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TJ Temperature

18K views 37 replies 11 participants last post by  superduty 
#1 ·
Hi all,
My TJ has over 200k on it so I'm assuming the cooling system has probably been warn out. Lately, I've noticed my TJ getting a bit hot when driving at 75 for long periods of time. I'm OK with that and can just slow down to 70 or so. But I've also noticed that it seems to get toasty when idling. I've even seen my temp gauge spike to red immediately and after a few minutes, cool off in a matter of seconds. Is this the gauges fault or is the engine really getting that hot? What could be the cause of the sudden temperature spikes?

My TJ usually sits just a tad over 210 when driving around, is that normal or should I get the cooling system checked out?

Thanks
 
#4 ·
210 is normal.
I've seen spikes like that caused by a blown head gasket. Pumps air into the system and t-stat closes. Just a possibility.
I'd go with a new t-stat and flush first. Check the hoses. While a water pump is not difficult or too expensive, don't throw money at a problem, find the cause first.
 
#6 ·
210 is normal.
I've seen spikes like that caused by a blown head gasket. Pumps air into the system and t-stat closes. Just a possibility.
I'd go with a new t-stat and flush first. Check the hoses. While a water pump is not difficult or too expensive, don't throw money at a problem, find the cause first.
At that mileage I would consider replacing the water pump, thermostat, hoses and doing a coolant flush for starters. Possibly a fan clutch also.
the spikes sound like a failing thermostat is sticking
Thanks for the help. Figured out by hooking up an obdii reader that it isn't spiking. I let it idle for about 15 minutes and it reached 238 or so. I then turned on the AC. It reached 250. It slowly climbed to both numbers. During this time the gauge stayed at 210. I turned the engine off at 250 and came back after a minute or so. I turned on the electronics and the gauge was at the Red. According to the obdii reader, the coolant was at 262.

Any ideas what this could be? It was about 70 degrees during my test. I'm assuming on hotter days, the engine can get to the 260 threshold to send the gauge to the red.

I should also mention that during driving, the engine stays at around 215 according to the obdii reader. Idling with AC causes it to overheat. What part of the cooling system would be the culprit for this?
 
#7 ·
Could be water pump, not moving enough water. Sometimes the blades get worn. Has it ever been replaced, 200K is a lot of service time.

Could be a clogged radiator. A flush might help with that.

Bad thermostat not opening all the way.

I'd start with the flush and t-stat first. I'd skip the anti-freeze right now unless you have a way to recover it when emptying the system if you do the water pump.
 
#9 ·
I would replace your waterpump if it has 200K on it. They are known to hit "end of life" at about 125K-150K.

If it were mine, I would replace the waterpump, thermostat, and coolant with the Zerex I mentioned... and it "should" resolve your issue. But depending on how hot you overheated your motor, its not uncommon for the head gasket to have taken a beating (cooked).
 
#16 ·
I was surprised about that as well. Seems like a dangerous way to have a gauge set up.

It just depends how long you ran it in the Red Zone on the temp gauge. The longer and hotter, the higher the likelihood of cooking the head gasket...which then you have a new problem.
Well, the gauge has gone up red maybe 5 times. Usually it just goes back down to 210 once I get moving a bit. I'm getting the head gasket and cooling system checked today at a jeep dealer. I think I might have a vacuum leak as well so things aren't looking too good.
 
#14 ·
Mine is a 2000 4.0L TJ with 94K on the odometer.
I replaced the water pump because it was leaking and did the thermostat and the fan clutch at the same time. It had been going up to just above the "0" but not into the red when driving in 103 degree temps with the jeep loaded and the A/C on and climbing hills on the freeway. Now the gauge stays steady at the center of the 210 mark no matter what .... and thats with a cruddy radiator. So a new radiator will be going in this 4th of July weekend. All of the above seems to show that the folks that say the cooling system is adequate in stock form for a good operating engine are correct.
Just my experience.
Cheers and YMMV.
 
#15 ·
Now the gauge stays steady at the center of the 210 mark no matter what ....
You might have a different experience if you accessed the temperature sender output directly.

Did you read post #6 above?

Figured out by hooking up an obdii reader that it isn't spiking. I let it idle for about 15 minutes and it reached 238 or so. I then turned on the AC. It reached 250. It slowly climbed to both numbers. During this time the gauge stayed at 210.
 
#17 ·
Just to add more information:

Since you have a 2001, I believe you have the smart dummy gauge. When reading the engine temps from the PCM, mine runs between 195-205*F when fully warmed up regardless of the weather or driving conditions. The temp needle should sit just to the left of 210.

