Morris Minor Owners Club

Had a discussion yesterday with Mrs Offshore when out and about in Martha about rotating the air filter box to winter setting.

Herself is of the opinion that rotating rearwards into winter mode is for heater purposes ie the heater cannot supply loads of warm air to the cabin if the incoming air is really cold.

I always understood that the heater (1970 Traveller) was powered off the hot water and engine cooling system.

Who's right and assuming I am right as usual (ahem) what is the purpose of rotating the air box? I always thought my bikes when I was a young sir ran faster or better when the air to the cars was really cold.

The air filter intake is pointed towards the exhaust in winter to give a quicker engine warm up which will in turn heat the water and thereby reduce the warm up time for the heater.
The air intake for the heater on a 1098 is via the fresh air trunking

The most important reason, I believe, is to prevent carb icing in cold weather. If you've ever experienced it, you'll know what a faff it is... A hot intake charge my s less efficient though (as hot air is less dense) - hence the 'cold' setting, for when the weather isn't too cold and there's no risk of the carb icing up.

As above - it has no worthwhile effect on warm up - the idea is to prevent carb icing. On the Mini they even fitted a little 'stove' over the exhaust manifold and the inlet connected to that to maximise the warm air effect. I had an Austin 1100 stumble to a complete halt on Shap many years ago - when driving in a snow storm. And yes -in warmer weather - turn it to the cold air position. However - it makes little difference since the ingoing mixture is heated after the carb on the manifold 'hot spot' - losing 2 to 3 bhp in the process.