Sudden but slow coolant leak - first post, be gentle

[Neilos]

Hi

About three months ago I purchased a 1999 C200. Prior to purchase I had a mechanic inspect the car and he gave it a clean bill of health.

The car runs and idles very smoothly and the temperature has not risen at any time. Yesterday however, the coolant warning lamp lit up. I checked the coolant level which was slightly below the expansion tank and I noticed some (but not too much) coolant had gathered in the plastic shelf below the engine.

I inspected the engine bay and could not see any immediate signs of a leak - but in no way am I familiar with engines.

I reviewed the log books and noted that the water pump was changed about 5 months ago and the coolant was bled and filled by a decent professional mechanic with Castrol Anti Freeze/Anti Boil.

I therefore topped up the coolant with 50% Castrol and 50% demineralised water and ran the engine for about ten minutes with no issues in that the engine was running smoothly and the temperature was normal. There seems to be no immediate sign of the coolant leaking - but will check it again tomorrow.

Fearing that it could be a head gasket issue I checked the oil and it seems a little darker than I would normally expect but no froth or milky residue. Also, as above, the engine idles well and there seems to be no oil in the coolant.

Before I take the car to a mechanic in Sydney, Australia, which will cost a fortune, if anyone has any ideas about what the root cause could be, I would be very appreciative to hear from you.

Regards
Neil

[bachusattackus]

I had a slow leak from my reservoir bottle, the nozzle at the top was cracked. I had to replace the reservoir bottle.

If it was the water pump, the fluid would be at the front of the engine, under the little cover at the top/front.

[Check Codes]

Welcome. Please take a moment to click user cp and edit details so you can easily add your vehicle and location to your profile, it's often useful information when you're seeking assistance.

99% of the time when the coolant leak is through the head gasket, it's inside the engine, so thank your lucky stars yours is external. (The converse is also true: it's exceedingly rare that a head gasket will fail in such a way as to allow an external coolant leak.) There are also hose connections that can leak and drip, and of course coolant will run down a hose or pipe, etc. until it hits a low point and drips off.

It's entirely possible you simply have a loose clamp and it's leaking only when the engine is at operating temp and shut down, then heat soak lets water temperatures (and pressures) rise a little, then it seeps out until the pressure falls off enough. In any event, just add your coolant mix as needed until you can have the shop look at it.

Good luck and enjoy the car.

[agillot]

Originally Posted by Neilos

Hi

About three months ago I purchased a 1999 C200. Prior to purchase I had a mechanic inspect the car and he gave it a clean bill of health.

The car runs and idles very smoothly and the temperature has not risen at any time. Yesterday however, the coolant warning lamp lit up. I checked the coolant level which was slightly below the expansion tank and I noticed some (but not too much) coolant had gathered in the plastic shelf below the engine.

I inspected the engine bay and could not see any immediate signs of a leak - but in no way am I familiar with engines.

I reviewed the log books and noted that the water pump was changed about 5 months ago and the coolant was bled and filled by a decent professional mechanic with Castrol Anti Freeze/Anti Boil.

I therefore topped up the coolant with 50% Castrol and 50% demineralised water and ran the engine for about ten minutes with no issues in that the engine was running smoothly and the temperature was normal. There seems to be no immediate sign of the coolant leaking - but will check it again tomorrow.

Fearing that it could be a head gasket issue I checked the oil and it seems a little darker than I would normally expect but no froth or milky residue. Also, as above, the engine idles well and there seems to be no oil in the coolant.

Before I take the car to a mechanic in Sydney, Australia, which will cost a fortune, if anyone has any ideas about what the root cause could be, I would be very appreciative to hear from you.

Regards
Neil

in a few ocasion , i have seen this engine leaking coolant at the right rear part of the head gasket .had good luck with BAR stop leak [ brown powder ] , this will buy you a couple or more years .

[Neilos]

Thank you for your responses.

I am pretty happy it is extremely unlikely to be a head gasket - partilarly given that its done only 98,000km or c. 60,000 miles.

Also, if its of any interest, when inspecting the car this morning, there seemed to be no sign of any futher leaking. Hopfeully I can nurse it until such time as a service is due.

Thanks again.

[Neilos]

Just to close the loop on this one, the problem was an incorreclty fitted water pump.

I had to have the water pump removed and re-installed with a new gasket seal (I think!)

Coolant has now stopped leaking and car is hummong along nicely.

[jc1kz]

Glad you found the source of the coolant leak and no real damage was done to the car....and thank you for closing the loop with the rnd result. Hope you enjoy the car for a long time worry free......