4.0 L Jeep engine running temp

[NewGuy]

I am not sure about the way my engine is running. This is my 1990 Jeep Comanche with 157K miles on it. It was parked in my Dad's barn from Oct 1999 to Feb 2005 and had
I have changed the plugs, thermostat and O2 sensor w/help from BITOG members, plus brakes, calipers and other non-engine parts. I am on the rinse phase of my first ARx treatment and it has made a huge improvement in the engine. I wish that I had removed the valve covers and taken pictures.

The thermostat that I installed was a 195 oF thermostat from Advance Auto. The previous thermostat was stuck open. The coolant temp now rises to the appropriate temp and levels off according to the gauge, but the hood and engine seem to be very hot after driving.

I probably need to do a coolant system flush, but I am hesitant as I have never done this before. This is not my daily driver, but it is a great little truck for trips to Home Depot or the landfill. I have a lot of sentimental reason to keep this truck running forever if possible.

Does any else have an older Jeep 4.0L with similar mileage? If the temp guage is at the appropriate setting should I assume that this engine was designed to run this way? Any thoughts or suggestions?

Thanks.

 

[MarkC]

The 4.0 is supposed to run at or about 210F. My 96 Cherokee has an aftermarket temp gauge that I had put in, and according to it, mine is usually running about 200F, rising to around 210-220 in traffic when the weather is warm. I've never checked to see if it's giving an accurate reading, but I think it's pretty close. My hood doesn't feel too hot, nor does the engine compartment seem too hot either. Maybe you can take your truck somewhere and have the actual coolant temp checked and compared to the gauge.
It wouldn't hurt to flush the system and refill with fresh stuff.
I think the 1990 has the closed coolant system and sometimes those get an air bubble, which may cause hot temps.

 

[Chris142]

That Jeep has a very small radiator. It's only about 1ft tall and 3ft long. It's normal for these to run 220 or more.

The electric fan comes on @ 225-230.

 

[blupupher]

The Cherokee's from this time also were known to get very hot under the hood, even though the cooling system was working fine. Mostly poor airflow. Many off roders would make hood vents for these vehicles to help the underhood temps.

 

[NewGuy]

Thanks for your comments. I think that I will go ahead and flush the engine. It is the closed system MarkC mentioned above and an air bubble is possible.

The truck runs great and I believe that the guage is working correctly. It may just be a design issue with the Comanche. The radiator is awful small.

Thanks again.

 

[Gary Allan]

The temperature kinda makes you nervous ..but my Wranglers run 205-210 routinely ..and they got plenty of rad. The 4.0 bypasses a decent amount through the heater core. That's allegedly how they get such great warmup times (that was told to my by a guru @ Evans Coolant here in Pottstown that owns a 4.0).

 

[TheTanSedan]

Go on over to Jeeps Unlimited and do a search on your year model cooling system. Many have had to do conversions to later, improved systems, reporting excellent results.

Stock op temp on our 2001 XJ is 210F. Because the JEEP coolant system is a little undersized due to size and ground clearance needs, I change very year (drain, refill with cleaner, drive 6-hours; take to dealer to do backflush [pulling block drains] and refill to spec with an addition of SCHAEFFERS Clean & Cool), changing hoses every few years (25m annually) as underhood heat is impressive . . need gloves to open hood most of the year. (Hood vents someday; see Euro-spec Cherokees).

Good luck.

 

[MNgopher]

I have an '88 Cherokee with the 4.0l, and it does run hot! But its normal for these things. Airflow is poor under the hood and the radiator is on the small side for an engine of this size.

Normal cruising temp is around 200-205, hot idling in traffic is 210-220, when its above 85 or so outside.

I have maintained the "closed" cooling system on mine. If properly maintained, it is no more troublesome than any open system. I flush mine every two years, and I am currently running Zerex G-05 coolant. I'm on my 2nd pressure bottle, and I replace the cap every two years (dealer only item

).

 

[HardbodyLoyalist]

Chris142 and blupupher are correct. The older Jeep 4.0L engines had cooling systems that were barely adequate for even moderate operating conditions. The cooling systems were far and away these vehicles' "weak spot."

Keep it maintained and it'll do its job. When the radiator, water pump, fans or thermostat start to go bad, however, you'll overheat quickly and often.

Fortunately, the head gaskets on these engines are rather stout.

 

[MNgopher]

I should be fair - my '88 Cherokee, while on its second pressure bottle (as in the 1st replacement of the original), it has had 1 set of new hoses and 1 new radiator installed three years ago. Of course, it was 15 years old at that point (Jeep was manufactured in '87), so a new radiator was not exactly a surprise. My only advice if you stick with the "closed" system is to make sure you get the "heavy duty" radiator, as it does seem to work well for me.

 

[NewGuy]

Thanks to all for the great advice. Jeeps Unlimited has a terrific article that outlines replacing a pre-91 closed coolant system with an open 91+ system. It seems that the radiator and most of the other smaller items are bolt-on. I need to price the parts as a 1990 Jeep Comanche isn't worth very much....but I really want to keep it going.

