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Hi All, in readying my engine for removal from my '39 Six, I obviously have to detach any and all things from it that are otherwise attached to the car so it CAN come out. One issue I am having is the fitting from the heat gauge supply line to the head. It does not look like it comes out easily. Is it pressed in there?? Threaded?? Can anybody help me with some removal advice???
Also, when unhooking the oil gauge line, is it necessary to maintain the oil in the line?? I presume some will drip out when I take it off. Would this screw up the gauge reading?? Or would the air just compress and 'delay' the eventual reading??

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The sensing bulb is attached to the tubing and is pushed into a hole in the head. A "hollow" nut then screws into the head and in doing so presses the bulb flange tightly against the seat in the hole sealing the coolant.

I would suggest a liberal dose of penetrating fluid making sure to squirt it on the thread area and as far into the hollow nut as possible. It may be needed to repeat for a few days. If you are lucky that will be adequate but if it has been years since the bulb was removed even the fluid may not help if rust has seized the nut to the flange. Sedimentation or calcium like deposits could have also "cemented" the bulb in the head. If that worst case has happened then the bulb may twist or pull off the tubing during removal and you are looking at a trip to Wolf repair to have the gauge repaired.

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Thanks Howard - that gives me a super-clear vision of what it SHOULD be. For what it's worth, the pic I posted is without my touching it. After examining your photos and going back and forth to my picture, it would appear someone has tried to remove it in the past and only managed to round off the nut and distort the collar of the sensing tube in the process. As you can see, there is a relatively new head gasket in place and the head and engine have been painted, so maybe whoever did that, tried, failed and decided to just leave it attached for the Head R&R. It looks like the painting job was less-than and there is a 'bald spot' around the sensor, so my guess is it has never been out. I definitely want to give the rebuilders the head as they want to magnaflux it,(not sure if that is the right term/spelling) and the block, for cracks and return the engine to me as a long block, which is my preference. I don't mind doing the re-torque after it is up and running but feel better about the thing coming back to me complete. So, one way or another, it will have to come out. Hopefully without wrecking it. Thanks again for the tutorial Howard.

Howard, you say 'with any luck' and, in this case, none was to be afforded me, as I went back, armed with the info you provided and tried to remove the collar nut, or what was left of it, from the head. I bought a good quality cold chisel and nicked the protrusion enough such that I could get a punch on it and tried tapping it around. Unfortunately it just kept breaking off. Now I have the sensor still in the head and any semblance of the collar nut sheared off flush with the head.
I think my only course of action now is to cut the line, drill out the hole as close to the threads as I can and either try an easy-out or, if that doesn't work, re-tap the hole. Any chance you (or anyone else) would know the thread size of that nut so I can at least tap it to the same threads to receive the new sender unit and nut that I will have to procure??? (you say through Wolfs??)

Yikes i have been pricing units to replace mine and they are expensive. Mine came out and works but its leed is to long and the face of the gauge is the wrong color (black the other gauges are tan)......not sure what to tell you....sorry

If it works like a regular capillary set up, when you cut the line the gauge is done??!!!???

Pat, yes, if I cut the line, the gauge is toast. I have emailed Wolf Instruments to see what the 'damages' will be. My current problem at hand is, the sending unit is in the head, the retaining nut that is sealing it in there is sheared off, flush with the head and the only way I know to get it out of there is to drill it and either 'get lucky' with an easy-out, or drill it close enough to the thread size that I can tap it. Either way, I destroy the sender unit. I really don't see that I have any other choice though - the big question is: are the sender units available and how big a deal is it to reattach one to my existing line??? I sure would like to get the thread spec on that retaining nut though.

The thread on the retaining nut is 5/8-18 (Fine Thread) assuming it is still the original size.
As measured on a 1937 115C which uses the same cylinder head as the 1939 Six.

Thank you Brian - that is most helpful. Ever had occasion to R&R one of these things?? Mine seems like it has 'become one' with the head!!!LOL Chris.

I had a hard time removing the bulb from a 1947 Clipper at one time but nothing like what you are dealing with.
The 115C came out easily.

Since its toast and you have no choice cut it as close to the head as possible and see if you can chisel the nut away (break it) in pieces and re chase the threads if you ding them. From what i have read here on the forum the bulb may be a problem as well it may "be as one" with the head.

I recently had to have the head done on my car, i busted the spark plug off and couldn't get it out oven with a easy out, the guy told me he could believe all the crap that came out when he cleaned it.