Scored a Temp Gauge at the Bone Yard

[Joe Flanagan]

But it doesn't work. I was thrilled that I managed to get the bulb out of the head without breaking it. Then I spent some time on my back under the dash removing the gauge. The face of it is at least as good as mine if not better. I put the bulb in a pan of boiling water and the needle goes a hair over 100 degrees and stops there. Doesn't go any further and I left it in the boiling water for a good long time. I don't see any holes anywhere and the line is in good condition, not kinked or bent in the slightest. Any suggestions? Oh, there is a Bendix drive in one of the pictures below. More on that in another thread.

[RobertKB]

Some dirt in the back of the gauge? Mopar gremlins? Bad luck? Maybe try giving the gauge a good clean and see what happens. If the bulb and tube are good it should read reasonably accurate. If not, at least your engine will never run hot! Ain't it fun pulling parts!?

[Joe Flanagan]

That's what I'm wondering, Shel. IS there any ether in it? I'm wondering if there isn't a pinhole or something somwhere either in the bulb or in the capillary tube that has let the ether escape. Could it be as Robert says and the gauge mechanism is just dirty? I'm amazed at how clean those things are when you open them up.

[P-12 Tommy]

Don't think it would move at all if the ether was out, but don't know for sure. I believe if there was a hole, it would all be gone, or you would smell it leaking out. A smell you can not mistake.

I'm with Shel on this one.

Tom

[randroid]

Folks,

Another guess is that there is a hair-line crack that only opens when the pressure inside the bulb or tube gets high enough to open it. I can imagine the pressure inside the capillary tube is measured in grams if not milligrams, but it's competing against atmospheric pressure and therefore has the advantage. Once the pressure has released enough ether the crack will close and can't be found. This isn't the easiest sort of repair to make, but the scenario makes sense.

-Randy

[TodFitch]

I'm with Shel on this one.

Tom

Me too. Sounds like it is still sealed. But if it is reading that low it is possible that it was damaged at some time in the past. Maybe the Bourdon tube could be tweaked or the linkage between the Bourdon tube and the needle is out of adjustment.

[Joe Flanagan]

Going on the assumption that the moving parts might be dirty and stuck, I moved the needle back and forth gently to free everything up. I also put a very small amount of oil on the moving parts. Put the bulb back in boiling water and now the needle goes up to 130. I can see the needle pulsating very slightly while the bulb is in the boiling water. It won't go any farther than that, though. Everything is intact. Everything moves freely when moved with finger pressure. As far as tweaking the Bourdon tube or any other mechanism goes, won't I basically be throwing all calibration to the winds? It may be that I can adjust the tube and linkages so that the gauge reads 212 degrees in boiling water, but will it read 160 when the water temperature is 160? 180, etc.? I've read other posts where they say "declare victory and leave it at that," so obviously this is a seat-of-the-pants kind of thing. Just trying to find the best approach. Which may be sending it out, though I'd like to avoid that.

Edited January 17, 2010 by Joe Flanagan

[Young Ed]

Ive never seen one with a slight leak. Its usually contained or gone.

[Joe Flanagan]

What do you suppose it means when the needle pulsates with the bulb in boiling water? It almost seems as if the Bourdon tube is trying to expand but can't overcome the resistance from the moving parts to which it is connected (linkage, needle, spring, etc.). Except that all of those items appear to be well lubricated now and moving freely. I'm really stumped on this one.

[greg g]

Joe perhaps you can adjust the needle to get the gauge into a useable range. Stick it in some Ice water after puttin in the hot bath and see how it reacts to that. Then perhaps dissasemble it clean it and adjust it to reflect proper operating range.

[JerseyHarold]

Then pulsing might mean that whatever liquid is in the tube is bubbling. I think if there is an old leak in the bulb and pipe, the ether has long-since evaporated along with its odor.

[TodFitch]

I wonder if maybe the ether is gone and it is just some pressure is being applied in the tube by the 200+ degree water.

Nope: The pressure in the capillary would be too low to read. If it would work with air do you think they'd bother to put ether in it?

And if the ether is gone then air would go in and out through the same hole so you probably wouldn't get any pressure at all.

[martybose]

Going on the assumption that the moving parts might be dirty and stuck, I moved the needle back and forth gently to free everything up. I also put a very small amount of oil on the moving parts. Put the bulb back in boiling water and now the needle goes up to 130. I can see the needle pulsating very slightly while the bulb is in the boiling water. It won't go any farther than that, though. Everything is intact. Everything moves freely when moved with finger pressure. As far as tweaking the Bourdon tube or any other mechanism goes, won't I basically be throwing all calibration to the winds? It may be that I can adjust the tube and linkages so that the gauge reads 212 degrees in boiling water, but will it read 160 when the water temperature is 160? 180, etc.? I've read other posts where they say "declare victory and leave it at that," so obviously this is a seat-of-the-pants kind of thing. Just trying to find the best approach. Which may be sending it out, though I'd like to avoid that.

A while back I posted my adventure with calibrating the water temp gauge, it's fun! From my experience, if you adjust it to read 212, it will not read correctly at a lower temp until you've tried 3 or 4 different ways to adjust it. I finally got mine to read within a few degrees from 120-212, and declared victory!

Marty

[Joe Flanagan]

I'll look for that thread, Marty. I need to know how one goes about adjusting it. It doesn't seem like there's a whole lot of leeway in the mechanism. How close is "within a few degrees of 120-212?"

[Joe Flanagan]

Found it:

"you have to adjust both the angle and the length of the link to the needle to get it right."

That sounds like a tricky operation. I will see what kind of mess I can make with this.

By the way, I've been having a devil of a time finding the right diameter copper tubing to use as the sleeve in a repair. Has to be 1/16" inside diameter. Tod Fitch suggested trying hobby shops, which I have not checked out yet. Does anyone know of any other source for this kind of tubing?

[Joe Flanagan]

I'll do that. I just need to find it.

[martybose]

I'll look for that thread, Marty. I need to know how one goes about adjusting it. It doesn't seem like there's a whole lot of leeway in the mechanism. How close is "within a few degrees of 120-212?"

According to my two thermometers, I was able to get it within 2 or 3 degrees across the full range. Maybe a needle's width from exact.

Marty

[Joe Flanagan]

I'd love to know how you did that. I looked at mine and can't see a way monkeying around with the linkage would get me anywhere close to accurate. I could play with it but I risk buggering the gauge all up. I do have an extra now, though, so maybe I should try it.

[martybose]

I'd love to know how you did that. I looked at mine and can't see a way monkeying around with the linkage would get me anywhere close to accurate. I could play with it but I risk buggering the gauge all up. I do have an extra now, though, so maybe I should try it.

Needle nose pliers, a pot of water on a stove top, several thermometers as references, and several hours of patience.

Marty

[Joe Flanagan]

I've got all of that except the several thermometers and the patience.