Talk Morgan Forums Morgan Sports Cars Morgan Plus Four, Supersport & Plus Six (CX & CXV Generation Vehicles) Attempting to stop the gauges misting

My CX like my 4 previous Mogs has guages that mist up.
Not helped I suspect by the cold weather and the high humidity near the Orwell River and N Sea where we live.

I got some advice on here to use a greenhouse heater to keep the car interior warm.
Here is my version with a 45W unit mounted on some wood.
First impressions over the recent cold spell to -5c was that the car interior was staying warm.

Once the salt on the road goes I will test the car and report back

It will be interesting to find out John, but it's the cold glasses in a warm pub effect, and I suspect the car heater makes it worse. I haven't had the courage to drive on a winter morning with the heater off but I reckon they may not mist up as bad. I also think that some gauge internals self generate heat, because my four small gauges don't mist up equally.

https://www.criboats.com/knowledge-base/what-can-i-do-about-fogging-gauges/
This is a useful link, solution appears to be to increase the ventilation flow around the instruments, as most instruments have a vent hole to allow trapped moisture to escape but also allows moisture in.

Well, John, my instrument cases are now with multiple holes top and bottom. I even applied a clear film to the fronts. Hardly any difference.

This is a manifestation of the instrument temperature being below the dewpoint of the air behind the glass. Inside my garage the humidity is currently around 80% and the ambient temperature is 5C. At those conditions the dewpoint is just under 3C, but the instruments are at ambient temperature so there's no misting.

Get in the car and start the engine to warm it up, the interior will heat up quicker than the instruments (they will lag behind), so let's say the car gets to 10C, relative humidity is unchanged, the dewpoint is now just under 8C, but the instruments are still around 5C. They have no choice but to mist up.

Will a low wattage heater in the car help? I have one in mine, but not for that purpose. I suspect that unless the temperature of the inside is kept in the low teens then misting would still occur. Or drive without any heating in the car, that should work (if you can stand it).

Which is why I thought to try this.

I'm not in anyway questioning your observations and explanations Of all the many many soft top cars I've had and some have been outside all year round, many garaged (but used all year round) creating all the dewpoint conditions you mention I've never had from my humble MG Midgets to my Mercedes convertibles (currently 9 and counting) and my Porsche convertible, ever had their instruments fog up. Yet every Morgan I've owned has this characteristic, and the MG Midgets had the same brand/maker of the instruments (from memory). I've certainly suffered from internal condensation on windows especially when mohair (even multi layer insulation) hoods become saturated but the instruments have always remained dry. Just thought it was worthy of note.

I know I should have qualified the solution with in the case of normal non Morgan car increasing the ventilation.............

I agree, I've never had it happen on other cars (including 2 soft tops), so the Morgan experience is unusual and remains a mystery. I guess what I am trying to say (and hoping to justify why) is that IMHO the 45W heater in the car (which I also have, so no complaints there) is unlikely to alleviate this issue.

And I think you are right but I thuoght it worth a punt. If nothing else it will reduce the moisture inside the hood but not stop misting once the hood is down.