How to demist Smiths gauges?

[paydase]

The gauges on my dashboard get misted when the engine warms up.
What is the right way to fix that: opening down the dash and heating the back of the gauges with a heat gun?

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[DWW]

You cab try a hair dryer but the humidity may remain enclosed as vapour may have nowhere to escape. Alternatively and more effective will be to remove dismantle each gauge and completely dry prior to assembling.

[bitsobrits]

Where is the moisture coming from?

The fact it only reappears when the engine in warm is curious.

Do you perhaps have a small leak in the coolant pipes that run in the bulkhead cavity? Or in the heater matrix?

[MarekH]

Warm air holds more moisture than cold air. If the whole environment behind the dash isn't warmed up, the moderately warm gauge interiors are just a magnet for the moisture all around as the exterior glass cools off, much like the all of the moisture inside your home condenses on the insides of the windows because it is colder outside than inside.

You need to run the car for long enough that the whole of the interior becomes warm enough to drive the moisture out with air circulation and then have not too high a temperature differential between the hidden interior of the dash and the visible cabin exterior.

kind regards
Marek

[RICHOT]

This happened with my '89 Porsche 911.

The 'cure' was to drill a small hole in the base of the instrument metal casing so that the air temp in the gauge is the same as that outside.

Worth a try - it worked for my 911. Having said that, my classics are kept in de-humidified garages so this 'problem' only really occurred when I took them out for a run and the ambient temperature was higher than that in the garage, thus resulting in condensation on the instrument glass where it was in contact with the milder air.

Good luck,

Richard

[Heuer]

Put one or more silica gel desiccant packets in the centre console until the warmer weather arrives.

[paydase]

Many thanks for the numerous answers.
I think Steve (bitsobrits) may have a point, and Marek explains why.

I indeed noticed that, when cold, there was some sort of "humidity" on the metal surfaces in the engine bay of my OTS while none in my FHC.
And both are parked in the same garage box...

I also noticed that there was a small leak of coolant escaping from the header tank in my OTS: coolant may vapourise during engine heating and use of the car and condense on accessible cooler parts such as the dashboard.

I will first replace the header tank and see how things improve.
Then dry the "contaminated gauges.

[Fuel.inj]

I go along with Richard regarding drilling a small hole in the lower part of the gauge casing. Misting on gauges is usually a PITA for Morgan owners but that answer seemed to cure the problem and I did it on my Plus 8 with success.

[RICHOT]

I should have added that I put two small holes, one in the top and one in the bottom of the casing (if possible) to let the air circulate in the instrument.

But with this current weather and fluctuating temperatures, most of the metal (and glass) objects are going to be colder than the humid ambient air, thus resulting in condensation on the colder surfaces ( that's how a dehumidifier works!).

R

[ralphr1780]

Turn the lights on, the incandescent bulbs will generate enough heat to demist, usually its good for some weeks before any mist is back.

[malcolm]

Turn the lights on, the incandescent bulbs will generate enough heat to demist, usually its good for some weeks before any mist is back.

Good, but not if you have LEDs like me!

[Philk]

If this is happening to the gauges, then there is a risk that this is also happening in hidden body cavities (which is how things can rot from the inside out). If you do not already have a dehumidifier and background heater in your garage, I would strongly recommend their installation.

[MarekH]

It's not a risk, as much a certainty. Witness how condensation appears on the inside of single glazed windows vis-a-vis double glazing. A sheet of metal is a much better conductor of heat than glass. It's why Waxoyl was invented.

kind regards
Marek

[RICHOT]

in my garages, as well as a dehumidifier I use a desk fan on the floor to circulate the air - works a treat.

Ask the wife whether clothes dry more quickly in a slight breeze than in still air.

I think this is the reasoning behind the Carcoon type of car storage 'tents'.

[paydase]

I fully agree on the humidity risks in hidden cavities, hence the need to cure it.

What is strange however is that this happened only on my OTS. The FHC which is nearby in the same garage does not show this problem.
Unless the humidity has been trapped in those OTS cavities long ago before I acquired it 6 months ago, which seems unlikely to me.

Anyway, after having let the hot engine cool down in my garage after my last test (so probably heating somehow the dashboard due to the released soaked heat, mist has disappeared, for the time being...)

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I have to investigate the cause, be it caused by the header tank leak or by something else.

[Simon P]

If the instrument glasses serve as a useful 'tell-tale' that you've got humidity in your hidden cavities, I'm not sure why you'd want to stop them providing this service for you? When you do all the other things to the point where the instrument glasses no longer mist up, then you know your work is done and you can sleep easy at night.....