How Hot is too Hot

[Mudderoy]

My temp gauge sits at 210 most of the time. Sometimes on the highway or around town it goes to 220-225 and stops (a/c on or off). It always comes right back down to 210-215 and has never overheated. I have replaced the radiator with a 3 row, the t-stat with a mopar one, flushed the coolant, clutch fan, coolant temp sensor on t-stat housing, and the tempeture switch on the back of the motor. The water pump is not new but it is good and pumping a good amount of water.The air has been bleed out of the system. When the temp guage is around 210-220 I used a temp gun on the motor and the temp gun never read above 195. Is their something that I'm missing or could I have a bad guage. Any suggestions??

Mine is doing the exact same thing now. I guess I'll try replacing my 16 psi radiator cap.

 

[Mudderoy]

Re: How Hot is too Hot (or Cold)?

Hi, I've been having a related problem with my temp. I found a couple earlier threads on it, but they haven't answered definitively my problem.
When i am idling, my dash gage reads around 200+-10. But, when i get to speeds of 50 and up, my temp starts dropping over a couple minutes to about 160+-10. This is happening in ambient temps of 50 to 90 degrees. The problem also seems to have started when I replaced the speed sensor on the transfer case. I know that this sensor helps control idle, can it have any impact on the cooling system? And if so, why would replacing a dead sensor with a live one start problems with lower temp readings than I'd want?
I have noticed a considerable drop in gas milage. I'm running a 92 with the HO 4.0L. I've seen many things suggested, but I'd like to narrow things down.
I think I should check the thermostat, but should I also check the sender unit? The gage itself for possible voltage problems? Some other miscellaneous part?
Thanks

This doesn't make any sense to me at all. I cannot imagin how you would drop in temp that much unless the thermostat was opening. You might want to put an IR gun on it and verify those temps, or change out the temp sending unit.

 

[Ecomike]

Re: How Hot is too Hot (or Cold)?

Hi, I've been having a related problem with my temp. I found a couple earlier threads on it, but they haven't answered definitively my problem.
When i am idling, my dash gage reads around 200+-10. But, when i get to speeds of 50 and up, my temp starts dropping over a couple minutes to about 160+-10. This is happening in ambient temps of 50 to 90 degrees. The problem also seems to have started when I replaced the speed sensor on the transfer case. I know that this sensor helps control idle, can it have any impact on the cooling system? And if so, why would replacing a dead sensor with a live one start problems with lower temp readings than I'd want?
I have noticed a considerable drop in gas milage. I'm running a 92 with the HO 4.0L. I've seen many things suggested, but I'd like to narrow things down.
I think I should check the thermostat, but should I also check the sender unit? The gage itself for possible voltage problems? Some other miscellaneous part?
Thanks

Q1, NO, has nothing to do with it.

Poor mileage, in your case probably a problem with the O2 sensor, but could be the TPS.

A common problem is O2 sensor wiring getting too close to the exhaust manifold, burning and grounding out. You might have knocked the O2 sensor wires loose doing the VSpeed sensor replacement. That might be affecting the gauge temperature reading too.

 

[Mudderoy]

Re: How Hot is too Hot (or Cold)?

Q1, NO, has nothing to do with it.

Poor mileage, in your case probably a problem with the O2 sensor, but could be the TPS.

A common problem is O2 sensor wiring getting too close to the exhaust manifold, burning and grounding out. You might have knocked the O2 sensor wires loose doing the VSpeed sensor replacement. That might be affecting the gauge temperature reading too.

How would it affect the temp gauge reading Mike? Teach me, I am a sponge.

 

[sprngfldxj]

I have been running a 13PSI Cap, why is the 13 worse then the 16?
Why do the Parts stores have it as 13 not 16?
What shoudl I be looking for in trouble if i run it at 13 not 16?

 

[Mudderoy]

It may depend on what year XJ you have. Mine is a 1998, and I'll have to double check, but I believe mine is 16 psi, which I was told is the OEM psi for my model and year.

 

[Ecomike]

Re: How Hot is too Hot (or Cold)?

