So I decided to put in a 160 thermostat today to replace my 190. Only problem is, I'm running 195-210 now. Temp goes to maybe 190 when I've got clean air in front of me, but immediately hits about 200 when I'm behind someone.

I flushed the radiator and all the hoses (including heater core ones) and had clean water coming out of it and all the hoses. The thermostat housing is clean as well so I know for a fact that there isn't any crud in there. Could it just be that the thermostat is allowing for too high of a flow and the coolant doesn't spend enough time in the radiator to get cooled? Coolant temp sensor maybe? Oh and the electric fan isn't kicking on at all unless I turn on the A/C.

 

I believe you nailed it when you stated "the coolant doesn't spend enough time in the radiator to get cooled". Also it's not staying in the engine long enough to draw more heat from it before going to the rad. IMO

 

thanks blue. I think I'm gonna get a 180 and see if I can get some stable temps from it that are hopefully lower than the 190.

 

the 4.0 is designed to run at 195 to 210,a lower t-stat really wont help any

 

The t-stat ONLY CONTROLS MINIMUM TEMP........the rest of the cooling system, it's condition and operating circumstances determine max coolant temps. The surface area of the XJ rad is pathetically small and the factory gauge is a joke like most other factory gauges. On a '98 XJ, the efan comes on at 218F and/or when the a/c compressor engages.

You want the fastest coolant flow possible, not slower. If coolant sits longer in the rad to cool, then it has to sit longer in the engine/head getting hotter.

http://www.stewartcomponents.com/Tech_Tips.htm

 

I wish I knew how hot mine runs but I have dummy lights. Anyway just throw in a 190 you probably wont get cooler temps unless you put a second e fan and bigger radiator.

 

......install an aftermarket temp gauge.

 

What's wrong with the factory gauges? Mine all seem to be working just fine...

 

Checked out the site you posted and it honestly made me have more questions than answers. If more coolant flow (which I have now) should help it stay cooler, why am I running hotter? Doesn't make sense. The purpose of coolant is to pull heat from the engine, go into the radiator, get rid of the heat, and then repeat the cycle over and over and over again. I agree with Ol'Blue that my coolant simply isn't staying in the engine long enough to remove the heat i.e. too much flow.

mike albo - your right, I'm just wanting to run a little cooler for durability's sake. A engine that runs 10-15 cooler will last longer.

tuxfan - I do plan on swapping the mechanical for another e-fan as well as going with a 3 core rad. Just need the $$ first. Hopefully adding an outside tranny cooler soon so that should remove some of the strain from the current rad.

 

If the needle is not on 100F or 210F or 260F, what temp is it? Granted, 3 numbers are better than a gauge that has C and H. My point is, ACTUAL coolant temp doesn't rise to 210F (or the middle of C and H) and just remain there, it yoyos as much as 40 degrees, possibly more (especially this time of year).

 

97-01's have 3 dashes between 100 and 210. Divide 110 by 4 and you find out the temperature range between each dash = 27.5 degrees. From there you can pretty much guesstimate. The coolant does yo-yo due to removing heat from the engine, then being cooled in the radiator, but the engine temp itself shouldn't if you have proper flow. The gauge shows the temp of the coolant in your engine, which should be pretty constant. I'm just getting too much flow so the coolant can't cool back down.

 

Did you read the 4th paragraph, the one that starts with "A common misconception"........

http://www.stewartcomponents.com/tec...ech_Tips_3.htm

How did you increase flow? You say you're "running hotter"........lot's of variables to consider, like coolant temp on a 80 degree vs 100 degree day, for example. Those are some smart engineers at Stewart Components with many years cooling system knowledge/expertise........don't think they would be making false statement about coolant flow if they didn't have proof.
A common misconception is that if coolant flows too quickly through the A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.</SPAN>
system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.</SPAN>

 

I read the whole article and am confused by the fact that more coolant flow would result in a cooler engine. It just doesn't spend enough time in the radiator. It may work in a race application, but that's far different from a Jeep. Not saying they don't know what they're talking about, but I can tell you it doesn't work in this instance. And the temperatures here have been very consistent so I know it's not that. Either way, I'm going with a 180 tomorrow and will see what happens.

 

If you plug in a scan tool (OBD-II) into the ALDL port under the dash, you will see actual engine coolant temps yoyo while the factory gauge will remain almost motionless. An accurate aftermarket temp gauge will also show the coolant temp yoyo, factory gauge won't. Is that bad?......No....it's just not telling you what's really going on.

How are you getting too much flow????????

 

The part that's different about the XJ is the tiny radiator. Radiator surface area far more important to good cooling than radiator thickness, according to the engineers.