Above average mechanic, so with that said "I'm at a loss"

2000 Jeep Grand Cherokee 4.7 (V8)

Few weeks back it started running a bit warmer than normal, OK. Changed the thermostat and ended up replacing the water pump while I was in there for preventative measures. Flushed (coolant still looked good at this point).

Took it for a 40-50 mile drive, little warmer than before but nothing out of the ordinary.

Week before last, took it about a 150 miles and wall was good. Next day on my way home in stop and go traffic for an hour and just as I was starting to get up to speed it started to get warm and than hot. Got pulled over, turned A/C off, heater on and got it home after I had let it cool down a bit. Probably ran 230-240 (not good I know).

Screw it, replaced the thermostat again (just in case). Pulled the radiator and replaced (some scale, but not terrible). Also replaced the clutch fan Should be noted I replaced the module that turns the electric fan on/off.

I've bled the coolant about 3x now. I took it for a drive last night and it started to get a bit past normal, brought it home. Parked it, ran it up on the ramps and bled it again. This AM, just took it out and it's shooting up to about 230-240 again.

I'm at a loss on what to do? Only thing I can think of is there's some air trapped somewhere, but what to do?

I've also replaced the radiator cap.


Wish a f'ing tree would just fall on it. I'll take a bath trading it in and I don't want to sell it to anyone in the condition it's in.

No signs of a blown head gasket - Jeep is running normal other than the temp.

Did you verify that the electric fan is working as intended/designed?

Being as I drive a jeep all day every day and have had them turn in to a tea kettle more than a few times I know how frustrated you are, I have tried every fix you have tried and none seemed to work, so my answer is replace the radiator, with a new after market, bolt in over sized radiator, there are several company's that build them and sell them, find 4- Wheel supply, on the net they sell several different brands.

There are other ways to fix this problem, but what i am telling works every time. Rio7

If you've already burped it and got all the air out, then it might be time for a new radiator. When you drained it, was it full of crud?

He says he's already replaced the radiator but didn't say with what.

Are you sure that it is actually HOT?

temp sensors go bad too!

On my phone and can't type well.

Put a cheap aftermarket, factory size radiator on it. At this point every thing is new.

OEM had some scale, but not bad. Putting a different clutch fan on later and will look into a bigger radiator.

Thanks for the replies

Before you spend any more money on the Jeep, get you an infared heat gun and check the engine's actual temp. Just aim it at a few points on the engine while its running hot. You might find that it's not as hot as the gauge says.
These things can be helpful for other things, too.

I've got one of those and will try it next, didn't think of it.

But do think it's running hot, I'll be back at it in the AM. Maybe a tree will fall on it overnight

Assuming the coolant system is good, then I'd look at either a headgasket that is starting to go, or something in the fuel management that is causing the engine to run lean. Wouldn't hurt to pull the spark plugs to see if any of them are showing tell tale signs of running lean. Are you hearing any pinging or detonation when accelerating or going up a hill?

Use the heat gun on another car that's running normal for a comparison.

Temp sensor or gauge was my first thought, but that I-R gun may help to find a hot spot if it really is running hot.

Parents had an 01 that started doing the same thing, intermittent overheating. Finally got worse and worse and a good family friend who is also a mechanic diagnosed it as a cracked head gasket.

Couldn't find my temp gun, but installed a different fan clutch vs the cheap one I got off feebay. I don't think that should or would make a different at anything but town speeds but it appears to be functioning better than the feebay one.

Ran it for quite a while, still was getting bubbles and once the thermostat opened up it had more bubbles. Bleeder valve on these is a pain in the a$$ and think I'm going to wait on the no spill funnel so I can have a steady flow of coolant in the funnel when the thermostat opens up.

Saying screw it for the rest of the week and going to concentrate on getting some tackle ready for a trip to Cass Lake, MN next weekend.

On the highway you shouldn't need the fan anyway. You'll get enough air flow from your high speed.

Upper and lower hoses new?

Had a truck that started collapsing the lower hose when warm. Replaced that and problem went away.

I replaced the lower, upper is a couple of years old but in good shape.

ARGH.......

Did a radiator pressure test, have an 18 lb cap on presently.

Put 18-19 lbs in it, lost a touch at first and than stable at about 17 lbs for 3-5 minutes.

Replaced the temp sensor following that, thinking sure enough all along its just that simple.

Temp gauge still climbed while under load.

Temp gun readings, which all should be about normal. Slim chance I got a bad sensor or between it and the gauge???

Readings

Top Hose - 180-185 (same as the top of the radiator)
Bottom Hose - 120-125 (same as bottom of the radiator)

Temp at base of sensor - 170-180 -On the brass part of the sensor 200

Thermostat housing - 215-220
Water pump - 200-225 depending on what part of the housing

Throttle body (both sides) 210-215
Valve Covers - 180-185

Everything points to a normal running engine, but I honestly don't trust it.

I'll probably throw another sensor at it, but ???

Have you tried running without the thermostat.
Friend of mine had one of those old Willys Jeep purple pick ups. We sat around waiting for it to cool off more than we hunted.

"Pulled radiator and replaced", replaced old one or installed new, not clear to me? Is the a/c condenser full of debris, blocking airflow? How hard to pull thermostat? Try running without theromstat. Just because something is new, don't mean it works.

It's a new aftermarket OEM spec radiator, as mentioned I wish I would have just spent the extra 100.00 on a double row radiator vs the single stack.

Condenser is in pretty good shape with no debris as I cleaned that out the first time I had the radiator out. Heat & A/C are working normal.

I've replaced the thermostat twice, the thermostat isn't terrible to pull other than the lower radiator hose is a bit*ch to get back on.

Someone on a jeep forum (you guys have been more help) said "it has to be a bad head gasket".

I've replaced a few head gaskets and this one has no symptoms. Pressure test is good, nothing in the oil, nothing out of ordinary coming out of the exhaust. Not gassing out of the radiator and not leaking a drop anywhere, nor is the coolant level changing. Also seems to be running great and each exhaust port is within 10 degree of one another.

If you can not find a malfunction in the engine, I'd check the reporting sensor and reading gauge. Wouldn't be the first sensor to go bad.

I deal a bit with instrumentation. If your temp sensor or gauge is going bad, I would be extremely surprised if that resulted in a false high reading. If it's going bad I'd expect the reading to either be all over the map, or it would read nothing at all.

Take it out for a drive, once it starts reading high pull over, pop the hood and take ir temp readings to find the source.

I believe the same thing in regards to the instrumentation and in regards to the 2nd part - I did, hence where the readings came from that I posted above.

It's not an uncommon problem on the 4.7 v8s. Like I said my parents was doing exactly what you described for a couple of years before it finally got worse. The mechanic I mentioned earlier has spent his life working on Jeeps and has owned a couple of 4.7 v8 WJ's. If it's a cracked head gasket, depending on the severity of the crack I could see it exhibiting exactly what you're describing.

Might want to do two tests. One is an analysis of your oil and one for exhaust gases in the coolant.

https://www.blackstone-labs.com/free-test-kits.php

Coolant test kits can be gotten at any major auto parts store.

4.7 L are notorious.
Heads/gaskets and pistons/bearings.

Wheelers with V8s often put in hood vents to help w air flow.

Had an 04 GC w 6 cyl.
Hated that thing.

Much prefer the older ZJ version.
Both of mine were 5.2L