98 TJ 4.0 running cold

[colbert190]

As the title says, 1998 Wrangler TJ 4.0 with manual transmission running cold in winter weather. Located in Watertown, NY this past week outside temperatures have been about 15 degrees F all week. TJ refuses to get up to normal operating temp and will just sit around 140, about halfway between the fully cold and 210 mark on the gauge.

Replaced thermostat with Super Stant 195 think that was the problem and no joy. Radiator and coolant is 6 months old. Tried putting a piece of cardboard in between the grill and radiator to restrict some airflow and no change to temp. Cardboard covers about 3/4 of the radiator.

Haven’t tested the temp with a different gauge however the heater is not very hot and when I crank the heat it cools off more from dissipating the coolant heat through the vents.

Need some help! It being 15 degrees out and affecting my cabin heat has been miserable to say the least!

 

[rouxbicon]

As the title says, 1998 Wrangler TJ 4.0 with manual transmission running cold in winter weather. Located in Watertown, NY this past week outside temperatures have been about 15 degrees F all week. TJ refuses to get up to normal operating temp and will just sit around 140, about halfway between the fully cold and 210 mark on the gauge.

Replaced thermostat with Super Stant 195 think that was the problem and no joy. Radiator and coolant is 6 months old. Tried putting a piece of cardboard in between the grill and radiator to restrict some airflow and no change to temp. Cardboard covers about 3/4 of the radiator.

Haven’t tested the temp with a different gauge however the heater is not very hot and when I crank the heat it cools off more from dissipating the coolant heat through the vents.

Need some help! It being 15 degrees out and affecting my cabin heat has been miserable to say the least!

A malfunctioning thermostat (or one with an incorrect temperature rating) is about the only thing that can make an engine truly run too cool, and it sounds like yours is truly running too cool, based on low heat output. I would probably throw another thermostat at it. Maybe try a Mopar, or perhaps another Superstat. Lacking those, whatever is available that is (a) 195 and (b) not "fail-safe"

 

[Jamison C]

Sounds like the symptoms of a missing/stuck open thermostat. I would go with Mopar. Stant was bought by Motorad and their quality ever since has been hit or miss; more of the latter as of late unfortunately.

 

[RMETeeJay]

Did the new thermostat make any difference? Since you already replaced that, another thing to check is the fan clutch.

 

[colbert190]

Thank you for the replies. I’ll order a Mopar Thermostat and if that doesn’t fix it will look into the fan clutch.

 

[NashvilleTJ]

Did the new thermostat make any difference? Since you already replaced that, another thing to check is the fan clutch.

How would the fan clutch make it run cold?

 

[RMETeeJay]

How would the fan clutch make it run cold?

Always fully engaged.

 

[NashvilleTJ]

Always fully engaged.

And how does that result in the engine running cold?

 

[RMETeeJay]

And how does that result in the engine running cold?

I guess that’s impossible, since it’s a separate loop? In which case it would most likely be caused by a stuck open thermostat?

 

[NashvilleTJ]

I guess that’s impossible, since it’s a separate loop? In which case it would most likely be caused by a stuck open thermostat?

A properly operating thermostat sets the minimum temp of the engine. It remains closed until the coolant temp in the engine exceeds its rating (195 in a stock TJ) - no matter the temp of the coolant in the radiator. The fan cools the radiator, not the engine. A failing fan clutch could result in overheating, but not the other way around.

 

[Jerry Bransford]

Thank you for the replies. I’ll order a Mopar Thermostat and if that doesn’t fix it will look into the fan clutch.

That will fix it. I don't know if Mopar even makes any thermostats that are not rated at 195 degrees but just make sure that's what it has.