01 XJ

I just replaced the factory water pump (and t-stat neck) with a HESCO high flow pump (and neck). Prior to the water pump swap, idle temp was around 180-185. Now it's idling at around 200. If I idle up to 2500 RPM, the coolant temp comes down to 185.

The cooling setup consists of:
- 3 core aluminum radiator
- Volvo 16" 2 speed fan
- 180 degree T-stat
- expansion tank mounted on firewall (self purging system)

I'm measuring a 60 degree temp drop across the radiator (hot tank at 195/cold tank at 135) using an inferred temp gun (painted tanks black to get reliable reading with temp gun). I seem to remember reading somewhere that high temp drop across the radiator means insufficient water flow (water's moving too slow) but would expect the new HESCO pump to be moving more water than my old 150K mile factory pump.

Ideas? I called HESCO but they wanted to blame the issue on the 180 t-stat and fans, even though those were there beforehand.

Edit/Note: All of this is sitting still in the garage with the electric fans providing airflow... no vehicle speed involved so radiator airflow is a constant.

 

Normal operating temp for the 4.0L is 210. Thats with the factory 195* thermostat. Running 200 is not a problem. The last time i used the code reader, it read a temp of 197. The gauge read 210.

 

Thanks, I get that it's not "technically hot" but it's "hot" compared to what it was before the pump swap.

As I said, I used to idle at 185 but now I'm idling at 200. With a higher flow water pump, if I were to see a temperate change I would expect to see it run cooler, not hotter. Off idle it comes down to 185.

note: all of this is sitting still in the garage with the electric fans providing airflow... no vehicle speed involved so airflow is not the issue.

 

Replace the t-stat? Could be your old thermostat was stuck open.

 

Going to try that this afternoon. I went home at lunch, drained and flushed the system (water in the block was nasty rust colored), and then ran it up to temperature.

I think either my t-stat is stuck closed or my radiator is plugged up. The hot side tank got to 208, cold side was 100 and the "hot" of the radiator stopped about 3" from the hot tank. Perhaps the new pump dislodged scale/rust in the block which plugged up the radiator?

 

Turned out to be a plugged radiator. I took the radiator to a radiator shop to have it pressure flushed and now it’s sitting steady at ~190 with the AC on.

I flushed the system 6 months ago and it was clean, so I have to assume that the new (20% increased volume) pump must have caused "junk" to turn lose in the block and plugged up the tubes.