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I have a 2004 rubicon that seems to run hot , I have A 165* stat in it , when i am pushing it on the road it will still run up to 190* , I pull the heater hose to fill it so i doubt it is air bound , it is an auto , and on 33" tire , A friend said to change the water pump , his thought was that something on the impeller maybe a fin broke off ? it has 136,000 miles , new radiator and still has the clutch fan , off road its fine unless I am pounding on it which never happens :beerdrinking:
 

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Discussion Starter #4
Why is running a 165* stat a mistake ? all my race engines built 3-8 more Hp at cooler temps 160* - 180* on the dyno , small block GM , are these 4.0 motors different ?
 

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So what your saying, is that the engine is running about 20 degrees less than normal, but to you, that is hot because your other engines that are cooler? Umm ok.

The 4.0, 2.4L and 2.5L engines were designed to use a 195 t-stat and run at about 210. Unless you did some major cooling changes (better nose aerodynamics, larger radiator, bored out ports, bigger water pump, etc,) then you should not expect it to run cooler than it was designed.

The 4.0L especially is a large engine in a small cavity with a flat nose in front of it. Unless your putting hood louvers on it, side lowvers, bigger fans, etc,,, it is what it is.
 

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And pulling a radiator hose to fill the radiator makes no sense. That is a great way to get an air bubble in the system. When cold, remove the radiator cap, fill the radiator if the coolant level is not at the over flow tube opening. If it is squeeze the upper hose to make sure there is no air in the system. Replace the cap and make sure the overflow tank level is between the max and min lines.
 

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As above running a colder thermostat than specified is a mistake. Older non-computerized engines do ok with nearly any temperature thermostats but that's not the case with newer computerized engines. Your Rubicon's PCM was programmed around the expected/normal 210 degree engine temperature set by the factory specified 195 degree thermostat. Install the correct 195 degree thermostat, a Stant SuperStat would be a good choice, and get used to the normal 210 (or close) degree engine temperature.
 

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And pulling a radiator hose to fill the radiator makes no sense. That is a great way to get an air bubble in the system.
Actually, it was a heater hose that was mentioned. And that's a great way to vent air out of the system, especially if you remove the heater hose from the water outlet housing.
 

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As above running a colder thermostat than specified is a mistake. Older non-computerized engines do ok with nearly any temperature thermostats but that's not the case with newer computerized engines. Your Rubicon's PCM was programmed around the expected/normal 210 degree engine temperature set by the factory specified 195 degree thermostat. Install the correct 195 degree thermostat, a Stant SuperStat would be a good choice, and get used to the normal 210 (or close) degree engine temperature.
What he said x 1911. One thing I've learned with these Jeeps (97 TJ here) it's all about the proper temp.
I'd suspect the clutch fan before the water pump, maybe?
Does it run hot all the time? Run hot only at a stand still?
Be more specific.
 

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Trey, from the base post "it will still run up to 190* ," he is not running hot. :)
 
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