85 300D coolant leak; cant find source
 

I have a coolant leak in my 1985 CA 300D and I cant find the source. Nothing from the visibles in the engine bay, includes hoses to and around thermostat. The leak hits the pavement right below the engine block, just forward of the firewall. My engine temp popped up to 110C and I realized the reservoir was nearly empty. Upon refill the temp corrected. I have messed with the coolant system a little for a veg conversion i have not used yet, but those two joints are leakless. I replaced the thermostat 2 months ago. And the monovalve 1 month ago.

Any suggestions?

Which side? ...Can you tell....I would suspect heater hoses, heater valve,? (pass side) Its not up where it could be the water pump, right?

Hate to say this, but at the worst case scenario, besides leaking out the head gasket, there is a freeze out plug in the back of the block near the top. The transmission hides it. I actually epoxied mine in just to be sure. Paul.

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'84 300CD 290,000

A radiator pressure tester would allow the system to be brought up to
the kind of pressure seen when hot and driving. Then you could
study that area where the leaks show up and see if it is visible.
I rented one recently at the local auto parts store.
Or... an old radiator cap and a tire valve stem make a usable one,
just need a tire pump to add a few pounds pressure.

I second that, unless its the heater core... can you smell that sickly sweet smell?

Water Leaks
 

1984 300d Turbo 137k
Check The Two Top And Botton Weep Holes Water Pump, Replace
Water Pump Diy 2 Hrs
A 15 Psi Tester Jc Whitney.com $100.00

If you can safely get the car up in the air or atleast higher on one side, have a look see by sliding under and inspecting. if you notice the water is coming out of the drains from the climate control stuff inside the car, you've got serious problems.

Hopefully its just a hose...

Thanks all. The leak hitting the ground is back by the fire wall. i have not had a chance to get under the car, so i cant really determine the leak path.

Q: how does one test the auxiliary water pump? Can I check for vibration with the ignition power on and the heat on, or need I turn the car over too?

The other thing I forgot to mention was that I did some fuel system work on the car and had a hard time priming the fuel system. The result was excessive cranking to get it started. Could this cause temporary leakage, or "spitting"?

Oh, and by the way, no sickly sweet smell. That would be coming into the cabin right? Poison!!

two drains
 

There are two drains from the heater/ac plenum that drain to the exterior. I would hope that if there was a problem, it would not leak into the interior. These also drain the ac condensation. One is where the ac hoses exit the firewall below the battery area via an oblong grommet & the other is more centered-like just above the transmission, Paul.

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'84 300CD 290,000

Thats a good idea. There not cheap to buy. I have one and use it every time I work on a cooling system. Its amazing how many times I find a small leak that otherwise would have gone unnoticed.
If I made one, I would want a gauge, you dont want to cause damage:rolleyes: