Could my cylinder head be warped or cracked???

Hey guys. I surmise this subject has been done to death, so please be patient!
I have a '95 XJ Limited/Classic 4.0L HO, AW4,NP242,Dana 30s. Virtually stock.

About 18 months ago my xj overheated while on a highway at 100km/hr. Turns out I split the radiator tanks. I replaced the radiator with an aftermarket Jeep one with steel tanks, replaced the thermostat and filled the radiator with new coolant. Had it pressure tested, and there were no other leaks.
A few months later, the water pump started leaking. It was stuffed, so I replaced it.

Anyway, a couple of days ago, my xj overheated again. I was losing coolant at a rapid rate, but can't tell exactly from where. I have checked the water pump, and that seems to be part of the problem. There is a small amount of coolant coming from there, so I will replace that again.
Anyway, the bulk of the coolant loss seems to be coming from the right hand side in the centre of the engine bay somewhere, but I can't tell due to the exhaust etc in the way.

Also, when running at normal temperature, the needle suddenly goes to the red zone. Not gradually, but within a couple of seconds.

Could I have slightly warped or cracked the head when it first overheated 18 months ago, and now that it's overheated again, could that have finished warping or cracking it???
Sorry for such a long post, but I think that with all this information, it should make it easier to diagnose.

Thanks in advance.

I have overheated a few xj motors and they do take a beating. You really should get that water pump swapped. It's worth a shot. I would get ur hands on a compression tester to see how ur head gasket is.

I most always troubleshoot from basic and easy to hard and/or exotic. You may have a pinhole leak on the bottom radiator hose that is pizzing on the side of your motor. There are more than a couple of ways to rub through the lower radiator hose near the steering box.

I had the front left freeze plug leak on my 87 on that side of the motor.

Most times when you are talking mechanics talk, all directions are stated as you are sitting in the drivers seat. You mentioned the exhaust manifold being in the way so I'm guessing we are talking about the left side of the motor:repair:.

One of my most useful tools is my thousand Lumen LED flashlight. It is tight but you can likely see more from the bottom, take a close look at the freeze plugs, Take the air box out and inspect your bottom hose, you may need a mirror to see the bottom. Look for places it may possibly be rubbing.

The coolant may just be blowing back onto the side of your motor from the leaky water pump. The typical path when the water pump starts to weep, is down the left side onto the top of the the pump inlet (lower radiator hose).

Most coolants contain a dye that lights up under UV light, maybe you can rent one from a local auto parts place? I have a UV light, it makes finding coolant leaks a whole lot easier.

Get a Gates Kricket 2 and adjust your belt to specs, over tightening the belt can really be hard on the water pump bearings. Use a quality coolant, I bought the store brand coolant once trying to save a few bucks and it somehow ate up my (relatively new, less than six months old) pump bearings in about six weeks.

Your temperature could be spiking from low pressure in the system (the lower the pressure, the lower the boiling point) or worst case scenario you are pumping exhaust gasses into the cooling system.

OK. I managed to get a mechanic over to check it out. Turns out my water pump, which is only a year old, was leaking and was corroded on the inside, and the thermostat was the wrong type. There is also a small pin hole in the radiator tank which I will be getting brazed tomorrow.
$600 later, my XJ is back up and running, and staying cool as a cucumber.
Thanks for the replies guys!!!

Ok.

1. NEVER INSTALL A REMAN WATER PUMP. For a few bucks more buy NEW, and for a few bucks more than that BUY A QUALITY NEW WATER PUMP.

2. Always use a belt tension gauge to set the serpentine belt on the XJ 4.0--this will HELP PREVENT PRE-MATURE WATER PUMP FAILURE.

3. Purchase a good RADIATOR CLEANER--not a "flush"--follow the directions, then put pre-mix coolant or 50/50 distilled water and coolant in the system. You should not have a corroded water pump in one year.

joe_peters said:

Ok.

1. NEVER INSTALL A REMAN WATER PUMP. For a few bucks more buy NEW, and for a few bucks more than that BUY A QUALITY NEW WATER PUMP.

2. Always use a belt tension gauge to set the serpentine belt on the XJ 4.0--this will HELP PREVENT PRE-MATURE WATER PUMP FAILURE.

3. Purchase a good RADIATOR CLEANER--not a "flush"--follow the directions, then put pre-mix coolant or 50/50 distilled water and coolant in the system. You should not have a corroded water pump in one year.

Click to expand...

Hey Joe
That's what I can't understand. The water pump I bought was new, from a reputable parts store, and I cleaned and flushed the radiator, and used a "top quality" brand-name coolant... The summer temperatures here in Western Australia can get up to 45C quite often, so I only use good quality coolant and cooling system parts. I honestly have no idea how it could have corroded in such a short time. The mechanic isn't sure either!
The only thing I didn't do is use the belt tension gauge... I think I'm going to have to invest in one... Just recently I had to buy a new idler pulley, as the bearings had died. That was only about 3 years old too... Obviously I'm tightening up the belt too much.
Anyway, thanks to everyone for their responses and advice.

alex673 said:

Hey Joe
That's what I can't understand. The water pump I bought was new, from a reputable parts store, and I cleaned and flushed the radiator, and used a "top quality" brand-name coolant... The summer temperatures here in Western Australia can get up to 45C quite often, so I only use good quality coolant and cooling system parts. I honestly have no idea how it could have corroded in such a short time. The mechanic isn't sure either!
The only thing I didn't do is use the belt tension gauge... I think I'm going to have to invest in one... Just recently I had to buy a new idler pulley, as the bearings had died. That was only about 3 years old too... Obviously I'm tightening up the belt too much.
Anyway, thanks to everyone for their responses and advice.

Click to expand...

Are you using pre-mix coolant or adding distilled water? Tough to have to keep replacing parts like that.

Good luck.

Pre mixed. My wife was driving it for about a year... Maybe she ran low and filled it with water. Dunno. Have to ask her.
Anyway, I'm just glad it's now fixed! I really didn't want to have to get another car!