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Unread 07-19-2013, 08:59 PM   #1
VTEK1
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1999 XJ Cherokee 
 
Join Date: Sep 2008
Location: Worcester, Massachusetts
Posts: 635
Really stupid cooling question

Unfortunately, I can't say i'm a newbie, but I'm kind of stumped. I just replaced my temperature sensor on the water pump last week. Since I did my Jeep sits right on 210 and the e-fan has been running a lot more than ever. My old sensor read just above 180 all the time and if it got to 210 the e fan would kick on.

Now, MA and the rest of NE have been experiencing a crazy heat wave lately so I'm sure this is more of a coincidence then anything however.....

I'm worried about the e-fan running all the time and does this mean that my old sensor was actually allowing my Jeep to run too hot!?

I replaced it because every once in a while it wouldn't send a message to the dash and would suddenly work if I gave it full throttle..... <---- is this a clog issue.

I'm thinking I'm going to just replace almost everything r/t to cooling because my XJ now has 178000 miles on it.

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Unread 07-20-2013, 09:21 PM   #2
79chiefs
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A cooling system overhaul would be great for the jeep. Get an ir heat gun and make sure the sensor is reading correctly. Your old sensor could have been wrong.
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Unread 07-20-2013, 11:48 PM   #3
5-90
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Quote:
Originally Posted by VTEK1 View Post
Unfortunately, I can't say i'm a newbie, but I'm kind of stumped. I just replaced my temperature sensor on the water pump last week. Since I did my Jeep sits right on 210 and the e-fan has been running a lot more than ever. My old sensor read just above 180 all the time and if it got to 210 the e fan would kick on.

Now, MA and the rest of NE have been experiencing a crazy heat wave lately so I'm sure this is more of a coincidence then anything however.....

I'm worried about the e-fan running all the time and does this mean that my old sensor was actually allowing my Jeep to run too hot!?

I replaced it because every once in a while it wouldn't send a message to the dash and would suddenly work if I gave it full throttle..... <---- is this a clog issue.

I'm thinking I'm going to just replace almost everything r/t to cooling because my XJ now has 178000 miles on it.
Critical question - year & engine?

There's no temperature sensor on the water pump proper, but there could be one, two, or three sensors - depending on year & engine. And, the various sensors would have different functions.

1987-1990 w/6-242 will have THREE sensors:
- Driver's side rear of the cylinder head. Drives the IP gage or lamp.
- Driver's side radiator tank. Drives the relay for the electric cooling fan.
- Driver's side of cylinder block, behind the exhaust. Generates the signal for the ECM.

1991-1995 w/6-242 has TWO sensors:
- Driver's side rear of cylinder head, as above.
- Thermostat housing. Drives the electric fan and generates the signal for the ECM.

1997-up w/6-242 has ONE sensor:
- Thermostat housing, drives ALL functions (feeds signal to ECM, ECM drives IP indicator and electric fan over OBD-II CAN Bus.)

I'd have to look up data for the 4-150 engine, as I don't deal with that engine much. And 1985-1987 w/Renault turbodiesel is another critter entirely, as are the 1984-1986 w/Chevvy V6-173...

Design operating temperature for the 4-150 and 6-242 run 205-210*F, although earlier years may be "pulled down" with some simple modifications - with no ill effect (OBD-I is somewhat picky about operating temperature, and may throw a code if it stays low. OBD-II damned sure will throw a code on you!)

You can see that this is not as simple as the question you post - more information, please!
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Unread 07-21-2013, 07:55 AM   #4
VTEK1
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99 4.0 xj
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Unread 08-27-2013, 03:33 PM   #5
TrucksBootsNGun
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Sorry to take off topic but stupid question, Your electric fan kicks on when the truck is just hot? Mine only kicks on if the AC is on....
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Unread 08-27-2013, 04:23 PM   #6
79chiefs
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Quote:
Originally Posted by TrucksBootsNGun
Sorry to take off topic but stupid question, Your electric fan kicks on when the truck is just hot? Mine only kicks on if the AC is on....
You need the sensor on the thermostat housing, unplug it and the fan should kick on.
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Unread 08-27-2013, 04:32 PM   #7
VTEK1
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As far as I know, it's a stock t-stat, all I did was replace the sensor. So I think the sensor was faulty.
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