The Stovebolt Site Forums The Shop Area Engine Shop 235 Head Temp Sensor

Have a 58-62 235 head (3835913) which has the temp sensor opening on the rear driver's side. Want to block this opening as my truck has the GMC thermostat housing where the temp sensor is located. Assumed that the thread size of the head opening was 1/2" NPT. However, neither a 1/2" iron plumbing plug nor a brass plug fit in the opening. Threads are clean and not burred. Has anyone had this come up before? Are the threads in the female opening in the head tapered or straight? Thanks in advance.

That's not the correct casting number for a '58-62 head, which does have 1/2" NPT threads. An earlier 235 head may have a 216 style thermometer opening which is like a 3/8" female gas tubing flare. It does not use pipe taper threads, they are straight cut. You may not have an easy time finding a plug for this, although you could use an adapter to go to 1/2" NPT and then plug it.

You may need to cut the bulb and fitting off a mechanical gauge to use as a plug.

Sorry, was thinking about the block casting number dates. Head is a 54-55. Think that I could use a regular straight cut bolt trimmed to fit in length with a compression washer under it? The bulb/fitting gauge combo was in there originally I believe, before it went to the machine shop.

I think you could use a set screw and believe they come in that size and thread.

Check with a machine shop that does engine work, they use them to plug openings in the block just like the one in the head.

PS-

Pipe dope or Permatex 2 on the threads-

In my area, Carquest has by far the best selection of plugs.

Thanks! Went to Lowe's and bought a 1/2" flare plug which appears to have straight threads on it. Lowe's has those "try it" bolt and nut racks where you can check your thread sizes. Tried a NPT fitting in the flare female spot and it caught after a thread or two just like what it does on my head. Tried the flare plug in the NPT female spot and it was just the slightest bit loose but went in cleanly. Think it may work. Will try tomorrow and will post the result.

F***ing fitting didn't work. Back to the drawing board.

You could also tap it to pipe thread and plug it.

Think that's exactly what I'm going to do Dave.

For what it is worth, I have sealed threaded holes in pressurized live steam pipes by wrapping a loosely fitting fitting with a lot of teflon pipe tape. It works if the fitting is not too loose. It is not an elegant solution, but works. Jimmie

Finally got this one figured out. Size is 5/8" 18 tpi. Straight thread. Neighbor Hank, machined one for me out of brass stock. Fits perfectly. Look at the miscellaneous album for the pics. Hank says he'll make these for a price!


http://community.webshots.com/user/geezer

Interestin story and fix