1991 300SE Coolant Leak Source?
 

103.00 engine has sprung significant coolant leak (4-6oz/day). I am at a loss to determine the source. It appears toward the rear of the block but not sure if it's a head gasket or not. Please share your experience with this kind of leak in the 103.00 engine. Any recommendations as to the normal chain of problem solving for this head-ache? Thanks, in advance, for taking time to reply.
Dick Mc D

How many miles on the car?
Has it ever had the head gasket replaced?
Was it sudden?
I think a head gasket would tend to start slow and get worse, but I would'nt say that was a rule.
The first place I'd inspect if I thought I had a leak at the back of the head would be the heater return line. There's a heater hose that returns (I think) coolant from the heater core back to the rear drivers side of the head. It attaches to a steel nipple that bolts (2) to the head. The other end of the nipple pushes into the head about an inch or so and is sealed with an o-ring that hardens and shrinks with age. This could be the source, or it could be the hose itself.

Take off the air cleaner and you'll see it on the head back by the oil filter. It's a little tough to get to but use a flashlight and feel around it for coolant. Check the hose for cracks or hardness. If it seems to be the source, try tightening the hose clamp if you can as a temp fix. If the hose looks like it needs replacing plan on doing the o-ring as well and maybe change the oil at the same time since it helps to remove the oil filter for more room.

If this turns out to be the source I'll post some extra info/procedure.

long-gone,
thanks for the thoughts...my plan is to check the hoses but I'm confident it's the water pump...the car has 130,000 miles and it's probably the time for a new one! I'll keep the board posted on my findings.
thanks again for taking the time to reply...

1988 300CE M103.093 w/115,000 mi.

Well, I had 3 coolant flushes in 2009. :o Radiator went in February. Seam opened up mid-right side of radiator where plastic meets the aluminium frame. Water pump replacement in late Oct. Christmas Eve the thermostat housing (plastic) cracked & broke. That one left me on the roadside. From the time the low coolant light came on it took about 20 secs (@20-25mph) to climb to 100 deg. Park it and dial AAA :rolleyes:
AFAIK, all the replaced parts were original.
You might want to have your thermostat checked & replaced if it is original.

You should hope it's the mentioned hose, water pump is an expensive job on these!
My water pump was original (as far as the well kept records reveal) and I replaced it at about 210K, not because it was bad but I had the head off and figured I do it while the going was easy.

BTW, I was mistaken, the above mentioned hose is the heater inlet, not the return hose.

Look at the drivers side of the oil sump. If there is collant dripping down the side, the water pump needs to be replaced.