Jeep Temperature: Thermostat or Sensor Issue

Here I cover some tips to help identify if your thermostat is opening and closing properly. It's as easy as watching your hoses and feeling them as your car engine warms up. I also show where the Jeep Wrangler 4.0 temperature sending unit is located and discuss the coolant thermostat.

(located towards back of engine on driver side)
Sends signal to temperature gauge in cab.

(located on the thermostat housing. Coolant temperature)

A few of my favorite tools:

Dewalt 1/4 impact driver
Be sure to get the kit with 2 batteries. You'll be glad you did!

Craftsman 165 Mechanics Tool Set
Excellent tool set that will last a lifetime.

1/2" Craftsman Impact Driver I use. Love this thing

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The craftsman tools and nothing super fancy, just fixing the Jeep!

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[davem]

Sold my YJ a few months ago, this video reminds me of how simple Jeeps used to be. Great video as usual!

[RR-nelb]

"I have a little leak ill fix later" Sounds like me do great job on other people's cars but have my cars on the waiting list. Lol

[bigbulls]

Great video ! Saved me some cash and taught me how to do some of my own work as I never had tools or garage till now so Thanks man

[volvoman]

I live on a tropical region, therefore I installed a 160 degree thermostat along with a new water pump, radiator and auxiliary transmission fluid cooler. I run the stock fan setup and also have a 3 year old fan clutch. It runs at 210 on the dashboard but sometimes it runs a little hot. I changed the sending unit 2 times and no change. I installed a separate temp gauge and placed the sensor on the radiator drain plug hole. And it stays at 180 and max out at 200

[johndough]

I overheated yesterday. This will help a great deal. Thanks man. I love my in line six. That thing loves to climb hills!

[edjohnson]

I have a 1992 Jeep YJ with a 2.5 engine.  I have only one sensor.  My gauge is not working but other gauges are working in the cluster.  When I bought the Jeep someone had put an after market temp gauge in.  Changed the sensor at the thermostat housing.  It worked.  I found the old sensor still plugged into the wiring plug harness. I put a new sensor in the where the aftermarket was and plugged the original plug back in.  The original gauge still didn't work.  Also the aftermarket didn't work.  I suspect the original wiring may be cut some place under the dash.  As mentioned other gauges are working in the cluster.  Thoughts. Your videos are good and enjoy them.  I just want the original to work.  Thank you.  P.S. I do not have another sensor at the back of the engine any where arrond the head.  I have looked and felt many times.  Is this a 4.0 addition?

[herbiesnerd]

My little diagnostic test for the thermostat off a cold start is to watch the temperature gauge as the engine warms up. When it hits the thermostat opening temp (195° for my YJ) the temperature on the gauge will suddenly drop when the cold radiator starts circulating.

I personally have never ever had one stick open but your explanation on how to tell if it stuck open is correct.

I have run plenty of engines with no thermostat in a pinch and the exact behavior you described as stuck open occurs.

In a pinch on the road if your thermostat does fail stuck closed, you can remove it. I did that once and salvaged the torn gasket and used my wives finger nail polish for gasket sealer!

[willthethrill]

Great info on the "heater" trick. If the heat coming out of your vents in the cab isn't HOT after the engine has been operating for awhile, check the thermostat and radiator hoses for temperature differences. If they are about the same, most likely the thermostat is stuck OPEN. This is the first thing I ask customers, "Does the heat coming out of your vents seem warm or hot?"

Also forgot to mention the tid-bit about the radiator fan. If the engine is up at operating temperature and the thermostat opens but the temperature isn't decreasing, the computer will have the radiator fan operate. If the fan doesn't work, then that's another path to troubleshoot.
Two different options here if the thermostat is GOOD so you are looking at the radiator fan now:
1) If the engine is running cold, verify the fan isn't ON constantly.
2) If the engine is running hot, verify the fan does turn ON when commanded. Most of the time, you can use a scan tool to operate the fan electronically. If you don't have a tool, pull the plug for the fan (not sure how to do it on an older vehicle with a fan clutch) and apply 12VDC to the pins/sockets. The fan doesn't always run at FULL speed, so 9 to 12 volts is a good test to verify the fan operating speeds (less voltage means lower fan speed, higher voltage means higher fan speed). I use a 9V battery for a lower voltage test. If the voltage test works and the fan is operational, then work back to the sending unit, coolant temp sensor, or the relay/control module to verify that it's putting out the correct voltage when needed, or operating at all.

You can get into the weeds on this error, but time put forth up front will save you money and time later on if the problem isn't diagnosed properly the first time. You hit all of the other key points.

[lloyd-qtmg]

An excellent contribution - 'on point'. Goes to show that you can teach an 'old dog' new tricks - like the heater hose warming before the radiator hose to verify the status of the thermostat! Thank you. Lloyd, Queensland, Australia

[gerryburkhardt]

Much appreciated for the clarification definitely helps it's just thinking about that to tell the difference and to pinpoint the problem and to help pinpoint the problem

[arturocantu]

Thank you to show how simple is to chance a termostat

[rjlinnovations]

Great sharing your video tutorials. It was so helpful. Sending my support

[gln]

If you have a problem with a P0188 or something related to that, always look at your temperature sensor plug to make sure you don't have a bad wire on that, that is what my problem came from. Very simple but it will give a P0188 code like mine has. Check the voltage on the plug if the wire is not appearing broken to make sure you have voltage there. Simple fix though. If it is broken or the wire is off, get a new plug connector for the sensor at somewhere like O'Reilly's.

[edwardkelly]

This was exactly the information I was looking for ( temperature sending unit )....thanx

[craigbaxter]

I own a 2003 JGC WJ w/4.0 and it just pulled a code P1281 today. That code is for the engine running too cool initially. I had just put in a new t-stat about two weeks before. I took apart the t-stat housing and wouldn't you know it, the t-stat was stuck open. So, if you have that P1281 code or your vehicle takes a long time to get up to operating temperature, consider replacing the t-stat.

[butcherbaker]

Said "So ...."38 times🤣 this is great I took a wrong turn and dont feel stable with your camera jitters but you are a good dude this video will help some people👍🇺🇲

[calabskier]

Appreciate your videos. I have a 95 yj, 4cl, 210k kms. Runs well, no leaks, but the temp gauge fluctuates a bit when up to operating temp, briefly showing a little hotter while driving, though most dead centre on the gauge while driving, and always dead centre when idling in traffic. When I turn the engine off but leave the key in acc, the gauge often runs up another 10 degrees C or so, to the next line on the gauge, but not to the warning line. It settles to the middle line as soon as I start it back up. Heat works great. Original rad, no visible leaks and I keep an eye on the coolant level both in the rad and reservoir, but I do faintly smell coolant sometimes when close to the rad after driving. Newer rad cap, new heater core and rad hoses this winter. I rebled the system thinking might be air. Haven't changed the t-stat though. Suggestions?

[senditentertainment]

can i just say that it made my day when you actually told everyone who asked the question. LOL

[alexandrariddle]

I just replaced my thermostat and temp sensor and the temperature gauge is still not moving. Is it time to change the temp gauge itself at this point?