4.0 Engine Overheating

[JMT]

My Twin's 04' Sport overheated last night up in the PNW heatwave. The thermostat did something wonky about a month ago, reading only 165* while we were on the highway doing 70mph. I assumed the PO installed a lower * thermostat and purchased a Stant 195*. Then the Jeep was running 210*, so we put off installing it. Then the overheating incident occurred. Now I assumed the thermostat might be sticking, so I replaced it and the housing. It's still overheating. The fan is working. Should I assume it's the water pump?

Thanks

Also, is there a difference between Mopar and Chrysler water pump? Part numbers are the same.

 

[JKP]

Overheating at hwy speed or idle? Or both?

 

[Jerry Bransford]

My Twin's 04' Sport overheated last night up in the PNW heatwave. The thermostat did something wonky about a month ago, reading only 165* while we were on the highway doing 70mph. I assumed the PO installed a lower * thermostat and purchased a Stant 195*. Then the Jeep was running 210*, so we put off installing it. Then the overheating incident occurred. Now I assumed the thermostat might be sticking, so I replaced it and the housing. It's still overheating. The fan is working. Should I assume it's the water pump?

Thanks

Also, is there a difference between Mopar and Chrysler water pump? Part numbers are the same.

Mopar/Chrysler are the same. Did you bleed all the air out of the system after replacing the thermostat? Do you know if the radiator is OE or an aftermarket brand?

 

[JMT]

Overheating at hwy speed or idle? Or both?

The first time my wife was driving across town and then stopped at a drive through while idling and it immediately came on "Check Gauges"
The second time (hours later) my son was driving across town to get home and the temps went over 210* and the "Check Gauges" came on.
The third time (next morning, still trying to get home), thermostat replaced, full coolant, I drove a couple of miles to home, let it sit and idle and the temp was about 215* at that time and I gave it some gas while idling and it just kept going up. I turned the Jeep off, made this post.

 

[JMT]

Mopar/Chrysler are the same. Did you bleed all the air out of the system after replacing the thermostat? Do you know if the radiator is OE or an aftermarket brand?

No, I did not bleed the air out of the system. I didn't know to do that and don't know how to do that.

The radiator is OEM.

 

[JMT]

One more thing I learned while reading about this is that the fan shouldn't kick on until it is time for the thermostat to open and the water pump to start, but on mine, the fan comes on immediately, even when the engine is cool.

 

[JKP]

It will bleed itself as the radiator cap is the highest point in the system if you just let it run with the cap off.

Did your coolant level drop in the overflow jug?

 

[JKP]

OEM fan setup or electric?

 

[Jerry Bransford]

No, I did not bleed the air out of the system. I didn't know to do that and don't know how to do that.

Did you position the new thermostat so its jiggle valve that lets air pass was positioned at the top? The brass gizmo on the flange this Stant thermostat is what allows air to pass through to assist the engine to eventually self-burp itself. If your thermostat doesn't have one, you can drill a 1/8" hole in the flange as close to the inside edge as possible, then mount it so the hole is at the very top. Eventually the cooling system will self-burp itself but doing this will speed up that process. Keep an eye on the coolant level to make sure it doesn't drop too much as the air leaves the system.

 

[JMT]

It will bleed itself as the radiator cap is the highest point in the system if you just let it run with the cap off.

Did your coolant level drop in the overflow jug?

No, the level did not drop.

OEM fan setup or electric?

OEM fan.

Thanks for help.

 

[JMT]

Did you position the new thermostat so its jiggle valve that lets air pass was positioned at the top? The brass gizmo on the flange this Stant thermostat is what allows air to pass through to assist the engine to eventually self-burp itself. If your thermostat doesn't have one, you can drill a 1/8" hole in the flange as close to the inside edge as possible, then mount it so the hole is at the very top. Eventually the cooling system will self-burp itself but doing this will speed up that process. Keep an eye on the coolant level to make sure it doesn't drop too much as the air leaves the system.

View attachment 262654

IDK if I did or not, I will remove and check. The new thermostat is a Stant 195*.

 

[JMT]

This is my big question now @Jerry Bransford and @JKP

While reading about this I learned that the fan shouldn't kick on until it is time for the thermostat to open and the water pump to start, but on mine, the fan comes on immediately when I start the engine, when the engine is cool. What does this mean?

 

[JKP]

The OEM fan will usually spin at a slower rate than the engine on startup. Once warm air is pulled through the radiator onto the clutch thermostatic spring, you should hear the fan speed increase.

When the engine is hot, the fan should be roaring.

Look for silicone oil on the outside of the clutch. This would indicate a leak and the clutch should be replaced.

If you decide to replace the waterpump, I would replace the fan clutch as well.

 

[JMT]

A good series of videos for anyone needing to flush their cooling system

https://www.carcarekiosk.com/video/..._4.0L_6_Cyl./coolant_antifreeze/flush_coolant

 

[Rob L.]

One more thing I learned while reading about this is that the fan shouldn't kick on until it is time for the thermostat to open and the water pump to start, but on mine, the fan comes on immediately, even when the engine is cool.

The fan should be on at all times and speeds up as the temperature increases

I would pop the radiator cap to let the air purge and verify coolant flow before I tore into anything. You should be able to notice the entry and exit pipes for the radiator are hot once the engine is at operating temperature. This would eliminate obstruction issues but not necessarily a bad thermostat or water pump. Pull the drive belt off to see if there is any play or bearing noise at the pump

 

[JMT]

If you decide to replace the waterpump, I would replace the fan clutch as well.

I just want to know what's wrong and replace that. It's my sons Jeep. I'm into it quite a bit, and they are just starting to work, so I don't want to pour money into it like I do my rig! LOL. If it is the water pump, I will replace the fan clutch though, but I don't want to replace all that if it's the radiator and those other parts are fine. It has 164,000 miles on it, which may mean I need to replace everything. IDK, I'm asking.

 

[Jerry Bransford]

The fan will always spin due to drag in its viscous clutch. The hotter the engine and thus clutch is, the faster the fan will spin. You can check its basic condition to see if the fan spins fairly freely by hand when its cool but that it gets very stiff and hard to spin by hand when the engine is hot as it should.

 

[JKP]

Here's everything you want to know about thermostatic fan clutches: https://www.haydenauto.com/media/5670/fan-clutch_operations-ts_6980012.pdf

The 2 modes of failure are seized clutch, which means it's operating as a direct drive and will be roaring, you engine will feel sluggish, and you MPG will drop; and not engaging properly due to leakage of silicone oil or busted spring, which means it will not turn fast enough.

As far as the waterpump, the impeller could be slipping on the shaft. Or, in a neglected system, the impeller can corrode away to nothing if it's a metal impeller.

 

[Ericict]

I just want to know what's wrong and replace that. It's my sons Jeep. I'm into it quite a bit, and they are just starting to work, so I don't want to pour money into it like I do my rig! LOL. If it is the water pump, I will replace the fan clutch though, but I don't want to replace all that if it's the radiator and those other parts are fine. It has 164,000 miles on it, which may mean I need to replace everything. IDK, I'm asking.

On the bottom of the water pump, there should be a small hole. You might need a mirror to see it. Check to see if you see any signs of fluid. Also pull the belt off of the water pump and check for internal play on the pump bearing. I had a vey similar issue and it was a bad water pump.

 

[Rob L.]

All kidding aside, I wouldn't rule out the ambient temp messing you up. I've have some one-off overheating instances that I could never attribute to anything except hot weather