TH350 oil level, engine off

WFarm · Sunday at 3:54 PM

I am planning to install a temperature sending unit in my TH350 and was leaning towards installing the unit in the 1/8” NPT pressure tap port, circled in yellow. With the engine off and tranny cold is this port above the fluid level ( assuming not overfilled) or will I need to drain fluid before removing the plug?

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Matt69olds · Sunday at 9:07 PM

Installing a temp gauge in the case is useless, there is no fluid flow. All you will read is the temperature of the transmission case.

Put the sending unit in the pan.

hey mister · Sunday at 9:41 PM

Ditto.

Replacement oil pans are made with ports for temp probes.

ali_c20 · 2025-04-21T01:37:27-0400

You can install the sender in the outgoing cooler line if you don't want to pull and drill the pan. There is a lot of debate where to put the sending unit, don't want to jump into that rabbit hole. You just need a fitting/ manifold to mount the sending unit.

https://www.glowshiftdirect.com/5-16-transmission-line-t-fitting-adapter/

https://www.summitracing.com/search/part-type/temperature-sender-manifolds

bucket · 2025-04-21T08:16:59-0400

Matt69olds said:
Installing a temp gauge in the case is useless, there is no fluid flow. All you will read is the temperature of the transmission case.

Put the sending unit in the pan.

I have to disagree here. While the test port may be a dead end, there is still flow of fluid with the trans in operation. Unless the th350 is somehow much different than a 700r4.

Matt69olds · 2025-04-22T17:27:31-0400

bucket said:
I have to disagree here. While the test port may be a dead end, there is still flow of fluid with the trans in operation. Unless the th350 is somehow much different than a 700r4.

Here is a hydraulic schematic from a service manual.

As you can see, line pressure comes out of the pump, and tee into the pressure test port. It then continues to the manual valve. The test port is dead headed at the pipe plug.

Adding potential issues, I remember someone here trying to use the pressure tap for a temp gauge, and finding out after installation the shifter wouldn’t move. The temp gauge bottomed out in the case, the broken pieces of the sending unit fell down into the manual valve and locked it up solid.

Lastly, the case is the last place you want to use to monitor temp. It will be the slowest to warm, and slow to cool down. You want to monitor the fluid temp, not the case temp.

TH350 oil level, engine off

WFarm

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