Running Hot

1996 XJ 4.0 auto

I've owned it since it was new. It has always run perfectly, with one exception.

In 2004, I had it serviced, and they didn't put the radiator cap back on properly. It was at night, and I thought the water droplets on the windshield were a rain shower until it began skipping, and I noticed the temp gauge was buried. It had cracked the head.

I replaced the head with a 1995 head, put in a 160 degree thermostat, and replaced the radiator with a new (stock) one.

I've had 50,000+ trouble free miles ever since. I live in Oklahoma, and the past few summers have been EXTRA hot. I've had no problem driving as long as I like in 115 degree heat, in traffic, with the ac running, and the temp never edged far past the 210 mark. It normally runs at what I'd estimate is 180. It's hard to tell for sure, as the only temps on my stock gauge are 100 all the way to the left, 210 in the center, and 260 all the way to the right.

The last few days have been different, though. I drive 16 miles to work, almost all highway miles. I leave for work in the hottest part of the day, which has been 95-98 the past few days. Within 5 miles, the temp goes past the 210 mark. By 10 miles, it's just below the red mark on the gauge , I'd estimate around 240-245, and stays there.

I checked the overflow tank, and it was low; it took just a bit under 1/2 gallon to bring it up to the "full mark". I checked the coolant in the radiator; it's brown-ish, but full. The cap looked ok, and I didn't see any signs of leaking anywhere.

I drove it to work yesterday, and it was the same; within 10 miles, it was almost up to the red zone on the gauge, and stayed there. Driving home last night, at 82 degrees, running the AC, the temp stayed right in it's normal operating range of about 180.

How do I troubleshoot this?

Thanks

Brown coolant?
I would start.with a flush and new coolant
check the thermostat isnt sticking
pressure cap

Well, check your grounds.

Now, that may seem strange, but I had a customer with an old Mustang that would seem to run fine WHEN THE HEADLIGHTS were on, but INDICATE overheating without the headlights on. It was bad grounds.

Get a pH reading on your coolant. If it's brown and has gone acidic you could have trace voltage in the coolant. I know it sounds weird, but a battery is two disimilar metals and an acid.....Drop your voltmeter in the coolant at the radiator and see if you're producing any voltage through the coolant itself. It's possible this could be throwing off your gauge.

What cooling system maintenance have your performed since 2004 ?

Coolant should be flushed and replaced every 2-3 years. Done that ? Thermostats are inexpensive and should be replaced as preventative maintenance every coolant change. Radiator caps should be replaced every other coolant change.

Radiators, water pumps and hoses should be replaced if you suspect they are weak/worn, if routine preventative maintenance has been neglected, or if symptoms/performance indicate they are failing.

My cars are serviced regularly. The coolant is replaced and flushed every 10,000 miles. It's 1,000 miles away from being due.

The cap is two years old, and tests good.

The thermostat is the same one I put in in 2004, but it appears to be working, as the coolant is circulating.

The hoses are good. The bottom one is the one with the wire in it, so I don't think the problem is the hose collapsing under pressure.

My first impulse was to flush the radiator and the block, and change the coolant, but I want to check for other problems before I do that; I don't want to put new coolant in, and throw my maintenance schedule off, just to have to dump it out if the problem turns out to be something else.

When I first looked at it, there was very little coolant in the bottom of the bottle. I'm wondering if it has sucked in an air bubble, and needs to be burped.

The past two days have been in the 80s, and there have been no problems. I'd think if it was a water pump, or a clutch fan, 10-15 degrees in outside temperature difference wouldn't have that great an effect on it, but I'm certainly no expert at cooling systems.

98NWCherokee said:

Get a pH reading on your coolant. If it's brown and has gone acidic you could have trace voltage in the coolant. I know it sounds weird, but a battery is two disimilar metals and an acid.....Drop your voltmeter in the coolant at the radiator and see if you're producing any voltage through the coolant itself. It's possible this could be throwing off your gauge.

Click to expand...

So, just set it on "volts", and immerse both leads in the coolant?

