VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Water temp sensor

I have a coolant leak at the temp sensor at the back of the head. Looks like it’s coming from the wire that goes to the gauge. The sensor wire is attached to the gauge. I don’t see a way of replacing just the sensor and wire and don’t see a replacement gauge, wire, and sensor on The Filling Station. Anybody have a recommendation?

Maybe you can clean sensor where leak is and use a high temp gasget or silicone sealer to stop the leak. Just a thought!

I assume your car is a 1932. That "sensor" is actually a bulb or closed vessel which contains llquid ether. As the temperature of the engine increases, the vapor pressure of the ether increases. It's attached by a very thin piece of copper tubing to the temperature gauge in the dash. The gauge in the dash is nothing more than a bourdon type pressure gauge, scaled to show temperature rather than psi.

So.......to the fix:

-- First, be VERY careful with the tube connecting the bulb with the gauge. It is quite fragile and can be broken very easily. If that happens, you immediately lose all the ether (which evaporates super quickly if not in a closed container) and the repair is quite complicated.

-- Drain the engine coolant before you begin, as you will be opening an entry into the water passages in the cylinder head.

-- The bulb is attached to the cylinder head by a two piece one-of-a-kind compression type fitting. The way to remove the bulb from the cylinder head is to very carefully unscrew the packing nut -- the one screwed into the adapter -- while holding the adapter from turning. But when you are doing so, be careful not to be turning the bulb itself because you will likely wring off the capillary tube leading to the gauge. You can keep the bulb from turning with the packing nut by lightly pushing downward on the protruding part of the bulb as you back out on the packing nut.

-- Assuming you have successfully gotten the packing nut out, you then lift out the bulb from the adapter. Usually, they are corroded in place and they can be hard to remove. Put some penetrating oil in around the bulb, give it some time, maybe gently heat it with a heat gun a couple of times, lightly tap the adapter with a hammer and it should lift out.

-- Then remove the adapter from the cylinder head -- it's just a normal pipe thread into the head. Once it's out, have a good look at its condition. They are often badly corroded and must be replaced if they are. The adapter is not just a standard pipe fitting and I don't know of anyone who is selling them. That said, most any machine shop should be able to reproduce it.

-- As for replacement gauges, the Filling Station sold them at one time, so you might call them to see if they expect to have them again. A few vendors, including me, have working used ones. They are hard to find and are therefore pricey.


Hope that helps. If you'll search here in the '29-'32 forum, you'll find quite a few old posts that will provide more information than I've given above. Good luck with the repair!

All the Best, Chip

If the problem is isolated to the sensor or its fitting and the sealant trick doesn't work, try Roy Martin, The Temperature Gauge Guy", for a reasonably priced professional rebuild of your entire unit.

172 Laurel Hill Dr.

South Burlington, VT 05403

(802) 862-6374

I’ve found the best sealer for the temp gauge prob to be the white Teflon paste by Rectorseal. As Chip said, the fitting can get pretty corroded and the white Teflon paste seals up the pitting the best I’ve found and stays pliable enough to remove easily if needed. The special fitting for the bulb, which is pipe thread on the outside and a standard fine thread on the inside for the prob jamb plug is not readily available for some stupid reason as many GM cars use the same fitting. Inside the fitting there is a shoulder that the bulb washer sits on, then the jamb plug is tightened to seal the bulb from leaking. Often, on badly corroded fittings this shoulder is gone and the bulb leaks. If that is the case, you will definitely need a new fitting.
I have turned new ones in the past out of both steel and brass hex stock but don’t have any left. They do come up for sale from time to time, so just keep a lookout on eBay and the old car forums. Sometimes people selling used Chevy/GM heads still have the fitting in the heads and you can buy them.

Just a thought.... Ether would evaporate, so it could just be antifreeze running down the tube. Also, does the temp gage still work? If so, all the more reason it is not the gage.

If the Recto seal doesn't work (don't like the sound of that ) , Roy Martin may have one of those assemblies. Photo from one of his recent jobs.

The Filling Station sells the adaptor for the temp gauge. Hendo

Good to hear. For a while they couldn't be bought new.

Thanks for all the replies. I would not have guessed the adapter would be different than a regular pipe thread adapter.
I removed the heater hoses and adapter going to the heater. Put a brass adapter in and filled it back up only to have it start dripping out on the floor.
Looks like I’ll have to make a shopping list with the filling station this afternoon.