Changed Thermostat

[S-FLY]

So, when I bought my xj, I didn't have much heat and it'd take forever to heat up.  I changed my thermostat yesterday and notice it was stuck wide open (must be a safety setting for when it over heats?).  Anyways, I noticed the old one had a little pass-through with a ball bearing type thing but the new one didn't have this... is this important?

[fug]

I just did my 95 for the exact same reasons.  I don't recall either the old thermostat or the new one having a bypass so I'm going to say... not important

[S-FLY]

Right on.  I'm just curious what it does really, my old one had it and Sprockett's old and new one had it and I thought we had the same motor.  Here is the thing in question (this isn't my t-stat, but the arrow points to the bypass):

[fug]

Mine was a Stant and looks like this

[S-FLY]

Found the answer, it's called a jiggle valve.  I guess they did away with them, it was for air to pass through.

[FiEND]

i installed on in a ford exploder and jeep grand on the same day.  the grand was a failsafe and had the valve, couldnt get failsafe for exploder and it dint have a valve

[cLAY]

I don't like the fail safes, everyone of them I had failed in the stuck open position. I've rarely had a failure with a regular.

The hole as you said is a jiggle valve for helping bleed air from the system. It should be installed in the 12 o'clock position when installed in a Jeep 4.0L to help bleed air from the system.

I usually disconnect a heater hose when filling the system to help bleed air out. My old '89 4.0L would get airlocked if I didn't.