Great deals on TJ parts on Amazon!

Looking for parts for your Jeep Wrangler TJ? Checkout the selection of TJ parts Amazon has to offer, many with 2-day Prime shipping!

Click the image below to browse TJ parts on Amazon.

Jeep Wrangler TJ Parts on Amazon

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.

98 Jeep Wrangler 4.0 Overheating

ryrhoades

New Member
Joined
Aug 22, 2021
Messages
6
Location
Huntsville, AL
My 1998 Jeep wrangler 4.0 is overheating (gauge gets into the red) after idling from cold for about 10 minutes.

When I bought the jeep in September of 2021 the following was done to the cooling system by a reputable shop.

  • Replaced all coolant hoses
  • replaced all heater hoses
  • replaced thermostat and gasket
  • Total coolant flush
Coolant level looked low so I flushed it again and added coolant and is still overheating.


I noticed today after the temperature gets up and after I turn it off, some liquid and air is coming out of one of the hoses leaving the radiator. See attached video. I am fairly new to doing my own work and am wanting to learn - but I can take it to the shop if necessary.

Any thoughts on what to try next?
 

Attachments

  • 20220127_112537.mp4
    11.8 MB

pagrey

TJ Guru
Supporting Member
Joined
Apr 10, 2018
Messages
7,143
Location
Los Angeles, CA, USA
Most people use the factory constant tension clamps. The screw type can leak like yours are. If the system doesn't hold pressure it can overheat, that's the first thing to fix. Make sure that radiator cap is new and either get a new clamp or tighten it so it doesn't leak. There's a thread somewhere on this site that has the correct clamps for that upper hose. Once you fix the leak if it still has issues it might help to know the driving conditions when it overheats.
 

JKP

TJ Enthusiast
Joined
Aug 20, 2020
Messages
622
Location
Warner Robins GA
First tighten the clamps and ensure the system is full as described above.

Then, if it only overheats at idle, I would suspect the fan clutch. When the engine is hot, the fan should be fairly hard to turn by hand. If it just spins easily, it is slipping too much.
 
  • Like
Reactions: Jerry Bransford

Yoda

TJ Enthusiast
Joined
May 5, 2021
Messages
171
Location
MA
Just food for thought....On my 93XJ I went through a similar situation. On hot days it would get close to the red and if I was towing a boat (2k pounds) it would get to the red often.

Replaced the radiator with a good name brand (its been a while, forgot which one). No change. Put an HD fan clutch on from a ZJ with HD cooling. No change.

Put a FlowKooler water pump and new thermostat.....no change!

Finally, I replaced the coolant temp sensor at the back of the head......FIXED!!!!

There are two coolant sensors. Once for the ECM that attaches to the thermostat housing and one at the back of the head that is for the temperature gauge ONLY. That sensor was junk. $30 and a new sensor later it was back to normal.

So I spent like $500 rebuilding my coolant system for it only to be a $30 sensor. I was never really running hot to begin with!
 
  • Haha
Reactions: hear

hear

TJ Enthusiast
Joined
Oct 18, 2020
Messages
823
Location
Prosper, TX
There are two coolant sensors. Once for the ECM that attaches to the thermostat housing and one at the back of the head that is for the temperature gauge ONLY. That sensor was junk. $30 and a new sensor later it was back to normal.

I'm sure I'll be corrected in mere moments, but I believe the TJ only has the one coolant temp sensor right near the thermostat housing.


Quasi-related: it is often said that the best way to get an answer on the internet is to post the wrong answer to a question. Then people will come out of the woodwork to correct the wrongness.
 

ItchyDong

Airframe & Powerplant LJ Mechanic
Supporting Member
Joined
May 20, 2020
Messages
485
Location
Dothan, Alabama
I'm sure I'll be corrected in mere moments, but I believe the TJ only has the one coolant temp sensor right near the thermostat housing.


Quasi-related: it is often said that the best way to get an answer on the internet is to post the wrong answer to a question. Then people will come out of the woodwork to correct the wrongness.
You are correct.
 
  • Wow
Reactions: hear
OP
ryrhoades

ryrhoades

New Member
Joined
Aug 22, 2021
Messages
6
Location
Huntsville, AL
Thanks for all the responses.

When hot, the fan is difficult to turn (I think ruling out fan clutch). It was over heating while at speed too, not just idle.

I tightened all the hose clamps and am no longer seeing the sizzling as the video in my original post showed.

I did not do a chemical flush, just ran water until it came out clear. An actual mechanic did the original flush in September. I just flushed because I didn't want to mix coolants.

