I have heard mixed things about the amount of temp sensors there are in a TJ. I’m currently moving from Maryland to Utah and don’t have time to fool around in the engine bay unfortunately. I know of the one located at the thermostat housing, but heard of there being another toward the back of the engine. I know where it would be thanks to a couple of YJ videos (I think). So I guess I’m asking is there two? And if so is the second one in the back any different than the thermostat housing one? Gauge is reading cold right now and kinda want to fix it at the next hotel stop. Thanks in advance!
Coolant Temp Sensors
- Thread starter Beepbeepjeep
- Start date
That’s what I thought, but my dad mentioned since I drove 10 hours today with only stops to gas up that the gauge should read some increase in temperature. Doesn’t that make sense? There’s no way I can drive all day and the temp only be at 100. Also it occasionally got up to 195 but then went back to 100. Not sure which one it is, but they are both cheap maybe I’ll do them both!
There's the water temp sensor from the thermostat housing, plus the thermostat itself. Nothing near the back of the engine. I'd start with the thermostat replacement and pulling/cleaning the sensor. The sensors fail, but I believe thermostat failures are more common
A thermostat failing in the open position will cause that problem. So-called "fail-safe" thermostats commonly fail in the open position so if there's one of those installed, replace it with a conventional 195 degree thermostat. It's real hard to beat a standard Stant thermostat and it's even harder to beat a Stant SuperStat thermostat.
BlackbirdTJ
New Member
There are two sensors on the Jeep TJ 4.0L. One of them on thermostat housing reads the temp and sends that information to ECU so engine can adjust fuel mixture. Other one is on the engine block (driver side on the back next to firewall) reads the temp and sends to cluster gage. As far as I know the sensor on the thermostat block is nothing to do with the cluster gage (temp gage)
BlackbirdTJ
New Member
I couldn’t find the official manual. But here s the back sensor location (attached image). Actually you can test yourself easily (I have done on my TJ) like if you remove the temp sensor socket on the thermostat housing (heat the engine and shut it off then remove the socket) your dash gage will show the current temperature of the water. Or vise verse, if you remove this socket your temp gage on the dash will go dead. I hope I am not misleading the forum. If so I d remove my posts immediately. Please let me know if I am mistaken.
Here's the segment of the FSM that describes that the ECT sensor in the thermostat housing is, in fact, what the gauge is based on.
I am currently driving for couple of days w/o thermostat. I am doing it because I do engine and radiator flushes.
I am seeing the same picture as you would see, the engine fails to heat up, because the cooling is constant and excessive. Thermostat stuck open will behave the same, so most likely your sensors are OK, but your thermostat is stuck open.
I have just received my Mopar thermostat today, planning to install it soon.
I am seeing the same picture as you would see, the engine fails to heat up, because the cooling is constant and excessive. Thermostat stuck open will behave the same, so most likely your sensors are OK, but your thermostat is stuck open.
I have just received my Mopar thermostat today, planning to install it soon.
This is the link to the part.
Mopar 5202 8186AC, Engine Coolant Thermostat https://www.amazon.com/dp/B00F6E3W8M/?tag=wranglerorg-20
Mopar 5202 8186AC, Engine Coolant Thermostat https://www.amazon.com/dp/B00F6E3W8M/?tag=wranglerorg-20
When you open your thermostat, you will see that it will be open, not like mine which is closed.
Incorrect. That's how YJ's work, but not TJs. And that pic isn't from a TJ.
Seems like I'm in the minority here, but to run all day and never break 100 in July is pretty much impossible even with a stuck open thermostat.
When it moved between 195 and 100, how fast did it move?
BlackbirdTJ
New Member
You are correct. It is my bad. 97 and earlier have 2 sensors and later versions have 1 sensor (coolant sensor on thermostat body only). I apologize for my premature answers I posted earlier. There is no edit on this website I guess. I couldn't figured it out.
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