So I’m having overheating issues again. When I drive on the highway it goes into the red doing about 75 mph. I recently replaced thermostat, radiator, water pump. Even replace the Heater coil because it was clogged up. I backed flush it four times now. No dirt in the radiator the coolant is at a normal color. The heads were also redone From previous owner. Someone told me get a new electric fan but I can’t see it being an issue when you’re on the highway and the fan it still kicks on.

 

Check fan clutch?

 

Also, did you verify thermostat is opening at correct temp?

Fairly easy to confirm if you have an infrared thermometer.

You can also use it to verify your dash gauge is accurate.

 

Do you have a fan shroud on it? It's important that you do because it directs air from the outside thru the radiator and doesn't pull engine compartment air into the fan.

 

This should be your next step. You could spend a lot of time, effort, and money chasing a ghost, otherwise.

 

I've seen some nasty air pockets when someone does that extensive of a cooling system overhaul.. you'd think flushing it will fix it but it may not..
you could always pull the thermostat and go from there...

 

In my years of dirt track racing, we found that an engine with NO thermostat will overheat at highway speeds because the coolant was going so fast thru the radiator it didn't have time to transfer it's heat. What we did was remove the center of a thermostat and install just the brass ring to act as a restrictor to slow it down. I don't advise running with no thermostat, just in case you were thinking of that.

 

Usually when frustration hits, it makes you overlook simple things. Just chill and think for a second. Highway driving, especially at 75mph, makes up for a lot of air flow regardless of the fan shroud as I tested this last week (no fan shroud driving around at 70-80mph with 100*F ambient temp never hit over 210).

Be sure to take a step back and double check from step one.

Usually with highway overheating something is going on with the flow (or in my case it was the CSF 2 Row copper radiator, flow was good but it just didn’t dissipate the heat fast enough, hopefully you have an Aluminum radiator).

 

Well same issues here. I just bought a 2000 a few months ago. Flushed the system and replaced fluids as soon as I got it home. I've been driving
it daily about 32 miles one way to work at speeds around 60 to 65mph and its done great. I recently got the AC going and still no issues. Last weekend decided to take a longer trip, about 112 miles one way, running 75 to 80mph with AC going. She red lined! I let her rest and topped off the fluid. Finished my trip with no AC and speeds of 75 to 80mph and it ran pretty hot but didn't redline. I've removed the radiator and flushed it this time. It appears to be the original. It was full of crap!! So I went ahead and removed water pump and thermostat housing and flushed the block and heater coil and it was also full of crap!!! I don't know where all this stuff came from unless I just did a terrible job the first time around. I'm replacing the thermostat housing with a Hesco High Flow, replacing the water pump with a Flowkooler and the thermostat with a high flow. I think I'm gonna reinstall the radiator instead of replacing it. I'll let you guys know if this fixes my issues. I sure hope so!!!

 

No way I'd take a chance with that radiator. Not when you can get a new one for less than $100. Just because you flushed the one you have doesn't mean it's capacity and therefore it's cooling ability hasn't been compromised.

 

Just thought I'd post an update on my issues. I drove the XJ about 140 miles at speeds from 25 to 65 and also idled at several traffic lights and my temp stayed below 210. Most of the trip I ran the AC between halfway and wide open. I decided to go ahead and replace the radiator EZEARL. So far so good! Fingers crossed!!

 

Good job! THANKS for the update.

 

For what it’s worth guys I’m posting another update. It’s hot as hell here in south Alabama and my XJ is still cooling great after all the replacement parts. I’m running the AC wide open and different speeds and idling at traffic lights she’s doing good. I will be replacing the electric fan soon though. The previous owner damaged one of the blades and it’s got some major vibration issues that are getting worse.

 

Funny you should say that about the electric fan. The factory one in my WJ always vibrated a tiny bit and it had a metal balance clip on one of the blades. Then it started vibrating violently because the weight had flown off! I replaced it with a Dorman and now except for the sound, you don't even know it's running.

 

Typically high speed overheating is caused by a water flow issue. Something clogged, no thermostat or stuck thermostat, waterpump going out, airbubble stuck in system something like that, while low speed/idle overheating is caused by an air flow issue, clogged fins on the ac condenser or radiator or both (issue for those who go "muddin" a lot), weak or failed fan clutch, no fan shroud, bad or worn out e-fan.

Seems like you got it sorted out now. I live in Texas and high temps are a regular deal for half the year, gotta have working AC here or you'll melt into a little puddle haha. My 100 percent stock cooling system keeps me cool around town and even running AC on the trails.