Finding a coolant leak M103
 

I've got a "mysterious" coolant leak on the TE. I've put about a gallon of coolant in it over the last week since Mom said the coolant level light came on.

I see no drips, all the accessable hoses are dry, but I do get a sniff of coolant around the water pump hot. Hoses get harder as it warms up, so the leak isn't huge.

Given that I cannot see the water pump weep hole, any hints on how to tell if that is the leak? I've got a new belt and tensioner to put on anyway, this would be a good time to do the water pump as well.

Thanks!

Peter

It's the water pump. Coolant leaks out the weep hole, down the body of the pump, between the two lower bolts and along the oil pan flange of the block. Yuo can probably snake a finger to the 7 o'clock position of the water pump snout to feel the weep hole. If you undress the area so you can see, you'll get the idea that the water pump is leaking from the main passage to the block or the water pump body is cracked. The leak from the weep hole is very covert when viewed from above.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

I had a coolant leak on my M103 engine as well. I initially thought it was water pump but it turned out to be the small hose at the back of the engine that goes inside the car. (The one connected to the lifting hook at the back of the engine).

Found it out by pressure testing the system.

Regards

Hook up a cooling system pressure tester. Auto-Zone and other mass marketers rent them. I too had a problem finding an M103 leak and this took care of it.

Thanks guys. I'd planned on borrowing a pressure tester shortly (have a friend in the radiator business), but with a whiff of coolant at the water pump, I'm pretty sure that's the problem.

215,000 miles and I don't know when it was replaced last, not bad.

As I said, now is the time since I gotta take everything else off anyway.

Peter

Larry Bible had this problem about three or four months ago, posted it, and got a very detailed answer about how the coolant from this leak flows. Check out Dr. Diesel's response:

http://www.peachparts.com/shopforum/tech-help/59053-water-pump-leaking.html

FWIW, on my (former) 300E, I had a leak from the side seam of the radiator that was very hard to locate.

I'm calling it a mystery leak because NOTHING shows any signs of coolant without pressure in the cooling system, so I'm more than happy to get hints. Had the same problem on the Volvo until I got a pressure tester on it and found a heater hose I didn't know was there, dribbling nicely.

Rad is completely dry as far as I can tell, at least on the back side and bottom.

Will keep looking.....

Peter

NAPA sells a dye to find leaks!
 

If everything else fails, buy that dye and with a black light you should be able to find the leak for cheap. Even if you have to buy a black light bulb from Home Depot. Very similar to the dye in the A/C system. Good luck!

If it helps, here's a picture of the weep hole on the water pump I took out of my 86 300E last weekend. It's at about the angle you'd see it when mounted on the engine. I've cleaned up the area around the hole for clarity. If you had a small inspection mirror on a wand and a flashlight, you might be able to see this area with the pump and pulley in place.

Gary

Thanks Gary!

I know there has to be one in there somewhere, but I couldn't find a way to look or get a hand in to check, and the engine was hot at the time, too.

I'm gonna borrow a pressure tester in the next couple days and blow it up. Gotta be leaking somewhere!

Peter

It's the water pump. Filled it up again today, and coolant was running off the oil pan just behind the AC compressor.

Gonna order on tomorrow, Mom will be driving the 300D until I get it fixed.

Peter