My 98 xj (recently purchased to get into jeeps) has a problem with the temp getting up to 210 and staying there and it causes the radiator cap to pop off so I bought a new one now the excess is coming out the overflow. It's not overheating bad but it's bad enough to boil over so to speak. I also developed a lifter/rocker noise that's pretty loud and don't know if that is normal or not. First time ever owning or working on a jeep. I am mechanically inclined just not on these bulletproof 4.0 😊 any help is appreciated

 

Welcome to the club! In multiple ways...

I'm dealing with the same thing. Engine running hot after being on the road for a while, it can easily boil over if I let it but I just slow down and turn on the heater and that's enough to get me home. There were no signs of a blown head gasket - good compression (cold engine), no visible oil in coolant or coolant in oil, no smoke in exhaust, tested negative for exhaust gases in the cooling system.

Entire cooling system was replaced last year. I flushed all the rust out and put in a another new radiator, but it didn't fix the problem. Still can't be on the highway for longer than 45 minutes without running too hot.

I took an oil sample and sent it to Blackstone lab and they said I have coolant in the oil. Not a lot but enough to indicate a problem. I took the head off this last weekend and the head is very much warped. I suspect that when the engine is fully warmed up, exhaust gases where leaking into the coolant. I couldn't detect it otherwise though but sure enough the head is warped enough to be true. I'm taking it to a machine shop today.

These 4.0 heads are pretty easy to get off, because you don't have to worry about the timing chain (the cam is in the block).

 

Thanks for the quick reply! I just flushed the system after a got it home thought I cracked the block but it had a pinhole In the freeze plug so replaced them all. So happy to hear I won't have to mess with a timing Chain I'll take the head off Wednesday and take a straight edge and some feelers to it. With the liftr/rocker noise is there a way to fix that or just replace them?

 

Umm, I'm not an engine builder but I know that this engine uses hydraulic lifters that sit on top of the cam, a push rod sits on top of the lifters, which push up on the rocker arms up in the valve cover which push down on the valves. I know that there's plenty of replacement lifters online for cheap, and if the push rods are not totally straight or are not flowing oil through them then they must be replaced too. Some say you gotta replace the cam if you're replacing the lifters but I'm not sure why that is

 

How can I check if the push rods are bringing up oil and if its not would there also be a problem possibly in the pick up tube and down in the oil pan? I'm at work currently so I'll check a few of these things when I get home and post results

 

If it stays at 210, thats good. Thats normal operating temp. If its going over that (as your title suggests) and boiling over, thats not good. Check the overflow tube for any blockages. You said the excess is coming out of the overflow, but id check the tube anyway. And check the radiator where the cap seals for any dirt that may prevent the cap from sealing. You bought a standard 16lb. radiator cap, yes? If its got a lever on it, throw it away. Also, gauges can go bad. Point an IR at the thermostat housing to see if the temps match the gauge.

Take the valve cover off and let the engine idle. Are you sure its coming from the top end? Loose flexplate bolts can sound similar. As can piston slap. Does the ticking stop once the engine warms up? If so, i wouldnt worry about it.

 

Thank you all for the help so quick and I heard of the flex plate making this noise I will check that as well. The ticking does not go away.it started when I drove it back from the previous owners house (he said it sat for 2months) it didnt have it when I started it in his yard everything seemed in order but on the ride home the cap blew off so I pulled over bought a new factory cap (without the lever) added water and some coolant from the gas station and it started ticking then would go away but at the last stretch towards my house the ticking was constant and still is. The oil level is where it is supposed to be on the dipstick but I added some to the top and the ticking quieted a little so I think something is not bringing it up to the rockers and I will get ahold of a laser to check temp I think the gauge is somewhat correct due to it coming out of the over flow when it gets up there but I might have over filled with coolant or have air in the system to cause it to come out. I will check all of these tonight if I can or Wednesday at the latest. How would I go about checking the flexplate issue?

 

Got home checked with an AR the gauge is a few degrees off but I pulled the thermostat and it was gasketed all wrong and clogged just gonna drill it for now. The push rods bring up oil to all the rockers just fine from what I'm hearing I think I have a flex plate problem. But good news is my overheating problem should be fixed ran it without the thermostat in it for 30-45 and it stayed right under 210!😁 next is the flex plate is there a way to fix it or do I replace? Thank you again for all of your help!

 

Nice job from williston finest!

 

Oh, that's ugly! I think you found your problem.

 

Looks like it pooped a little.

 

Yup now just fix the flex plate and I'm back to stock and running good.almost time for some upgrades! Thank you all for your help 😁