Higher RPM = COOLER ENGINE??????

[94XJ4x4]

This kid I'm talking to says he has an overheating problem. anyway he says when he revs up to 2000 in neutral it cools the engine down because the fan moves faster (4x faster) and the coolant moves faster. Whaaaa???? I say BS! but i could be wrong... although I doubt it. It sounds like a no brainer to me. I know its stupid but can some let me know who is right?

 

[rockwerks]

He is partially right, the mechanical fan does spin faster but the extra cooling comes from the increased speed of the coolant. The 4.0 tneds to get hot under some intraffic idle situations and placing the jeep into neutral and reving it a few times will drop the engine 20*. Try it hes right!

 

[ROBZ95Xj]

He needs to check his t-stat and radiator i replaced both and now she runs perfect.

 

[94XJ4x4]

no shit.... well dont i feel like an ass. haha

 

[BrettM]

it's true.

 

[rockwerks]

He needs to check his t-stat and radiator i replaced both and now she runs perfect.

you live in NH, trust me in AZ 120* heat ya need ot doit from time to time to keep it under 220

 

[Atl XJ]

Yup, works or me too in the Atlanta traffic in the summertime when its in the 90s. Mine runs cooler in traffic with the A/C on since it kicks in the auxillary fan but when its hot I'm usually running the A/C anyways. I do need to put in an override switch for the fan though for bad traffic and wheeling when its not hot out.

 

[sidriptide]

also could be an under-lying problem with the fan clutch...

 

[bjoehandley]

I've had to do that with the Lebaron I owned a quite a few times. I've also been using my defroster on my XJ from time to time to help drop the temps when mine has gotten warm in traffic, defrost also kicks on the electric fan and helps too.

 

[Atl XJ]

also could be an under-lying problem with the fan clutch...

Yeah, good point. I run much cooler in traffic now that I replaced my fan clutch.

 

[woody]

I used to have to do that on the trail (88 'closed' cooling with new fan clutch and new 195* t-stat + water wetter) rev it up to 2000-2500 for a minute or three and it would quickly come back out of the red. I figured it was due to the faster fan speed and/or faster coolant circulation.

The 'problem' was a perpetual air leak in the closed system (never had a coolant leak, but I could bleed a pint or so worth of air out every 3 or 4 days)

I replaced "everything" else besides the fan clutch when I converted it to open cooling...it is MUCH happier now.

 

[tchase]

Yeah I learned that when I was about ten driving my dad's truck hauling hay in the fields, thing would get pretty hot creeping around the field while loading, pop it into neutral and rev it up a bit and it would drop back down. This came in handy when I first got my XJ, the rad wasn't the greatest and she'd get pretty warm in traffic.

 

[DenLip]

He is partially right, the mechanical fan does spin faster but the extra cooling comes from the increased speed of the coolant. The 4.0 tneds to get hot under some intraffic idle situations and placing the jeep into neutral and reving it a few times will drop the engine 20*. Try it hes right!

This is "a normal thing". In fact, one of the upgrades in the Ford "Police Interceptor" Crown Vic... is a higher idle speed for increased cooling when the vehicle idles for long periods in front of the donut shop...

Den

 

[Snarky]

Yep, And actualy on page 125 of the 1993 Jeep Cherokee manual, it tells you what to do when the engine coolant temperature gauge needle goes into the red zone.

It says to pull over to a safe place and stop the vehicle. Shift automatic transmission to P (park) (manual transmission to Neutral) and set parking brake. Then increase engine speed slightly. Bring the idle speed back to normal after two or three minutes.

 

[Slip Kid]

Yea it's totally true. Overheating on the highway? stick it in 3rd for a bit. The fan is irrelevent at speed, the cooling comes from the water pump moving the water faster.