C3 Oil Temp Sensor Adaptor

[Paul L.]

I realize that this going non-original but not too far as my clock has never worked. So I wish to install an oil temp gauge in my 1979 instead of the clock. I have the gauge and the sensor but I need the adaptor for that blind plumbing plug at the back of the block near the distributor. Any sources for that? Or is it just a brass automotive 90 degree fitting? If yes, what is the diameter and pitch? Many thanks!

[Joe L.]

Re: C3 Oil Temp Sensor Adaptor

Paul-----

I don't know what the original configuration of the fitting was. However, the threads into the block are 1/8" NPT (or 1/8-27). You need an adapter which has a male 1/8"-NPT fitting on one end and on the other end a fitting compatible with the temp sender. It looks like it MIGHT be 1/8" or 1/4" NPT. If it's 1/8", then a GM #9409927 should work if you need a 45 degree elbow or GM #9409931 for a 90 degree elbow. These type fittings are also easily available in hardware stores.

[Paul L.]

Re: C3 Oil Temp Sensor Adaptor

Joe,
As usual, thanks. I will try those numbers on the GM database tomorrow but realistically I think the automotive/hardware parts area is where I will find what I need.

[Joe L.]

Re: C3 Oil Temp Sensor Adaptor

Paul----

Both elbows remain available from GM for about 4 bucks each. Also, by "original configuration", I was referring to the configuration used for 81-82 Corvettes that originally used the oil temperature gauge. That's the configuration that would be best to duplicate. You cannot achieve "original configuration" for a 79 since the oil temp gauge was not originally used for that year.

By the way, as far as your clock goes, if you convert it to a quartz movement, then you will have a working clock for the indefinite future. The old "tic-toc" mechanisms were decidely unreliable and short lived; the quartz movements solve this problem.

[Paul L.]

Re: C3 Oil Temp Sensor Adaptor

I wish to get rid of the clock; see no use for it. I prefer function re the oil temp gauge. As I write this I realize that I am not going original. So I guess that points come off?

[Joe L.]

Re: C3 Oil Temp Sensor Adaptor

Paul------

Undoubtedly

[John H.]

Re: C3 Oil Temp Sensor Adaptor

Paul -

That tap in the back of the block is NOT where you want to put an oil temperature sensor, as there is no oil FLOW there - just a static column of oil where you can read pressure. What you want to read is the temperature of the oil in the sump; the best way is to remove the pan and weld in a threaded bung for the sensor, below oil level, or there are sensors available that thread into a special drain plug (AutoMeter, etc.). Putting the sensor in the tap at the back of the block won't tell you anything.

[Paul L.]

Re: C3 Oil Temp Sensor Adaptor

John,
I have to disagree with you on this one. (And Joe, I did some research on this subject today on-line to GM. Your #09409927 - oil pressure gage fitting - is the correct adaptor.) When the electronically tuned receiver (radio/stereo) was introduced in 1981 as an option it contained a clock. So the clock in the gage bezel was replaced by an oil temp gage. For some reason, the oil pressure sensor previously located near the oil filter was moved to the location on the block near the distributor. And the oil temp sensor found a home near the oil filter. As noted I do not know the reason for this configuration but I have to assume that it works....

[Craig S.]

Re: C3 Oil Temp Sensor Adaptor

Paul - I agree with John on this one....the oil temperature bulb needs to be in a large volume of static oil (sump) or, in a high flow spot where LOTS of oil flow is occuring to get an accurate reading. You mention "near the oil filter" in your post, and, there are several locations in the block oiling passages where this indeed would be in a high flow area...it all depends on where the castings are drilled. For instance, the older BB engines had provisions for external oil cooler plumbing on the side of the block above the filter boss casting area that was directly in the main flow path of the oil through the filter. The 81 may have had a temperature port provision for this. However, the older block pressure check points that John mentions is indeed a zero flow static point, and the oil there will just match the block temperature at that point and give an incorrect reading. I installed a temperature guage years ago on my old Honda 750 K1 bike and put it in the oil tank since it had a dry sump system...and it worked great. Changing the oil was a bit fun though since I used the sump drain plug hole for the attachment bung and it was tricky to pull the sender quickly to avoid a mess....Craig

[Paul L.]

Re: C3 Oil Temp Sensor Adaptor

Thanks Craig. I was trying to stay with GM original on the install. You will see below the oil pressure sensor near the oil filter as it appears on my 1979. That sensor was moved up to the distributor area for 1981 and the oil temp sensor replaced it in that location. I will do a second post with a pic of the GM oil sensor.

[Paul L.]

Re: C3 Oil Temp Sensor Adaptor

I am not saying that this is the best method but this is how it was done by GM! I will give it a try.

[Joe L.]

Re: C3 Oil Temp Sensor Adaptor

Paul, John, and Craig-----

I agree that a seemingly better place for the engine oil temperature sender would be in the oil pan. However, for 81-82 Corvettes the sender was located in-block as Paul described.

Also, for later C4 Corvettes with LT1 or LT5 (ZR1) engines, the oil temperature sender was located in-block. So, right or wrong, GM was pretty consistent about where they put these senders.

Another interesting thing is that 92-96 LT1 and LT4 engines had a low oil sensor mounted in the side of the oil pan. For this application, the oil pan has a screw-in fitting into which the low oil sensor is mounted. Theoretically, I don't see why GM couldn't have used a combination sensor here or put a second screw-in fitting for the oil temp sensor. But, they didn't.

[Craig S.]

Re: C3 Oil Temp Sensor Adaptor

Paul John & Joe - now I see where the temperature sender is going....not where I was thinking, this spot is right in the flow of the oil through the filter, pretty much where I was thinking when I referenced the BB engines oil cooler ports. By putting the temperature sender there, it should see lots of oil flow, and the pressure feed can be on the vertical port behind the intake manifold on the block. I was thinking the temperature sender was going in that back hole in the block versus right above the filter boss. It probably will be reasonably accurate there, and if the general did it...it should work fine...Craig

[John H.]

Re: C3 Oil Temp Sensor Adaptor

I agree - I thought from Paul's original post that the "back of the block" location he was referring to was the pressure tap location adjacent to the distributor, not the tap adjacent to the oil filter housing; the one by the oil filter will work fine, as it's directly in the flow from the filter to the main oil gallery.

[Paul L.]

Re: C3 Oil Temp Sensor Adaptor

Thanks to all contributors. And Merry Christmas!