Smiths guages problem

[rads42]

I have a problem with my Smith's oil and water temperature gauges that's stumping me a little so I was hoping someone here had a suggestion. Both gauges read low at only about 50 C when the car's hot. At first I thought maybe the car had a stuck t-stat or something so it was never "warming up" Even though 50 was too low even for that. Also the thermostatically controlled fan comes on pretty often and that's set to come on at 75 C so I know the car is actually up to temp which would point to a gauge or sending unit problem. So last night I took the water temperature sending unit it and put it in a pan of 95 C (210 F) water to see what would happen and it didn't react at all....needle never moved. I tried this with the key off and then with the key on, no change. Anyone have any ideas? It just seems odd that both gauges would have the same problem but now that my experiment didn't work at all I'm even more puzzled.

[RockBit]

The water temp sending unit grounds through the intake manifold. If you take it out and put it in a pan of water you must attach a ground wire between the sensor body and the car. Key must be on for the gauge to be powered during the test.

Are your gauges Smith electronic? If so, that’s what I have. I struggled at first but got all of mine working.

[ACademic]

Are these mechanical or electric gauges?

Mechanical gauges with a temperature scale have an ether filled bulb fitted at the end of armoured capilliary tubing. It doesn’t take much to create a leak in these systems and my guess is this is what’s happened. In that case, the bulb and capillary tubing (the combined unit) must be replaced.

[rads42]

They're mechanical, sorry I should have mentioned that in the original post. Thanks for the feedback.

[jhv48]

Mechanical gauges act just like a thermometer and should read the correct temp if the sensor is placed in a bowl of boiling water. Not dependent on ignition key or a ground.
Did this just happen or has it been like this forever? Usually when the hollow capillary tube of a mechanical gauge is breached, the gauge ceases to function altogether.

Are you sure the gauges are mechanical? There would be a protective wire sleeve wound around the entire capillary tube from the sensor to the gauge. If all you have is a wire to the gauge from the sensor, then you have electric gauges and the sensor will have to be grounded and the ignition switch on in order to test it.

Did you use some sort of sealer or tape to seal the sensor when it was installed in the engine? Sometimes that will inhibit a proper ground but then the gauge either works or it doesn’t. Your particular problem is a head scratcher. Both temp gauges failing at the same time is highly suspect.

[rads42]

Originally Posted by jhv48

Mechanical gauges act just like a thermometer and should read the correct temp if the sensor is placed in a bowl of boiling water. Not dependent on ignition key or a ground.
Did this just happen or has it been like this forever? Usually when the hollow capillary tube of a mechanical gauge is breached, the gauge ceases to function altogether.

Are you sure the gauges are mechanical? There would be a protective wire sleeve wound around the entire capillary tube from the sensor to the gauge. If all you have is a wire to the gauge from the sensor, then you have electric gauges and the sensor will have to be grounded and the ignition switch on in order to test it.

Did you use some sort of sealer or tape to seal the sensor when it was installed in the engine? Sometimes that will inhibit a proper ground but then the gauge either works or it doesn’t. Your particular problem is a head scratcher. Both temp gauges failing at the same time is highly suspect.

I bought the car like this so I don't know how long it's been going on. The gauges are definitely mechanical and have the wire sleeve over the tube. I was stumped that the gauge didn't read and I know the key position shouldn't make any difference but I was so puzzled that it didn't read anything so putting the key on was my only guess.
I'm in agreement that both gauges reading incorrectly the same is almost impossible hence my call for help. This has to be something simple I'm missing.

[Blas]

I would guess that you may have had a spark that made a small hole in the capillary tubing allowing the gas to ever so slowly leak out. Usually the gauge will begin register low and finally stop registering completely. You can get them repaired but as I recall it is faster and cheaper to just replace them once this happens. Careful routing of the capillary tubes away from any possible source of electrical transfer - the coil, cap and especially spark plug wires is a must.
I have a spare set of gauges I was thinking of selling, but really don't want to break us the full set.
Blas

[patrickt]

I agree with Blas. Call Peter at Nisonger at 914.381.3600 and ask him what kind of deal he can work for you if you send him the broken ones. These guys are not that hard to replace. The hardest part is getting the little screw brackets that hold them in out from the back of the dash. Then you just fish them through the grommets in the firewall and screw them in the manifold and oil pan. Easy afternoon job.

[Blas]

Just remember to disconnect the battery when under the dash. It is amazing what damage the gauge bracket can do if it fall someplace “live”
Blas

[jhv48]

And, if you do end up replacing them, ditch the mechanical gauges and have them send you a pair of electrical gauges. They look the same, are a piece of cake to wire and you’ll never have to worry about that @&$£>%#* capillary tube again.

[tortuga]

Originally Posted by jhv48

And, if you do end up replacing them, ditch the mechanical gauges and have them send you a pair of electrical gauges. They look the same, are a piece of cake to wire and you’ll never have to worry about that @&$£>%#* capillary tube again.

Those mechanical guages are cool in theory but very unforgiving of having their capillary tubes disturbed in any way. The Electrical guages are the way to go.

Steve H
SPF 1764