I posted this question to jeepforum.com but it was essentially received with crickets, maybe you guys can help.
BLUF: Temp will jump from ~220 to 240+ in about a second then after a couple of minutes pulled over it drops back down to from 240+ to ~215 in about a second.. and I dont know why.
I have a 2000 XJ with 170,000 miles, auto, 33" tires, stock gearing, a winch in front, a new radiator (and cap), I flushed the coolant when I replaced the radiator, new 3x10" electric fan set up from Dirt Bound Offroad. and the T-stat is ~ 1 year old (stock temp).
In more detail here's whats Happening:
Starts and idles fine, first fan kicks on at 185*, other 2 fans kick on at 205* and temp stays constant. - no issues at this point
Shorter drives around town (stop and go) no real issues (a little warm but nothing major).
But on longer hwy drives the temp goes up to ~220* (or whatever that first dash is after the 210* mark) and if I have to travel at a sustained higher load (like up a long hill) the temp will jump to 240+* but here is the thing that I cant figure out; it is not a steady temp climb, but a quick change from ~220* to 240*. I pull over, turn off the engine and let the fans run for a minute or two and the temp will drop back to ~215* and when it drops it does it all at once, from 240+ to ~215* in just a second.
Here are my theories:
1. I may have a dieing water pump that can't keep up with the higher load, but that doesn't explain the quick temp changes
2. I may have a head gasket that is its last legs and is letting exhaust into the coolant and causing the temp gauge to read the temp flux, but I dont think that would be limited to highway driving under load.
3. The winch is blocking airflow, but I have electric fans and they should be able to keep air moving in that center section where the winch is and it doesn't explain the quick temp changes.
4. The head has a small crack and when it's hot and under pressure exhaust is getting into the coolant giving me the temp spike, as it cools the gap closes so the pressure can build again and that drops the temp. I dont have milky oil, I cant see anything blatant through the oil fill cap and I tried the auto parts store's coolant / combustion gas test but I couldn't get the engine up to the questionable temp before the tester blew off the radiator -so I can't confirm (or rule out) this possibility.
I don't want to keep throwing money at parts that may or may not solve the problem (especially a new head). I'd like to accurately diagnose the root cause then fix that.
What do you guys think? Do any of those ideas hold water? Have any better ideas to what may be causing this?
Thanks in advance for any help.
BLUF: Temp will jump from ~220 to 240+ in about a second then after a couple of minutes pulled over it drops back down to from 240+ to ~215 in about a second.. and I dont know why.
I have a 2000 XJ with 170,000 miles, auto, 33" tires, stock gearing, a winch in front, a new radiator (and cap), I flushed the coolant when I replaced the radiator, new 3x10" electric fan set up from Dirt Bound Offroad. and the T-stat is ~ 1 year old (stock temp).
In more detail here's whats Happening:
Starts and idles fine, first fan kicks on at 185*, other 2 fans kick on at 205* and temp stays constant. - no issues at this point
Shorter drives around town (stop and go) no real issues (a little warm but nothing major).
But on longer hwy drives the temp goes up to ~220* (or whatever that first dash is after the 210* mark) and if I have to travel at a sustained higher load (like up a long hill) the temp will jump to 240+* but here is the thing that I cant figure out; it is not a steady temp climb, but a quick change from ~220* to 240*. I pull over, turn off the engine and let the fans run for a minute or two and the temp will drop back to ~215* and when it drops it does it all at once, from 240+ to ~215* in just a second.
Here are my theories:
1. I may have a dieing water pump that can't keep up with the higher load, but that doesn't explain the quick temp changes
2. I may have a head gasket that is its last legs and is letting exhaust into the coolant and causing the temp gauge to read the temp flux, but I dont think that would be limited to highway driving under load.
3. The winch is blocking airflow, but I have electric fans and they should be able to keep air moving in that center section where the winch is and it doesn't explain the quick temp changes.
4. The head has a small crack and when it's hot and under pressure exhaust is getting into the coolant giving me the temp spike, as it cools the gap closes so the pressure can build again and that drops the temp. I dont have milky oil, I cant see anything blatant through the oil fill cap and I tried the auto parts store's coolant / combustion gas test but I couldn't get the engine up to the questionable temp before the tester blew off the radiator -so I can't confirm (or rule out) this possibility.
I don't want to keep throwing money at parts that may or may not solve the problem (especially a new head). I'd like to accurately diagnose the root cause then fix that.
What do you guys think? Do any of those ideas hold water? Have any better ideas to what may be causing this?
Thanks in advance for any help.
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