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2000, coolent temp spikes out of no-where!

md21722 said:
I would not try the stop leak hack job repair.

As far as the talk about air pockets, if the coolant system is underfilled, you can overheat the engine and the dash gauge will not show it.

A properly working XJ coolant system is adequate to drive across the desert in California or Arizona in the daytime, 100F+ ambient, with the A/C, on long uphill grades on I-8/ I-17. I don't drive those roads every day but I have done it repeatedly in my 2001.

Over time engine components get old and lose their performance and then the coolant system loses its ability in extreme temperatures. Fan clutches get weak, radiators/condensers get clogged with dust and leaves, catalytic converters don't flow as freely, thermostats may not open properly, ...

I would look at the misfire code as well. A weak head gasket can cause some funny problems.

And consider testing the coolant sensor through its entire operating range or replacing it.
Click to expand...
CTS is new.

Missfire code is fixed, bad coil.
 
If I had this type of problem I would probably drive around with a live data scanner and see what temperature the PCM is getting from the CTS and compare with an actual IR thermometer.
 
Agreed with previous, I'd get a new cap, mine was on like a 70° angle this weekend when my rubber decided to go, spiked to 260 got my spare cap from the box, threw it on, back to 160 again
 
xjtrailrider said:
The cap is new
Click to expand...

When I was debugging unsolvable cooling problems on my diesel years ago, I bought a radiator/radiator cap tester and went through 6 radiator caps at the part store before one tested and actually held the label spec pressure on the cap. Same goes fan clutches, and some T-stat vendors (I use only Murray T-stats made in Israel now), being brand new means nothing unless you test it and verify it actually works to spec. I also bench Test new T-Stats before I install them now and fan clutches with boiling water and IR temp gauges.

One of the top chemists at Preston told me in 1994 when I was doing research under a US DOE grant, that all car manufactures add the Bars Leaks type dry sealant leak stop pellets to the radiators on all new cars and trucks and have done so since way back in the 1920s or so. That is so the radiators, heater cores, and head gaskets can go leak free long enough to get past the factory warranty. One of the best kept secrets in Detroit LOL.

Also one of the main ingredients in the Green Antifreeze/coolant formula is a leak sealant that works in combination with the fibers in the Bars Leaks, leak stop pellets. It is called Sodium Meta-silicate. It neutralizes acids, CO2 from head gasket leaks, and forms a white concrete like material when the coolant leak dries at the leak location, and leaves the silicate behind forming a fiber-silicate seal in the head gasket, or hose or radiator tube leak as they form. It is a self healing process that seals mini leaks as they form. Silicate is one of the main parts of concrete. The fibers collect and get stuck at the high velocity leak site, and the silicate dries and forms an organic fiber-silcate seal resembling the head gasket material itself. The fibers do not clog the radiator or heater core internals.
 
Last edited:
Ecomike said:
When I was debugging unsolvable cooling problems on my diesel years ago, I bought a radiator/radiator cap tester and went through 6 radiator caps at the part store before one tested and actually held the label spec pressure on the cap. Same goes fan clutches, and some T-stat vendors (I use only Murray T-stats made in Israel now), being brand new means nothing unless you test it and verify it actually works to spec. I also bench Test new T-Stats before I install them now and fan clutches with boiling water and IR temp gauges.

One of the top chemists at Preston told me in 1994 when I was doing research under a US DOE grant, that all car manufactures add the Bars Leaks type dry sealant leak stop pellets to the radiators on all new cars and trucks and have done so since way back in the 1920s or so. That is so the radiators, heater cores, and head gaskets can go leak free long enough to get past the factory warranty. One of the best kept secrets in Detroit LOL.

Also one of the main ingredients in the Green Antifreeze/coolant formula is a leak sealant that works in combination with the fibers in the Bars Leaks, leak stop pellets. It is called Sodium Meta-silicate. It neutralizes acids, CO2 from head gasket leaks, and forms a white concrete like material when the coolant leak dries at the leak location, and leaves the silicate behind forming a fiber-silicate seal in the head gasket, or hose or radiator tube leak as they form. It is a self healing process that seals mini leaks as they form. Silicate is one of the main parts of concrete. The fibers collect and get stuck at the high velocity leak site, and the silicate dries and forms an organic fiber-silcate seal resembling the head gasket material itself. The fibers do not clog the radiator or heater core internals.
Click to expand...

I picked up another t-stat today, I will put that on tomorrow and don't know where I'm going after that
 
Great thread, wish I had tried the new cap when we were hauling a 4400# trailer x-country in the summer a few years ago. Our '98 exhibited the same symptoms. ~210°F then a second later, the gauge would be pinned. Now reading this, it could have just been a cap, I'm not sure. I flushed the rad, replaced the t-stat and didn't have any more problems on the trip (except blowing both rad hoses) it was kind of a nightmare.

This is pretty cool info:

Also one of the main ingredients in the Green Antifreeze/coolant formula is a leak sealant that works in combination with the fibers in the Bars Leaks, leak stop pellets. It is called Sodium Meta-silicate. It neutralizes acids, CO2 from head gasket leaks, and forms a white concrete like material when the coolant leak dries at the leak location, and leaves the silicate behind forming a fiber-silicate seal in the head gasket, or hose or radiator tube leak as they form. It is a self healing process that seals mini leaks as they form. Silicate is one of the main parts of concrete. The fibers collect and get stuck at the high velocity leak site, and the silicate dries and forms an organic fiber-silcate seal resembling the head gasket material itself. The fibers do not clog the radiator or heater core internals.
Click to expand...
 
xjtrailrider said:
This is my 2000;

It will, for no particular reason, spike the coolant temp while sitting ata stoplight or drive through.

I'm not loosing coolant. In fact when this happens, I don't notice any change in how it runs. Just the gauge will jump from 215 to 250 in a mili-second and as soon as I start moving, it drops just as fast to normal.

I think its the coolant temp sender.

Both the e-fan and clutch fans are new, new radiator two years ago, new hoses, new water pump two years ago. I just put a
T-stat in last summer.

Thoughts?
Click to expand...

The other day a poster on another Jeep XJ forum had a similar problem. He found bad connections inside of the ECT sensor connector. Replaced the connector and it fixed his problem.

You might try having someone sit in the drivers seat while the engine is running (parking brake set) and look at the temp gauge while you wiggle the ECT sensor wiring to see if the temp spikes.
 
Those same symptoms are very common around here, I have to wonder if something in the gauge circuit makes it go to full HOT when it trips anything over (for instance) 220°F. So, you're at 220, not great but not the end of the world, ALSO not 260, like the gauge says.
 
So far its fixed. It had a 195* t-stat in it that I think was opening much later than that.

I put in a 180* and its running happy at a tick below 200.

Time will tell, hot, muggy, VA Mountain weather will be here soon.
 
The 1996 Ford Taurus and 2001 Saturn SL1, both OBD-II rigs, are programed to turn on the E-Fans at exactly 221 F. I think the 96-01 Jeeps, being OBD-II may be programed exactly the same? Mine are all old school Renix. But they will get to 220 F at the T-stat exit on the hottest, high humidity days up to 105 F, 95% humidity with AC on.
 
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