CHT and gearing down to help cooling, myth OR fact, Get out your facts and scientific equations Options

[nditiz1]

It has been burned into my brain when I read it the first time that when going up a hill drop a gear (5th to 4th) to increase cooling thereby lowering the temps of the engine. Raby, Mark Henry, I'm sure others have stated the same thing.

I must admit my sample size is small (3 cars) AND 2 of which already had pre-existing issues with the engine health, but in all 3 scenarios when cruising on the highway going 75/80 dropping a gear down only momentarily lowers the temps only to shoot them back up possibly even higher as I am trying to maintain speed at a lower gear which requires more pedal. In each of the 3 cases I have been using a CHT over cyl 3. Two of which were a Dakota Digital and one was an aircraft spruce analog gauge. The one engine that was not plagued with less ponies was a rebuilt 2056 (by me). Maybe I built the engine wrong, I don't know. I guess I would like to hear what others have experienced. I am also not doubting the physics. More RPM = More fan turning = More cooling. Lowering gearing means the engine does not have to work as hard to pull up the hill. That last statement should have a caveat though. There must be a certain point of force vs gear ratio vs drag vs speed that would determine that staying in 5th would ultimately be more beneficial than dropping to 4th as far as work the engine is doing (probably a question for Phil - @superhawk996 )

So am I wrong in my limited testing and it does in fact shed heat driving on the highway 75-80 mph with ambient 85 - 90 or was it just a myth started because the physics seem to point that direction.

[iankarr]

Living in the mountains near Salt Lake I've had a lot of seat time in front of CHT and oil temp gauges. Downshifting definitely has positive effects on cooling. Lugging increases temps quickly. That said, there's definitely a sweet spot between gearing, RPMs and speed. For me, @superhawk996 s observations bear out...dropping down a gear and going a bit slower seems to have the most positive effect. And of course that relationship changes depending on grade, humidity, and a bunch of other variables. I will say this...having a CHT gauge has taught me a lot about how to drive an air cooled car. I also sometimes want to turn it off because ignorance is bliss. Maybe that's why they didn't come from the factory with them (IMG:style_emoticons/default/wink.gif)