running hot at 240
CF Veteran
Joined: Jul 2012
Posts: 3,686
Likes: 6
From: Hudson, FL
Year: 1999
Model: Cherokee
Engine: 4.0L Inline 6
It's because there's muck in your engine block that needs to get washed out so that the coolant can actually get where it needs to go. It happens when coolant systems aren't well maintained and the muck is like a heavy green mud. Sometimes you see it in the radiator, but it's everywhere, clogging things up.
Air in the coolant system can also cause hot spots.
Air in the coolant system can also cause hot spots.
CF Veteran
Joined: Oct 2013
Posts: 1,589
Likes: 2
From: Denver
Year: 99
Model: Cherokee
Engine: 4.0
Get several gallons of distilled water, and some of that Peak cooling system flush. Dump all the antifreeze, use the peak flush, run it around for 20 minute drives a couple times, get it on the highway, etc, and dump it.
I kept a little bit of antifreeze in the distilled water mix while I was doing the flush to help prevent any corrosion but its probably not even that important.
I got about a gallon of silt/rust/grime out of my engine block, and now it runs at 195F instead of 210 or 220 like it was. I also replaced all the parts, but the flush REALLY helped. I did probably 6 flushes. Run it with mostly water for half hour, let it cool, dump the lower rad hose, repeat repeat repeat
I kept a little bit of antifreeze in the distilled water mix while I was doing the flush to help prevent any corrosion but its probably not even that important.
I got about a gallon of silt/rust/grime out of my engine block, and now it runs at 195F instead of 210 or 220 like it was. I also replaced all the parts, but the flush REALLY helped. I did probably 6 flushes. Run it with mostly water for half hour, let it cool, dump the lower rad hose, repeat repeat repeat
CF Veteran
Joined: Jan 2015
Posts: 1,508
Likes: 5
From: Oregon Coast
Year: 1999
Model: Cherokee
Engine: 4.0L I6
running hot at 240
Get several gallons of distilled water, and some of that Peak cooling system flush. Dump all the antifreeze, use the peak flush, run it around for 20 minute drives a couple times, get it on the highway, etc, and dump it.
I kept a little bit of antifreeze in the distilled water mix while I was doing the flush to help prevent any corrosion but its probably not even that important.
I got about a gallon of silt/rust/grime out of my engine block, and now it runs at 195F instead of 210 or 220 like it was. I also replaced all the parts, but the flush REALLY helped. I did probably 6 flushes. Run it with mostly water for half hour, let it cool, dump the lower rad hose, repeat repeat repeat
I kept a little bit of antifreeze in the distilled water mix while I was doing the flush to help prevent any corrosion but its probably not even that important.
I got about a gallon of silt/rust/grime out of my engine block, and now it runs at 195F instead of 210 or 220 like it was. I also replaced all the parts, but the flush REALLY helped. I did probably 6 flushes. Run it with mostly water for half hour, let it cool, dump the lower rad hose, repeat repeat repeat
Senior Member
Joined: Mar 2012
Posts: 974
Likes: 14
From: Racine, WI
Year: 1997
Model: Cherokee
Engine: 4.0
That's not my water pump ha ha but I will see how bad mine is when I pull it this weekend. Guy said he changed it but at this point his word means bull doo doo. It had the original chrysler thermostat in there from 1991.
So far I've done:
New radiator
New t stat
New t stat housing
New upper and lower hoses
New 50/50 coolant
New front and back temp sensors
Next on the list is the fan clutch and water pump. It's a sketchy situation because the gauge will show 240 but the fan won't come on until a few minutes later. So my aux fan is working and if it's supposed to come on at 220 that means my gauge is reading wrong. I also have pointed an ir thermo gun right at the thermostat housing and it reads 180-190 tops. When I point it at the temp sensor that's located on the thermostat housing it shows 211-215 never above 220.
So far I've done:
New radiator
New t stat
New t stat housing
New upper and lower hoses
New 50/50 coolant
New front and back temp sensors
Next on the list is the fan clutch and water pump. It's a sketchy situation because the gauge will show 240 but the fan won't come on until a few minutes later. So my aux fan is working and if it's supposed to come on at 220 that means my gauge is reading wrong. I also have pointed an ir thermo gun right at the thermostat housing and it reads 180-190 tops. When I point it at the temp sensor that's located on the thermostat housing it shows 211-215 never above 220.
P.S. Wait, is your XJ an 88 or a 91??? Your profile says 88, but you say your water pump is original from 91, so which is it?
Last edited by mschi772; Aug 14, 2015 at 05:52 AM.
CF Veteran
Joined: Oct 2013
Posts: 1,589
Likes: 2
From: Denver
Year: 99
Model: Cherokee
Engine: 4.0
Thread Starter
Senior Member
Joined: Mar 2009
Posts: 979
Likes: 0
From: Tucson, AZ
Year: 1991
Model: Cherokee
Engine: 4.0
Your aux fan is controlled by one sensor while your gauge gets its info from a different one. That's why they're not going to be in perfect sync with each other. Your gauge reading 240 constantly is either due to a bad sensor, a malfunction in the wiring, or a bad gauge. You don't need to keep blowing money on cooling system parts--your IR gun confirmed that you have a normal running temp. At worst, you have a localized restriction somewhere in your engine. Coolant flush is wise. This should be done regularly as a matter of maintenance, and it sounds like it hasn't been.
P.S. Wait, is your XJ an 88 or a 91??? Your profile says 88, but you say your water pump is original from 91, so which is it?
P.S. Wait, is your XJ an 88 or a 91??? Your profile says 88, but you say your water pump is original from 91, so which is it?
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