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Panthor98 03-31-2013 09:08 AM

Running hot/power loss
98 jeep TJ 4.0 inline 6 automatic
4.5 inch suspension, 1 inch body
35 in tires, geared.

Ok, so on the way home from a long trip I experienced power loss going on a long uphill slope. Was cruising at about 70 and slowed down to about 55 pegged. Never had this problem and I had nothing changed on my jeep. I started to run hot at about 220-225.

A quarter mile from the house I overheated and had to pull over, I had coolant all over the motor and side of the jeep, reservoir was boiling. When I got it home I did the following:

New rad cap. Flushed system 5 times. New thermostat. Old coolant was full of dirt, not oil. Finally got it clean. Also had to patch a pin hole right where the cap screws on the radiator.

So, jeep ran great, cooler than ever for 2 weeks. Then yesterday I was headed to hit some trails. On the way there we hit a long uphill slope. Started running hot, about 225, covered not only my jeep but the guy behind me as well in coolant. Also I had the same power loss.

I hit the trail, pretty good off roading consisting of switch backs, up and down hills, rock gardens with slow crawling etc. No over heat problems, no coolant loss. On the way home there was no uphill grades really, cruised at 70-80 no problems.

What is the deal? Why do I loss power on upgrades and spit coolant all over/overheat. But city/highway/offroad I'm ok.

Any ideas. Simple checks first.

Thanks guys, sorry for the book lol

PiePuncher 04-01-2013 01:32 PM

Thermostat stuck on close,.causing pressure build up and fluid forcing its way out the cap? The high heat and fluid will cause the power loss. Where did the fluid come from this time? Is fan shroud still in place?
Sounds like thermostat is sticking. U could run without thermostat and see if that solves the problem. Your heater will not work well with the thermostat out

Panthor98 04-01-2013 01:52 PM

Thermostat is new from the first time it happened. Heater works great. Coolant came from overflow bottle. Fan shroud busted up pretty good, missing bottom. I checked lower hose, I know there is a spring in there to keep it from collapsing, does the spring go the entire length of hose? I noticed the spring stops about 4 inches from radiator. And I'm able to squeeze there...?

Thanks for the reply.

PiePuncher 04-01-2013 02:49 PM

The spring won't b an issue.
You are running hot and building up pressure. I understand you just replaced your thermostat but u also stated it worked fine for two weeks, then happened again. It's possible something has made the thermostat stick closed.
The reason I said to see how it runs without one was to see where the problem lies. If your issue went away while running no thermostat, that would b your issue. The heater will work well w the thermostat in but not so well if at all when u take it out.
Could b the water pump but still sounds like stuck thermostat to me. R u blowing any smoke out the tail pipe? Does water pump sound funny or ever have water coming out of it externally?
I too have a 98 wrangler and our cooling systems are beyond simple.

Panthor98 04-01-2013 03:30 PM

Gotcha, I will take the thermostat out and check. It ran great for 2 weeks but I didn't really put it under any load ie long upgrades. If I take it out or it is stuck wouldn't it run hot no matter what? It runs great even at 80 mph, slow, fast, street, highway, off road etc, only on uphill slopes. No water from pump, no leaks that I can see, no funny noises etc. Also no smoke from exhaust.


PiePuncher 04-01-2013 08:13 PM

On the highway, the wind and cold air is forced through the radiator, cooling your engine temp. On a steep upgrade, u are more than likely going slower, forcing less air through radiator to cool it.
If your fan shroud is beat up or non existent, less air is being forced to the radiator from your fan.
Your problem should b something simple. I have a feeling that running without the thermostat will solve your problem. And the answer to your question about it running hot all the time with stuck thermostat, no, it wouldn't unless the temperature is 100 out. Keep air blowing steadily through the radiator and u could be fine. Get stuck n traffic and u might b f#$%ed

Panthor98 04-01-2013 09:14 PM

Understood about the air flow at higher speeds, I hope u are right about the t stat sticking. Maybe this will go e u more insight... I have been in stop and go traffic a lot, stuck on freeway stop and go for 20-30 min, I have also sat idle for 15-20 min. Sitting idle/stop and go my jeep runs really cool, I would say 190-200 range, highway speeds I run about 205-210.

