Mysterious Coolant leak... - PeachParts Mercedes-Benz Forum

mikethezipper · #1 12-25-2009, 02:22 PM

I have an 84 300D which has mysteriously developed a coolant leak on the front of the engine at what SEEMS like to be the hole that the arrow is pointing at. This is on the front of the engine just under the water pump:

What do ya'll think this is?
So here is the story:
I had just four days prior done a system flush, drained out all the old green crap, and had degreased it, had run a jar of coolant flush (was waiting for the citric acid to arrive). I replaced the thermostat as well. All was well in the world. Then I drove the car out of town, and when I parked it, there was a nice leak coming from the front of the engine. I checked every hose, the thermostat area, etc, but it doesn't seem to be coming from any of those places. It seems to be (but it is so cramped I can't tell for sure) to be coming from that hole. What is that hole? It seems to stop leaking when the reservoir tank is only about a 1/3 full, and will leak if I add more to it. I drove it 30 miles like this, and it was fine (no overheating etc) I stopped to check on everything, and added some more water just to be sure, and added 1/3 a cup of citric acid, just because I could. Well within 400 feet my car went to 110 degrees, so I pulled over just to see that now the leak seemed worse, but not that much. I pulled the thermostat (which is brand new) and now it doesn't overheat, but it still leaks in that hole. I have since drained everything out, but the leak is still there. What gives?

I disconnected the top hose from the radiator with the engine running, and it sprayed water everywhere, so I'm assuming the water pump is still good.

I'm about to pull the fan off and try to plug up the hole with some high temp muffler putty, but I wanted some input first. Thanks!

tbomachines · #2 12-25-2009, 02:43 PM

Are you absolutely positive it isn't coming from the bottom of the water pump housing?? IMHO it is nearly impossible to tell exactly where it is coming from since the bottom water pump housing bolts are behind the crank pulley, unless you have the engine out and you can move around it easily. Money is on water pump housing...

mikethezipper · #3 12-25-2009, 02:57 PM

I am not positive. I'm going to see if I can find some playdoh or something and jam it in that hole to see if that stops it, if not, I'll look elsewhere. Any idea on why the leak would materialize now? An old timer that saw me on the side of the road recommended putting black pepper in there and letting that clog the leak, not my way of doing things, but it was funny/interesting.

kerry · #4 12-25-2009, 03:29 PM

Leaks in that area almost always come from the water pump seals which could have failed as a result of the flush.

Brian Carlton · #5 12-25-2009, 04:02 PM

Quote:

Originally Posted by kerry

Leaks in that area almost always come from the water pump seals which could have failed as a result of the flush.

Agreed.

mikethezipper · #6 12-26-2009, 02:27 PM

So after spending a good two days trying to get the viscofan off, and finally succeeding, four wrenches later, I found that the leak is most definitely coming from the bottom weeping hole of the water pump. I'm in the process of getting a new one. Any objections to getting one from Autozone tomorrow as opposed to waiting a week (or more) for one from peachparts?

tbomachines · #7 12-27-2009, 01:01 AM

Also replace ALL the screws holding the water pump on with new ones of the same size/thread. After all of the heating and cooling the bolts can become very brittle. When I did my WP the first time (long story...) I ended up snapping off 3 of the bolts off in the old housing. Its a good thing I had a spare or else it would have been up to the screw extractor. The 10mm screws holding the fan on are definitely a PITA--a good soak in PB blaster and a good set of tight vice grips make them pretty easy though. Good luck, let us know how it goes. Be sure to order the gasket as well.

As far as the alternator bolts, I'd tighten them down pretty good so the entire load isn't resting on that little tensioner bolt. If that bends you'll have to order a new one since they are an atypical sort of thing. Tension the belts just as you would normally--enough not to slip.