Honda Prelude Message Board, Pictures, Forum, Specs, Performance Mods

Coolant Bypass Mod

Just about every stock car has a feature called the cold start valve. The cold start valve is located on the bottom of the throttle body and it has two lines that run into it, one in and one out. The lines transfer coolant which in a cold start situation, helps warm up the engine faster by warming up the air in the throttle body via-coolant. In a cold climate(one that has regular temps below freezing) it has a purpose, but in summer months or a climate that doesn't have a winter of freezing temps, the cold start valve hurts hp because hot air is bad air. So you have two lines to modify:

1. The coolant line coming out of the block into the cold start valve, and
2. The coolant line coming out of the cold start valve and back into the block.

The mod is simple: Bypass the valve by running line #1 where line #2 connects back into the block. Now you have coolant going out of the block and back into the block, which is essentially what it did before, but it doesn't go through the throttle body which drastically reduces air temps in the intake manifold. This whole cold start valve is just for warming up a very cold car, but it's not needed in a hot climate. V8 guys have been doing this for years in F-Bodies and Mustangs with all kinds of success. The idle may change, but again, that's life. People have reported up to 8hp at the wheels with this mod alone.

The yellow line(it's black on a stock car) is the line that goes into the throttle body. Now find the line that goes out of the throttle body(it's kind of under the Tbody, sorry i don't have a better picture) and remove it entirely. Be sure to do this when the car is cold!! A little bit of coolant will pour out and if the car is hot there will be a lot of built up pressure and you'll get hot coolant everywhere(probably in your face). Disconnect line #1 from the throttle body and connect it into the block, where line #2 used to connect to the block. Now you're done!

NOTE: If you experience Idle fluctuation due to this mod, please see the Idle air control valve mod

Page Modified: June 24, 2007
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