Blocking coolant flow to heater core.

[mulberryworks]

In general, you want the coldest air possible flowing into your mainfolds because cooler air is denser. If the coolant flow you have now is not assisting your car's warm up, I think you have your answer.

Right, in general that's true. But in very cold weather, driving with a cold manifold will cause problems as the fuel will condense on the inner walls of the manifold changing the mixture. I don't think most of our cars are driven in such weather anymore so that's not a big concern.

 

[Ohmess]

Mmmmm... Makes me wonder why BMW routed the coolant that way on these carb'd cars. We may never know. It may have been the most direct route (though the most complicated given the hoses, clamps and castings).

Cheers

I think it was to enable the operation of the chokes they used on the Zeniths.

 

[JFENG]

In general, you want the coldest air possible flowing into your mainfolds because cooler air is denser

I think the phrase, “in general,” is incorrect.

When you want max HP, denser air is better. How often do you drive WOT?

These cars were designed for regular use in Europe where they have real winters and chilly spring/fall days.

At cold start warmer air and manifold mean less enrichment is needed (less pollution, better combustion, better for the engine). That’s why they used warm air off the exhaust manifold and coolant to warm the manifold.

BTW, at WOT, the air doesn’t warm up that much as it passes thru the intake system. At more moderate power levels, having the intake air a little warm doesn’t hurt that much. It is not ideal, but at the time it was a good compromise for all around drivability.

The technology in our carb’s E9’s is really very crude. Carbs became obsolete by the mid 1970’s w the introduction of L-Jetronic (and D-Jet and K-jet). And those injection systems obviated the need for coolant heated manifolds.

John