Howdy,
This is my first post as a jeep owner, so hi!

I recently bought this rwd XJ with around 145k miles for a low price. I may keep this bad boy for a while, but I may sell it again for cash once its running right. Thats a hobby of mine.

Here's what is wrong:
*Not my favorite color (gold), and the paint is peeling in places.
*A/C is clogged in the line somewhere - I will fix this since this is Texas.
*Needed a new battery. Easy fix.
*Overheating. <<------

The overheating issue is the worst kind, I think. When I bought it the radiator had been recently changed, and I've tried 3 different radiator caps. I've removed the thermostat with the boiling water test and it works fine, opening up around 190 degrees F according to my meat thermometer. You can feel water going through the upper hose when it opens, which is before the overflow tank even starts to overflow.

So thats the big problem, after about 20 minutes of idling, the overflow tank fills up completely and starts overflowing. The three radiator caps I've tried out are 1) the one it came with 2) a stant venting type and 3) one I got at autozone. None of them seemed to make any difference.

I also tried the procedure in the FSM where you remove the thermostat, put back on the housing, start the engine, rev it 3 times, and watch for bubbles. I didn't see any bubbles.

I'm leaning towards head gasket though, but I thought I should go to the experts before I tear into it.

Here is a video of what is happening:


Anyone have any other ideas?

 

Did you just call your jeep a car...?

#shunthenonbeliever

 

I'd start with a simple compression test. Always a good idea for a "new-to-you" vehicle. The compression spec. for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders. If you have low numbers on two adjacent cylinders, that is likely a head gasket failure. If you don't have a compression tester, they can be rented inexpensively from most parts stores; call around for availability.

If compression is good, I'd perform a "block test" where you sniff the coolant for the presence of hydrocarbons (oil). Any shop can do this for you and some parts stores (NAPA) sell a kit where you can do it yourself.

Good luck and keep us updated!

 

Given the recent changes (rad and thermostats) it's also possible the head has air trapped in it. The angle and hose layout of the 4.0 can sometimes make it a problem to get the air out.

Try pulling the upper heater hose and filling through the heater core until full ( hold the hose higher than valve cover). May help, may not, but is a cheap solution. With excess air in the head the Temps will rise and sit steady around 220 to 240 ish. Try put less coolant in the bottle as air will push it's way out and literally burp out over time.

 

I'm not sure what you mean

 

I'll do these tests and post back. I was already looking into the block test. I hadn't planned on doing a compression test, because in my experience they give you a false negative pretty often, but if I get time I will.

 

Compression testing still one of the gold standard tests. If it's positive, you have your culprit. It's 30 minutes of your time. That is time well spent.

You must adopt a testing based strategy to get to root cause. Compression test is definitely one of those tests.

 

TJ, I like your choice of words there. I might quote you, in a future

 

I am going to do the compression test today because its a good idea as tjwalker stated above on any vehicle that is "new to you". However, I'm doubtfull it will indicate a problem in my case.

A compression test that comes back positive indicates the following:

1) Piston Rings Leaking
2) Valves Leaking
3) A head gasket leak between 2 adjacent cylinders.

I'm no professional mechanic (I make my living as software engineer and musician), but my analytical brain tells me that none of those conditions should cause the overheating/boiling over symptoms I'm having. I'm interested to hear arguments against this logic, but that's why I'm more interested in the block test. A positive on that indicates exhaust gasses in the coolant. Combustion gasses leaking into the coolant passages to me are a much more viable explaination for why my overflow tank is overflowing.

Perhaps I'll be wrong (its been known to happen). I'm going to do the compression test first since I already have a compression tester.

 

How are the fan clutch and electric fan? Fan clutch can be hard to test because they lose their effectiveness over time.

If the radiator or condenser are plugged with dust and dirt, you will overheat too.

I always like to do compression tests to see what the engine is like, and maybe it will give you a clue.

If it's not an airflow problem, pull the head and have a look.

 

These are good ideas. I hadn't mentioned that I already did check and swap the fan clutch. The old one was stiff - no free wheeling, but it was caked with oil on the spring, and I didn't like it that I couldn't hear a change in the fan speed as the engine warmed up. So I swapped it for a new one. I can hear a difference in the fan speed as the engine warms now, but it hasn't solved my problem.

The radiator was changed by the previous owner, and it looks brand new. They left the old one in a box in the trunk.

I still need to check the condensor. I may be replacing it due to a blockage in the A/C system.

 

Here are the compression test results:

1: 178
2: 178
3: 178
4: 182
5: 183
6: 176

No problems here.

 

Here are the spark plugs. #2 electrode has a greenish tinge to it. That doesn't mean coolant though, it usually means oxidation from what I've read. Strange that #2 is the only one with a greenish tint though.

 

The blown head gasket, or cracked head, is around the #2 area.

 

Results of the Block Test

Baseline:


On this test, I continually squeezed the bulb from cold engine until it warmed up, about five minutes later. This does not follow the directions:


And in this test I started with a warm engine, and squeezed the bulb for two minutes exactly. This does follow the directions.


In the test where I was following the directions, the coolant was probably starting to boil and only yeilded a clear color. The first test in the picture looks slightly yellowish, but it didn't strike me as yellow at the time. I did rev the throttle a few times during each test. Neither test gave me what I would call 'Yellow".