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Unusual Coolant Leak

7K views 17 replies 6 participants last post by  JBsable99 
#1 ·
Hello. So here's the back story--

I was sitting in my car before work last week (just catching a few more comments from the local sports radio station) when I noticed that I had steam/smoke coming from under the hood. It wasn't a whole lot but it persisted so I popped the hood and discovered that I had a coolant leak. A quick look revealed that coolant was leaking out from the gasket where the thermostat housing meets the intake manifold. After I got home from work that day I checked on how tight the bolts were and they were pretty snug. I snugged them up a bit more just to slow the leak until I could completely replace the gasket. Everything seemed to be working just fine until I was sitting at the airport waiting for a friend to arrive. While I was waiting, with my car parked and running, coolant suddenly began spewing out of the expansion tank cap!! It was not slow leak either. I lost almost a gallon of coolant in less than 1 minute. I let the car cool for a couple minutes, refilled the expansion tank, capped it, and thankfully got it back home. A quick check at home revealed that the leak at the thermostat housing had worsened after the airport incident. The next day I changed the thermostat gasket and the expansion tank cap. Everything was fine until...

...about 15 minutes ago. I've been periodically checking my work and tonight I saw that coolant has started to slowly leak from the same spot. I just changed the gasket last Saturday. I can change it again, but that does not seem to be the root cause. I know that the housing bolts are tight. Could it be that my thermostat is failing the stay open after it has opened? (maybe that could explain the fountain of coolant at the airport--a sudden pressure build up from the thermostat closing)

Anyway, does anyone have any suggestions? Has anyone experienced this before? A flush is due, perhaps I have a blockage elsewhere? Failing water pump?

Thanks!
 
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#3 ·
Yep. If it was backwards I would have some major problems keeping the engine cool.

To stir the thinking pot:
I topped off the expansion tank this morn to the high cold fill line. When I got to work I checked the level and it had actually risen over the 20 minute drive. Coolant was still dripping from the thermostat housing as a slow leak. The rising level has me wondering if the system is developing an air lock that is pushing coolant out of the system. An air lock may explain why I had coolant bubbling out of the expansion tank at the airport. Perhaps my water pump is failing and the coolant flow rate is not suitable for pushing air out of the system.
 
#4 ·
Your problem with boilover is possibly due to the fact that you do not have full pressurization of the cooling system with that leak. As long as coolant is circulating through the radiator at a normal flow rate while the engine is running, it will stay below the boiling point. Once you shut off a running engine or lower the circulation flow rate, the coolant temp will rise sharply since there is no longer sufficient heat removal at the radiator and the engine block is heating the coolant within the block.

This would cause the coolant to flash to steam which then will force coolant from the block into your overflow tank. Especially if your coolant system cannot hold the pressure it was originally designed to hold. Often, the leak is at the pressure cap or from a crack in the tank.

You need to take care of that leak and a coolant change and/or flush wouldn't hurt.
 
#6 ·
Use a decent gasket cement (I recommend Gasgacinch) on the thermostat gasket. NOT silicone/RTV.......
 
#7 ·
Thanks for the feedback everyone. I will replace the stat and gasket with Motorcraft parts. Would any of you replace the expansion tank too? It isn't very old, maybe 1 year. I had to replace it last winter because it cracked open.

About the gasket cement, what is the purpose? To create a seal or keep the gasket stuck to one of the parts during assembly (or both)? Gaskets at O'reilly and Autozone have one side covered with adhesive.

I will hopefully be able to do it this weekend and be able to give feedback. I am still trying to wrap my head around why the leak started in the first place. I would have expected the initial leak to have developed 1 or 2 weeks after I replaced the stat back in October, not 3 months (that's not to say that it can't happen though). I keep going back to rickpark's comment on the flow rate and how that affects pressure, so I think I'll examine the water pump too. At least the temp gauge shows normal temp.
 
#8 ·
About the gasket cement, what is the purpose? To create a seal or keep the gasket stuck to one of the parts during assembly (or both)? Gaskets at O'reilly and Autozone have one side covered with adhesive.
Gasket cement is used to hold the gasket in place until you put it together. It's not a substitute for a gasket. If the thermostat comes with a sticky side, then you can just stick it on one of the parts and press/smooth firmly to remove any air bubbles.

I agree coolant leaks can be a sign of reduced flow because of a bad water pump or clogged coolant passage or hose.
 
#12 ·
I was thinking coolant pump when you said the car boiled over while idling. Time to change it in my opinion.
 
#17 ·
Update:

Everything seems to be ok! I replaced the stat and water pump (& gaskets) along with a few hoses that needed replacement. My car heated up nicely in about 5-6 minutes. I don't see any leaks anywhere right now.

Heat didn't work very well this morn, but then again it's -12 here in Minneapolis.

Thanks for all the help!
 
#18 ·
Update...

The "leak" is back. I call it a leak because it is quite slow this time, but nonetheless a leak. Coolant is seeping out from the interface between the stat housing and the LIM just as it was before. The seepage hasn't been enough to start dripping onto other engine parts, yet. I noticed it this morning after I got to work.

My driving habits since the last repair have been to and from work; 40 mins round-trip at mostly highway speed. The car does warm up nicely (from a temp gauge perspective, not hot air though). I don't see any other leaks in the system. The key word is "see".

I intend to take this into a mechanic tomorrow (Thursday) and have them conduct a pressure test. My hope is to determine if the stat gasket/housing area is to blame for this leak, so I was thinking the mechanic could do this:
-pressure test
-replace gasket
-flush n fill
-pressure test
Does this sound like a good idea? Any other direction that I maybe should be taking instead?
 
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