Wont start after overheating. Please help, thanks!

[subtraction]

Hello everyone had an XJ a few years ago and had to get rid of it but it was very reliable and gave me very few issues and my girlfriend really enjoyed it.

Well time came to get her a new car so I found a very clean 98 XJ locally and went and picked it up. Well on the way home after about 45min of highway driving it began to overheat. Got to about 245f before I could get off on the shoulder and shut it off. Coolant was leaking very badly out of the radiator cap. I let it cool off and cranked it back up to head the 10 more min until I was home. After about 5 minutes I began slowly losing power then suddenly temp spiked to 260f and the engine cut off right as I was pulling onto the shoulder.

I just left it and had it towed at that point. The next day (today) I began trying to diagnose the problem. Replaced the radiator cap first off. But when I went to crank it would turn over but wouldnt start. Put in a new battery and checked the spark plugs. They werent firing so I replaced all 6 spark plugs and the crank shaft position sensor. Went ahead and changed the oil too since it was deep black, didnt look milky just very old. I was then able to get it to start up after cranking for about 20 seconds. It was EXTREMELY rough and I had to feather the throttle to keep it from dying.

I was able to keep it running and drive it around the block but it was very rough and died once when stopping and going in reverse but it started back up fairly easily. I then promptly got it back in the garage. I still let it run and there was a fair amount of steam or smoke coming out of the crankcase breather and from the throttle body. I eventually shut it off after about 5 minutes. Went back out about 20 min later and now it just wont start again. Cranks and turns over and will occasionally go chug chug chug like its wanting to start but wont.

Im at a loss. I need to pull the plugs again and see if they stopped firing again. Could my headgasket have gotten blown? The oil not looking milky and I took the rad cap off and cranked the engine and no coolant was getting blown out so I am hopeful its not the head gasket. Ive also noticed a small crack in the exhaust manifold and im sure that would make a rattle but should still start/run. Would a bad throttle position sensor cause this problem?

Thanks guys and I would really appreciate any help. We spent all the money we had set aside for a car on this XJ and im really hoping to get it up and running reliably asap.

Edit: I just went back out after letting it cool down completely and it started up after about 10 seconds of cranking and gas pedal to the floor. Still idled very rough I think im going to replace the tps but im really worried about that steam/smoke coming from the crankcase. Thanks!

 

[trippled]

I think a compression test is in order before you do anything else. You may have damaged the motor depending on the extent of the overheat.

 

[Tim_MN]

As suggested already, since it was badly overheated a compression test might be a good idea.

The no-start symptoms point to a low voltage issue from:

• dirty, corroded, damaged, or loose battery/alternator/ground wire connections
• internally corroded battery wires
• a short circuit or parasitic drain
• a failing battery
• a failing alternator

Perform routine maintenance of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Battery terminals and battery wire connectors should bright silver, not dull gray and corroded. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, wire brush, and clean until shiny the cable/wire ends and whatever they bolt onto.

Jeeps do not tolerate low voltage, bad wire connections, or poor grounds.

Place your DVOM (Digital Volt Ohm Multi-Meter) on the 20 volt scale. First check battery voltage by placing your multi-meter's positive lead on the battery's positive post ( the actual post, not the clamp ) and the negative lead on the negative post. You need a minimum of 12 volts to continue testing. Next, leave your meter connected and take a reading while the engine is cranking. Record this voltage reading. Now connect your positive lead to the battery terminal stud on the starter and the negative lead to the starter housing. Again, crank the engine and record the voltage reading. If the voltage reading at the starter is not within 1 volt of battery voltage then you have excessive voltage drop in the starter circuit.

Typical voltage drop maximums:
• starter circuit (including starter solenoid) =0.60 volt
• battery post to battery terminal end = zero volts
• battery main cable (measured end to end) 0.20 volt
• starter solenoid = 0.20 volt
• battery negative post to alternator metal frame= 0.20 volt
• negative main cable to engine block = 0.20 volt
• negative battery post to starter metal frame =0.30
• battery positive post to alternator b+stud =0.5 volt with maximum charging load applied (all accessories turned on)

Test the output at the alternator with your volts/ohms multi-meter. You should be measuring 13.8-14.4 volts. Load testing the alternator and battery is still recommended.

 

[subtraction]

Okay, I can get it to start consistently even though it hesitates and takes a few seconds of cranking. I did a compression test this morning.

Cylinder number
1- 60psi
2- 80psi
3- 75psi
4- 90psi
5- 110psi
6- 40psi

The engine was cold... should I have startd it and let it warm up some before pulling all the plugs, unhooking the injectors, and then performing the test?

I am at this point very worried the engine is shot... what are the chances this could just be the head gasket? Or would it most likely be the head is messed up? What about other interbal engine components being screwed.

At this point im looking at repairs ive never tackled before. I am considering cutting my losses and fire selling it as a very clean body XJ and hoping to get $800 of my about $2550 spent thus far.

 

[RCP Phx]

Something is definitely messed up!! Compression should read about 150 with no more than about a 5% difference between them.

 

[subtraction]

I just ran the compression test again and got new figures...

1- 65psi
2- 80psi
3- 90psi
4- 100psi
5- 110psi
6- 50psi

I then ran it again "wet" pouring a little oil down each spark plug hole and got these figures.

1- 65psi
2- 85psi
3- 90psi
4- 110psi
5- 115psi
6- 50psi

Is that a good sign that I didnt really have a spike in compressiom after running it wet?

Could all of this just be caused by a head gasket?

 

[old_man]

Be careful, not all compression testers have the right shape and seat properly on a 4.0L head. This will give you low and erratic readings.

Having so many cylinders bad, is not commonly caused by a head gasket. Not having the compression come up when "wet" tends to indicate burned valves due to overheating. A bore scope would be handy to take a look.

You might get by with just a valve job and not a new head. If money is an issue, you could probably score a good used head and just do a quick swap.

If you do that, make sure you fix the original reason it overheated.

 

[trippled]

Agreed. Also need to check the head for flatness and give the cylinder walls a good check for any scoring. Compression definitely not looking good tho.

 

[subtraction]

Sorry for the delay. I had some time and pulled the head off today.

The head gasket seemed to be in good condition and not blown out anywhere. I also couldnt see any cracks anywhere.

The top of a few pistons had a lot of carbon build up the rest looked clean. The cylinder walls seemed nice and smooth except for at the top of a few of them there seemed to small spots of hard built up carbon or something.

The valves themselves looked really black and old... no idea how they should look though so I snapped a picture. I think maybe I should just order a remanufactured head with new valves. But id hate to spend the $300 and still not have the problem fixed.

https://i.imgur.com/03sm26q.jpg

 

[old_man]

From this shot the valves do not look that bad as far as heat damage but the problem with burnt valves is that the seal between the valve and the head is everything. I would grab a spring compressor and pull a few valves and see what the mating surfaces look like. Pix please.

What do the tops of the pistons look like? Close up pix please.

 

[Ecomike]

I see tell tail signs of coolant head gasket breach on cyl 3 and 6, green color and a spot where the gasket surface looks like it was leaking. Also those 2 cyls were wet carbon fouled in color, running too cold.

It take the head to shop and have them service it.