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Odd temp issue

T3hk1w1

T3hk1w1

NAXJA Forum User
Location
Houston
Well, I just finished flat-towing my C101 Jeepster from Falfurrias, TX to Houston (It sucked) and I have a new and strange issue with my engine. As I was driving along the beltway in Houston, after almost 280 miles of smooth running my oil temp indicator suddenly went from 215 to 250(it didn't peg at 260) and the "Check guage" light came on. I pulled over, shut her off, popped the hood(After ensuring it was not on fire). No smoke coming from the engine, plently of coolant in the reserve bottle, none of the other typical signs of overheating. I turned it back on and the temp was at 220, so I pulled back onto the road. About 10 minutes later it did it again, temp went from 215 to 250 in under 1 second. This time I ignored it and after about 15 sec it dropped back down to 215 just as suddenly. It behaved fine for the rest of the trip home(only 15 more miles). Any idea what happened? Is my temp sender going?
 
Are you referring to oil temperature or coolant temperature? Stock gauge on the lower right side is coolant temp. at least it is on my 99. Mine pegs at 260.

You are going to need to "verify" that what you see is actual or a false reading. The fact that it goes from one temp to another so quickly (1 second) is a clue that the high number may not be real but you shouldn't take any chances as overheating is bad news. Could replace the sender (I'd try that first) or rig in a different gauge temporarily and try that.
 
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Could be a loose wire on the sender. Again are we really talking about oil temperature or coolant temperature. Oil temperature would have to be an accessory gauge.OEM gauges did not include a gauge for oil temp. Sounds like a mechanical/electrical issue with the gauge moving so quickly from one temp to another. Oil or coolant neither will cool that rapidly.
 
Thought so.....definitely concentrate on sending unit and associated connections/wiring first. New sending units shouldn't be too expensive I don't think.... if wiring/connectors check out, you may want to just pop for a new one.

If I remember right, there are two sending units, one that sends coolant temps to the computer and one for the gauge. I believe the sending unit for the GAUGE is located on the back of the head. Someone please correct me if I'm wrong.
 
I found on MY Cherokee that there was actually a SHORT going to the electrical fan. If the wire moved 1/8 inch up or down, the voltage dropped significantly, but NOT enough to shut the fan off, so it was really hard to trace the problem. I finally busted out the ole voltmeter and went to town. I simply tied in the "hot" wire of the fan to a spot that is live whenever the engine is on.

Anyhow, here's the link to my thread (ODDLY, named the same), maybe some ideas in there.

http://www.naxja.org/forum/showthread.php?t=943263&highlight=coolant
 
This is not an answer to your question, but with alot of towing you should have an auxilery tranny cooler. There are alot of write-ups about using the stock ones from an exploder you should be able to find if you search.
 
Just a thought but if you have a leak you could be air locked. Coolant will then bubble backwards through the system filling up your resevior making you think there is plenty of coolant, but it is not circulating properly. Sometimes then it will cycle and cool you off again, then get locked again. I would make sure that you have it filled properly and that it cycles properly. A bad thermostat can cause a similar problem.
 
kind of an old thread here, but I'm having the same issue. It seems like if I hit about 220 on the temp gauge, it immediately goes over to 250 and the check gauges light comes on. Mine is definitely temperature related, as it only did it pulling a long grade in 105 ambient temp and A/C on. Had no boil over, just the gauge acting screwy.

T3hk1w1, did you ever find out what the problem was with yours?

I have a stock (except K&N Intake) 98 XJ with 4.0 and full gauge dash.
 
You can get a sudden jump like that if the radiator cap opens to bleed excess pressure at 220 F. Try a new cap and check to the sensor and sensor wire for any looseness.
 
Yeah, cracked head at the #6 cylinder causing all sorts of trouble. Ended up replacing the engine. No more coolant issues now, although the new engine drinks gas like there's no tomorrow, and I haven't been able to figure out why...
 
T3hk1w1 said:
Yeah, cracked head at the #6 cylinder causing all sorts of trouble. Ended up replacing the engine. No more coolant issues now, although the new engine drinks gas like there's no tomorrow, and I haven't been able to figure out why...
Click to expand...

Probably one of the closed loop sensors has gone bad. Look into the O2 sensor and CTS, Coolant Temp sensor topics here in older threads.
 
I've already done most of these, I've started several threads related to it. I've replaced both O2 sensors, and checked the MAT sensor. I could never figure out how to check the MAP sensor while the engine was running.
To clarify my previous post, I know that it's running way rich-I just don't know why.
 
T3hk1w1 said:
I've already done most of these, I've started several threads related to it. I've replaced both O2 sensors, and checked the MAT sensor. I could never figure out how to check the MAP sensor while the engine was running.
To clarify my previous post, I know that it's running way rich-I just don't know why.
Click to expand...

If it is a 91 or newer, a bad CTS, or bad O2 / CTS sensor wiring will keep it in open loop mode. You need to back probe the O2 sensor wires while the engine is running, and check the O2 wires, power off with an ohm meter for faulty wiring. Also need to verify the CTS ohm resistance per FSM spec at various temperatures, and check the CTS wiring to the ECU/PCM.

If coolant gets on an O2 sensor the silicates in the coolant can kill the O2 sensor. O2 sensor wires have been known to get cooked on exhaust manifolds.

What year is yours again?

MAP sensors rarely go bad, when they do the engine runs like shit.
 
2000.
Does the FSM have the procedure for checking O2 sensor wiring?
 
T3hk1w1 said:
2000.
Does the FSM have the procedure for checking O2 sensor wiring?
Click to expand...

I would start with an OBD-II scanner, get a free reading at some place like AZ. There are 4 wires, 2 are grounds, one is a 12-14 volt feed that runs an internal heater in the O2 sensor, it is the fatter, largest gauge wire of the three. The ground wires are usually black. The fourth wire needs to be tested with an old style analog (has a needle indicator, not a digital display) multi meter (volt-ohm meter). The fourth wire should oscillate between 0-1 volts at idle, and hold a near steady 0.45 +/- ,05 volts at 2000 rpm.
 
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