Next time it's running warm pull over, leave the engine running, and pop the hood.
Now with a stiff bit of cardboard or a hand full of rags, and leather gloves on for good measure, try to stop the mechanical fan from turning. A good fan clutch will be stiff enough to keep going strong, a bad one will make the blades easy to stop. This is a bit "cowboy" but I haven't found a better way to test a fan clutch. Just be sure the clutch is hot enough to be fully engaged before you condemn it.
Next, pressure test your cooling system. From 15 or 16 lbs (whatever your cap is rated at) you should see almost NO pressure loss over a 5 minute span. If you don't have access to a pressure tester, either buy one rent one or pay a shop to use one. Loss of pressure = lower boiling point, loss of coolant, potential for boiling coolant in the pump or block (which equals flow loss) etc.
If those two things are good, check the thermostat. It opens, but does it open fully? is it impeding coolant flow in any way?
Radiator could also be partially blocked up. If you have an infrared temperature probe, shoot several locations across the radiator. Most radiators I'm familiar with, you want to see temperatures hottest near the inlet, cooler at the outlet, and fairly even from side to side at a given level. Cooler spots may point to a blockage.
If all this is good, the head gasket is fine & you don't have a bunch of junk in your radiator fins, there's a fair chance you inhaled an air bubble along with the last of the coolant in the expansion tank. Air pockets definitely can show up as freaky-high temperatures on the sender without much rhyme or reason as to when. I've never had to bleed air out of my Cherokee but the general policy is to pick a high point on the cooling system & run the engine with that point open.
Lisle makes a funnel kit that adapts to your radiator filler neck. You attach it, fill it 1/2 way with coolant and let the engine run a while. You can make the filler neck the highest point on the motor by raising the nose of the car with jacks. Let it run & watch for bubbles.
Or you could crack the temp sender unit in the thermostat housing, though I wouldn't necessarily recommend that.
Or add a bleeder in the heater core lines... Etc.
Be sure to report back to us whats up. And do try to verify the gauges information before you go nuts tracking down ghosts.

yossarian19 said:

Next time it's running warm pull over, leave the engine running, and pop the hood.
Now with a stiff bit of cardboard or a hand full of rags, and leather gloves on for good measure, try to stop the mechanical fan from turning. A good fan clutch will be stiff enough to keep going strong, a bad one will make the blades easy to stop. This is a bit "cowboy" but I haven't found a better way to test a fan clutch. Just be sure the clutch is hot enough to be fully engaged before you condemn it.
Next, pressure test your cooling system. From 15 or 16 lbs (whatever your cap is rated at) you should see almost NO pressure loss over a 5 minute span. If you don't have access to a pressure tester, either buy one rent one or pay a shop to use one. Loss of pressure = lower boiling point, loss of coolant, potential for boiling coolant in the pump or block (which equals flow loss) etc.
If those two things are good, check the thermostat. It opens, but does it open fully? is it impeding coolant flow in any way?
Radiator could also be partially blocked up. If you have an infrared temperature probe, shoot several locations across the radiator. Most radiators I'm familiar with, you want to see temperatures hottest near the inlet, cooler at the outlet, and fairly even from side to side at a given level. Cooler spots may point to a blockage.
If all this is good, the head gasket is fine & you don't have a bunch of junk in your radiator fins, there's a fair chance you inhaled an air bubble along with the last of the coolant in the expansion tank. Air pockets definitely can show up as freaky-high temperatures on the sender without much rhyme or reason as to when. I've never had to bleed air out of my Cherokee but the general policy is to pick a high point on the cooling system & run the engine with that point open.
Lisle makes a funnel kit that adapts to your radiator filler neck. You attach it, fill it 1/2 way with coolant and let the engine run a while. You can make the filler neck the highest point on the motor by raising the nose of the car with jacks. Let it run & watch for bubbles.
Or you could crack the temp sender unit in the thermostat housing, though I wouldn't necessarily recommend that.
Or add a bleeder in the heater core lines... Etc.
Be sure to report back to us whats up. And do try to verify the gauges information before you go nuts tracking down ghosts.

Click to expand...

Thanks for the good information. I'm off work next on tuesday, and plan on digging into this then. I have to admit I'm a little iffy on grabbing ahold of that fan, though ... : )

EDIT: What about replacing the mechanical fan and fan clutch with a flex-a-lite fan and a spacer?

seanof30306@yahoo. said:

The past two days have been in the 80s, and there have been no problems. I'd think if it was a water pump, or a clutch fan, 10-15 degrees in outside temperature difference wouldn't have that great an effect on it, but I'm certainly no expert at cooling systems.

Click to expand...

Everything has as tipping point.

Are the radiator and water pump still the originals ?

seanof30306@yahoo. said:

Thanks for the good information. I'm off work next on tuesday, and plan on digging into this then. I have to admit I'm a little iffy on grabbing ahold of that fan, though ... : )

EDIT: What about replacing the mechanical fan and fan clutch with a flex-a-lite fan and a spacer?

Click to expand...

I would advise against spending money on parts that you aren't sure are bad. Also, most electrical fans that can easily fit into place won't pull as many CFM as the mechanical, and will require some wiring etc. You've only got 3" to work with, more like 2.5" really, and thats after replacing the studs with bolts.

And, yeah, testing a fan clutch my way is not without its element of risk. You don't want to "grab" the fan, you want to touch the blades with a softish object that will neither damage the blades nor get caught up in anything nor hurt you. Folded over cardboard is good. Probably better than a handful of rags, now that I think of it.

Tim_MN said:

Everything has as tipping point.

Are the radiator and water pump still the originals ?

Click to expand...

