible to replace, it I wopuld have done it prior to appying the J-B-Weld. I think by know its probably too late. I don't think it will come off that easaly with the J-B-Weld all over the place.

If it does however start leaking again, I'll take a chance, remove it and replace it.

Thanks again

Phil

pberku · #6 09-27-2004, 01:20 AM

After a year of frustration I finally found the source of my antifreeze leak. Its the water-pump housing. The part into which the thermostat mounts.

The leak is extremely small and does not show-up when the system is pressurized for testing. I found it by pure perseverance.

I tried to tighten the thermostat bolts, but this did not help. I then changed the thermostat and gasket, Did not help either. I then noticed that the inside of the aluminium water-pump housing is pitted, and the thermostat gasket can not seal properly. I don't know why it pitted. I have been using MB antifreeze, and so was did the previous original owner.

The leak is very slow, maybe 4 Oz every 800 Miles. Now that I know where the leak is, I can live with that. I am just glad that its not the Head gasket or the heater core. I would like however to fix it. Short of buying a new water-pump housing, any suggestions on how to fix the pitting so that the thermostat gasket can then form a tight seal.

Thanks

Phil

tomm9298 · #7 09-27-2004, 01:30 AM

Yes, aluminum hates tap water. Switch to distilled water. ABout 60 cents per gallon.

kmaysob · #8 09-27-2004, 02:52 AM

form a gasket on the water pump gasket should fill the pit.