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New Motor Running Cool

BALTANAKT

NAXJA Forum User
Location
Berthoud, CO
Hey All,

My '91 XJ is running cooler than it should be. Was wondering if I could get some thoughts.

- Warms up to 195, drops to 160, and repeat
- Heat works, but on cool side (indicating cool temp reading is accurate)
- New thermostat (Motorad)
- New water pump (NAPA)
- New radiator (SPECTRA PREMIUM/COOLING DEPOT CU1193)
- New fan clutch (GPD)
- Coolant is full
- System burped twice

At this point I can only imagine the thermostat isn't doing it's job properly or the system is just cooling too efficiently.

Any other thoughts?

Thank you
 
Verify the temp with an external thermometer?
 
Hey All,

My '91 XJ is running cooler than it should be. Was wondering if I could get some thoughts.

- Warms up to 195, drops to 160, and repeat
- Heat works, but on cool side (indicating cool temp reading is accurate)
- New thermostat (Motorad)
- New water pump (NAPA)
- New radiator (SPECTRA PREMIUM/COOLING DEPOT CU1193)
- New fan clutch (GPD)
- Coolant is full
- System burped twice

At this point I can only imagine the thermostat isn't doing it's job properly or the system is just cooling too efficiently.

Any other thoughts?

Thank you

I had two of the discount store brands that did that which was especially annoying in the winter of 2002 in Connecticut. I changed to an OEM thermostat 16 years ago and still going like the first day. Others recommend the Super Stant brand ass having good luck with them.
 
On a different vehicle I had a Motorad open too cool. It was supposed to be a 180 deg but I was having trouble with the temp being too low, when I swapped it out I tested it it appeared to open all the way at 164deg.

I’ve used super stant in our jeeps with no problem but if you can find oem that will probably be better.

Oh I just saw a thread somewhere where they used some kind of reduction device to control the flow to keep the temperatures right. I look around for it later.


Sent from my iPhone using Tapatalk
 
Found it. It was at the MJ forum, they placed restrictors to help control erratic temperature fluctuations, like from 215 to 160.
I can’t post the link since I’m reading it with this same app, i can link to it later if you’d like.


Sent from my iPhone using Tapatalk
 
As cruiser stated, any remaining air would have escaped through normal operating cycles. If I were in your shoes, the first step I'd take would be to take out the thermostat and test it in a pot of water on the stove with a thermometer. They are not accurate as you will see, including the OEM units that draw more faithful followers. But they SHOULD be reasonably close. If it is close enough that you are happy with it, re-install it. Then test the coolant temp sensor. You can look up online the resistance readings that are acceptable for a good piece, or just toss it and purchase a new one, install. If that does not help the situation, then look at installing a restrictor as one of the guys mentioned above. You can find a couple good examples online of how to make it, its pretty simple and quite effective. But only add a restrictor as a last resort, because the basic cooling system, if assembled with good parts, should operate well without the restrictor. I've just gotten done with a rebuild a little while back, and almost all of the cooling system components were replaced as part of the project, and it is amazing how narrow the coolant temperature band is. Once it reaches operating temperature, I never see the needle move, and I do not use a restrictor.
 
I have a chart with the values.

But, I'm telling you. I installed 3 Super Stats in each of my Jeeps a few years back. They all took a long time to heat up and had temp swings.
So, I got all of them replaced under warranty and installed the new ones.

Same deal.
Bought one from the dealer and installed it in one Jeep.
Warmed right up to 195 in less than 3 miles on a 20* morning. stayed there with maybe a needle width of fluctuation.

Needle stays in the same spot on hot days also.

Installed one in each of the other Jeeps and duplicated the results..........
 
New thermostat from Jeep dealer today. $34.

Came in a MOPAR box but was made by MOTORAD. Same brand as my current t-stat.

This new one has the vent hole where as my current t-stat does not.

I put it in a pot of water and it seemed to open/close at 195*.

Will install as soon as I can and report back. In other news, averaged 13mpg over last 124 mi. Hoping this is due to running cold as all sensors are new and it did 18mpg before swap. -_-

Current t-stat part #: MOTORAD 300195
New dealer t-stat part #: MOPAR 83501426-AD
 
New thermostat from Jeep dealer today. $34.

Came in a MOPAR box but was made by MOTORAD. Same brand as my current t-stat.

This new one has the vent hole where as my current t-stat does not.

I put it in a pot of water and it seemed to open/close at 195*.

Will install as soon as I can and report back. In other news, averaged 13mpg over last 124 mi. Hoping this is due to running cold as all sensors are new and it did 18mpg before swap. -_-

Current t-stat part #: MOTORAD 300195
New dealer t-stat part #: MOPAR 83501426-AD

It seems that MotoRad makes different stats for the OEM market versus the aftermarket.
 
UPDATE: Mopar (Motorad) Thermostat Results

Installed new thermostat from Jeep dealer today. I am bummed that this new one still has me running cool.

Temp Inside Vehicle:

IMG_0720.jpg


This is it's highest reading. It will drop down a needle width when I accelerate from a stop.

Temp on Front of Thermostat Housing

IMG_0723.jpg


Temp on Thermostat Sensor

IMG_0721.jpg


Temp on Sensor at Back of Head

170* (no photo)

Thoughts

  • Very strange that the dealership part was made by Motorad (same make as my first thermostat) rather than MOPAR.
  • I think my poor gas mileage (13mpg) could be attributed to running cool
  • I could try a NAPA thermostat
  • Maybe my pump is too powerful
  • Maybe my radiator is too effective

Any thoughts?
 
Also, Tested both thermostats and they opened at 195 as advertised.

Maybe I should try a 205 degree t-stat?

OK. They opened at 195,... progressively or quickly? Here is the theory,... if the thermostat open (even at the desired temperature) all the way out quickly, it will allow the hot water to flow to the radiator. Cool/colder water will take its place. This cold water being colder than the thermostat specs, it will close again until the water that surrounds in the thermostat housing reaches the 195 set temperature then it will open again. This could be repeated several times before it settles down.

When I tested those I had, I would allow it to open fully then add some cold water (not a lot) to see how quickly it closes and at what temperature then allow it to get hot enough to open again. I repeated it several times noting how quickly it opens and closes and whether or not it opens and closes completely with minor temperature changes. I find the OEM unit to open in small increments thus doing a better job at controlling temperature.
 
Try covering your radiator with card board to block all incomijng air. If your readings rise while drivijng you'll know your radiator is too big, (too many cooling fins).. ..
If not, having replaced everything in the heating system other than your heater core, I'd guess a restricted flow from the heater core out line.

Spitball'n for ya.
 
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