Some say the high flow part of things doesnt allow enough time for the coolant to be actually cooled via the radiator....Gojeep has a mod on his website, where he restricts the flow in this setting, resulting in far more stable temps...its been a while since I came across that, will see if I can find a link.

EDIT: haven't gone through the whole articles again, but here you go for part 1
http://jeep-xj.info/HowtoWaterpump.htm

and here you go for the restrictor part
http://jeep-xj.info/HowtoRadiatorRestrictor.htm

 

Hi Guys,

This morning I made the radiator flush, a thorough cleaning was achieved, I changed the brand of coolant, I bought Mopar (was using AC Delco) and changed the radiator cap. Then I did a test on the highway and the temperature improved, remained at the usual levels, dare I say it a little less than usual. Tomorrow I will make a test more thoroughly, because I go to visit my family in another city that is 250 miles away. That's the litmus test, if all goes well, I will come to the conclusion that the problem was that the radiator was too dirty, or something like that.

Thank you very much for your usual support and will be reporting them as my champion behaved throughout the trip.

 

Sounds promising.

 

Hi, I made the trip over the weekend and during the road course the temperature remained normal (Below 210˚ F) levels. Upon reaching the mountainous area where my relatives live, I made several climbs, during this period the temperature increased up to half (210˚ F) but at the end of the hill and get back on flat ground, down to normal levels. Never before had climbed so steep hills with my XJ, but I imagine that this is normal behavior.

I think this test is already solved the problem of the temperature up to highway speeds.

Thank you very much for your help and am available for any questions.

 

I've seen/read that second link above numerous times......it's full of false info starting midway thru the 1st paragraph.

"The reason is that once the thermostat opens, you loose pressure inside the block which allows the coolant to boil off the side of the hot spots against your cylinders and inside the head".

That statement in that link is just false.....the thermostat does not create/form/increase pressure inside the block whether said stat is fully open, fully closed or in any of the infinite positions in between open/closed. Pressure starts to rise equally throughout the entire cooling system as coolant temp rise above ambient temp, presuming the cooling system is sealed well enough to hold presure. A cold rad begins to pressurize well before the stat begins to open.

Virtually every paragraph in that link has at least one false statement and every cooling system expert out there will disagree with the info in that second link all day long and say cooling system "restrictors" should never be used in a daily driven street vehicle.

 

I had this problem on my 96. After replacing the entire cooling system it was still doing it. But only at highway speeds, and worse in the mountains. It turns out I had a partially blocked muffler and it wasn't breathing well enough to remove all the heated exhaust gas in a timely manner. It sounded normal and it looked decent enough from the outside. After replacing that I ran thirty degrees cooler.