If the needle is at or to the right of 210, then the engine is running warm and has the beginnings of a problem. If the needle is climbing towards red, then there is a problem.
 
#18 ·
Just to add more information:

Since you have a 2001, I believe you have the smart dummy gauge. When reading the engine temps from the PCM, mine runs between 195-205*F when fully warmed up regardless of the weather or driving conditions. The temp needle should sit just to the left of 210.

If the gauge is at or to the right of 210, then the engine is running warm and has the beginnings of a problem. If the needle is climbing towards red, then there is a problem.
I believe the same holds true on the earlier TJs, though the gauge may function more as a gauge.

In terms of actual temps, I agree with the above. On my '98 when the gauge is dead center on the 210 the actual engine temp, per the scan gauge is 219. And during normal engine temps it will run just to the left of the 210, which is typically 203-210. Unless it's very cold outside mine is typically 201+.

When it's over 100 degrees outside mine unfortunately goes to the right of the 210, which according to many folks here it should not be doing. I have replaced every part of the cooling system except heater core. I've used oem radiator and water pump. I did install an aftermarket t stat. I'm thinking if swapping that out. I'm also going to do another engine flush. I'd like to get it to the left of 210 regardless of conditions. Even it was recently 110 degrees engine got to 241 with a.c. on. I shut down at that point, unknown if it would have kept going.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 
#20 ·
Last spring before my fan clutch started failing, my temp would stay just above 210 and would fluctuate up and down. I assumed this was normal until I started overheating. Now with a new clutch and thermostat, my gauge behaves in what I now what I now believe is a normal fashion. Now that I know how it works, the dummy gauge does provide quite a bit of information.
 
#27 ·
How am I still running hot? 206 cruising around at 40 with the AC on is hot? Running at 85 down the highway with AC on at 215 is hot? Those seem pretty cool to me... How could it be cooler?
 
#32 ·
I daily drive mine and usually have Torque displaying the engine temps, among other things. This is what I have been seeing on a regular basis for a long time.

As I mentioned earlier, I used to believe normal engine temps were 210+ until I had to begin replacing worn out parts of the cooling system. I was quite surprised to find that 195-205 seemed to be what normal really is, regardless of any other factors. It's a rare day that my engine climbs above that.

I saw ambient temps above 100* several times during our heat wave last week. Wish all you want, but the engine didn't care.
 
#34 ·
I daily drive mine and usually have Torque displaying the engine temps, among other things. This is what I have been seeing on a regular basis for a long time.

As I mentioned earlier, I used to believe normal engine temps were 210+ until I had to begin replacing worn out parts of the cooling system. I was quite surprised to find that 195-205 seemed to be what normal really is, regardless of any other factors. It's a rare day that my engine climbs above that.

I saw ambient temps above 100* several times during our heat wave last week. Wish all you want, the engine didn't care.
Do you monitor your intake air temps at all?

Do you see fairly high numbers when it's over 100 ambient? Temps around 175?

Sent from my SAMSUNG-SM-G930A using Tapatalk
 
#33 ·
I wish mine didn't care and acted similarly. I too run torque when driving (a great use for my unused galaxy s4). I'm not sure why my jeep behaves differently.

I'm going to flush it again. Then I'm going to install an oem t stat, though I doubt that could be the problem.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 
#35 ·
Back when I had the OEM intake, I recall temps were steady in the 180-90s. I run a Windstar cowl intake which puts the intake manifold between 10-100°above ambient depending on many things. Based on what I've seen, there is little to no correlation between intake temps and engine temps.
 
#36 ·
My factory gauge rises from cold to 210F and then sits exactly straight up on 210F until I shut it off. It has done that since new in 2003 no matter what the ambient temperature or use of AC. I always wondered about that unmoving 210F.

If it's really running as hot as 250F while showing 210F, then Jeep has fooled (and failed) me.

I hate when a manufacturer considers its customers to be excitable idiots who can't handle a real gauge, so they feed us idiot-gauge tranquilizers to keep us dumb and happy until the gauge finally moves to hot in order to inform us that the engine has melted and we should pull off to the side of the road and call for help.
 
#37 ·
The oil gauge on most TJ's is a dummy gauge (not sure what year they swiched, but my `04 has the dummy gauge)

Get an OBDII Reader and a smart phone App to confirm your temp gauge readings.

The Temp gauge is a real gauge, but is poorly scaled. On mine, once it gets past the "dot" to the right of 210 the temp is at 220.
(I did these readings with an OBDII when my Jeep was running hot — new radiator fixed my problem, I now run to the left of the "dot" @ 200)

 
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