2001 XJ runs hot after head, radiator, and thermostat replacement

I have an '01 XJ 4.0L w/156K miles that runs hot, but doesn't seem to be overheating.

A little backstory: Waterpump, radiator, and thermostat were replaced about one year ago. Aftermarket radiator developed a crack in the endtank and coolant would shoot out when it got hot. The owner would keep adding water to the cooling system to keep the level up in the overflow tank. Long story short, the cooling system got pretty mucky and the crack in the endtank got larger and the car overheated and compression was lost on a cylinder (blown head gasket).

I replaced the cylinder head with a spare one I had lying around. It came off an engine that ran great and had no cooling issues, but it had rod knock, hence why it was now a spare. I also replaced the radiator and thermostat and did my best to flush the cooling system out. Compression has been restored on the cylinder and the truck runs great, but it runs hot. The gauge will stay between the 210 tick mark and the one after it - the electric fan is constantly on trying to bring the temps down and even if you're travelling at 50MPH, it will never drop below 210 (temperature outside is probably around 45 degrees right now).

Here is something interesting that I also can't seem to figure out. If you let the truck idle after a nice cruise it will obviously increase in temp. As soon as it hits the first tick mark past the 210 level, the gauge shoots up to 260 degrees and the 'check gauges' light comes on. So, we're looking at about a 40-50 degree increase in a split second - not physically possible, so I'm thinking it's just the way the system was designed as a precautionary measure to alert the driver that the cooling system is getting hot before it gets TOO hot, or the electrical system is screwed.

Couple other things about the vehicle - the heater core is partially plugged - no heat in the truck except for when you first turn the heat on, you'll get a few seconds of hot air before it turns cold. There just isn't enough flow into the heater core to give constant heat. The coolant level is topped off and looks good - nice and green! The radiator seems to be doing its job...the top radiator hose is hot and the bottom is cold. There seems to be plenty of pressure and flow in the coolant lines. I can't find any traces of coolant in the oil.

Anyone have any ideas on what may be the cause?

I have seen those temp "spikes" usually when there is air trapped in the system.

You may have a bad fan clutch, it should engage at about 200 degrees on the gauge.

I would:

1. Check your fan clutch. Start the engine and let it idle for about 5 minutes to ensure that the silicon fluid is spun back into the reservoir, shut the engine off and spin the fan by hand, noting the amount of travel and resistance. The restart the engine and let it warm up fully. Shut off the engine and spin the fan again. It should barely move with a lot of resistance. If it feels easy to spin, replace the fan clutch. I recommend the use of NAPA 272310, ZJ HD fan clutch--not the max cool--$44 and direct fit replacement. It is noisy, but it really moves the air.

2. Buy a commercial flush product, not one of the 15 minute jobs, one that you leave in the system for like 500 miles; follow the directions. When you get to the neutralize/flush with water part pull the heater hoses and flush it backwards/forwards/backwards with low garden hose pressure--small tubes and somewhat fragile if too much pressure is applied. Fill with 50/50 mix of coolant and distilled water, or use the premix kind. Install a new radiator cap. When you fill the system park the vehicle nose-up at an angle with the radiator cap at the highest point. Fill the system, cap off, and run the engine. When the thermostat opens the level will drop and then add coolant until full, cap it and then top off the recovery bottle to the HOT or FULL mark.

Ok, now drive it and post back results.

Thank you for the tips - the owner of the Jeep just took it for the night so I can't do any tinkering with it. I want to say the fan clutch had a lot of resistance when I checked it last week, but I'll follow your instructions to make sure of that.

I saw a couple of different coolant flushes at NAPA the other day - some of them look pretty extreme, so I may pick up a bottle or two of that stuff and try that out. Hopefully this Jeep will be around for another 500 miles as the owner of it wants to trade it in for a newer pickup, but we'll see. I could take it to work for a week and loan him mine if needed.

The fan clutch has definitely gone bad - it spins with resistance when the engine is cold, but after it heats up, it spins with barely any resistance at all...the opposite of what should happen. I have a spare fan clutch that I can swap in just to see if it makes any difference. If so, I'll probably go with the heavy duty model from the ZJ for good measure.

Still, I'm not sure this should affect the temperature while the truck is moving. Air moving at 50 MPH through the radiator should be enough to cool it down.

I also have the privilege of owning my own 2001 XJ so I can compare the two side-by-side. Tonight I had both trucks next to each other, started them cold, let them get to operating temperature (although mine only goes to 210 degrees) and I used a laser thermometer to take temp measurements at common points throughout the engine. Some spots were cooler on my XJ, some spots were hotter. The one major difference in temps that I saw was the thermostat housing on my cousins hot-running XJ was about 215-230 degrees depending on where I pointed it, while mine ran in the 170-200 degree range. I took measurements at certain spots on the cylinder head and both trucks were about the same temp.

One thing I did notice with the hot-running XJ was that the power steering pump is making a nasty whining noise, so it might be on its way out and causing a lot of extra resistance for the engine. I'm going to remove the belt tomorrow and spin each accessory to make sure they are all working fine.

Sounds like you have a handle on things.

Don't forget to post up the final results; we all keep learning on here.

this was very helpful as i have a 90 xj with the same overheating probelm and my coolant bottle keeps bursting, it too has a new raidator and 165 thermostat. mine will stay at 165 as long as im moving and as soon as traffic backs up so does my temp. im going to check the fan clutch and my ps pump is leaking so i might check that as well. also i found a metal cooland bottle for the 90 model i6 if anyone else has the bottle problem
http://www.macsradiator.com/replacmentjeepradiatorfilltanks.aspx