[creeper2012]

Ok, I've read several threads on people's jeeps overheating on them... no new news, they get hot when not everything is working properly on both the open and the closed systems.

One question that I've had has been difficult to find many straight answers to. I may be opening up a whole big can of worms here, but I'm curious to hear what everyone has to say...

Jeeps (4.0's) are designed to run around 195*, correct? If someone puts a colder (say, 180*) t-stat in them, will they actually run colder? Or does it not let the cooling system cycle propperly? (I.e., not letting coolant sit in the radiator/block long enough to transfer heat)

Let's go off of the assumption that all fans are properly shrouded and in good, working condition and the systems are full of a 50/50 mix of antifreeze and water and all air has been purged from the systems.

Lets hear it!!

 

[BigBear]

I use a Mr Gasket 180F and have had no problems. The jeep still gets to the operating temperature of 210F. The only thing happening is the coolant leaves the block at 180F before it boils. I have everything upgraded in the cooling system and it still reaches operating temp so, NO it will not run 180F with it in, maybe in the winter.

 

[DTarve23]

the best possible thing you can do as far as cheap upgrade goes IMO is to put your electric fan on a toggle switch so that it will run constant when you want it to. Here in Texas at a pretty constant 100 plus degrees during summer months my jeep will run all day at about 190 degrees if I leave the fan on while Im driving. I have never seen an XJ that runs the "195Degree" optimal temperature without help ie upgrades or constant maintenance and low mileage most run about 200-210 wich is running hot to me before I get beat up about that statement keep in mind that is my experience here in Texas with our heat

 

[creeper2012]

Good replies so far! I was always under the impression that a colder thermostat would keep the engine colder, which is why I came up with this thread.

As I've gained more experience, however, I've realized that some engines just naturally tend to run hotter than others and they need hotter thermostats to keep their systems working like they're supposed to.

When I first started workin' on vehicles, I thought t-stats worked almost like a metering valve, that once it opened, it would constantly stay open but only let just enough coolant through to keep the engine at a constant temperature.

Eventually, I figured out that a good-working radiator cools off coolant quick enough that t-stats actually fully open and close and allows 'cool' coolant to sit inside the engine for a few moments to soak up heat as well as letting 'hot' coolant sit inside the radiator for a few moments to allow it to cool off.

I believe that with a cooler t-stat in a 'hot' running engine, the radiators can't keep up and coolant flows constantly, however with a hotter t-stat, coolant temps fluctuate closer to how warm the engine 'likes' to run and the radiator can actually cool it off quicker because, say, 100* air is colder to 210* coolant than it is to 190* coolant... see what I mean?

Just my opinion though... let's hear some more input guys!

 

[Guy90]

While on the subject of t stats and overheating, I recently replaced both my hoses coming from the tstat going to the the heater core and over flow tank, this was because the hoses were swapped from the last owner, now I already knew I had a small coolant leak randomly at the back of the engine, now that I replace the hoses, the leak seems a little bigger. It's not much but a drip every few seconds, until the truck is off it will leave a basketball size spot. Once again not extremely bad but that's not the main problem.
Today coming home from work a week after I've replace the hoses I noticed my jeep running hotter than usual like 220*, pulled in my drive way and coolant is spewing threw the overflow tank cap, why all the sudden? It is a little warmer today than usual but this never happened before. I opened up the tstat housing and I have NO TSTAT !!!! No gasket for the housing either, just silicone gooped all around it. So I got a new stat and gasket, cleaned the housing and found a really thin crack in it. So I obviously need a new tstat housing and id like to make it a closed system with a durango inline filler cap. Do u think since I replace my tstat will fix my over heating issue? Sorry to go on and on but this is all the sudden. Any info is much appreciated

 

[LeonFickett]

For what its worth, My Jeep Runs at 210*. It has since I bought it. Runs smooth and happy without overheating. I wouldn't worry about trying to get it to under 200.

 

[creeper2012]

I've always been told that engines may have trouble warming up with no stat... NOT OVERHEATING!!! Lol, but I'd be more likely to put in a 195 or slightly hotter stat in than leave it completely without one

 

[4.3L XJ]

Engines with no stat will have trouble warming up, except on a hot day. Then they will run hot and not cool down from the coolant not spending enough time in the radiator to remove heat. But you can run a 180° stat. However this will not let it run cooler except on cooler days or light load. The problem with running hot in XJs is two fold. First, marginal cooling system to start with. Second, the temp sensor for the gauge is at the back of the engine in the head, the hottest place in the engine cooling system. It might be 220° there, but only 195 at the stat. It is a problem with a long engine block with the coolant coming all the way from the front. You can change the design parameters by moving more air through the radiator. You would be amazed at the difference.

 

[creeper2012]

Engines with no stat will have trouble warming up, except on a hot day. Then they will run hot and not cool down from the coolant not spending enough time in the radiator to remove heat. But you can run a 180° stat. However this will not let it run cooler except on cooler days or light load. The problem with running hot in XJs is two fold. First, marginal cooling system to start with. Second, the temp sensor for the gauge is at the back of the engine in the head, the hottest place in the engine cooling system. It might be 220° there, but only 195 at the stat. It is a problem with a long engine block with the coolant coming all the way from the front. You can change the design parameters by moving more air through the radiator. You would be amazed at the difference.

Good point. My only concern with MY xj is that it'll go up to 210* at an idle and even with mild driving, it won't hesitate to make friends with the red line. I know the first thing I need to do is get my shrouding taken care of because the one for the clutch fan had been 'trimmed' and broken when I got it... just havent remembered to grab one while at a JY. Another issue I've got is that I'm running a radiator with a cap and I still haven't deleted my pressure reservoir, so I'm sure that's not helping. Will running a 195*+ thermostat make the gauge read higher than 210* normally (if I'm running a 180* now)?

 

[4.3L XJ]

That depends. Probably just in hot weather. Get those shouds fixed, flush it and check that fan clutch while you are at it.

 

[Guy90]

Thank u everyone for the help I got my jeep coolant running properly. Motor stays at about 190* to 200* and my heater is HOT. Loving it.

 

[ldub100]

It was 108* here today and I had to run to the post office. My wife waited in the Jeep with the A/C running while I went in and waited in line. I was in there a good 15 minutes and when I came out, it was sitting right at 210* on the gauge.

 

[creeper2012]

Nothin' wrong with that. ^

 

[stephnsons]

Very informative thread.

 

[heinsdorf]

Water pump setting impeller tolerance to resolve cavitation. Anyone do this? I have once on the closed system Bosch and it immediately resolved the overheating..