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Discussion Starter · #1 ·
Car overheated - turned engine off before temp needle got to red line. Had car towed home. Replaced thermostat with Duralast P/N 15139. Old thermostat tested good on the stove with a cooking thermometer monitoring water temperature. Pulled water pump - impeller had exploded. Replaced water pump. Filled with coolant and was sure to bleed system to get coolant into head. Cranked car - it doesn't overheat but, it runs hotter than it previously ran. Previously, the temp gage needle ran at about 1/3 full scale. Now it runs at close to 2/3 full scale. I don't get any white smoke out of the exhaust and I don't smell coolant at the exhaust with the engine running. Has anyone out there ever replaced the original thermostat with a Duralast? If so, did you see a change in the normal engine operating temperature?

P.S. Original thermostat looked good - no corrosion. When I initially drained the coolant to replace the thermostat, the coolant was clean with no trash or debris in it. I bought the car new and have been very particular about performing proper maintenance.
 

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Temp must be slightly off in new thermostat. There never 100% I personally don't like the needle being above the halfway mark in the temp gauge. I'd change it back to the old one, and return the new one, or try a different brand.
 

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I have used Duralast thermostats before. Worthless POS if you ask me. I have learned the hard way, nothing beats a Motorcraft. The original thermostat lasted your vehicle up to know, why mess with success? I have used Stant and Napa and Beckley too, all garbage. When I put in a genuine Motorcraft thermostat, problem solved.
 

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Discussion Starter · #4 ·
Checked Haynes manual, thermostat is speced at:
Opening Temp - 193 to 200F
Fully open Temp - 224F

Hooked up my scan tool and drove the car. When the car temp gage indicated the temp at which the car previously ran with the old thermostat, the scan gage read 195F. The temperature continued to rise until it settled out at 219.2F at an ambient temp of 96F. It appears as that is within specs for the thermostat. However, I put the old thermostat back in this morning and the car temp gage is right back where it was before I replaced the thermostat. That is the temp the car has run at since I bought it new. Given the specs, it is hard to say the new thermostat is bad, however, I like the old one much better.

Does anyone have any insight about thermostat specs vs actual engine operating temperature?
 

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3 or 4 degrees will make a lot of difference on the gauge when in the middle zone.

t-stats only control the minimum temp. The fans are what control the running temp. But if one t-stat is rated 5F higher then the minimum temp will be higher.

OEM is 192F/89C

Is there a temp rating stamped on the Duralast one?
 

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i had a similar experience.
mine always ran at about a third, then after changing rotted out pipes and installing new ford hoses and a ford thermostat, the gauge ran about midway.
i didn't like that and it never gave me any problems, but changing back to the original thermostat changed nothing
i think i may have some restricted radiator cores
 

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The radiators externally get clogged with plant fibers. I have a new radiator if needed.
 
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