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2004 Rubicon 4.0L Running Cool

Tux

New Member
Joined
Nov 8, 2019
Messages
3
Location
New Mexico
As opposed to everything I have been able to find here and on Google, my TJ is running too cool, not overheating. 2004 Rubicon TJ, 4.0L, manual trans, purchased new in '04. Hit 65K miles and decided to do some preventive maintenance. Drained coolant, replaced all hoses, pump and thermostat (Super Stant 195°) refilled coolant with Zerex G-05. Temp gauge always used to point due north at 210°. Now it points about 3/16" to the left (low) of 210°, probably around 175° to 180°. Engine seems to be running fine but haven't driven it enough to determine if gas mileage has gone down. Just to be sure I didn't get a defective thermostat, replaced it a second time with another identical Stant 45359. Still running cool. I do detect a faint odor of unburnt fuel when I park it in the garage, as though the engine is running too rich.
 
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OP
Tux

Tux

New Member
Joined
Nov 8, 2019
Messages
3
Location
New Mexico
Solved part of my problem. Found out my Torque Pro app can provide realtime data while driving so plugged in the OBDII blue-tooth scan tool and connected to my smart phone and went for a drive. The temp gauge is indicating about 170° but the scan tool is registering 203° once the engine is warmed up. So the problem is the gauge, not the engine. Next step is to reset the ECU and see if that corrects the gauge problem.
 
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Chris

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Sep 28, 2015
Messages
41,532
Location
Salem, Oregon
I was literally just about to respond and say that it’s likely the gauge, not the engine. Glad you got it figured out, and thanks for the update!
 

Goatman

TJ Addict
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Apr 23, 2019
Messages
1,890
Location
Upstate NY
Check the sending unit. It is likley to be the problem more than the gauge. Also much cheaper and easier to change out.
 

Jerry Bransford

TJ Guru
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Nov 9, 2015
Messages
12,365
Location
Escondido California
Check the sending unit. It is likley to be the problem more than the gauge. Also much cheaper and easier to change out.
X2, the coolant temperature sender is mounted adjacent to the thermostat housing. Swapping it is a quick job. Maybe related to having been working on the thermostat housing next to it.
 
OP
Tux

Tux

New Member
Joined
Nov 8, 2019
Messages
3
Location
New Mexico
Failed to mention that I replaced the sending unit with a brand new one. Again, real time OBDII info indicates 203° while gauge only indicates 170°.
 

TJ4Jim

TJ Addict
Supporting Member
Joined
Dec 9, 2015
Messages
1,511
Location
Brookings, Oregon
Failed to mention that I replaced the sending unit with a brand new one. Again, real time OBDII info indicates 203° while gauge only indicates 170°.
Did you use a Mopar sensor, most of the aftermarket ones are crap.