Stumped on overheating problems...

[Weasel]

87 4.0 XJ.

Have replaced the radiator with a new Modine unit and it briefly solved the over heat issues. Started over heating again and noticed the guage was sitting at 125-150 all the time. Changed the T-stat. Still over heating. The guage does seem like it broken so I need to replace the sending unit. Where is this located?

Also had a leak from the pressure bottle, changed the hoses and clamp and still have a leak. Notice that the bottle was building pressure and seemed to be causing the leak. If you opened the cap the leak stopped and in a few minutes leak start again, open cap it stops, ect.

Someone has suggested that the head gasket is shot but it doesn't seem logical how it could have blowen so quickly. After all the overheat stopped for about a 1-2 months after the new radiator was put in. And this is all on a buddies rig, which is making this difficult to troubleshoot or determine when the problems started as he never notice his guage quit working.

 

[Eagle]

I would suggest replacing both the temp sender (+/- $10 from a dealer) and the plastic pressure bottle ($19.95 from Quadratec). The system can't work if the bottle doesn't hold pressure, and if it's the original bottle on an '87 there ain't no way it's gonna hold pressure.

Also, be sure there's no air in the system. The coolant level should be at the halfway mark in the bottle when the system is cold.

 

[Weasel]

do you know where the temp sensor is located?

 

[Planetcat]

The clutch fan may have coincidentally gone bad after the new rad install. It's $45 at Pep Boys and if it's the original on the '87, it should be replaced anyways.

 

[Eagle]

On an '87 the temp sensor is located at the back corner of the head, driver's side.

 

[5-90]

Eagle is correct - the temp sensor is at the driver's rear of the head. You might get a coolant dribble when you change it - move quickly when you swap the sensors.

You should probably have changed the fan clutch while you did the radiator - you were in there anyhow. The average life of a thermal fan clutch is about five years. Quick test - get your engine up to operating temperature, shut down, and try to spin the fan by hand. It should be difficult - if it's easy, the fan clutch is shot. Replace with aftermarket (I usually use Hayden) HD Thermal unit. Expect to have to unbolt the upper crossmember and tilt the radiator assembly forward, to make room for clearing the studs and hub on the water pump shaft.

Change the coolant bottle - NOW. If you aren't holding pressure, you aren't going to have effective cooling. The cooling system for the water-cooled engine depends on building pressure to raise the boiling point of the cooling fluid - in our case, I believe it is 13psi above atmospheric. No pressure results in a slightly depressed boiling point - it's not much, but it's enough to matter. The bottle is fairly easy to replace, and the price on the Qtec unit makes me suggest changing it each time you change the fan clutch, and keep a spare on hand in the event of material failure or other drastic occurence (OEMR is about $50, IIRC. I need to follow my own advice and keep a spare on hand...)

Make certain you have all the air out of the system - I think there is a method for "burping" from the temp sender, and Eagle mentioned a way to do it wiht engine runtime, but I just drill a pair of 1/16" holes in the thermostat flange and let the system see to itself. With the two holes installed at 12:00 and 6:00, the system becomes effectively self-burping.

I seriously doubt the head gasket has gone - a compression check would make you certain. However, I don't recall a head gasket weeping coolant causing overheating in a noticeable manner - except from the lost coolant over time.

Now the dumb question - if you don't have a working temperature gage, how certain are you that you are overheating, and what gives you the idea? I just want to be certain...

Anyhow - changing the temp sensor is pretty easy. Changing the fan clutch is technically simple, just a PITA. Changing the "football" is damn near nothing to do - it's easier than the CTS. I'd say about two hours for the lot, if you jump on it and think ahead on the fan clutch...

5-90

 

[Kejtar]

I briefly glanced through other responses and I didn't see Sequoia chimng in: He had a new radiator which for some reason got clogged internally with loose solder (bad worksmanship??) He jumped through hoops doing everything else (in a process IIRC he cracked his head or something like that) cause he couldn't believe that the new radiator would give him problems. So also check out the radiator while looking at everything else.

 

[EMTJeepers]

just a silly question, but did you change the cap? I had an old dodge and replaced everthing (except the cheapest part.. the cap) and it was the cap the whole time...
Just my two cents.

 

[Weasel]

On the older closed systems there was no cap to replace.

Getting the guage fixed is the first thing I'm having done and without it I cannot be certain it is overheating. It's a buddies Jeep and he doesn't seem to catch on realy quick with these things.
He asked me the other day what could be causing his Jeep to overheat. I askes what his temp was running at and he says 125. Thats wierd, so how do you know it's overheating.
Well the coolant in the bottle is boiling. So I look at it and tell him your guage is broke.
No he's says it works.
Well does it ever get up to 210?
No.
Then it's broken, this engine doesn't run at 125.
Oh. :twak:

So I'm going to fix the guage then switch him over to a open system similar to whats on MadXJ, then we can have a good base to troublshoot these problems.

