Hi all,

I would like to know if it would be safe to install this 1/8" NPT temperature sensor probe in the test port of my 1990 E40D transmission with it's longer "nose", or if I need to get a port extension.



Thanks,
Steve

 

That is probably too long to fit.

 

Hey Mark,

As a former transmission engineer, do you think it would be better to put the sensor in the test port or to put it in the output fluid line?

Thanks,
Steve

 

The test port is a better location for the sensor.

 

Thanks! That is where I installed it this weekend! I did not know if the "nose" on the sensor would damage anything inside the transmission, so I got a 1/8 NPT male/male fitting and a 1/8 NPT female/female fitting, joined them together to make a M/F 1/8 NPT extension. I'm waiting for a radiator to come in so I can't fire it up and test it out yet.

Steve

 

It probably wouldn't damage anything inside the transmission, but if you tried to install that sensor without an extension the transmission would probably smash the sensor before it was tight enough.

 

An update I meant to post in this thread earlier: I got my radiator installed and was able to go for a test drive. My new dual temperature gauge works great, and provides temps for the engine coolant and transmission case. Went for a 20 minute interstate drive and engine temps topped out around 199F and the transmission around 183F.

The transmission temps were slower to come up than the coolant temps, so I suspect there is some lag in measuring off of the test port as opposed to, say, being inline with the transmission fluid outlet line. But this is for an RV and most of our driving is long-haul so I think this will do fine for giving us an idea of the overall transmission temperature. Previously there was no sensor at all so this is definitely an improvement!

Attachment 285027

Steve

 

Transmission temperature does come up much slower than engine temperature. The engine burns fuel that creates a lot of heat. The transmission shouldn't be burning anything. In my opinion, the test port is the best place to put a temp probe.

 

Good job. Was that set a kit?

"The transmission shouldn't be burning anything."-----Mark, that gave me a chuckle!!

 

Yup, it's this one:


I added a 1/8 NPT-to-1/8 NPT female-male adapter to the test port of the E40D transmission, so that the nose of the sensor would not hit anything inside the transmission.

I installed a new filler neck / thermostat housing on my 460 engine that "came" with a 3/8" NPT threaded hole:


However, the thing was evidently plated after drilling and tapping and so required re-tapping the 3/8 NPT hole. I put a 3/8 NPT-to-1/8 NPT male-female adapter in this hole for the sensor:


The instrument panel in that location of my 1990 E350 is mostly hollow in the dash frame (which is why the battery gauges are there ) - I had to remove a little bit of material to allow clearance for the gauge behind the panel. Originally I mounted the gauge flat/flush with the panel face, but the gauge includes an angled bezel to allow the pod to be angled towards the driver, so I did that to make it easier to view.

I'd like to find pod holders for the driver pillar post but they don't seem to be available for 1990.

Yes, I realize that the transmission runs cooler than the engine, but what I was trying to say is that the engine sensor, being immersed in the coolant directly, runs up in temperature faster than the transmission sensor does. The engine sensor gets up to max temperature within 5 minutes of 60MPH running. The transmission doesn't max out until about 20 minutes of running. I suspect you'd get a faster gauge response if you were measuring the transmission fluid output directly. And if you start to overheat the transmission I suspect there would be some lag before you would know it. Still, it is a wet port, and it's super convenient to use, and the transmission engineer says it's the best place for it, so I'm happy with it.

Steve

 

The test port is an accurate reading, the transmission doesn't heat up as quick as the engine that's why the temp is lower.

 

The temp is lower because, as Mark pointed out, nothing is burning in the transmission. The transmission naturally runs at a lower temperature than the engine. The issue is not the value of the temperature, but the speed at which the sensor is able to read the hottest temperature in the transmission. The test port probably gives you a good measurement of the transmission case temperature. It is a wet port, but as I understand it it is a dead end for reading pressure and so does not have a steady flow of transmission fluid through or around it. I could be wrong on that though. Whereas a sensor on the output port of the transmission fluid coolant line would probably see hotter temperatures faster. It just depends on what you are interested in measuring. If you want to measure the actual fluid maximum temperature, then the output is probably the best place to put it. If you want to measure the case temperature, then the test port is fine. I think the test port is perfectly acceptable for measuring the transmission temperature, as long as one understands that it is probably lagging behind the actual fluid temperature. It may take 10-20 minutes for the transmission case temperature to match the fluid temperature. In practical use this doesn't matter. But if you had a sudden overheat condition, I suspect you'd see it faster on the fluid output line than you would at the test port.

For any heat-generating machine with coolant, barring actual sensors embedded in the heat-generating part of the machine, the coolant exit temperature is going to give you the fastest reading of temperature changes in the machine. Practically, this probably doesn't matter.

Steve

 

I my opinion the best place for the most accurate temps is in the pan, buy the test port isn't bad.

 

I would think the pan would be where the cooled fluid is deposited on return to the transmission, to be picked up by the pump, and so reading the temperature there would give you the fluid temperature at its coolest, except from the line just before it enters the transmission.

Steve

 

By my actual measurements when I was a Ford automatic transmission cooling engineer, I can tell you that's not right.

Exactly right. If you always want to see the coolest temperatures inside the transmission the pan is the best place for that.