Question about A4 trans temp sensor for LS1 F-body

[Joel_SS]

Today I was using the scantool to monitor my trans temp and compare the reading to my aftermarket guage. My sending unit for the after market guage is in the daig port on the side. While crusing today on the freeway @ 65-70MPH with the verter locked guage was reading about 165-170. Scantool was reporting 190+. What part of the tranny is the stock sensor pulling the temp from?

[joecar]

Stock sensor is in the pressure switch module which is at the bottom of the valve body, so it's measuring the fluid temp near the bottom of the pan, physically between filter and valve body.

[Joel_SS]

Why such a big diffrence in the two. Which one should I believe?

[joecar]

I don't know....

The fluid is sucked from the pan bottom, thru the filter, into the pump, and then on to the pressure regulator, and into the line pressure passage;

the pressure tap on the side of the case is on the line pressure passage;

I would have thought the pump would have heated up the fluid;

this means one (or both) of the sensors must be wrong...

if you have a handheld laser temperature gun (Sears, $100 or so), you could point it at the pan when it's hot and see what it says, see which sensor is the closest (the temp gun accuracy is calibratated to 1 or 2 degrees).

[Joel_SS]

Intresting... Isn't the fluid in the pan just retunred from the cooler?

BTW: Guage is an Autometer short sweep electric.

[joecar]

Intresting... Isn't the fluid in the pan just retunred from the cooler?

No. The cooler return feeds the lube circuit (which lubes the planetaries, the bearings, and the rear of the the trans.).

The pan is filled by the following:
a. lube exiting from the planetaries and bearings (this fluid has gotten hot doing it's lube function);
b. valves/solenoids exhaust/exit fluid.

Edit : I'll see if I can dig up some diagrams.

[joecar]

Could the action of sucking fluid thru the pump cool the fluid...?
That can't cause a 25 degree temp drop, I don't think it can.

[ChipsByAl]

http://members.cox.net/crashed/efi/39.jpgJoel did you say the aftermarket sensor is in the line pressure tap on the drivers side? If so there is minimal fluid flow there. If the pic I posted comes up you can see that #39 the plug only has one way pressure to it. There is no flow past it. I would believe the factory sensor.

[joecar]

http://members.cox.net/crashed/efi/39.jpgJoel did you say the aftermarket sensor is in the line pressure tap on the drivers side? If so there is minimal fluid flow there. If the pic I posted comes up you can see that #39 the plug only has one way pressure to it. There is no flow past it. I would believe the factory sensor.

Al,

Good comment, I agree with that ... pressure but no flow at the tap;

the main passage flows, but the branch to the tap is static (otherwise fluid would come out of the tap, but the tap is plugged by your gauge sensor); so temp at the tap is temp of static fluid in tap branch.

[joecar]

Here's another diagram showing the tap (see # 39 on lower left):