It doesn't matter which heater hose you clamp, the flow will be stopped, just as if the valve was shut. My experience tells me to use the clamp on the interior hose, not out under the hood, where the hoses tend to be deteriorated by the environment there.

To check whether the clamped hose is more effective than the closed valve, you might use a thermometer in the air flow, alternately releasing the clamp to convince yourself there's a difference when you do.





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Art Benstein near Baltimore

If you send me $20 I'll send you a how-to explaining how to make $20 from people on the internet.