Radiator cap is the 18psi cap. I'm pretty sure that's what's needed.

The thermostat was replaced in September, so I've kind of ruled that out for now.

I did notice today that coolant never appeared to be pulled out of the coolant jug(see picture). Shouldn't it get pulled when it's hot? When cool and I take the radiator cap off, should I be able to see coolant? It's wet but not full.

Y'all rock!

20220129_143107.jpg


20220129_143113.jpg
 

pagrey

TJ Guru
Supporting Member
Joined
Apr 10, 2018
Messages
7,143
Location
Los Angeles, CA, USA
You should see coolant in the main radiator when you take the cap off cold. The system wont draw from the overflow tank if it has a leak like yours did. The overflow should be half full, to the mark. The overflow system basically doesn't function if the system has leaks. It sounds like yours still isn't entirely full, keep on adding until the radiator is completely full.
 

JMT

The Jeep Guy
Supporting Member
Ride of the Month Winner
Joined
Feb 27, 2017
Messages
17,403
Location
🌎
Yes, you should be able to see coolant when you open the cap.

Do the lines stay cool as it warms up from cold and then suddenly get hot when it reaches ~210F? Could it be the water pump?
 
OP
ryrhoades

ryrhoades

New Member
Joined
Aug 22, 2021
Messages
6
Location
Huntsville, AL
So After fixing the leaks like I think I have, fillup the coolant tank even if it takes more than the fill line to see it in the radiator? I'm extremely new to this, I guess maybe I should add coolant to the radiator cap, now that I think of it.. 😑

@JMT today it seems that the lines going from the radiator to the engine, and from the engine to the (heater core?) Were cool until the engine was hot. When I went to shut it off, cane back and felt them they were warm.
 

williambmac

TJ Expert
Supporting Member
Joined
May 5, 2019
Messages
3,244
Location
Fucktard state of NJ
Yes, you should be able to see coolant when you open the cap.

Do the lines stay cool as it warms up from cold and then suddenly get hot when it reaches ~210F? Could it be the water pump?
If there is no circulation, I would bet on the water pump also.
I had three 4.0 water pumps fail. The impellers separated from the shaft.
Two were Mopar, one was Napa brand.
 
  • Sad
Reactions: JMT

pagrey

TJ Guru
Supporting Member
Joined
Apr 10, 2018
Messages
7,143
Location
Los Angeles, CA, USA
So After fixing the leaks like I think I have, fillup the coolant tank even if it takes more than the fill line to see it in the radiator?
No, the overflow tank should be half. Add to the radiator when it's cold or when you are slowly warming it up with the cap off. Don't open the radiator hot to fill, that should be obvious but no big deal. The system can trap air, keep adding to the radiator until it's full. Don't overfill the overflow tank.
 

JMT

The Jeep Guy
Supporting Member
Ride of the Month Winner
Joined
Feb 27, 2017
Messages
17,403
Location
🌎
So After fixing the leaks like I think I have, fillup the coolant tank even if it takes more than the fill line to see it in the radiator? I'm extremely new to this, I guess maybe I should add coolant to the radiator cap, now that I think of it.. 😑

@JMT today it seems that the lines going from the radiator to the engine, and from the engine to the (heater core?) Were cool until the engine was hot. When I went to shut it off, cane back and felt them they were warm.
Those lines should get really hot at 210. I wouldn’t describe them as warm.

If not hot you have no circulation and that can be the water pump or thermostat. You replaced the thermostat recently. Was it a Stant? Did it have a small hole in it like this one? This is what you want. The hole is positioned at the top when you install.

 
OP
ryrhoades

ryrhoades

New Member
Joined
Aug 22, 2021
Messages
6
Location
Huntsville, AL
Those lines should get really hot at 210. I wouldn’t describe them as warm.

If not hot you have no circulation and that can be the water pump or thermostat. You replaced the thermostat recently. Was it a Stant? Did it have a small hole in it like this one? This is what you want. The hole is positioned at the top when you install.

It was well above 210 and the lines were not hot. Definitely could touch them.

I'm not sure what the thermostat is. A local mechanic did it very recently after I bought it. I'll take a closer look at the thermostat.
 
  • Like
Reactions: JMT

JMT

The Jeep Guy
Supporting Member
Ride of the Month Winner
Joined
Feb 27, 2017
Messages
17,403
Location
🌎
If you have engine cool and you remove the radiator cap, you can turn the jeep on, turn the heater on at the HVAC and watch the coolant where the cap is. You should be able to see it flowing when the thermostat opens. If it’s not the water pump is out. If it is flowing it’s the thermostat. Video shows you where the thermostat is located