I was hitting trails Saturday right after I puked coolant and was running hot at 240 or so from a long upgrade. My jeep cooled down by the time I aired down my tires, hit the trail, stop and go rock crawling, never shut off the jeep, was about 2 hours steady hard wheeling, during this I never reached pass 210. Then hit highway home, about an hour and a half at 75 mph, never past 210. So it seems to be only under load. Any change in thoughts based on this?

PiePuncher 04-01-2013 09:27 PM

I live in Texas and never run 210..... It has been upper 70's to upper 80's here already.(for two months) Our nights have a low of 55 and we never had a las Vegas has very cool evenings and cool/warm afternoons but nothin like here. If all fluids are fine, no smoke, no radiator fluid mixed w other fluids, I am still stuck at thermostat....... They have a tendency to stick in close. I actually do not run a thermostat here in Texas, no need. I don't use my heater and it keeps my engine temps low.

Panthor98 04-01-2013 09:28 PM

By the way, I really appreciate your help/opinions, nice to get some feed back and insight on this issue, its a real downer and a pain hoping the group I'm heading out with doesn't hit a long upgrade, its a little embarrassing slowing down from loss of power not to mention spraying the jeeps behind me.


PiePuncher 04-01-2013 09:32 PM

Red permatex makes making the changes easy. U don't have to keep buying gaskets, just make your own seal

PiePuncher 04-01-2013 09:37 PM

that's funny, I'm sure they don't care, unless they are new to the scene. I've had my jeep since 99 and realize, $+!+ happens and things will brake. It's part of the game. I have had the worse happen and even though my jeep is old, all the parts are new... :) the good thing about your jeep being a 98 is that it is easy to work on. The newer ones have more sensors and crap to go bad... B thankful u have a TJ

Panthor98 04-01-2013 10:28 PM

Copy that, ill be removing the thermostat. I will let you know the outcome...
Thanks again.

Panthor98 04-04-2013 08:47 AM

Did a pressure check on the coolant system... Absolutely would not hold any pressure, not 1 pound. After searching and searching for a hole/crack/seal leak I finally noticed that the inside lip of the radiator where the cap mounts, it is recessed where the caps seal sits. The recess is not allowing the seal of the cap to sit flat. So there is absolutely no pressure build up.

Looks like I will be buying a new rad. Hopefully this will fix the problems. Would no pressure cause my symptoms? Ie running below op temp under normal conditions and running hot under load/puking coolant.

Any suggestions on radiator type? All aluminum, 1-2-3 core???


PiePuncher 04-05-2013 01:44 PM

No reason to go overboard on radiator. Just get u one that works. Sounds like u found your issue.

Spitse 06-25-2013 03:43 AM

Did you ever find a resolution? I am having very similar issues. But it came after a new radiator and thermostat.

Noob25 06-25-2013 06:27 AM

Me as well.. Except mine will over heat when it gets warm.. Just at idol even. Replaced thermostat and it did nothing.??

Noob25 06-25-2013 06:29 AM

I wonder.. Could it be the water pump.

Panthor98 06-26-2013 09:23 AM

Not sure if i found the issue or not. Im pretty stumped on whats going on.

I put the following new items in.

Water pump
Fan shroud

The funny thing is around town/stop and go i run really cool, like 180, highway speeds up to 65 i rin at 210, 70 and up at 215. But whenever i hit an up-hill slop or long hill ill shoot past 220.

Panthor98 06-26-2013 09:27 AM


Originally Posted by Noob25 (Post 3897018)
Me as well.. Except mine will over heat when it gets warm.. Just at idol even. Replaced thermostat and it did nothing.??

If its at idle i would check your fan.

Panthor98 06-26-2013 09:30 AM

Would an exhaust leak pre-cat cause these issues?

Or im starting to thing maybe the O2 sensors are bad? Idk

Spitse 06-26-2013 07:00 PM

Well I got a call on mine. Cracked head. Only would present itself under load. There was a little water in tailpipe. The big thing was temp gauge said 215, but after running hard, it was boiling in overflow. They checked the block temp with the laser temp gauge and it read 195. So the boiling was really air.

Now the question do I take it in or do I try myself? I've done an engine and tranny swap before in a ford ranger, but this may be fun.

Panthor98 06-26-2013 10:02 PM

Ouch, that sucks. Sorry to hear that. Well at least you know what the issue is. If it were me, and it just might be, i would do the work myself. Shouldn't be to difficult, just tedious.

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