Temp gauge goes off the scale

[tomgt6]

I have a 63 spitfire and when I turn the car ignition on without the car running the temp gauge go right past hot and off out of site. The gas gauge is working as it should. I have a new voltage stabilizer in it.

It did this for two temp sending units in the thermostat housing. New wire from thermostat to gauge.

What do you guys think? What should I test next?

 

[Andrew Mace]

Would switched wires on the gauge cause this?

 

[tomgt6]

I tried flopping the wires from one side of the gauge to the other and still get the same result.

 

[Andrew Mace]

Light green/green wire (power from the stabilizer) on one side, and green/blue on the other (lead from sender)? Ground wire in place?

 

[tomgt6]

Isn't the Green wire your ground in a way. Doesn't the sensor in the housing open and close more allowing more ground? There is Power to stabilizer, Stabilizer grounded by being screwed into back of a gauge (no wire ground or spot for it)like it says. Gas gauge works on same power and ground in the voltage stabilizer just different wire from the gas tank not the front of the engine.

 

[Andrew Mace]

I think you still need a "real" ground to complete the circuit. And I seem to recall there's usually a black wire with a ring connector to go on the mount post for the gauge (under the knurled knob) to ensure a good ground.

 

[tomgt6]

Why would the fuel gauge work then. Also I have ground wires on that screw under neath the stabilizer that work for the dash lights. But I will check again.

 

[TR3driver]

I believe you have either a defective/wrong gauge or (more likely IMO) a short to ground somewhere in the wire between the gauge and the sender. A distant possibility would be the wrong sender(s) for your gauge.

A quick test for shorted wire would be to remove the wire from the sender, and see what the gauge does with the key on. If it still rises, there must be a short, either in the wire or inside the gauge.

Andy, the "hot wire" gauges that require a VS do not require a ground for the gauge itself. They operate only on the current that flows between the VS and the sending unit, so only the VS & sending unit need be grounded. These gauges also don't care about polarity or connection order, as the internal circuit is just a length of resistance wire that gets hot and causes a bimetal strip to deflect the needle.

But there are similar looking "balanced" gauges that do not require a VS and do require a ground for the gauge itself. They may also take a different sender. These were sold as aftermarket gauges, and used on some Triumphs (eg TR2-3 fuel gauge). Possibly someone got the wrong gauge by mistake? One telltale for this type of gauge would be if the needle moves suddenly ... the hot wire gauges respond rather slowly.

 

[Andrew Mace]

Randall, it all makes sense to me. What would be the effect of a sender intended for a non-VS gauge, i.e., "balanced" gauge?

 

[dklawson]

Randall beat me to it.

I believe Smiths introduced the voltage stabilizer in late 1964. The earlier moving-iron gauges operated without the stabilizer and are easily identified by quickly moving/bouncing needles. The gauges that need/use the voltage stabilizer work by resistance heating of an internal bimetallic strip... and they respond slowly without much needle bounce.

I am more familiar with the early fuel gauges than the temperature gauges. However, all the early moving-iron gauges must have a good earth on the gauge case or they won't work. As you have pulled a new wire from the sender to the gauge, make sure you also have a good earth connection for the gauge case.

You can learn a lot about the early moving-iron gauges by Googling for Barney Gaylord's MGA-Guru web site and looking over his pages dedicated to the MGA fuel gauge and its calibration.

 

[TR3driver]

What would be the effect of a sender intended for a non-VS gauge, i.e., "balanced" gauge?

I'm not sure about that. I've even got a Smiths aftermarket temp gauge in the parts bin, but never investigated what it needs for a sender.

However, the sender for the "balanced" TR3 fuel gauge actually works backwards to the sender for the TR4 "hot wire" fuel gauge, so mixing them would result in the gauge reading backwards.

 

[tomgt6]

So if I understand this:

1. Pull the wire off the sending unit. If still goes up there is either a short in the wire or the gauge casing may not be grounded.

2. Make sure case is grounded.

3. Check wire again for open circuit.

4. May be wrong gauge for that car. (Same silver bezel and white background as the fuel gauge with the jauger (now ever you spell it) name.

Thanks guys I may be getting somewhere.

 

[tomgt6]

Question though. If the bulb is grounded isn't the case grounded?

 

[TR3driver]

I believe Smiths introduced the voltage stabilizer in late 1964.

Had to be earlier than that, as even 1961 TR4s had them. I'm less familiar with early Spits, but I was under the impression they had them as well, from their introduction in 1962.

 

[martx-5]

My first Triumph, a '62 TR4, had a voltage stabilizer.

 

[dklawson]

I'm more familiar with when BMC introduced the stabilizer than Triumph. It very well could be as early as you say ('61... '62). I'm guessing Andy would know for sure.

As Randall said, you can't mix the two gauge systems regardless of what year they were introduced. Again, I'm more familiar with the fuel gauges and they definitely have sending units that operated in the opposite direction to the senders used with later bimetallic gauges. Their resistance range is different also. Presumably the sender for the temp gauge would also be "opposite" than that used for the early gauge.

It's easy enough to tell whether your gauge needs the stabilizer or not. In general, the early gauges without the stabilizer use "thinner" needles and they respond immediately to changes at the sending unit. The early gauge needles are also likely to flick about when you hit bumps while driving. Above, Tom says that when he turns on the ignition, the temp gauge goes above the end of the top of the scale. If that happens "immediately" and quickly, it's an early gauge. If it slowly climbs to the top of the scale, it's a later gauge.

My comments above concerning the gauge case needing a ground connection were concerning the early gauge. They won't work without the case being grounded. The later gauges only need their case grounded for their illumination lamps.

 

[DNK]

Doug- Wouldn't both gauges jump to the end when grounded?

 

[dklawson]

To make sure we're talking about the same thing, let's discuss grounding the sending unit wire and assume the gauge itself has a good ground connection and proper power supplied.

An early type gauge (moving-iron w/o the voltage stabilizer) will go to EMPTY or COLD when the sending unit wire is grounded. If you pull the sending unit wire off the sender and hold it in free air the gauge will read FULL or HOT.

On a later, bimetallic gauge grounding the sending unit wire will make the gauge read FULL or HOT. Holding that wire in free air will make the gauge read empty or cold.

The two gauges behave in exactly opposite directions to the same input.

 

[DNK]

Well, I'll be danged. That is what happens when you only own new cars (71)

 

[Andrew Mace]

I believe Smiths introduced the voltage stabilizer in late 1964.

Had to be earlier than that, as even 1961 TR4s had them. I'm less familiar with early Spits, but I was under the impression they had them as well, from their introduction in 1962.

Randall, I think you are correct about the Spitfire, but I'll try to do some research on that. On the other hand, the largely similar Herald did NOT have a stabilized temperature gauge for much of its life, possibly not until the 13/60 models came along, as they were the only Herald (other than early twin-carb. 948s) to have temperature gauges as standard equipment in all markets.

Tom, the Herald 1200 temp. gauges look an awful lot like those for the Spitfire. Of course, the two different types of senders look very similar as well! Are there any numbers on the face of the gauge that might help identify it?