More tales of flakey temp gauges

My gauge has been flakey for some years.
Will read normal, then creep up, then suddenly, immediately fall to 195, or just go up fairly fast to say 220, when an IR gun confirms 190-195, taken various places on motor/cooling system.

Drove the car yesterday, gauge went to 210-220. Shut off car for 90 minutes at cars/coffee thing, got in , drove to someplace else, gauge never went over 185, shut off for 30 minutes, came home after than, gauge never got over 185.

Same issue with three diff T-stas, it's gotta be a ground issue either in the gauge, or the bias coil (instrument cluster) grounding site on the chassis.

I try to ignore it and just pay closer attention to the oil temp, as 210 +/- seems about normal under ordinary driving conditions

Doug

 

We are so obsessed with our temp gauges. I had a similar experience this morning, driving around the gauge ran close to 110 for the majority of the time Got home and opened the needle valve on the top of the radiator while the engine was idling. Once I thought that I had all of the air out, checked the gauge and it had dropped below 90. Not once did it drop below 90 during the drive.

 

I have the same issue. Makes you nervous when in slow trafic on hot days. I shoot various areas with IR gun and temps seem normal. I put new thermostat, tank cap and bled air. Fans turn on at 180. Temps read normal when at highway speed, but jumps up in slower traffic. I'm wondering if the "thermoster" or guage should be replaced?

 

That sounds more like an airflow issue than a temp gauge.

Are both fans working?

You may want to upgrade your fans, also.

if you have a carb'd car, getting to the temp sensor/thermistor is an incredible pain in the ass.

Doug

 

That is exactly how my 1984 QV's coolant temperature gauge behaved, right down to the conflicting IR gun readings. A confirmation test that it's the instrument panel wiring - what do the smaller gauge needles do when you turn on the parking lights or headlights? My fuel gauge, coolant temp gauge, and oil pressure gauge would all jump 2 needle widths higher when the lights were switched on, indicating weak ground paths and high impedance (dirty, corroded) wiring connections.


After reading a few posts over the years about checking and cleaning the connections on the back of the coolant temp gauge, in October last year I finally pulled the instrument panel and cleaned every single blade connection on the gauges and lights wiring with emery paper, and squeezed the female blade connector side if it was even a bit loose; used Stabilant-22a contact enhancer; switched all lights but the alternator warning light to LED bulbs; installed a jumper connection to bypass the dimmer switch; and added an additional ground wire to the end of the ground wiring in the panel, bolted to a stud on the underside of the dash above the brake pedal.

Result was no more needle movements with lights on, and the coolant gauge behaves perfectly with no jumps or random overheat indications.

Removing instrument panel after taking out 4 screws behind the corner lights
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One cleaned blade, one uncleaned dirty blade
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Cleaned each blade in each connector
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Stabilant 22a - expensive on Amazon, but worth every penny
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LED bulbs in speedo, per other threads
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1" bridge bypassing the dimmer
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Tap on the black ground wire added
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Black wire from tap going to one of two unused studs on dash underside above brake pedal, to add additional ground point
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My oil temp has been pegging or nearly pegging for a decade now with normal water temps on a easy around town drive in 70 degree weather. My solution after new sending units and a gauge from another QV which changed nothing, was to just ignore it.

So I ignore it and just watch the water

 

BTW, mine never seemed to be a problem for the first 10 or so years I had it.

Thst oil temp thing just seemed to start out of nowhere.

I have a few threads questioning it here back when it seemed it wasn't going to let me fix it.

 

Hey Gordon- mind telling us what the little LED bulb spec is?

Cheers
Tom

 

My oil pressure gauge used to go to zero after the car was warmed up. Freaked me out, so i put in a Tee connector at the gauge sender with small mech gauge on the Tee.
When the OP gauge in the car read zero, the mech gauge read 85 PSIG.

That problem sort of corrected itself, now the OP gauge only goes down to 45 at running temp, the mech gauge still reads 85.

Go figure.

Doug

 

The important thing for the type of gauge that is typically in a car is for it to be consistent. Since, as we all know, they are hardly "scientific quality" instruments for absolute measuring, as long as they move consistently, they can be considered "reliable" because they will show relative changes in temp/pressure/whatever.

When cleaning/renewing the electrical connections it's helpful to apply di-electric grease to each terminal before reconnecting. This will eliminate or at least greatly reduce any future oxidation and subsequent electrical contact issues.

 

All fine and good. Just be aware that if you have a gauge that reads perfectly normal while you're cruising along but goes high when you're stuck in traffic and dependent on the fans for airflow, that's not a gauge problem.

 

Nearly 20 years ago now I became dis-satisfied with the Veglia gauges, and so I swapped them all to VDO's.

Very happy with the change. For example, the oil pressure gauge varies with engine rpm - just as it should - enough that it could almost serve as a tachometer.

Details and pics in this old thread: 308 gauges: Out with Veglia, In with VDO | FerrariChat

 

Did you have to change out the senders also?

 

Yup.

Discussed in detail in the old thread which I have noted.

 

FWIW, the Veglia gauges in my '89 328 work fine. They move consistently and in accordance with the readings of external gauges temporarily attached. Maybe by '89 they had sorted out any electrical issues with the earlier gauges/senders?

 

About 10 years ago, when i was building my '37 Ford pickup streetrod, I wanted the instruments to look almost exactly as original.
I send my original form instruments to a place in phoenix,and they upgraded the workings and restored the faces to as new. It was not cheap.

I am thinking about giving them a call to see what they can do to upgrade the small gauges, while retaining the original Veglia faces.
Doug

 

Doug, since that will require removing the instrument panel, would you not consider trying the wiring cleanup, Stabilant contact enhancer, and ground wire supplement first? As I said in my earlier post, my coolant temp gauge was behaving exactly like yours, and after the wiring cleanup of the panel harnesses all gauges are functioning perfectly. It does seem a bit extreme to make the leap to a not cheap re-invention of the instrument panel when a very cheap known fix is a proven option...

Gordon