Winter Air Cleaner Position (Heat Riser?)

[Jetaway]

Greetings, all.

Not sure what the technical term is, perhaps the heat riser. On the front of the stock air cleaner housing of my 1972 240Z is a flap that can be set for summer (flap parallel to intake throat ) or winter (flap blocks throat, air drawn into air cleaner from tube which draws air warmed by the exhaust manifold). I've looked in a 1970 owner's manual, quite a few repair manuals and some searching on this site, and I've been unable to answer this simple question:

How cold is winter? Or: At what temperature should I position the flap for winter driving?

We have a pretty temperate, if dreary, winter clime here. Lows drop into the 30s a handful of times during the winter, but freezing is an every couple of year thing. Lows typically run in the low 40s, highs into the mid 50s, but 60 is a warm day.

I flipped it to winter around a month ago and while it runs smooth, it seems a bit flat and the mileage is running 10% -- 20% less than expected. But between a badly vented gas tank (hard to get a true fill to fill reading), winter conditions, (cooler air, but perhaps a bigger effect from strong winds, different gasoline formulations, more idling, heavier electrical draw) two carbs to keep balanced, and spark plugs and other ignition parts aging, I can't definitively say that the flap position has had an effect.

Any suggestions from the factory or, even better, insights from experience?

Chris

[Darrel]

You're in ca, you have no winter.

[barth4567]

Live in Oregon. Had these cars for over thirty years. Never ran the switch in the winter position. Never. My 1972 gets driven pretty much every day. And it did get cold this winter a couple of times. For what its worth.

[Arne]

The '70 240Z didn't have it, so that's why the '70 owner's manual didn't mention it. The sticker on the air box says to flip it for conditions below 15° C (59° F).

[Jetaway]

Darrell,

Oh, I don't know. I've had to wear a stocking cap a couple of times this winter. Haven't had to pull out the tuque though since moving here a dozen years ago. Oh -- I do recall frost on the windshield of the other car this winter. Once. Which is good, because I just can't seem to recall where I put the ice scraper. Probably next to the tuque.

Barth4567

Similar climate, thank you.

Arne,

Thanks for the word from the factory.

And: Are they nuts? 59 degrees? The temperature passes through 59 probably 280 days a year here. Am I supposed to rig up a cable to the interior? Stop the commute traffic on the Altamont saying "Excuse me, gotta switch over the heat riser?"

Thank you all, I'll be flipping it back to summer in a couple of minutes.

Chris

[Darrel]

Darrell,

Oh, I don't know. I've had to wear a stocking cap a couple of times this winter. Haven't had to pull out the tuque though since moving here a dozen years ago. Oh -- I do recall frost on the windshield of the other car this winter. Once. Which is good, because I just can't seem to recall where I put the ice scraper. Probably next to the tuque.

Thank you all, I'll be flipping it back to summer in a couple of minutes.

Chris

bastard!

[Zedyone_kenobi]

It is really to help warm up, I would not worry too much about it. After the car is warm, it makes no difference. But Arne gave you the history, its nothing more than a novelty in Cali.