Thread Size for Oil Temp Sender Unit

[Andrew Foster]

[Don Nelson]

[Don Nelson]

[Zach Grant L1011jock]

Andrew,
Like Don said, it sounds like the probe is designed for the secondary oil temp location on the front of the engine. There should be a plug installed on the case near the base of the #1 cyl. Remove the plug, insert the probe. EI should refference this in their directions.
-Zach

[Andrew Foster]

Don and Zach,
Thanks for your reply. Let me give a bit more background about our situation.
2 years ago we installed the Airparts of lockhaven stc oil temp guage which replaces the original factory guage and uses a new probe. This probe location is the original, at the vernaterm. We also have an EI Bar graph that has a oil temp probe location at the bottom of the oil pan.

We have been seeing a very high oil temp reading on the factory guage. 200 in cruise, versus 145 on the EI. As high as almost redline on the factory and only 160 on the EI.

We have new oil coller lines, great baffling, new oil coller, and new accessory case and vernatherm. We think it is the guage from AIrparts that is lo longer accurate.

Our plan is to install an additional EI probe at the factory location and do some test flights and see if it is the guage is reading inaccuratly or if in fact the oil temp is running that high, which obviously would be not good.

The facory probe location I have learned is a 5/8-20 thread. I am having an adapter machined out of brass to install the 1/8 NPT probe at this location.

I'll post results in a couple weeks or so when we get things going. Thanks so much for everyones help

[Charlie Tripp]

Andrew,
The bottom of the oil pan will have the lowest oil temp. The best location for an oil temp probe is in the oil journal (galley/passage) in front of cylinder #1 located on the case half. This will be a hotter location than the factory location and should be a ¼” fitting.

[Andrew Foster]

Charlie,

Do you think a 30 to 60 degree diffrence between the temp in the oil pan and the temp at the vernaterm could be accurate?

[Charlie Tripp]

Oil helps dissipate heat in an air-cooled engine. The induction runners attach to the oil sump with the induction air helping cool the oil. The factory or replacement oil temp gauges are notoriously inaccurate. I would place the EI probe in the location Don & Zach have suggested. Then you should have an accurate reading on your oil temp.

[Andrew Foster]

Thanks for all the inupt, greatly appreciated, here's the update

We installed, for test flights only, an Electronice International probe at the vernaterm location to get a digital readout of temps in cruise and climb, here are the results. We also have a probe at the bottom of the oil pain.
This is a carb 250, 1961. Engine was already warm from a parts flight when we started. Sea level airport. oat on ground 95, oat at 4500 85

Flight condition Oil pan Temp Vernaterm temp
warm idle 154 194
Intial climb 110mph 151 200
2500 climb 110 mph 148 210
4500 climb 110 mph 148 212
level cruise 4500 10 min 145 204

From this i gather our oil coller is working well as the oil in the pan once colled by iduction air is dropping in temp.
Do you consider 204 oil temp on a hot day to be normal?
Thanks for all the feedback
ps looks like the chart is not transcribing to the forum. so for clarification the first number is oil pan temp, second number is vernatherm temp

[Zach Grant L1011jock]

Andrew,
I believe you have very "normal" oil temps. I would guess these would read about 180 on the stock guage with the usual error.
-Zach

[Andrew Foster]

Zach,
Thanks for the feedback. It's good to know that you think these are "normal temps"