Hi, I've been having a related problem with my temp. I found a couple earlier threads on it, but they haven't answered definitively my problem.
When i am idling, my dash gage reads around 200+-10. But, when i get to speeds of 50 and up, my temp starts dropping over a couple minutes to about 160+-10. This is happening in ambient temps of 50 to 90 degrees. The problem also seems to have started when I replaced the speed sensor on the transfer case. I know that this sensor helps control idle, can it have any impact on the cooling system? And if so, why would replacing a dead sensor with a live one start problems with lower temp readings than I'd want?
I have noticed a considerable drop in gas milage. I'm running a 92 with the HO 4.0L. I've seen many things suggested, but I'd like to narrow things down.
I think I should check the thermostat, but should I also check the sender unit? The gage itself for possible voltage problems? Some other miscellaneous part?
Thanks

Here is one guess, you may have a stuck open thermostat, and a bad fan clutch, or no thermostat and a bad fan clutch.

 

[Ecomike]

I have been running a 13PSI Cap, why is the 13 worse then the 16?
Why do the Parts stores have it as 13 not 16?
What shoudl I be looking for in trouble if i run it at 13 not 16?

Parts store computer data is not always right. The OEM is 16 lbs. A higher pressure cap raises the boiling point of the coolant.

 

[Ecomike]

Re: How Hot is too Hot (or Cold)?

How would it affect the temp gauge reading Mike? Teach me, I am a sponge.

When my O2 sensor wire shorted to ground, the O2 heater wire dropped my system voltage, volt gauge went crazzy, and the others did too, either affected the ground or dropped the gauge supply voltages. May or may not be related. If he did ground out the hot wire to the O2 sensor heater, it might have melted neighboring wires. Long shot but wierd shit does happen.

 

[92xjsp]

Re: How Hot is too Hot (or Cold)?

Hi, I've been having a related problem with my temp. I found a couple earlier threads on it, but they haven't answered definitively my problem.
When i am idling, my dash gage reads around 200+-10. But, when i get to speeds of 50 and up, my temp starts dropping over a couple minutes to about 160+-10. This is happening in ambient temps of 50 to 90 degrees.

After this happens, what does the temp gage do in the next 15 minutes? If it stays at 160, then it seems to me it has to a faulty gage or sender because it's impossible it could really run that cold, even with a stuck open thermostat.

 

[gbyrnes]

All right. thanks for all the suggestions. I'll try checking the actual temps and see about that sender unit/ O2 sensor/ thermostat. The problem happens even on long runs, more than 3 hrs long. When I'm on trail, and running slowly, things act normally. It's on the highway that things act funny. The day before yesterday I made a run from northern NM to Albuquerque. It took 3 hrs and 20 min, and after I left the dirt road and got up to speed, the temp gage started to do its thing. It was unchanging as long as i was at speed.
And could you explain more about the fan clutch. I'll admit to being guilty of just starting to get into the heart of my Jeep.
Thanks, Gerald

 

[gbyrnes]

Re: How Hot is too Hot (or Cold)?

Q1, NO, has nothing to do with it.

Poor mileage, in your case probably a problem with the O2 sensor, but could be the TPS.

A common problem is O2 sensor wiring getting too close to the exhaust manifold, burning and grounding out. You might have knocked the O2 sensor wires loose doing the VSpeed sensor replacement. That might be affecting the gauge temperature reading too.

The Speed sensor on my jeep is on the attachment on the rear of the transfer case. To me, this wiring seems to be a good distance from the exhaust. I just popped in a new speed sensor, without messing with the wiring beyond un-plugging and re-plugging at the sensor. I don't think that would be it, and an emissions check shows everything within local legal tolerances, so apparently it's not to bad of a problem with the vehicle and more of what I should be getting used to. FWIW, the milage highway is from 12-15 mpg.
Thanks again, gerald

 

[CharlesS]

