Running hot, 2000 XJ, entirely stumped.

[HeavyMetal]

2000 XJ.

Few weeks ago I was taking a trip to VT and it involved a lot of hill climbing on the highway, this jeep has always run fine and never had cooling issues. This day it started running around 220-230, and then the temp eventually spiked directly up to 260+ on a hill ascent, radiator boiled over, yadda yadda. Had overheating problems the whole trip on the highway.

Fluid was nasty, all rust corrosion in it, brown. Not milky or an oil situation.
So once we get home, over the past 3 weeks or so, i change the radiator out for a 3 core CSF w/ new rad cap, add a b&m trans cooler, flush the system, change the waterpump, run a new tstat, flush 4-5 more times, and the temp still creeps up on the highway only under load. It accelerates the heating up quite a bit when running the AC.

I have no cooling problems on the trail, or around town, although it may run up to around 220 max around town, which makes sense given my setup now anyway. This system should run at below 210. (changed the 195 tstat for a 180 tstat today, no change).

Anyone have any ideas? I have no evidence of a bad headgasket or head. I am all out of ideas other than changing the lower rad hose and coolant temp sensor. I even hard wired the e-fan to run constantly just to see.

[92xjlaredo]

Yours have dual cats on the exhaust manifold? I read somewhere they had some goofy things with those setups and heat dispersion.

Although the thermostat change out with zero influence is a bit confusing. Even mine (single cat system) runs a little warm on inclines.

[CntStpTheStnk06]

Will I had the same issue with my 01 and it was a cracked head. It would only happen under load and i couldn't find it with a pressure test. I had rusty coolant but no oil in it. I am hoping for the best for you but wanted to at least share in case you come up with no remedy.

[CumminsJeep]

I hate to say it but I vote cracked head. Just because there is no oil in the coolant or coolant leaking into the exhaust it doesnt mean it isnt bad. I would have someone do a block test and check the coolant for exhaust gases if you havent already.

[HeavyMetal]

sweet

[CntStpTheStnk06]

sweet

Ya man sorry for bad news :/

I learned this the hard way. I wont ever purchase a 2000 or 2001 4.0 i was told they were the two worst years known for this issue.

[Bigbike]

Im going with head again :/ luckily they are not hard to come by and not hard to do.

[92xjlaredo]

How many miles are on that?

[HeavyMetal]

entire cooling system changed for new better parts

did a leakdown test, determined there was a large leak, cylinder head swap to an 0630 head

nothing has changed. i challenge any mechanic to solve this

[Burton58]

What are the chances the gauge itself is faulty. Maybe after the head issue it got screwy. Doubtful but you never know

[Lycaon]

What are the chances the gauge itself is faulty. Maybe after the head issue it got screwy. Doubtful but you never know

i was going to say maybe the sensor is tweaked out too, have you done a leakdown since the new head went on?

[HeavyMetal]

sensor is new

not just monitoring on the jeep gauge on the dash

i have not done a leakdown test since replacing

[#DEZERTDAD]

I went through this with Scotty and Julie's orange XJ when I had it. The original head was cracked inside, I could see the coolant flowing in through the oil fill cap while the motor was running. Did a head gasket job and she ran hot under load/on highway. Did the job all over again with another new cylinder head and the problem was fixed. I'm not saying you're having the same issue/situation but maybe the new/replacement head is no good either???

I'd do a leak down test again

[HeavyMetal]

I went through this with Scotty and Julie's orange XJ when I had it. The original head was cracked inside, I could see the coolant flowing in through the oil fill cap while the motor was running. Did a head gasket job and she ran hot under load/on highway. Did the job all over again with another new cylinder head and the problem was fixed. I'm not saying you're having the same issue/situation but maybe the new/replacement head is no good either???

I'd do a leak down test again

i had the new head tested at an engine/machine shop, and resurfaced to boot

ill do another leakdown though, just cuz

[customcreationsllc]

First is all the air out of the system, do you have good heat out of the vents?
XJs can be hard to bleed all the air out.

Maybe a cracked or warped block? Was there any scars in the cylinders that didn't go straight up and down? Usually a crack.
You didn't clean the block with any power tools did you? That can easily leave divots, but it is harder on a iron block.

Do the coolant hoses get hard fast? like before they get real hot or start pushing coolant out even before it over heats. That is usually a sign that the combustion is getting into the coolant system. Combustion will air lock the system then it over heats. They sell a kit to test if combustion is getting into the coolant system basically a dye that you connect to the coolant cap. I never got it to work good.

Unless the thermostat is stuck shut which I'm sure you already checked. Just throw it in some boiling water and see if it opens.
Or the fans are not working or blowing backwards.