I'm alos ruling out the head gasket for a few different reason. 1)The I-6 doesn't blow head gasket that easily. 2)No antifreeze in the oil. 3) No antifreeze smell in the exhaust.

 

[RichP]

Incorrect, the cap on the bottle IS a pressure cap and they do go bad.
Sending unit first.
Get it nose down and remove the sending unit from the back of the head. That will also allow trapped air to escape and you can top off the system thru there also....

On the older closed systems there was no cap to replace.

Getting the guage fixed is the first thing I'm having done and without it I cannot be certain it is overheating. It's a buddies Jeep and he doesn't seem to catch on realy quick with these things.
He asked me the other day what could be causing his Jeep to overheat. I askes what his temp was running at and he says 125. Thats wierd, so how do you know it's overheating.
Well the coolant in the bottle is boiling. So I look at it and tell him your guage is broke.
No he's says it works.
Well does it ever get up to 210?
No.
Then it's broken, this engine doesn't run at 125.
Oh. :twak:

So I'm going to fix the guage then switch him over to a open system similar to whats on MadXJ, then we can have a good base to troublshoot these problems.

I'm alos ruling out the head gasket for a few different reason. 1)The I-6 doesn't blow head gasket that easily. 2)No antifreeze in the oil. 3) No antifreeze smell in the exhaust.

 

[Weasel]

learn something every day.

 

[xtremewlr]

I just went thru doing the switch to an open system like you are going to do. Solved all my overheating issues and the engine runs at around 180 to 195 at all times now on the freeway and in traffic. Still havent had a chance to wheel with the new system but I think it will be fine. I have a few pics of the process and parts that I used if it helps you any.

http://xj.rockmongers.com/gallery/radiator

 

[poomba]

I would suggest replacing both the temp sender (+/- $10 from a dealer) and the plastic pressure bottle ($19.95 from Quadratec). The system can't work if the bottle doesn't hold pressure, and if it's the original bottle on an '87 there ain't no way it's gonna hold pressure.

Also, be sure there's no air in the system. The coolant level should be at the halfway mark in the bottle when the system is cold.

Agreed. I did a number of things, but it was the replacing of the plastic pressure bottle (and yep, from quadratec), that fixed my problem.

 

[Eagle]

On the older closed systems there was no cap to replace.

...

So I'm going to fix the guage then switch him over to a open system similar to whats on MadXJ, then we can have a good base to troublshoot these problems.

RichP is correct. The plastic bottle is part of the pressurized system, it is NOT an "overflow" bottle. Sorry, I thought I had said that. It's possible to buy just the cap, but with age the bottles warp and most folks find that a new cap won't seal on an old bottle.

The new bottle from Quadratec is so cheap, why try to convert a new radiator to an "open" system? The so-called open system doesn't cool any better, it just has the pressure cap in a different location.

 

[Weasel]

I know in the stock location it's not a overflow bottle. The reason I like the open convert system is it is so much easier to fill, and coolant and burp air from then the other system. Actually I'm suprised you guys have had suck ppor luck with the bottles. Both the one in his Jeep and mine seem to be in perfect shape.

Oh and also the clutch fan seems to have lots of resistance.

 

[RichP]

The correct way to test the fan clutch is to drill a hole thru the top of the fan shroud between the fan and the radiator. Insert a long thin thermometer and start the engine cold. You should see the thermometer temp drop because when the engine starts cold the fan will 'roar' until it disengages after about 30 seconds. From then on the thermometer will pretty much sit there untill the tstat opens and dumps the first hot water into the rad at which point it will start to rise to the temp of the air flow. Once the air flow reaches the temp that the fan clutch re-engages you should see the thermostat start to drop as the fan pulls cooler air in, though still hot from the exchange as it passes thru the cooling fins, then start to rise again as the fan disengages. That is the ONLY way to test them. Spin test, resistance test, 'it feels right', 'I used ESP' test will not work. The only thing that will work is to measure air flow. Thermometer is the easiest though I guess you could use a wet bulb. You have to be EXTREMELY careful not to hit the fan too.... and that thermometer has to go up to about 250F and have a big enough dial or digital readout to see the temp changes.. Long term you could probably mount a remote solid state sensor in there and use a digital meter to read it with in the cab....

 

[Eagle]

Actually I'm suprised you guys have had suck ppor luck with the bottles. Both the one in his Jeep and mine seem to be in perfect shape.

Huh?????

Also had a leak from the pressure bottle, changed the hoses and clamp and still have a leak. Notice that the bottle was building pressure and seemed to be causing the leak. If you opened the cap the leak stopped and in a few minutes leak start again, open cap it stops, ect.

Which is it? Either it's in perfect shape, or it leaks. It can't be both. It's a pressure bottle. If it's in perfect shape, it'll hold pressure and not leak.