The engine runs fine with the current system, but it runs on the hot side. I may price some different radiators as mine is one of the smaller ones. I will also do a flush of the coolant system.

These older Jeeps are great vehicles. Nothing fancy and nothing high tech at all, but my 1990 has almost 160K and it runs great. I have hauled things on this truck that would make most larger trucks yell for help!! I don't think that I will be pulling a trailer with it for long periods of time as the cooling system is marginal without a heavy load.

Thanks again for the advice. I will post with some results from whatever I choose.

 

[TheLoneRanger]

NewGuy, the reason our Jeep 4.0's appear to run hot is because of the location of the temp gauge sender. It's at the rear of the engine near the top; at the very hottest part of the cooling system and near a combustion chamber (and an exhaust port to boot).

They're actually running cooler than the gauge shows. However, the stock 1-row radiator is indeed marginal for summer conditions.

I converted my 89 Sport to an open system a couple of years ago. With the installation of a 2 row radiator, and a 180* thermostat, mine now stays rock steady on 180* in all conditions.

The only 'extra' parts I needed were an overflow bottle and universal thermoswitch from AutoZone, and a 1/2" to 5/8" hose adapter from Home Depot.....

 

[adreed24]

New Guy,

I have a 1987 Jeep Cherokee Chief (220,000 miles) with the 4.0 liter engine (same as your Comanche, I had one too). About 2 years ago, I had trouble with the Cherokee engine overheating; it overheated to the point where the coolant would gush out of the coolant bottle mounted on the firewall, (passenger-side).

To make a long story short, I found out that the radiator had partially collapsed inside, but only in certain sections.

I found out that the Jeeps with the 4.0 liter engines, came from the factory with a "1 core" radiator which was actually too small to do a proper cooling job.

Since your Jeep is somewhat old with substantial mileage, you may want to think about replacing your "1 core" radiator, with a "2 core", which I did. The engine runs much cooler now.

Don't get a "3 core" radiator, because in the winter months, the engine will run so cool, that you will have trouble getting heat in the passenger compartment.

There is a great Jeep owners website that you might want to visit. I've used it many times.

Here's the link: http://www.jeepforum.com/forum/index.php

Many Jeep owners on this site have gotten new "2 core" radiators for their Jeeps from Auto Zone; these people seemed pleased with the prices. I got mine installed at a radiator shop.

 

[Chris142]

quote:

---

Originally posted by adreed24:
New Guy,

I have a 1987 Jeep Cherokee Chief (220,000 miles) with the 4.0 liter engine (same as your Comanche, I had one too). About 2 years ago, I had trouble with the Cherokee engine overheating; it overheated to the point where the coolant would gush out of the coolant bottle mounted on the firewall, (passenger-side).

To make a long story short, I found out that the radiator had partially collapsed inside, but only in certain sections.

I found out that the Jeeps with the 4.0 liter engines, came from the factory with a "1 core" radiator which was actually too small to do a proper cooling job.

Since your Jeep is somewhat old with substantial mileage, you may want to think about replacing your "1 core" radiator, with a "2 core", which I did. The engine runs much cooler now.

Don't get a "3 core" radiator, because in the winter months, the engine will run so cool, that you will have trouble getting heat in the passenger compartment.

There is a great Jeep owners website that you might want to visit. I've used it many times.

Here's the link: http://www.jeepforum.com/forum/index.php

Many Jeep owners on this site have gotten new "2 core" radiators for their Jeeps from Auto Zone; these people seemed pleased with the prices. I got mine installed at a radiator shop.

---

Please stop refering to a radiator as a "1core" "2core" etc!

It drives us radiator guys batty! A radiator only has 1 core. This is the area between the tanks.

The # of rows can vary. You can have a 1-row core, 2-row core etc.

The proper terminology is a "1row" "2row" etc.

As for an oversized radiator overcooling.

Impossible! The minimum engine temperature is controlled by the thermostat. So if your engine is running too cool you have a stat problem.

The # of rows is pretty irrelevent today. The tube count and fin count can be changed to increase the eficiency of the radator.

A 1-row core with 5/8 tubes set 3/8'sinch apart and with 22 fins per inch will cool better than a 2-row with 3/8's tubes set 1/2 inch apart and with 6 fins per inch.

 

[MNgopher]

The 2-row would be what I referred to as a "Heavy Duty" radiator in my post earlier (as it would come from the factory on my '88 Cherokee, as mine originally did (I still have the window sticker!))

 

[NewGuy]

This is great advice. Thank you!! I will go to AutoZone or Advance Auto this week and price a new (2-row core

) radiatory. My wife and I are expecting a baby within a few weeks, so major purchases have been put on hold. It would be nice to have a plan to fix the problem though.

Thank you to everyone who posted advice.