Trans temp question

Joined
Sep 17, 2008
Messages
772
Location
royal oak, mich
2002 Ford F-150 5.4L 4R70 trans. The temperature guage I have is digital that starts reading at 72 degrees. Below that temp it blinks 'LO'. I have been getting fluctuations in temp reading as if there may be a thermostatic temp bypass in the cooling system for the trans or I have a sending unit that is goofy. I had the trans flushed and filter changed then had the trans temp guage installed. The trans is starting to heat up faster now at these temps than it ever has since I had the guage installed. I get up to about 125 and suddenly it's reading below 70 then it climbs back up to 125 and stays there for the most. Any ideas?
 
Joined
Jan 24, 2008
Messages
3,358
Location
Maryland
Where is the sending unit for the trans temperature gauge mounted. Is it mounted in the pan, cooler line, or somewhere else.
 

kaboom10

Thread starter
Joined
Sep 17, 2008
Messages
772
Location
royal oak, mich
The sending unit is mounted in the trans output to the cooler line. The sending unit is in a custom holder that measures the temp but doesn't impede the flow. My trans shop sells the kits and also installed it. The guage is mounted on the 'A' pillar just under the grab handle.
 
Joined
Jan 24, 2008
Messages
3,358
Location
Maryland
Is this measuring the cooler line that is hot or cold. The hot cooler line would be going to the radiator, and the cooler one would be coming back to the trans. It sounds like they put it on the trans cooler line where the fluid leaves the cooler and goes back to the radiator. Do you have an external trans cooler on this car that came from the factory. Remember whatever trans temps you are seeing, you can bet they are about 50 degrees higher at the torque converter. What brand of Mercon V trans fluid did you use in this truck.
 

kaboom10

Thread starter
Joined
Sep 17, 2008
Messages
772
Location
royal oak, mich
The temp sender is in the output line as to monitor the hottest temp from the trans at that point. I replced the factory trans cooler with a larger one with a thermostatically controlled electric fan.
 
Joined
Jan 24, 2008
Messages
3,358
Location
Maryland
 Originally Posted By: kaboom10
The temp sender is in the output line as to monitor the hottest temp from the trans at that point. I replced the factory trans cooler with a larger one with a thermostatically controlled electric fan.
Is this fan you bought a stacked plate design or a tube and fin design, also what brand of trans cooler did you get.
 

kaboom10

Thread starter
Joined
Sep 17, 2008
Messages
772
Location
royal oak, mich
It's tube and fin but much larger than what I got with the towing package from the factory. It's what the owner of the trans shop recommended and I trust his judgement. Let's say if I handn't put a pizza box top over it to impede air flow I wouldn't have made it to 90 on cold days.
 
Top