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Temp Sending Unit

IMORTL

IMORTL

NAXJA Member #1156
Location
Corona
I'm having problems with overheating. I broke a hose last week and the water pump started leaking. i have replaced the hoses and the water pump. flushed and replace AF. and when I start it it gets hot in like 3-5 minutes. 240. I replaced the thermostat. still shows 240 to pegged past red in 5 minutes.... if I turn on the heater it comes out cold for at least another 3 minutes... I think its the sending unit...


any thoughts?

What if I replace that and it doesnt fix it? What else could it be?

1990 XJ 4.0L
Stock cooling w/ AC
New upper & lower hose (last 3 months)
New water pump
looks like new pressure tank (bought it 1 year ago)


ken
 
IMORTL said:
I'm having problems with overheating. I broke a hose last week and the water pump started leaking. i have replaced the hoses and the water pump. flushed and replace AF. and when I start it it gets hot in like 3-5 minutes. 240. I replaced the thermostat. still shows 240 to pegged past red in 5 minutes.... if I turn on the heater it comes out cold for at least another 3 minutes... I think its the sending unit...


any thoughts?

What if I replace that and it doesnt fix it? What else could it be?

1990 XJ 4.0L
Stock cooling w/ AC
New upper & lower hose (last 3 months)
New water pump
looks like new pressure tank (bought it 1 year ago)


ken
Click to expand...
That sounds like the sending unit to me. I would think if it was at 240 you would have fire blowing out your vents in the heat position. And to me it doesn't seem like it could get that hot in 3-5 minutes, although I don't know where Corona is I guess.
JMHO
-Collin
 
BigBlackHeep said:
That sounds like the sending unit to me. I would think if it was at 240 you would have fire blowing out your vents in the heat position. And to me it doesn't seem like it could get that hot in 3-5 minutes, although I don't know where Corona is I guess.
JMHO
-Collin
Click to expand...
sounds like an air pocket too me could be a blown head gasket as well
 
Corona is just South Side of Hell... So it does get hot here... but not this time of year... Ice water prices drop quite a bit...... :)
 
if I turn on the heater it comes out cold for at least another 3 minutes...
Did you purge the air out of the system? How did you refill your system?
 
purge the air? what do you mean?

i opened the radiator drain unitl i saw drips... closed it.. then filled the rest through the pressure tank while running it and let the bubbles come out... do i need to do anything else? the manual didn say i had a purge nut like my WJ...

ken
 
To purge the system take the heater hose off of the thermostat housing and continue to fill the coolant bottle until the water comes out of the thermostat housing. then put the hose back on and top off the bottle. This is a common problem with the 87-90 XJs. If you are still overheating after you purge the system then you have other problems.
 
I had the same problem with my MJ and i was told to put the back end of the car as high in the air as possible and loosen the temp sending unit, almost all the way out but not quite. and start it up and let it run util hot. I let it cool back down and started it up a couple times, all the time i had to temp sending unit loose. It worked for me. and i think the xj is the same setup as the mj. i have an 89
 
Well I did a search on "Purge Air" and read those posts...

with teh engine running, I removed the temp sending unit... Im pretty sure that a gush of air came out before a rush of AF... Plugged it back in and tighened it back down. Drove around for 15 minutes... Seems to be working fine now....

bottle was empty when i got home so it must have sucked it in...

cooling now.. will refill when cool....

thanks for your help
 
That's why I reach for the drill whenever I'm changing the thermostat. It's amazing how well two small holes in the thing can help - makes the system self-purging. You just watch your coolant levels for the first day or so, and once they're consistent from one time to the next, you can ignore it...

5-90
 
For those not in the loop, you drill a small hole in the edge of the brass disc of the thermostat - in far enough to allow air to bubble through when you bolt it down in the 12 o'clock position.

Murray thermostats have the hole drilled and a bobber rivet crimped in the hole for many late models, not just Jeeps alone. I just can't remember if the one for the 4.0 does - if it's backward compatible to detroit iron it's left off.
 
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