do we have to heat the inlet manifold

[rob]

there are 3 rubber pipes which supply hot water to the inlet manifold would it be safe to plug them as we want to keep the inlet manifold as cool as possible in summer in NZ

[WideOpenThrottle]

I wouldn't! It will prevent proper circulation of your cooling water & be counter productive!

[WideOpenThrottle]

This also helps idle smoothness as i think it senses engine temp from the coolant water and has a direct bearing on the Idle Speed Control unit and the Air Valve. So i would say you would need to keep them?

[dynofiend]

The TB heater has very little effect on inlet air temperature. Probably none at all infact. It is primarily designed to prevent the butterfly freezing shut on cold days and maybe even to maintain a constant air mass so that what has been sensed by the AFM is consistent with what is being chucked into the cylinders.

The volume of air moving through the inlet tract is moving at such a high volume that the heater has no effect on air temperature. Imagine holding a zippo lighter infront of a desk fan, and trying to measure the temperature difference in the air from 2 meters away and youll see what I mean.

[WideOpenThrottle]

I think you nailed it dynofiend-this is what i just read too!
A. Since the first engine sucked in air, intake air has been heated to some extent. Remember on cars equipped with carburetors there was a large tube that connected to the air cleaner? Well the other end of that hose was connected to a heat collector around the exhaust manifold. This is how warm air got to the carburetor.

There's two reasons we want to heat the incoming air. The first is that the atomized fuel will mix with warm air better than cold air. This was actually more important with carburetted engines rather than fuel injected engines.

The second reason is to keep the throttle chamber from freezing. Yep, that's right. I said freezing. As in ice forming inside the throttle chamber.

Anyone who lives where it gets cold in the winter has heard of "wind chill". It'll be 30° with a wind chill of 10°. As the air moves through the throttle body, the same wind chill affects the inside if the throttle body. Under certain conditions, such as high humidity, condensation will form inside the throttle body and the moving air will freeze it. This ice will keep building up until it chokes off the air supply and the engine dies.

By running hot coolant through passages in the throttle body, it keeps the throttle body warm and prevents this ice from building up.

Some early fuel injected engines did not have heated throttle bodies and ice formation was such a problem that heated throttle bodies were retro fitted at the dealerships.