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post #1 of (permalink) Old 11-21-2002, 08:51 PM Thread Starter
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heater question

What is the reason for running the hot water through the engine manifold, and is necesary to leave it that way?
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post #2 of (permalink) Old 11-22-2002, 06:24 AM
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Re: heater question

I fairly sure it it to improve fuel atomization, how well the fuel mixes with the air. My '85 258 has an electric heater in the floor of the intake under the carb. I made a bypass valve setup to stop the flow of coolant to the heater in the summertime which also stops the coolant from heating up the manifold. I got too hot one day in traffic and realized the heater box was getting hot even when the heater was off. Newer cars have a vacuum operated valve to stop the flow of coolant when the a/c controls are in anything other than a warm or hot setting.
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post #3 of (permalink) Old 11-22-2002, 07:46 AM
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Re: heater question

The purpose is to warm the intake manifold as quickly as possible after a cold startup. It is to vaporize the gasoline better, for emissions reduction and better running during warmup. Those setups usually have a thermostat in the loop somewhere, possibly switching a vacuum line that operates a water valve.

Other engines use a flap in the exhaust manifold that directs the exhaust under the carb until a bi-metal spring gets hot, moves the flap, and bypasses the flow straight out the pipe.

As emission rules becape more stringent, they went to the electric heater, because it can go to work immediately instead of waiting for hot water or hot exhaust.

If it's functioning properly it has no bad effects. If the thermostat sticks open, it can theoretically get the intake manifold too hot and reduce power slightly.
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