The water pump is original, the radiator was replaced in 2004.

yossarian19 said:

I would advise against spending money on parts that you aren't sure are bad. Also, most electrical fans that can easily fit into place won't pull as many CFM as the mechanical, and will require some wiring etc. You've only got 3" to work with, more like 2.5" really, and thats after replacing the studs with bolts.

And, yeah, testing a fan clutch my way is not without its element of risk. You don't want to "grab" the fan, you want to touch the blades with a softish object that will neither damage the blades nor get caught up in anything nor hurt you. Folded over cardboard is good. Probably better than a handful of rags, now that I think of it.

Click to expand...

I agree about replacing parts that I don't know are bad; that's why I wanted to gather information here before I started just replacing things.

And I was asking about a mechanical Flex-a-lite fan. In my younger days (before electric fans became so commonplace), one of the first mods my friends and I would do to our cars was to replace the factory clutch fans with Flex-a-lit fans. I searched it on here, but haven't found any info on it.

seanof30306@yahoo. said:

The water pump is original, the radiator was replaced in 2004.

Click to expand...

If the coolant is brown, I'd imagine your original waterpump is probably due for replacement. The waterpumps on these engines can corrode and the fins turn into flat pieces of metal that don't move any coolant.

I'd also recommend running the factory 195* thermostat. The cooler thermostats open sooner, but don't impact maximum operating temp. They only cause the motor to take longer to warm up which hurts fuel economy.

A properly maintained stock open cooling system should never need any modifications. If you are trying to apply Band-Aid solutions to cover for neglected maintenance, your results will be disappointing.


I expect a maximum lifespan for thermostat to be about 4-6 years. They are inexpensive, and simple to replace. I would consider a new water pump and a new fan clutch as preventive maintains by replacing them before they fully fail.

There is a difference between throwing new parts at an undiagnosed problem, and preventive maintenance replacement of parts that routinely wear out.

Rust in the coolant is never a good sign.

UPDATE:

OK, first, I never said the coolant was "brown". I said it was "brown-ish". To further elaborate, the coolant is definitely green, it just has a slight brown-ish tint to it. Last Tuesday, I had the coolant tested; guy said it is still good. I still plan on changing it, and having a radiator and block flush done, but I want to work this some more first.

I asked the guy at the shop who tested my coolant about checking it with a volt meter; he said he'd never heard of it. What setting do I set my volt meter on, and what is a good, and a bad reading?

I went to Autozone and used their coolant system pressure tester. The cap tested good, but a new one was less than 8 bucks, so I got one, and threw the old one under the back seat for a spare.

The manual for the tester said to check the vehicle's manual for the pressure to test at, but not to go over 30lbs, regardless. I couldn't find it in my manual, and didn't remember Yossarian's having said "15-16 lbs" here, so I pumped it up to 30lbs. Over 5 minutes, it leaked down about 2-3 lbs. I repeated the process several times, with the same results. I looked under the Jeep and all around the hoses, water pump, etc., but didn't see any fluid leaking out under pressure.

Driving it to work the last week, there appears to have been an improvement. The two previous days, where the temp had almost gotten into the red zone, were 97-98 degree days. 4 of the 5 days I drove to work last week were a bit cooler, at 92-93. One day was in the 80s. On any of those days, the hottest it got was a little past the 210 centerline on the gauge. Maybe the 4 or 5 degrees difference in temp made a difference. I'll find out tomorrow, as it's supposed to be the hottest day of the year (so far).

I tested both the old and the new caps, and they released at the identical pressure, so I don't see how the new cap could have been responsible for the improvement. The only other thing I can think of is putting the system under 30lbs of pressure several times may have forced some air bubbles out (if there actually were any there). We'll see how it does tomorrow.

This evening, I was driving home and talking about this with a friend who is an ASC certified technician who used to work at a Jeep dealership. He said I could test the clutch fan by getting it well into operating temp, then shutting it off, and rotating the fan by hand. If it rotated freely, it was bad. He said when the vehicle is hot, the fan should be hard to move.

I got home and tried it. The fan rotated easily, but there was some resistance, albeit not much.

Next I tried slowing it down while it was running, using Yossarian's method. I have an old wool car wash mit, so I wadded it up, and gingerly kinda stuck it into the fan. It shredded it.

Next I shut it off, and stuck a rolled up newspaper into it, and started it up. The fan didn't move.

I'm really not sure what these tests mean. I saw a video on youtube where a guy stopped a bad fan clutch with a single sheet of rolled up newspaper. Clearly, mine's not anywhere near that bad. I'm still coughing up bits of car wash mit.

Next, I'm going to change the thermostat. That 160 degree thermostat sucks in the winter, anyway, and it just makes sense to change something that inexpensive as a maintenance item.

My buddy also told me I can burp the cooling system by driving the front wheels up on ramps to make the radiator cap the highest point in the cooling system, and running it till it's warm. I figure I'll have to burp it after changing the thermostat, anyway.

We'll see