Correct Thermostat Gasket '98 SOHC Exploder

[XLTrunner]

I have developed a small coolant leak around the newly installed t-stat upper housing (actually, the entire thermostat housing is newer). Everything seemed good for a few wks and maybe 750 miles. Now, I'm seeing same 'ol leaking problem; except this time it's also around the lip where the upper t-stat cover bolts down. I've noticed that there are two styles of 0-rings being sold...one is traditional 0-ring with round cross-section. Other is round (of course), but the cross section is square. As finicky as these housings seem to be, was one version meant to seal better than the other? My initial thought is "no"...but, maybe there is a reason for both styles. I didn't pay any attention to the old one I removed and noticed on a '99 housing I pulled over the weekend at the junkyard that it had the square cross-section style gasket. Any thoughts?

 

[koda2000]

I have developed a small coolant leak around the newly installed t-stat upper housing (actually, the entire thermostat housing is newer). Everything seemed good for a few wks and maybe 750 miles. Now, I'm seeing same 'ol leaking problem; except this time it's also around the lip where the upper t-stat cover bolts down. I've noticed that there are two styles of 0-rings being sold...one is traditional 0-ring with round cross-section. Other is round (of course), but the cross section is square. As finicky as these housings seem to be, was one version meant to seal better than the other? My initial thought is "no"...but, maybe there is a reason for both styles. I didn't pay any attention to the old one I removed and noticed on a '99 housing I pulled over the weekend at the junkyard that it had the square cross-section style gasket. Any thoughts?

There are two O-rings on the SOHC thermostat housing. One goes between the engine and the housing, the other goes with the thermostat. I think the thicker larger one is the one for the thermostat, I can't remember which is which, but I know that everyone tried to sell me the wrong gasket until finally a guy at Advance had the right one. Fortunately I'd brought the old one with me for comparison.

Are you sure it's the O-ring that's leaking? Those plastic housings are know to crack and leak.

 

[swshawaii]

Ditto koda. Far more likely the lower housing seams splitting or the threaded sensors are leaking.
Very easy to over tighten both housings, factory torque spec is only 89 inch, or 7-8 foot pounds.

thermostat and sensor housing- do they crack?
http://www.explorerforum.com/forums/showthread.php?t=173044

4.0 SOHC plastic thermostat housing (Upgrade)
http://www.explorerforum.com/forums/showthread.php?t=239493

 

[XLTrunner]

I know of the two gaskets used on these housings. The smaller one that goes between the engine and housing is of the square cross-section style. The new complete housing (Four Seasons brand from Rockauto) came with that one...but, I bought my own thermostat and thermostat gasket; which I'm certain was a true 0-ring with the round cross-section. Remember noting there was a pretty good gap when I trial-fitted the upper housing to the lower...but, figured that was due to the new gasket and would compress down once installed; which it did. I didn't think I torqued the bolts (top ones and bottom ones) all that tight as I had read it didn't require much. As I mentioned previously, everything seemed a-okay for a few weeks and then the leaking resumed. I went back in and gently snugged up all but one lower bolt that I couldn't reach without removing the Upper Intake again. I'm thinking the gasket between the engine and lower housing is the culprit for the bulk of the leakage...but, the seepage around the Upper housing (it's definitely between where the Upper and Lower bolt together) is new and that's what got me to thinking maybe there's something to the square profiled gasket having more surface area to protect against leaks?

So, before I tear back into things again to gain access to everything, I'm wondering if I shouldn't start over with another new housing (which brand this time?) in case I did crack this one...or, try just replacing the gaskets and see what happens. I'm running out of nice weather to be doing this in my driveway, so time is of the essence.

UPDATE: I took a closer look at the Upper T-stat housing and thermostat itself that I removed from the '99 XLT in the junkyard and both look to be originals. Thermostat says MotoRad and Germany on it. Gasket is definitely a tapered square cross-section...taper maybe due to compression of housing cap. The Fel-Pro replacement (35617) I just bought is a true 0-ring and fits a little sloppily when it rests on the thermostat flange. Hmmmm......