Cooling parts, 99 Cherokee
Herp Derp Jerp
Joined: Nov 2011
Posts: 18,251
Likes: 17
From: Parham, ON
Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
The fuel injection system is designed to be operated in the 195-218 range for economy, emissions, and power.
Lower stats are basically pointless as the rest of the cooling system is still designed around the above parameters anyway.
There's no reason to mess with it.
Lower stats are basically pointless as the rest of the cooling system is still designed around the above parameters anyway.
There's no reason to mess with it.
CF Veteran
Joined: Nov 2009
Posts: 8,172
Likes: 17
From: The Republic of TEXAS
Year: 1998
Model: Cherokee
Engine: 4.0L HO
We run a 180 Stant SuperStat year round (Chrysler/Jeep sold 180 Mopar stats for XJs at the dealer parts dept) and we get good gas mpg, good performance, good heater in the winter and runs a little cooler in the summer 95+% of the time. We r talking only 15* difference, no?
I've never seen a reference in the FSM to normal/designed operating temp.
I've never seen a reference in the FSM to normal/designed operating temp.
CF Veteran
Joined: Feb 2012
Posts: 2,282
Likes: 18
From: central IN
Year: 1997
Engine: 4.0
i disagree. my xj runs 185-195 all the time with use of a 180 Tstat. I haven't lost mileage or seen any other ill effects in 10k miles of use. heat is the #1 killer of most everything. why run the engines hotter when they already have a tendency to run hot/overheat ?
Herp Derp Jerp
Joined: Nov 2011
Posts: 18,251
Likes: 17
From: Parham, ON
Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
1999 XJ FSM Page 7-4
Running too cold of a thermostat can trigger DTC P1281. I found this as a definition for P1281 in an OBD-2 4.0L:
Seems pretty clear-cut to me. 
Originally Posted by Chrysler
THERMOSTAT
A pellet-type thermostat controls the operating temperature of the engine by controlling the amount of coolant flow to the radiator. On all engines the thermostat is closed below 195°F (90°C). Above this temperature, coolant is allowed to flow to the radiator. This provides quick engine warm-up and overall temperature control.
A pellet-type thermostat controls the operating temperature of the engine by controlling the amount of coolant flow to the radiator. On all engines the thermostat is closed below 195°F (90°C). Above this temperature, coolant is allowed to flow to the radiator. This provides quick engine warm-up and overall temperature control.
Symptom: P1281-ENGINE IS COLD TOO LONG
When Monitored and Set Condition: P1281-ENGINE IS COLD TOO LONG
When Monitored: The ignition key on, engine running, Ambient Temperature greater than 20°F, and Vacuum is less than 179Hg.
Set Condition: The engine does not warm to 85° C (181° F) while driving for more than 3 minutes and less than 1 hour depending on Engine load and Start up Temperature.
When Monitored and Set Condition: P1281-ENGINE IS COLD TOO LONG
When Monitored: The ignition key on, engine running, Ambient Temperature greater than 20°F, and Vacuum is less than 179Hg.
Set Condition: The engine does not warm to 85° C (181° F) while driving for more than 3 minutes and less than 1 hour depending on Engine load and Start up Temperature.
Herp Derp Jerp
Joined: Nov 2011
Posts: 18,251
Likes: 17
From: Parham, ON
Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
The minimum temperature of the thermostat has no impact on your cooling system's ability to reject heat.
CF Veteran
Joined: Nov 2009
Posts: 8,172
Likes: 17
From: The Republic of TEXAS
Year: 1998
Model: Cherokee
Engine: 4.0L HO
Since a warm-up cycle is counted at 160 and the efan on temp is 218, sounds to me like the normal coolant temp range is 160-218......at least it is for a '98 XJ.
Thread Starter
Newbie
Joined: Jul 2013
Posts: 5
Likes: 0
Model: Cherokee
A mechanic friend of mine said if I was going to have the radiator off I should replace a few of the pulleys since that can sometimes extend the life of the component, figured may as well swap them out. Bought this jeep brand new when I graduated high school and anything that helps it last longer is worth a few extra bucks, even if it doesnt it gives me something to do.
CF Veteran
Joined: Feb 2012
Posts: 2,282
Likes: 18
From: central IN
Year: 1997
Engine: 4.0
omgwtfbbq it's not in the fsm. whatever is being said is false and wrong on all accounts. come on man.
Last edited by s346k; Jul 19, 2013 at 09:50 PM.
Herp Derp Jerp
Joined: Nov 2011
Posts: 18,251
Likes: 17
From: Parham, ON
Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
But what are you actually gaining by running a cooler thermostat? Why did you make the change? Okay, it runs a little cooler some of the time... and? What I'm getting at is there is no reason to change it from what it was designed for.
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