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Running hot issue

1K views 5 replies 5 participants last post by  gregberg 
#1 ·
Ok so I am having an issue of my 94 YJ 2.4L running hot. It used to run around 210 and then all of a sudden one day started jumping up to 250 and then falling real fast back to 210. I replaced the thermostat and no luck. I decided it might just be a bad new thermostat so I have replaced it now with three different types and temps. I have replaced the sending unit, waterpump, all pulleys, and belt. Anytime I take the thermostat out I can drive for hours and never reach above 210. As soon as I put a thermostat in it it runs hot again. With the thermostat out and the cap off of the radiator you can see the water moving really good and with the thermostat in there is absolutely no movement at all. I have made sure the thermostats were in correctly and not backwards like 15 times lol. I am so lost with this. It is now getting in the 20's here and heater would be great so anyone that has any ideas please help. Btw I have a friend that has a 70's model CJ that told me to drill a hole in the new thermostats because jeeps are known for this issue but the new one I have already has a seep hole in it so I have not altered it at all.
 
#2 ·
I'm not familiar with the 2.5 but I want to help.
Have you "burped" it with the thermostat in?
Put one of the thermostats on a pot of water on the stove along with a thermometer and turn the stove on. Watch the thermometer and when it gets to the thermostats degree rating the thermostat should be open or at least opening. Use that thermostat.
You stated that you checked for correct installation at least 15 times. Have your buddy come over and check one more time. As Human Beings, sometimes we get a mental block. It has happened to me more than once.
Improper timing can make an engine run hot but if it runs cool without the thermostat it is unlikely that is your issue.
A blown head gasket can also make an engine run hot by forcing coolant out of the system. Again, not likely in your case.
Good Luck, L.M.
 
#4 ·
Do you have anything you can independently verify the engine temp? An IR temp gun can tell you what it is going out, coming in, and any odd hotspots.



Is your radiator new, or original?





When does it spike? Moving? Idling? Hwy? Traffic?
 
#5 ·
The thermo should be a 195*. The weep hole should be in the 12 o'clock position when mounting it in the housing.

Don't trust the gauge, the YJ gauges are mediocre at their best. You can get an IR temp gun from Harbor Freight for a few bucks. Or maybe a buddy has one.

When ever I do a new thermo replacement, I jack up the front end with a floor jack until I can set the front axle on the highest setting of my jackstands. Then I start it and let it get up to temp (make sure the overflow tank is filled to the correct height) Then let is sit there and idle for 15-20min. Once the system is pressurized the radiator will "burp" and take a drink from the overflow tank.
 
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