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Engine 4.0 Cherokee 1992 - thermostat

pszczepan

NAXJA Forum User
Location
IN
Hi !

I own Jeep Cherokee 1989 and in my jeep thermostat has bimetal-mechanical thermoelement,
Recently I installed head from Jeep XJ 92 to my engine. Everything works OK but I see that Jeep 92 has some socket on thermostat. The thing is that now my engine all the time has temperature under normal.
Now I think that thermostat is still open and the engine cannot warm up.

Maybe jeep 92 has electrical thermostat and mentioned socket supply juice from the ECU to the thermostat.
I have older ECU - so it is incompatible .
Let me know if it is true - if yes - what voltage goes to the sockets- thermostat

thanks
Pawel
 
My 92 uses a standard mechanical thermostat but the engine temperature sending unit is mounted in the thermostat housing which I believe is unique to the HO engines.
 
Bainer said:
My 92 uses a standard mechanical thermostat but the engine temperature sending unit is mounted in the thermostat housing which I believe is unique to the HO engines.
Wrong info---The sensor in the T-stat housing is for the ECU only.97-98 and above this sensor DOES supply info to the ECU which supplys the dash guages.
On the 4.0 motor up until 97-98 the temp sensor for the dash guage is located on the top back of the head.
Wayne
 
pszczepan said:
Hi !

I own Jeep Cherokee 1989 and in my jeep thermostat has bimetal-mechanical thermoelement,
Recently I installed head from Jeep XJ 92 to my engine. Everything works OK but I see that Jeep 92 has some socket on thermostat. The thing is that now my engine all the time has temperature under normal.
Now I think that thermostat is still open and the engine cannot warm up.

Maybe jeep 92 has electrical thermostat and mentioned socket supply juice from the ECU to the thermostat.
I have older ECU - so it is incompatible .
Let me know if it is true - if yes - what voltage goes to the sockets- thermostat

thanks
Pawel

If I'm reading this right, what you're asking about would be the "additional" sensor hole in the thermostat housing - nearly every automotive thermostat I've run across in the last 25 years or so uses a wax pellet to open and close the valve - you're referring to a "thermal sensor." It has nothing to do with maintaining engine temperature - it merely reports it.

Anyhow, your 1989 has three temperature sensors:
A thermal fan switch - should be in the driver's side radiator tank
A sensor for the electronic control unit (ECU) - on the driver's side of the engine block
A sensor for the dash panel gage/light, located at the driver's side rear of the cylinder head.

Starting in 1991, Chrysler combined the function of the two "lower" sensors (the one in the radiator and the one on the block) into a single sensor that mounted in the thermostat housing - that's the hole you're (I think) talking about. They kept the separate sensor for the gage/light until 1995/996 or so.

That hole is a standard pipe thread (3/8" NPT, I think) so you can just leave an old sensor in there, or just put in a pipe plug from the hardware store. You could also use it for another sensor for another application - I think most Chevvy units are also threaded 3/8" NPT, and therefore will fit.
 
Replace the thermostat with a no cooler than 190 degree F thermostat. I have used a high flow one from Napa. It is the largest one available. Plug the threaded boss for the 92 sensor. Done.
 
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