MSAM9699

I am a new jeep owner and I'm concerned about the temperature when idling. I am not used to seeing 210 when idling on a vehicle. I feel as if I'm going crazy thinking about it. When I'm driving it goes down below 210 like I'm used to but when I idle it goes to 210. It is 90+ degrees where I am at and heat index is even hotter than that. But in the late evenings when it cools down it still does it. Once again, not over heating. Just working myself up over it and just needed some input.

Thanks!

(I think I also posted this in the cheorkee xj forum, my bad, I'm totally new to this, I have a Grand Cherokee (WJ?))

dave1123

What you're describing is normal for a WJ, at least a 4.0 like I've been driving for 6 years. I wouldn't be concerned unless it goes over 210*F. That's the cut-in point for high speed of the electric fan. Mine varies constantly between 195 and 210. I'm OCD when it comes to watching my gauges, especially when it's hot outside and my A/C is on. That comes from owning an old Chevy truck where you sometimes had to turn the heater on to keep the engine cool! The cab becomes a steam room!

EZEARL

On the XJ forum he says his fan kicks on at 210. Could be his temp gauge sending unit is causing his gauge to read wrong. If his fan is coming on his temp may well be as high as 218+. If I were him I'd verify the temp.

dave1123

It's possible because the actual gauge reading is the PCM's interpretation of the voltage being sent back by the temp sensor. ALL the temp sensors on the engine and trans are just variable resistors anyway. The most accurate readings would be by using a lazer gun.

The way the fan works on my 2000 4.0 is it doesn't run at all on startup until the temp reaches 210*. Then it kicks on high speed and runs until the temp drops to 195*, shifting to low speed then. It stays running on low until you either shut the engine off or the temp climbs back up to 210*, cycling between the two. This is the temperature range that's best for proper fuel mixtures and lowest emissions. The engine doesn't start to stress until around 230*. Coolant at 18psi doesn't begin to boil until around 240-250 and that's when steam pressure tends to blow apart radiators and hoses. Pistons start to skuff at 260 and seize above that.

Today's engines are designed to run at higher temps to help control emissions. You can thank the EPA for that! One of the reasons for dropping the 4.0 was it's inability to provide good fuel economy and low emissions. It seems short stroke and higher reving engines work better for that. Also it's tall height, long length, and heavy weight were not suitable for modern body styles. The 4.0 is a torquey tractor engine. Just what you need for low speed off-road work.

97grand4.0

Aside from the WJ, when should the electric fan on a 98 xj 4.0 kick on? This has the two fan setup, one on the water pump, and the electric supplemental fan next to it. Runs under 210 but hotter than my zj and I never see the electric one kick on.

dave1123

Hey man, I'm stupid when it comes to XJs. I've been proved wrong too many times to comment! These XJ guys are relentless in telling me ZJs and XJs are different. I WOULD THINK 210.

EZEARL

My '96 XJ's fan comes on at ~218 or whenever the a/c compressor comes on. Newer XJ's come on at a bit higher temp (223?) or when the a/c pressure drops to a certain point.