1991 190E 2.6 Oil Filter Housing Leaking Coolant?

A few weeks ago I flushed the coolant in my 1991 190E 2.6, refilled and ran the car for approx 500 miles with no problems. The other night my wife mentioned that the radiator light had come on intermittently will
driving home, so I checked the coolant reservoir bottle, and sure enough the coolant level was down to the sensor. I refilled and she drove the car another 50 miles -- I checked again and found that the coolant level was down about 1 inch in the coolant reservoir.
I checked all of the hoses, radiator, thermostat etc., (some of you may recall that this car had had a head gasket replacement in March of last year - see: http://tinyurl.com/gu8z ) and still could not find a leak. I finally noticed coolant leaking under the car on the drivers side and appeared to be dripping from the engine block, bell housing area.
I have eventually located the general area of the leak; it appears to be coming from the oil filter housing - the unit that the oil filter is mounted on and connects into the block. I can find no leaking or wet area above the unit, but definitely coolant just below the unit (it pools on the block lip just beneath the unit, and then produces the drip/leak mentioned above). No oil dripping from the unit, no oil in coolant, no coolant in oil, no hose leaks that I can find, car is running fine, temps are between 80 - 90c under summer driving conditions, just this new & very prominent coolant leak.
So, before I attempt exploring further my questions are:
1. Anyone else heard of coolant leaks from this unit/area? 2. Is there an O-ring or gasket that could have broken down & I can replace? I'd hate to spend $$$ having a simple $2-3 gasket replaced if this is the case.
Any suggestions/advise appreciated.
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There is an o-ring seal on the heater pipe connection to the head right above there.
Bill Ditmire Ditmire Motorworks,Inc. 425 White Horse Pike Absecon,NJ 08201 http://www.ditmire.com 609-641-3392
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Bill Ditmire wrote:

Thanks Bill, the heater pipe & hose (the one leading from the head above the unit into the driver side firewall) looks fine on the exterior. Without taking too much apart, I was able to get my fingers into the area around the top of the oil filter housing unit and didn't notice any oil, coolant, or anything wet above the unit -- only the pool directly below the unit. I'll take the airfilter housing etc., off tomorrow and see if I can find anything obvious. Would a faulty o-ring seal in the heater pipe display similar symptoms?
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Sure. A trickle of water follows the easiest path to the ground, and is hard to follow visually.
Bill Ditmire Ditmire Motorworks,Inc. 425 White Horse Pike Absecon,NJ 08201 http://www.ditmire.com 609-641-3392
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Bill Ditmire wrote:

I experimented a bit this morning -- I topped off the coolant, turned off all heat/cooling and drove my son to work, round trip 50 miles, using only the standard air vents for air circulation. No coolant loss, no drips, no wet spots under the filter housing. I plan to let the engine cool down and then do some more checking this morning -- I'll start the car, bring it to normal operating temp and then turn the heater & cooling on... I suspect that the drip/leak will re-occur after I've done this. In the meantime I'll do some research on how to replace the heater pipe o-ring :-)
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Bill Ditmire wrote:

Just an update -- I found the problem. The problem was right where you suspected, fortunately it wasn't the o-ring or the connector pipe leading into the head, but instead is a bad hose to the heater pipe at the head.
The reason that I didn't detect any wetness at this connector yesterday is I checked that area when the engine was hot and had been turned off for several minutes. The engine heat was probably dissapating the coolant rapidly on that part of the engine. So, every time I turned the car off, waited a bit to check around the head heater pipe etc., that coolant had evaporated and I was only able to find the left over puddle that formed around the base of the oil filter unit and below.
The hose was cracked where it connects to the head heater pipe, so I cut about an inch off and re-attached. That cracked & split, so I cut a bit more off -- same result. Note: I hadn't intended to leave the old hose on, just figured that I'd get it working long enough to get to the parts store. Anyway, got the hose off and will replace with a new one from MBZ tomorrow ($30.49 including tax). I figure that it'll be $30 well spent rather than trying to jury rig an after market hose from Kragens & wouldn't like to think of the mess if the hose had cracked on the drivers compartment side of the firewall.
Thanks again for your help & kind advise!
For others that may have a similar problem in the future; the heater hose on my 1991 190E 2.6 is MBZ part #201 832 0594 and is the hose that connects from the rear of the head through the firewall on the drivers side to the heater unit. Getting to the hose in the engine compartment is a snap, and getting to the other end behind the firewall was pretty easy as well. All you need to do is remove the plastic leaf guard tray (don't know if this is the correct term) that covers the area between the windshield/wiper assy and engine compartment firewall, undo the clamp on the other end & slide the hose out of the firewall hole. There is enough room on the drivers side of the firewall (from the top) to undo & redo the hose and clamp, so no need to attempt taking off the firewall panel itself. Caution - be sure to drain the coolant from the engine/radiator/coolant reserve bottle first!
All in all about 15 minutes to get the leaf guard tray off and remove the hose. Hopefully about the same to replace it, and an hour or so to refill & test.
Symptoms for my problem:
- Loss of coolant - primarily when the heater or cooler is used - Coolant drips underneath the driver side of the car - Coolant puddle at the base of the oil filter unit that connects to the block (you can see this with a flashlight by looking at the bock just in front of the oil filter assembly -- I saw a small puddle, twisted a paper towel like a stick, and was able poke it down into the area to dab up the liquid & confirm that it was coolant and not oil).
Detection:
- The car didn't have any major coolant drips or major loss of coolant while driving with the heater and/or cooling system off. - The only way that I found the leak was to start with a cool engine, start the car and let it run for approx 5 minutes with the heater on high, then shut the car down and check for dampness/leaks around the heater pipe & hose that connects to the engine head. That brought the car up to temp, opened the thermostat, and yet kept the head etc cool enough that I could detect the wetness with a paper towel and not burn my hands in the process.
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