XJ running hot on hills, offroad, city driving, i have some questions...

I am new to wrenching on the 4.0l, so if this is no issues, let me know. '95 sport, 155k, auto.

I bought this jeep 2 months ago and am slowly fixing it up to be a trail rig. The coolant was horrific looking, so i used a 3 hour cleaner, put in a new thermostat, and flushed it 8-10 times with clean water. Still looking for a radiator cap. Before the flush, the temp gauge would cycle from 210 down to 160 (maybe?). Now on the highway it sits at 210, or a kiss under it.

On friday night we were driving around downtown for a good hour and the thermostat got up to around 225 (maybe?) and pretty much sat there until we started driving, then it would drop to 210. Same when I went offroading, and climbing large hills.

On saturday i took the jeep to get s-10 rear leafs, and when i got home i sat the jeep there to see if the aux fan would kick on. I was really warm (50f), and sure enough when it sat there after a long drive it eventually kicked on around 240 (maybe?).

Every car i have owned the thermostat just sits straight up. My wifes 4.0l (06 wrangler) and my buddies (00 XJ) the aux fan kicks on and off keep the termostat right at 210.

Is the aux fan kicking on too late?
What temp is it suppsed to kick on?
Is this normal behavior?
Why does the termostat not sit like other vehicles?
What work can be done to help keep it cool?

I am meeting my buddy after work with an infrared to test what temp the thermostat housing actually is.

thanks for the help!

robhurlburt said:

I am new to wrenching on the 4.0l, so if this is no issues, let me know. '95 sport, 155k, auto.

I bought this jeep 2 months ago and am slowly fixing it up to be a trail rig. The coolant was horrific looking, so i used a 3 hour cleaner, put in a new thermostat, and flushed it 8-10 times with clean water. Still looking for a radiator cap. Before the flush, the temp gauge would cycle from 210 down to 160 (maybe?). Now on the highway it sits at 210, or a kiss under it.

Click to expand...

Replace that radiator cap. If you've got low pressure in the system, that will definitely impact its performance.

On friday night we were driving around downtown for a good hour and the thermostat got up to around 225 (maybe?) and pretty much sat there until we started driving, then it would drop to 210. Same when I went offroading, and climbing large hills.

On saturday i took the jeep to get s-10 rear leafs, and when i got home i sat the jeep there to see if the aux fan would kick on. I was really warm (50f), and sure enough when it sat there after a long drive it eventually kicked on around 240 (maybe?).

Click to expand...

Couple of possibilities: failing fan clutch and/or coolant temperature sensor. Depending on the thermostat you used, that may also be a factor even with a new one. Best luck I've had in that regard recently is with the OEM units, but the Stant SuperStat Premium also comes recommended - and in any case, use a 195degF 'stat; don't be tempted to go lower. Also, re-check the basics - coolant mix, trapped air in the system, leaks (esp. around the freeze plugs), radiator condition, hoses, etc.

Was the system reverse- and forward-flushed after running the cleaner through it with the heater at full heat? Also, you mentioned it's a 3-hour cleaner; my experience has been that the 8-hour Prestone one works about the best. It's OK to drive around with it in there for a few days to get to the 8-hour mark.

Every car i have owned the thermostat just sits straight up. My wifes 4.0l (06 wrangler) and my buddies (00 XJ) the aux fan kicks on and off keep the termostat right at 210.

Click to expand...

Some movement above 210 isn't unusual, but it shouldn't be above it by much or for very long. More:

Is the aux fan kicking on too late?

Click to expand...

I can only refer to the 2000 FSM on this one, but regardless of whether the A/C is running or not, the auxiliary fan is set to come on at 223degF (per Section 7, p.9). If your coolant temperature sensor is flaky, though, this could impact when it kicks in.

What work can be done to help keep it cool?

Click to expand...

Search, or check the related threads at the bottom of this page. Not to dismiss you on this, but there's been a lot written on it over the years.

Key here is to get it functional again before getting into upgrades. Start with the recommendations above and go from there - it sounds like you've got most of the issues at least understood, but some more work may be required to get it to where it needs to be.

New radiator cap and clutch fan would be a good start.

As mentioned, get OEM cooling components functional is your goal.

The #1 cause of temperature creep at IDLE is a faulty clutch fan. Often overlooked, inexpensive, and best .........easy to replace.

OK, took the long way home from work yesterday.
-highway, sat at a kiss below 210
-got home parked it, watched the temp gauge rise until the e-fan kicked on, e-fan brought it back to just below 210. I let this cycle like this twice.

casm said:

Replace that radiator cap. If you've got low pressure in the system, that will definitely impact its performance..

Click to expand...

got one on order, thanks

casm said:

Couple of possibilities: failing fan clutch and/or coolant temperature sensor. Depending on the thermostat you used, that may also be a factor even with a new one. Best luck I've had in that regard recently is with the OEM units, but the Stant SuperStat Premium also comes recommended - and in any case, use a 195degF 'stat; don't be tempted to go lower. Also, re-check the basics - coolant mix, trapped air in the system, leaks (esp. around the freeze plugs), radiator condition, hoses, etc.

