VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Oil guage question

I have a 1941 3100 AK truck with a 1954 235ci motor. I have the dash out to replace the temp sensor. After pulling the dash back, I noticed the oil guage had been leaking oil onto the back of the dash. The guage is the original guage that indicates 0-30psi. It maxs out since the 235 puts out more than 30 psi of oil pressure. I am guessing the guage has started leaking due to constant over pressure or perhaps I have a connection issue. I ordered a new 0-60 psi guage to replace it. My question is does the connection utilize a flair fitting or should I plan on using some type of sealant on the connection such as Teflon tape or Permatex Aviation sealant? That dash is a PITA to remove so I don’t want to have to remove it anytime soon. I have a new glass panel for the instrument cluster the previous owner included with the truck but the instrument cluster seems like you would have to pry it apart to replace the glass. I don’t want to damage it as all my Guages should be working now. How hard is it to disassemble? Thanks

Typical the line connection to the oil gauge uses a nut and ferrule connection. The limitation with that type connection is that it is not re-use friendly.

The first time you connect and tighten the nut the ferrule is collapsed on to the outside diameter of the tube. The seat in the nut and a corresponding seat in the fitting on the back of the gauge fit over the outside diameter of the ferrule. So both the outside and the inside of the ferrule are deformed. The next time you use it things might not match the same way, especially if one of the parts is new.

You could try some sealer on the OD of the ferrule. An alternative is to cut the old line as close to the ferrule as you can. Then install a new ferrule. Remember to put the nut on first!

Actually...

I have to respectfully disagree with you Rusty.

I had to deal with this on a '46.

There is no ferrule on the line in this case, and the threads in the gauge are female.

A special fitting with male threads and a male taper built right into the fitting is used.

The fitting is slid onto the line, the line is pushed into the gauge, and when the fitting is tightened into the gauge.

The tapered end of the fitting is what wedges between the line and the gauge.

I know of no other set-up that will thread into the gauge and work.

I'll try to find a picture and post it.

Below is a picture of what you need.

You just cut a little off the old oil line, slide this fitting on the line, push the line into the gauge, and thread the fitting into the gauge and tighten.

Chevrolet used this set-up for many years on mechanical oil gauges.

PS

This is assuming an original style gauge that fits right into the panel and uses female threads is used (like the 60 lb gauge used in GMC trucks of the same time period).

PPS

Apparently Eaton/Weatherhead calls it a "Threaded Sleeve Nut" for 1/8" tube.

Thank you for the correction. I was going by memory on what was on my ‘37.

Thanks for the info. Is the fitting reusable or do you need a new fitting each time you reconnect the guage?

Hi Planepal

Generally if the fitting is going back into the same gauge, yes it is reusable.

But in your case, I believe you said it may have already been leaking?

And, you are installing a new gauge, correct?

I'd still give it a try, but you will probably need a new fitting.


Once you've installed a new one and tightened it into your new gauge however, you should be able to disconnect and reconnect at will. 🙂

Thanks for the info. Always something new to learn.

I finally found the fittings at NAPA. It was the 6100X2 part number. If you’re installing a new guage, order a few since they’re under $2 each. And they are reusable since I hooked up the guage and tested it (no leaks) and realized I had to disconnect it to get it back into the guage housing. No leaks after I reinstalled it. Thanks again for the help.