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Discussion Starter #1
Hey, once again, I have a slow-moderate (drains my system in about 2 days) leak in my coolant system. I had a massive leak before and replaced the t-stat housing (~12k miles ago). I got about 82k on the 2002 zx3 zetec. Any thoughts? the leak is coming from what looks like right under the t-stat housing. Could it be the housing again?
 

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Token Engin-nerd
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yes it could and this time make sure you replace the o-ring that goes between the housing and the block.

also replace the valvecover gasket, this is the source of the problem
 

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Discussion Starter #3
why would the valve cover be the source of the problem, wouldn't that cause an oil leak?

I want this problem to be gone for good, not back in another 12k miles. Guess i'll have to take the t-stat housing apart to see if its cracked again, is there a higher quality housing I can buy?
 

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Token Engin-nerd
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the valvecover leaks oil down the side of the head and the oil causes the oring to expand and break the housing
 

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Discussion Starter #5
So I replaced the valve cover gasket and t-stat housing, it ran fine, cycled coolant backthrough the system like it should. Now this morning its leaking from the screw on the piece that is re-used from the old housing and then screwed into the new housing. Should I replace that part? or do the screws have to be crazy tight?
 

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Token Engin-nerd
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not crazy tight but yes nice and tight

you may need a new thermostat o-ring as well.
 

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Discussion Starter #7
well if i'm doing that should i just replace that other housing that is screwed on? and probably should do a new thermo at the same time

also, I put the thermo in but not seated in that groove, screwed it all together and hooked up hoses before I realized that it was wrong, could that have messed that housing up?
 

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Token Engin-nerd
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we are talking about the piece that the upper radiator hose attaches to correct? That is called the thermostat cover

the thermostat cover should be fine, just replace the thermostat and thermostat oring and you should be good.
 

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Discussion Starter #9
yes, the part that you have to take off the old housing, then remove the thermostat and screw into the new housing. Do you think that the bad t-stat oring would cause it to leak from the screw holes?
 

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Token Engin-nerd
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yes that is a possibility

could just be you dont have it tight enough

but be careful its a really coarse thread going into plastic, it will strip easily
 

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I.S.A.I.K.I.
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yes, the part that you have to take off the old housing, then remove the thermostat and screw into the new housing. Do you think that the bad t-stat oring would cause it to leak from the screw holes?
That is possible but you would really have to torque that sucker down to develop a crack through the front of the housing.

I know of the drip trail. Starts at the front right corner of the block underneath the T-Stat, travels down the bottom of the block and then along the flanges where the engine and tranny mount together.

Pete is correct about the valve cover contributing to the failure of the thermostat o-ring. The petroleum breaks down the makeup of the large O-ring.

When you tear it apart again, you'll see that the O-ring will be convoluted and will have a small "U" shape in it.
 

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Token Engin-nerd
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they shouldve made it out of viton but looks like instead they forded out oops i mean cheaped out and went for Buna-N
 

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I.S.A.I.K.I.
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Yeah, they fubared on that one as well.

When I replaced my T-stat housing this past summer, what I described could only be propriortary to my instance but being nearly identical in Zetec design, I'm betting that this is what the OP is dealing with right now.
 
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