Click to expand...

i replaced it with a stant superstat 195*, and checked the housing yesterday. it was running at 200*. As far as i know there is no trapped air, it mostly runs hot at idle after a long drive, then the e-fan kicks on and cools it.

casm said:

I can only refer to the 2000 FSM on this one, but regardless of whether the A/C is running or not, the auxiliary fan is set to come on at 223degF (per Section 7, p.9). If your coolant temperature sensor is flaky, though, this could impact when it kicks in..

Click to expand...

do you know how to check the coolant temp sensor?

birchlakeXJ said:

As mentioned, get OEM cooling components functional is your goal.

The #1 cause of temperature creep at IDLE is a faulty clutch fan. Often overlooked, inexpensive, and best .........easy to replace.

Click to expand...

my goal is to get what is in there working best possible. If i need to buy a new radiator, i might as well buy something more HD.

Thanks for all the info guys!

robhurlburt said:

OK, took the long way home from work yesterday.
-highway, sat at a kiss below 210
-got home parked it, watched the temp gauge rise until the e-fan kicked on, e-fan brought it back to just below 210. I let this cycle like this twice.

Click to expand...

This sounds not entirely unusual. However:

i replaced it with a stant superstat 195*, and checked the housing yesterday. it was running at 200*. As far as i know there is no trapped air, it mostly runs hot at idle after a long drive, then the e-fan kicks on and cools it.

Click to expand...

You mentioned that the cooling system was flushed; it's possible that the radiator has debris trapped in it from that episode or is still scaled. Internal damage due to age and use is another possibility, and damaged vanes on the airflow surfaces will also be a problem. You may want to pull the radiator, take it to a shop, and have it flow- and pressure-tested. Makes sense to upgrade to something heavier-duty if it is shot, but flush the hell out of the cooling system before installing it. You don't want old crud gumming it up.

Fan clutch: you'll have to test that by hand and determine if it's working or not, but it will affect your idle and low-speed temperatures greatly. Worth upgrading while you're in there to the NAPA unit if it is shot.

do you know how to check the coolant temp sensor?

Click to expand...

Hang off on that one for right now (or search for the procedure, because I don't recall exactly what it is for your year ). Temperatures are registering on the gauge and the aux fan is kicking in, so we know it's at least basically-functional. Let's see what happens once the correct radiator cap is in and the system is up to normal pressure; one step at a time makes it a lot easier to go through it methodically.

Someone makes a 21 lb that will fit. I have done a bone yard round up of caps. trying to find a high pressure cap. Don't remember what it came out of but it has work well for over 4 ~5 years now.
What will happen with a 21 ponder? The rad/heater core/water pump seal will not last as long. That's IF it pumps up that high.

casm said:

You mentioned that the cooling system was flushed; it's possible that the radiator has debris trapped in it from that episode or is still scaled. Internal damage due to age and use is another possibility, and damaged vanes on the airflow surfaces will also be a problem. You may want to pull the radiator, take it to a shop, and have it flow- and pressure-tested. Makes sense to upgrade to something heavier-duty if it is shot, but flush the hell out of the cooling system before installing it. You don't want old crud gumming it up..

Click to expand...

This is entirely possible. I flushed the heck out of the system (fill with water, run to temp, drain) a TON of times. The coolant in there is ALREADY starting to turn brown. How do I get ALL the crud out? Will those flush systems (the ones where you add a "T" and the garden hose) work? I heard the plastic tends to crack after a while, so i would probably just replace the hose with a new one after the flush. The 3-6 hour worked well i guess.



BTW, its not loosing coolant, and there is no coolant in the oil, plenty of power, no oil in coolant, not buring oil, no white bubble from radiator etc. I am almost 100% positive the head gasket is fine, I just wonder if the PO ever changed the coolant in it.

Mine runs around 210 all the time. I was worried, but everyone on here kept telling me it was normal. I have not had any problems so I am guessing they were right. you can only get a radiator so clean. Did you flush the block realy well also. It is a steel block and it is going to put a rust color in the water no matter how clean the system is.

Also, if a PO dumped StopLeak in it at some point, or used tap/city water instead of distilled in the anti-freeze mix, you're going to be washing mud out of it for a while.

Kevinma255 said:

Did you flush the block realy well also. It is a steel block and it is going to put a rust color in the water no matter how clean the system is.

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At least 8-10 times. i just gave up as i had been flushing it for 2+ hours or so.

hubs97xj said:

Also, if a PO dumped StopLeak in it at some point, or used tap/city water instead of distilled in the anti-freeze mix, you're going to be washing mud out of it for a while.

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how do i get rid of the mud at once?

robhurlburt said:

how do i get rid of the mud at once?

Click to expand...

You replace all of the cooling system components and while the water pump is out you flush the water jacket well.

Honestly, it sounds like your fan clutch is not working well, everything else sounds pretty normal.

I'd replace the fan clutch and see if your idle temp creep goes away.