Wrong thermostat?

I’m changing the t-stat in the '94 Taurus 6-cyl 3.0L, about which I recently posted. I got a cheap Stant t-stat (190-deg) from the chain parts store. The old t-stat has a ball check valve near the rim, and the Haynes manual says to mount it with that valve at the top. The new t-stat does not have a valve. Do I go ahead and use it, or do I go back to the store tomorrow morning and get one with a valve? (Second option involves a lot of car shuffling.)

I believe that the main difference between the el-cheapo thermostat and the good thermostat is the device that makes it more likely to fail in the open position. Using the cheapo one will make it more likely to fail in the closed position, which will result in overheating, though perhaps not any more likely to fail in general.

It’s really up to you. I use the cheap ones because I change them very regularly and know to watch the temperature gauge.

The failure mode info is useful. Any thoughts on the missing ball check valve?

Drill a small hole in the base…

Thanks, but it’s too late (I wonder if the design relies on calibrated leakage) :>)

See my follow-up post on “Wavering Temperature Guage”

That check valve makes it easier to purge air out of the cooling system as it’s being filled. That’s why they want it mounted at the TOP position.


I feel certain that the small hole is there to speed filling the cooling system but it also seems to moderate the temperature AND, if there is a weak head gasket or cracked head the vent prevents air locking and catastrophic damage due to the head temperature going ballistic when air locked and dry, then suddenly being washed with cold water… Just my observation.

This discussion has moved to Wavering Temperature Guage.