[W126 Coupe] Coolant Leak

[Dick Spellman]

Hi Mike:

Obvious stuff would be the expansion tank cap, remove the cap and check 
the condition of the rubber gasket. While there look for any sludge 
(white gunk) on the coolant cap or on the surface of the coolant (brown 
spots) in the expansion tank if oil was getting in there from an 
internal head gasket failure. Sounds like your describing a leak along 
side the block itself. If so, you've got the freeze plugs and the head 
gasket. Pressure test (leak down) would have shown some activity in this 
area if either were bad and/or you have a small external head gasket leak.

If the leak is closer to the passenger compartment maybe check the two 
heater hoses that feed into the intermediate firewall and one that runs 
through the auxilliary pump on route to the heat exchanger? You've 
checked the top seal on the monovalve for leakage? The heat exchanger 
itself could have a leak but you would smell the anti freeze for sure 
when driving with heat applied any leakage would follow the two center 
drains to either side of the tranny. These are self closing rubber 
snouts that are not easily seen but sit directly under the inner firewall.

Not much else I can think of where the water pump, top & bottom hoses 
and vent hoses are all solid.

Regards,

Dick

Mike R. wrote:

> I have a coolant leak that I can’t find. The anti-freeze drips off the 
> passengers side of the engine, up front but there isn’t anything 
> obvious for the source. The water pump weep hole is dry and as far as 
> I can see, even with an mirror, there isn’t any leakage from it the 
> water pump/motor gasket. I’ve looked at the thermostat housing as well 
> as the upper and lower radiator hose connections, but nothing there 
> either. I looked under the intake manifold just a little (place on the 
> passenger side in front of the front intake runner), but no puddles 
> under there either.
>
> I tried some air pressure in the system through the overflow tank and 
> did make it drip a little faster, but nothing apparent for a source. I 
> drove the car and that seems to have _slowed_ down the leak. Went out 
> to a restaurant last night and back, nothing on the ground under the 
> car at the restaurant or my garage this morning. Self healing leaking? 
> Any ideas where to look??
>
> There is a hose, ~1”, that starts somewhere near the water pump and 
> goes toward the back of the engine compartment over the air pump – 
> what’s that for?? Nothing apparent from it but I couldn’t see where it 
> attached on the front of the motor.
>
> Thanks,
>
> Mike R.
>
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