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Coolant Temperature

98XJSport

Destiny is the rising sun
Location
Western Maine
I have a 98 4.0 XJ. Every once in a while, after I drive home from work, I get a check engine code. What happens is 1. I stop after driving at normal operating temp. 2. I start the jeep after about 5-10 mins, and it seems normal. 3. Suddenly my temp guages jumps from 210 to 260 and usually gives me the check engine code.
My question, is it possible to get this temp jump from a mechanical defect, ie waterpump stalling or such? Ive replaced the t-stat, flushed the rad, and replaced the engine coolant temp. sensor, with no real positive results. The first time I checked the code for this problem it gave me the coolant temp. sensor, but I haven't been able to check it again because of the inconsistancy of the problem. Note, it also only lasts for about 5 or 8 turns of the key. Also, it seems to drive...not right, like its not shifting right. Any ideas?
 
98XJSport said:
I have a 98 4.0 XJ. Every once in a while, after I drive home from work, I get a check engine code. What happens is 1. I stop after driving at normal operating temp. 2. I start the jeep after about 5-10 mins, and it seems normal. 3. Suddenly my temp guages jumps from 210 to 260 and usually gives me the check engine code.
My question, is it possible to get this temp jump from a mechanical defect, ie waterpump stalling or such? Ive replaced the t-stat, flushed the rad, and replaced the engine coolant temp. sensor, with no real positive results. The first time I checked the code for this problem it gave me the coolant temp. sensor, but I haven't been able to check it again because of the inconsistancy of the problem. Note, it also only lasts for about 5 or 8 turns of the key. Also, it seems to drive...not right, like its not shifting right. Any ideas?
Loose wire bad connection on the coolent sensor.
 
A loose wire/bad connection on the sensor would cause the temperature guage to drop to zero, not spike. I can't think of any way that the sensor could suddenly drop in resistance for a few seconds or recieve a voltage spike that slow...
 
I wonder if a defective radiator cap that would lose pressure in about a 5 minute time frame would do this?
 
98XJSport said:
A loose wire/bad connection on the sensor would cause the temperature guage to drop to zero, not spike. I can't think of any way that the sensor could suddenly drop in resistance for a few seconds or recieve a voltage spike that slow...
No not true, unplug the sensor and the gauge will go up not down.
 
I tried it, guage zeros. The temp. increase decreases the resistance in the sensor I believe. I would have to go find my manual again to knwo for sure...
 
98XJSport said:
I tried it, guage zeros. The temp. increase decreases the resistance in the sensor I believe. I would have to go find my manual again to knwo for sure...
don't bother.
70deg=3700 ohms
100deg=1600 "
160deg=450 "
212deg=185 "
 
Possible the radiator is clogging up a bit then? That would make sense, I suppose, it was pretty sludgy at the time of flush and could probably use another flush again.
 
If the needle is "jumping" it is surely a sensor/gage problem. If the engine was really overheating it would take some time, so you would see the needle climb up over a minute or so. Also if you were really at 260 the engine would run very badly, knocking/pinging, severe loss of power, etc.
 
98XJSport said:
I have a 98 4.0 XJ. Every once in a while, after I drive home from work, I get a check engine code. What happens is 1. I stop after driving at normal operating temp. 2. I start the jeep after about 5-10 mins, and it seems normal. 3. Suddenly my temp guages jumps from 210 to 260 and usually gives me the check engine code.
My question, is it possible to get this temp jump from a mechanical defect, ie waterpump stalling or such? Ive replaced the t-stat, flushed the rad, and replaced the engine coolant temp. sensor, with no real positive results. The first time I checked the code for this problem it gave me the coolant temp. sensor, but I haven't been able to check it again because of the inconsistancy of the problem. Note, it also only lasts for about 5 or 8 turns of the key. Also, it seems to drive...not right, like its not shifting right. Any ideas?


I have a 97 and had the exact same thing happen. I relpaced the t-stat with a 180 degree t-stat and everything has been ok.
 
Ive replaced the tstat with a new stock one, what is the temp of a stock tstat? Either way at 210 they should both be open. Does the tstat close when the vehicle is turned off? I dont believe it does, but Im far from an expert.
 
When I say it jumps from 210 to 260 its not like it instantly goes there it goes up over like 10 seconds or so. Not jumps like it does when you start the engine and it almost instantly goes to the current temperature.

My concern is that if it was just a faulty guage why would I be getting check engine codes?

EDIT- Im not sure how the engine runs when it does that, im almost never in drive, and if I am im just barely out of the parking spot. But I do know afterwards while the light is still on it seems to shift funny, even though the temperature is back to normal.
 
Well same thing happened last night, but it was different this time. It went from 210 to about 225, then dropped to about 180 and sat fow a few seconds, then eventually went back to normal.... But the light is still on, and i can get it scanned tonite hopefully.
 
98XJSport said:
Well same thing happened last night, but it was different this time. It went from 210 to about 225, then dropped to about 180 and sat fow a few seconds, then eventually went back to normal.... But the light is still on, and i can get it scanned tonite hopefully.
Ok I don't think that the sender for the gauge would cause your "Check Engine" light to come on.
I think your back to a bad connection of air in the system.
 
Got it scanned, got a temp error code of low voltage to the temp. sensor. Which would seem like a worn wire grounding out somewhere. But the rest of the times it would have been a high voltage to the sensor causing the error. Which would be like crossing the two wires before they reached the sensor. Its kinda a stretch for both to be happening, but not unthinkable. But what gets me is why would it only happen after this specific sequence of events. If there was some bad wiring somewhere I should have the problem constantly, not after doing a specific sequence of events and nothing else... could a dying altenator have any affect on this?
 
Note, it also only lasts for about 5 or 8 turns of the key.
IN many vechiles you can clear the codes by cycling the key 5 times.

It does still sound like you have a wiring issue. Still I would pull the radiator and have it rodded out. Also Prestone makes a inline flush that attaches to your upper heater hose. You screw on a garden hose and it flushes not only the radiator but the block and heater core if you run the engine with the heater on. Most auto part stores carry them.

Have you replaced both sensors or just the one on the thermostat housing?
 
98's have just the one coolant sensor, located in the thermostat housing. It runs both the dash gauge and also serves as the coolant temperature sensor for the computer to use.

Forgot to ask...
I know you were talking about pulling the wire off of the sensor and checking to see what the gauge does. DId you clear any troublecodes it would have set by doing this, BEFORE you got it scanned?

I also was going to mention, that since its just the one sensor giving you gauge info and computer input, I could see that if its malfunctioning, it would give the computer faulty information on the actual temperature of the engine and modify its run parameters accordingly. I would imagine that this could account for it "seeming" to not run right or even shift right. If its not the coolant temp sensor malfunctioning, and it really is that hot, then its got to be the waterpump, thermostat, airpocket, plugged radiator...something along those lines. I can't remember if you did the factory thermostat (195 degree) or not. It would have had an air bleeder on the flange that is put in with the bleeder at 12 oclock.

Dave
 
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