I've can not figure out why the thermostate housing keep cracking? on 2004 Ford Explorer

I have a 2004 Ford Explorer that constaintly leaks around the thermostate area. First it was the O-ring, and then I found that it was the thermostate housing. I have changed it twice now.

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2 answers 2 comments
DO NOT overtighten!! O-ring type seals do not need to be very tight , overtightening will stress the housing and warp it causing it to fail prematurely even with a good (OEM) part.
they are plastic and both surfaces need to be very clean as not to bind while tightening. where did you buy yours? aftermarket tend to be thinner plastic
Thanks for your response. I the first thermostate housing I ordered online and the second one I purchased from O'Riellies auto parts. I made the mistake of over tightening the first time but didn't damage it. It last about six months and the come to think of it the second one last about six month, give or take a couple weeks.
your buying cheap parts