Heat Ranges and Gas Mileage

Like many on the board here, I am concerned with the temp gauge. When driving down the interstate or driving for at least a five minute period with consistent speed, the temp needle always stays a few hairs below 210. I am comfortable with this. For others it seems to be generally the same, a few notches higher or lower maybe.

In traffic, it goes past 210 onward to 220.. sometimes even 230-235. It rarely goes this high, but does sometimes. It NEVER goes to the red though. With all the talk of electric fans, 3 core radiators, and 180* thermostats.... are these truly necessary? Isn't it true that hotter temperatures allow for better gas mileage? Isn't it also true that the 4.0 in our jeeps is designed to run hot?

My guess is that as long as you're not going dangerously close to the red or into the red, the temps are fine and probably designed to be high in order to help gas mileage. I'm beginning to think that purchasing and installing the items above, if you don't have a serious heating problem, will hurt your wallet and won't improve gas mileage or longevity of the engine.

Can anyone help back this claim up?

The factory 195* thermostat shows 210* on the instrument cluster. A properly maintained factory cooling system should never exceed 215-220* under even the most severe conditions. Hood vents will lower engine compartment temps and can lower engine temps by 5-10*. If you have the early closed cooling system, converting to an open cooling system will help keep running temps a bit lower.

Overheating the engine can cause damage or excessive wear to engine compartment components, or cause a head gasket or head failure.

The Jeep 4.0L already runs lean, higher running temperatures are not a good idea.

If you are heating up sitting in traffic you need to check your fan clutch.

When mine was acting like that it was a cracked head. It was fine on the highway for hours but when I sat in traffic or climb a hill it would slowly heat up.

210 = Fine

220-235 = Not fine. If you are in this area, you most likely have one or more components that is not doing its job. Radiator, radiator cap, water pump, fan clutch, thermostat, serpentine belt. What is the age / mileage of each of these components?

I'm with you, if it's not in the red I really wouldn't bother. Mine always stays at 210 or a few hairs above. I've also heard the same, that some engines are designed to run hot and actually run more efficiently when hot.

I must agree with Tim_MN post #2 his # is 584 which leads me to believe he is a long time Jeeper.

Now my thought after looking at your temperature number they are too high, but then when you take into consideration that gage you are look at is only an electronic interoperation of your system degree of the real operating temperature of your engine they may be just fine. All it would take is one slightly corroded connection any where in your system and your numbers are out of norm.

I must agree with Tim_MN post #2 his # is 584 which leads me to believe he is a long time Jeeper.

Now my thought after looking at your temperature number they are too high, but then when you take into consideration that gage you are look at is only an electronic interoperation of your system degree of the real operating temperature of your engine they may be just fine. All it would take is one slightly corroded connection any where in your system and your numbers are out of norm.

I don;t think any engine is designed to "run hot". The gauge is there for a reason and the cooling components as well. There are two fans for areason, and a thermostat, etc.. The key is efficiency. If the lines and radiator, block passages are gunked up with corrosion that will make the system less efficient, if the fan clutch is worn out and not spinning when it ought to at full force, thats not efficient. If the electric fan isn't engaging when it needs to or not at all the system isnt acting as designed and will not work correct.
If all the parts work well on their own you will have an efficient system and ought not run hot. There may be occasions when pulling a trailer in 110 degree weather like i was yesterday to the landfill. The needle crept up to 215 or so but no further and went back down after i dropped off all the junk from the trailer.
A cooling system flush, working fan clutch, and proper antifreeze/coolant levels may very well help your situation out.

Confirming your ACTUAL temp would help a lot. Then you would be able to get an idea how far off the stock temp gauge is.