All right. thanks for all the suggestions. I'll try checking the actual temps and see about that sender unit/ O2 sensor/ thermostat. The problem happens even on long runs, more than 3 hrs long. When I'm on trail, and running slowly, things act normally. It's on the highway that things act funny. The day before yesterday I made a run from northern NM to Albuquerque. It took 3 hrs and 20 min, and after I left the dirt road and got up to speed, the temp gage started to do its thing. It was unchanging as long as i was at speed.
And could you explain more about the fan clutch. I'll admit to being guilty of just starting to get into the heart of my Jeep.
Thanks, Gerald

The fan clutch is engaged by the heat of the engine operating after about 5 minutes or so....
There is a temperature sensitive viscous liquid (on some fans) or a bimetallic strip (on other fans) that will allow the fan to spin at full engine speed to draw in the required air flow at idle to moderate road speeds...
At highway speed the air flowing thru the radiator should be sufficient to keep the engine cool.... assuming you have proper coolant flow and the radiator fins and tubes are clear of obstructions....

 

[gradon]

Your thermostat is either a 160* or is effectively one. Once you hit highway speeds the air cools it to the temp of the t-stat(mine used to run @180* on the hi-way when I had a 180* t-stat. The problem with this is that at that temp--160*-- the ecu still thinks it is warming up and is running a richer start-up map=using more fuel.

 

[Ecomike]

Your thermostat is either a 160* or is effectively one. Once you hit highway speeds the air cools it to the temp of the t-stat(mine used to run @180* on the hi-way when I had a 180* t-stat. The problem with this is that at that temp--160*-- the ecu still thinks it is warming up and is running a richer start-up map=using more fuel.

I have run mine at 160 F, 180 F, 190 F and 200 F, with no difference in mileage. 87 Renix.

It does sound like he might have a 160 thermostat and dead fan clutch, and possible an old slow O2 sensor eating into his mileage, or bad O2 sensor heater, or no power to the O2 sensor.

 

[gbyrnes]

OK thanks. I checked out the sender, it's good. Now i'll see to that clutch and thermostat.

 

[Deadman 94 xj]

Well I figure I'll jump in here as well.

My issue is similar to the OP's problem.
Mine runs hot at hwy speeds at about ~220* to 225* and at idle the fan kicks on at about ~239-40*.

It stays pretty steady through out the range. I will say that it seems to reach op temps rather fast, faster than an old jeep I had. Maybe it's just me but worth mentioning.

I replaced the 13psi radiator cap to a 16psi and also replaced the temp sensor at the rear of the block. Neither resulted in any change.
The rad fluid is very clean but also very green. Maybe too rich?

I have not done any tests to find out if the gauge is working correctly or not. From what I've searched, I think it's probably correct.

I'm not sure what t-stat is in it. I haven't had to open it up since I bought it. I'm pretty new at cooling issues so please bare with me here.

Thanks

It's a 96

 

[Ecomike]

Well I figure I'll jump in here as well.

My issue is similar to the OP's problem.
Mine runs hot at hwy speeds at about ~220* to 225* and at idle the fan kicks on at about ~239-40*.

It stays pretty steady through out the range. I will say that it seems to reach op temps rather fast, faster than an old jeep I had. Maybe it's just me but worth mentioning.

I replaced the 13psi radiator cap to a 16psi and also replaced the temp sensor at the rear of the block. Neither resulted in any change.
The rad fluid is very clean but also very green. Maybe too rich?

I have not done any tests to find out if the gauge is working correctly or not. From what I've searched, I think it's probably correct.

I'm not sure what t-stat is in it. I haven't had to open it up since I bought it. I'm pretty new at cooling issues so please bare with me here.

Thanks

It's a 96

Sounds like the radiator and condenser fins are dirty, or the inside of the radiator tubes are plugged up, scaled up. Best guess is it needs a new radiator, but you might clean the outside fins, check air flow, and check the coolant water concentration with a hydrometer.

It also sounds like the fan clutch is toast.

Change the cluthch first, then clean the condenser and radiator fins and remove any leaves stuck between the two. Then try a radiator flush with a fresh 50/50 mix. That might get you down to a peak of 215 F.