Help/Opinions with Overheating issue

[mooncster]

Hopefully you guys can help me out a little. The family just bought a 1989 Cherokee 4x4 with the inline 6.

Around town it does fine, but when you go up hills or are on the freeway the temp. rises and redlines. I've replaced the thermostat, hoses, waterpump, and the pressure cap but it's still doing it. I've also burped the system to ensure there isn't any air in it and checked to make sure the clutch fan is operational (it is). I've also made sure the radiator isn't clogged or jammed and that there is plenty of airflow.

Any ideas or suggestions that I might of missed? I'm gonna go out with a temp gauge and double check to make sure the temp sensor is accurate, but I think it is.

Thanks again for all your help, hopefully I can get this guy up and running a bit better!
~Geoff

[Matthew Currie]

How about radiator fin rot? Are there any blown out or missing sections of radiator fin between the tubes? Check especially down in the lower corners and at the bottom of the tubes.

[RichP]

Rule of thumb, overheat/hot in traffic normal on hiway, fan clutch, overheat/hot on the hiway, radiator. As for the pressure cap on the closed system, if the tank is warped you can replace pressure caps till the cows come home and it still won't seal. None of my jeeps are closed but I know if I was going to replace the cap I'd do the tank right along with it...
If it's the original radiator, it's time, another overheat can also be the lower hose collapsing from lack of a spring in it once the engine really starts moving coolant thru the system..

[cklaus]

What dilution of antifreeze are you running? gauge could also be off (wouldn't that be nice)

[87manche]

what about the lower rad hose? Check that it's not soft, it may be collapsing at speed/high rpms.

[Runnin'OnEmpty]

Around town it does fine, but when you go up hills or are on the freeway the temp. rises and redlines.These are classic symptoms for a corroded and clogged radiator. It may still flow, but the flow is impeded enough for overheating to occur. Might be time for a replacement rad.....

[churky89]

Possible causes:
Cooling system clogged or restricted
Bad waterpump
t stat "froze"in closed position
closed system....the list for this system is long...personally I HAD that system in my 89'and finally swapped out to the open system.
Before I did the swap:
Overheated at traffic lights,or any time I had to set in traffic....could set in the driveway n it would over heat.....
I know there are people who will swear by the closed system and that they have had no problems....
Since I did the swap very seldom gets past 210....in any situation
Also wired a switch to the aux fan so I can turn it on anytime I want.
There are no modifications necessary IF you do the swap.....IT IS A DIRECT SWAP OUT.
Think the rad is for a 95' as is the heater valve.
Got everything I needed at the local AutoZone...rad has LTW
If you do the swap...I highly recommend:
1.Backflush the engine w/chemical flush(I used Prestone)until clear water comes out...if the system is really clogged you may have to do this twice.
2.Swap out the waterpump at the same time
3.Replace all hoses and clamps(upper and lower hoses are the same on the closed and open systems)

[mooncster]

Thanks for the input guys...checked everything else out...there was a new radiator put in 8000 miles ago...I did a full flush on the system, backflushed it etc. The lower hose has the spring and isn't collapsing. the fluid solution is about 55% anti and 45% water. I pulled the thermostat again last night and it was bad (was brand new) so I bought another, tested it to make sure it would work and put it in. Ran great today for about an hour then started to overheat again. I know there's no air in the system and the temp gauge is accurate. Damn gremlins lol. I think I'm gonna look into swapping it to an open system...any last thoughts? Thanks again

~Geoff

[Saudade]

Did the party you bought it from tell you about any recent work they did/had done to it?

[langer1]

Thanks for the input guys...checked everything else out...there was a new radiator put in 8000 miles ago...I did a full flush on the system, backflushed it etc. The lower hose has the spring and isn't collapsing. the fluid solution is about 55% anti and 45% water. I pulled the thermostat again last night and it was bad (was brand new) so I bought another, tested it to make sure it would work and put it in. Ran great today for about an hour then started to overheat again. I know there's no air in the system and the temp gauge is accurate. Damn gremlins lol. I think I'm gonna look into swapping it to an open system...any last thoughts? Thanks again

~Geoff

Open systems don't cool any better than a closed one, a bad cap on your tank will also cause it to over heat. Try a new cap.

[Jess]

burp system through temp sending unit in rear of head

[mooncster]

I've burped it through the temp. Sensor multiple times already, learned that from this site :). As for previous work, I have all the paperwork for the life of the vehicle...the only thing that hasn't been replaced is the resevoir bottle and the pressure cap, which I'm gonna order tomorrow. Do I need to do the bottle? There are no cracks or anything, though it does look like it has expanded over the years.

[Runnin'OnEmpty]

One other thing that comes to mind is the fan shroud. Check to ensure that it has one, and that it dosen't have a piece broken out, etc.....

When it overheats, does it burp coolant out the tank overflow?

When you shut it off, can you hear coolant boiling/burbling in the block?

[mooncster]

Good ideas...fan shroud is fine, and when the engine is off there isno boiling sound, but when I looked...the resevoir tank is higher than normal and does not bleed out for a LONG time, perhaps that might lend an idea as to whats going on, but I can't figure it out lol.

[old_man]

You have said that the gauge redlines. You did not say it boils over. Does it boil and blow out liquid? If not, then your gauge is not reading correctly.

If it is indeed overheating on the road, I would do a spark plug reading. Running too lean will cause an engine to overheat to the point where even the perfect cooling system will not handle it.

[Runnin'OnEmpty]

If the tank is located on the passenger side firewall, that's the normal stock location.

When my 89 overheated, it burped coolant out the tank overflow. The cure was a new 3-row radiator.

When my 96 overheated, it boiled coolant in the block; could hear it after shutdown.

Sounds like your overheating maybe isn't too severe. As was stated, I'd try a new pressure cap and see what that does.

If you want to convert to an open system on the cheap, there's a kit available that installs in the upper radiator hose. You have to cut the hose in two, and clamp a filler neck in place. Then you conect the hoses routing to the tank. Available from any parts store or Summitt Racing. (I doubt if that will cure the overheating, however.....?)