What besides a thermostat can keep an engine from heating up?

hscrugby

Well-Known Member
Joined
Mar 22, 2005
Location
Raleigh, NC
It's a 98 TJ with 4.0.
I'm on the fourth thermostat, (first was AZ, second was advance, third was carquest, and this one is from the dealer.)

I don't think it's the temp sensor is bad, but i'm not 100% as I don't have a way to actually test the temp of the fluid compared to what it's reading. But I compared the "feel" of the hoses with a guy at the grocery store, (thanks random dude) and his felt a LOT hotter than mine. Now granted the, "how much does it hurt to touch something" isn't really a "scientific" experiment, but oh well.
Should I just replace the temp sensor? It's like 20-30$, but I'm tired of throwing money at crap, (read 23904239424 gallons of antifreeze) and not figuring this out.
The antifreeze is staying nice and green, and the oil looks fine too.
 
What temp are you showing on the guage? Auto guages (besides speedo/tach) are notoriously innaccurate.
 
jeepinmatt said:
What temp are you showing on the guage? Auto guages (besides speedo/tach) are notoriously innaccurate.
Click to expand...
well since it has a hash, then vertical is 210, then a hash to the right
if the angles are \ | / it's probably 2/3 of the way to 210.
 
mbalbritton said:
Are you running a Water/Anti-freeze mixture or straight Antifreeze?
Click to expand...
Premixed stuff.
So 50-50. (I'm lazy, and don't like mixing it myself)

Braxton, jeeps are supposed to run right on the 210.
Mine was that way for a long time, then I replaced radiator, water pump, thermostat, hoses, etc, and it's never warmed up since.
(water pump got replaced twice, cause the fan clutch went out and took out the water pump bearings with it.)

I'm pretty sure I have a heater core issue, (with it clogged slightly) but that's something else. And I'm still to lazy to deal with that. But the jeep not getting out of warmup mode, and probably trashing my cat is annoying.
 
I ran a 180 in mine for 40k miles, and none for 10-15k miles, and now Ive got 90k miles and still on the stock cat.
 
From your description, sounds like it's at 190+, which would put it out of open loop mode.
Are these 195* thermostats? Have you tested any of them?
 
First, check the amount of heat at the heater core. Is one hose substantially warmer than the other? If so, pop off the hoses and back flush the core with a garden hose until its clean.

Also, if the hoses are hot (as hot as the radiator hoses) it could be a blend door issue. Trace the AC vacuum lines under the dash and see if the blend door is not fully moving.

My bet is on the core being clogged or at least restricted.
 
I think stock tstat for a 4.0 is 195. Some people run a lower temp one, and claim it does fine, but I've also heard that the computer is setup for 195 and will not run correctly until it heats up all the way. To each his own though.

Will it eventually heat up if you run it long enough?
 
"Stock" is considered 190, 192, or 195 depending on where you read.
The FSM for a 98 says in two different places a 190 and a 192.
The dealership's was supposed to be a 190, I've done 195s, 192s, and 190s.

This new thermostat, (sposedly a 195) gets it a hair warmer, but it's still not where it should be on the gauge. And the weird/annoying thing, as soon as I got up to speed, it cooled off a bit, (noticeable on the gauge) and then went back up when I slowed down.
I left it idling for 20 minutes (waiting on wife) after work, and it never hit 210.
It "used to" (it's been a while now) get to 210, and just stay there never moving.

As for the heat, I'm pretty sure it's slightly clogged, but not bad. After I got home, I idled for a bit again, and then cut the heat on high. It started out nice warm air, then cooled of some from the vents, but the disturbing thing, is that the temp gauge needle dived a bit. Cutting the heater on shouldn't make enough of a difference to cool off the engine that much. I need to borrow a digital camera, (I destroyed mine the other day. Oops.) and film it so you guys can see how much it's moving. It's weird.


Charlie, they don't sell a 210 tstat. 195 is as high as it goes.



Just a random thought, bad radiator cap couldn't cause this would it? like recirculating coolant from the reservoir to much or something? At this point I just want it to warm up to where it should be. :D
 
check your fan clutch if your jeep has one to make sure it will spin freely. if it is locked and spinning all the time it can cause this problem too.

also if you have access to a obd II scan tool check to see if there are any codes for low operating temperature. i'm not a jeep tech but other manufacturer's have these.
 
jeepman13 said:
check your fan clutch if your jeep has one to make sure it will spin freely. if it is locked and spinning all the time it can cause this problem too.
also if you have access to a obd II scan tool check to see if there are any codes for low operating temperature. i'm not a jeep tech but other manufacturer's have these.
Click to expand...
Fan clutch is good, that was just replaced a little while ago.
(Also replaced water pump cause the bad fan clutch made the water pump bearings go bad. :( )

No codes are being thrown, I have a scanner.

Anyone want to buy a TJ? :lol:
 
#1 you need something more accurate than the stock gauge.

Most hardware stores will sell a liquid thermometer that reads to boiling point, if not get a kitchen one and just dont mix it with food.

With out a radiator cap stick thermometer in top of radiator and lets see what you are really running.

Also too low of a psi cap will let air bleed out and never build enough temp, too high and it will run hot.

you replaced radiator, same size? how about water pump? high flow?

Frankly I am a bit stumped Ive never had anyone want a jeep to run hotter...

Another option many OTR truckers use is a small piece of cardboard in front of the radiator blocking partial air flow....
 
Should really measure the resistance of the temp sensor while using a real gage. The same sensor feeds the computer as well, so it's not just a matter of a shitty oem gage. (though it is). You might try just running a restrictor rather than a thermostat.

Like skihi said though, at least it's not overheating...don't let it be such a headache.
 
Are you sure you heater control valve is working? Did the vacum hose come off or is it stuck? I would look at that as well.
 
Well, as many of you might can guess, there is ONE reason it's a headache.
Wife is getting annoyed at it. :D

If she's annoyed, well, it ain't fun for me.
I might pick up that radiator cap. Worth a shot at least.


Radiator is same size, and was "supposed" to be an OE spec replacement, except it's not plastic top/bottom.
Water pump I replaced it with was OE dealer part.

I'll try the thermometer at least. I've never run it with the top off? I just assumed it would spray out somewhat.



The fact that the heater isn't hot doesn't bother me much. I can deal with that, it's the engine running cold that I want to fix.
And I think the vacuum is for moving between defrost vents, floor, dash. That works fine. The blend door is cable controlled, and that "sort of works". (I can move the blend door by hand, if the cable hops off. My "helper" dropped the hvac box when I was replacing the AC evaporator. :D )
 
Its more than likely just the sender. Jeeps throw a code really easy if they are not running hot enough. I put a lower thermostat in my TJ to help with temps on the trail when moving really slowly. If I am on the highway with plenty of air moving through the radiator the check engine light comes on. If I just sit and let it idle it till it gets all the way warm the light goes off. I have read the code when its on and it comes up manufacturer controled air and fuel meetering, which on chrysler products showes to be a stuck open thermostat or low running temp. If the lights not on I would not worry about it.
 
Advance Auto Parts sells that cap if you don't wanna wait for mail order.
 
So didn't get a cap today, (actually was kind of busy with work for part of the day :D ) but since it was warm out, jeep popped up to just a hair under 210, stayed there, never moved, I could have the heat on high, and it stayed HOT. (Not burn your hands hot like it used to, aka I couldn't wear sandals if I had it on the floor) but the gauge never dropped etc.
Is it possible the radiator is bigger, and just cooling things off "to much"?
If so, what can I do when it gets colders besides the pizza box up front?
 
Back
Top