TH350 - where can i measure oil temperature

Hi hardline community,
Matthias here from germany. We just updated our "Avalanche" Buggy to LM7 5.3 V8 and TH350 transmission. I really need to monitor trans oil temperature in some races and i would like to fit a sensor (the best would be 1/8 NPT thread) somewhere into the transmission or at the beginning of the oil line to the cooler. Is any of the marked bolts able to go out and fit a sensor? My TH350 knowledge is basically zero and i would appreciate any help. Thank you!
By the way: Yes driveshaft fitment is veeeeery close





Regards,
Matthias Kocher

Weld a bung to the back of the pan. I don't think any of those would be a suitable spot to install a thermocouple. I use the middle port to run a line pressure gauge in a TH400.

You can use the pressure port on a TH400 for an accurate reading. It is a direct thread in for most sensors. Not sure if the TH350 has the same port. No welding, no mess.

Weld a bung on the pan for the th350.

Weld or tap a port in the pan.

The pressure port works too, but only in gear since the oil must be flowing for the sensor to register, correct @redneckengineered ?

The pan is the a good location but you can also put one in the line going to your transmission cooler. They make a t fitting specifically for this purpose. I purchased one from Glowshift guages but I am sure they are available locally for you as well.

Bebop said:

Weld or tap a port in the pan.

The pressure port works too, but only in gear since the oil must be flowing for the sensor to register, correct @redneckengineered ?

Click to expand...

No clue honestly, never noticed.

I put mine in the port you circled closest to the bell housing. That is a 1/8 npt port if I'm not mistaken and most sending units screw directly in to that port. I have heard you will get a more accurate reading from the pan but this location has worked for me.

redneckengineered said:

No clue honestly, never noticed.

Click to expand...

Hi @redneckengineered did you put a sensor in the pressure port?

Lil ugly said:

The pan is the a good location but you can also put one in the line going to your transmission cooler. They make a t fitting specifically for this purpose. I purchased one from Glowshift guages but I am sure they are available locally for you as well.

Click to expand...

I have always heard that's not a good reading. Flash temp from the converter and other factors are involved. Definitely better than not having a gauge but I think the pan will give you the best feedback on that trans.

Thinking back, i bought a weld in bung but tapped mine instead since the aluminum pan was thick enough.

Matze1989 said:

Hi @redneckengineered did you put a sensor in the pressure port?

Click to expand...

Yes been that way since 2012. It's 1/8" NPT and the sensor screws right in. But like I said this is on a TH400, TH350 may have something similar. You really don't lose anything to try it, run it that way until your next fluid/filter change and when you drop the pan you can do a bung then. My wife has a TH350 and hers is in the pan but it came that way when we got the transmission.

I'd wonder how far off the case temperature would be from the fluid temperature at that location. Doesn't really matter what you are reading as long as it is indicating accurately enough.

I used the pressure port on my original, bone stock th400. When I upgraded to a ptc 400 I tapped the pan. Saw an average of 20° cooler with the new trans. Though, new trans has a deep pan but a waaaay looser converter so kinda hard to really compare the two.

Thank you all for those replies. Really love that you all are sharing your knowledge with a european offroader .
I will try to keep you updated which route i go with the sensor.

By the way here is a video of the engine change which has been done a few weeks back:

Just a few days ago I found myself in a RV forum and this very topic came up. Although I was preset with my own ideas of whats best, I found a compelling argument for either location, whether it's pan, case or output.

1. The pan has the obvious advantage of seeing oil temps enter the case, but has a disadvantage since you cannot see temps inside of case or max oil temp leaving. Theoretically you could have safe pan temps, "scorched" fluid exiting and a huge cooler to bring it all back down, but you'd never know the fluid was exceeding its limit & breaking down on ya.
2. Side of case or inside likely sees the best average temp of fluid within the case components, but still cannot see max temps leaving. It's a common oem location, probably for good reason.
3. Outlet port advantage is you get to see the true max temps after it leaves the case. Placing here means you're trying to prevent the fluid from exceeding its own max temp limit (but ignoring trans critical component temps). Banks temp gauge dials (so I'm told) are set to read this higher range.

Some guys ran two gauges. Myself, I run one in the pan and struggle to get it over 180F. 150F is usually what I see, but I'm just a weekend crawler.
And I know a guy that uses the output tee and he constantly sees up to 240F.

My understanding was that hot fluid from the converter goes to the output to the cooler and also directly to the pan. So if that is true you would know regardless of your cooler size. I have heard that if the temp from the converter is much hotter than people think and the oil really doesn't break down if its flashes high very briefly. I'm no expert but try to listen to them.
Two gauges are probably ideal but if I had to choose 1 it would be the pan based on what I have heard.

I think that's the diagram:



This guy builds trans for a living and suggests putting it on the hot line to the cooler:

Looks like I was wrong regarding fluid flow direction to each component. Thanks for the clarity on that!

And just to throw a wrench into the convo, the oem sensor location on my Allison 1000 in the tow rig bolts to the pressure relief manifold/valvebody inside the pan.

Apparently Allison used two different locations for reading temps (VB & output to cooler), and this varied by transmission type and chassis (various RV models for example).

Depending on which location you have means monitoring two different ranges and understanding that each has its own recommended max.

It depends on who you ask and your purpose. TCI and some other transmission companies will say from the pan. I think Ed at PTC told me this too. B&M will say return after the cooler. Others say pressure line before the cooler.

If I was drag racing on a trans brake I would do the pressure line pre cooler. For my application, I think the pan shows me a better idea of what my trans is seeing internally and the temp will stay there longer than a few seconds in case I don't look while I am in it hard.
Im not worried about getting 100k miles out of my fluid. Since I switched from Amsoil to Hy-Guard its cheap. I'm more worried about what my clutches and seals are seeing. Just my uneducated thought process.