Intake Manifold Coolant Bypass Modification

Intake Manifold Coolant Bypass Modification

Began: February 10, 2002

Reason: The engine coolant lines to the intake manifold heat up the intake manifold to allow for better atomization of fuel on cold days at start up. But that same process acts as an air heater that heats the air going into your engine all the time.

Objective: Remove the engine coolant lines to the intake manifold and route the engine coolant directly to the water box.

Warning: This mod may not be for everyone. If you live in very cold climates you may have problems, it could cause your car to idle rougher at startup. This mod is not a permanent modification to your vehicle, in fact it is easily reversible.

Tools and Parts Needed: At least 3' of 5/8" radiator hose, two worm gear clamps (you can recycle the best two of four you will get off the old radiator hoses you will remove), a flat head screw driver (preferable a short one), a socket wrench with 15 mm socket, a pair of pliers, an oil pan or something to catch small amount of engine coolant in, a knife or shop scissors, and a few rags.

The Project: The mod is very simple and should take about 15 to 30 minutes from beginning to end. You will be removing the intake manifold to water box metal hose, and the heater core to intake manifold molded plastic hose, and bypass the intake manifold by placing a 5/8" radiator hose from the heater core to the water box.

First remove the air box from on top of the throttle body. Directly below the throttle body is the intake manifold (in the middle of the picture below). Identify two hoses going into the intake manifold were the arrow is pointing in the picture below (look from the driver's side of the car). They are right next to each other, the one closest to the front of the car will be solid metal, the one closest to the rear will be molded plastic.

Identify the heater core hose, it is circled in the photo above. There are two hoses connected to the heater core, one is the coolant in (the top one), the other is coolant out (the lower one), we will be removing the lower, coolant out, hose. Trace the metal hose that goes from the Intake Manifold to the water box in front of the engine (see picture below).

Lastly identify the 15 mm bolt (labeled 1 in the picture above) that holds the metal intake manifold metal to the water box hose (pictured below), connected to that bolt is both a ground and a metal clip that holds the metal intake manifold metal to the water box hose.

First remove the 15 mm bolt (labeled 1 in the picture above) and loosen up the clip that holds the metal hose. Then loosen up the clamp (labeled 1 in the picture below) that holds the metal hose to the water box. Go to the intake manifold, loosen up the clamp that holds the same metal hose to the intake manifold. Pull down on the vertical section of the metal hose that connects to the base of the water box. This may take some serious prying, do not worry the metal hose will not break, nor will the water box, just keep pulling to you feel it start to move. Be careful a little coolant will most likely come out of the water box unless you are doing this mod after you have drained your radiator and coolant system. Have something like an oil pan to catch the coolant that will come out of the hose. Reconnect the 15 mm bolt and make sure you have the ground connected to the bolt when you screw it back in. It may be a good idea to clean the bolt, ground connector and the block surface to get a good electrical ground.

Once that half is off, pull horizontally on the other half of the hose that connects to the intake manifold. I had to use pliers to pull this half off mine, you can try using the metal hose as leverage to facilitate pulling it off, but it is on pretty good. Again you don't break it, give it all you have, it will eventually come off.

Move over to the heater core, loosen the worm gear clamp (labeled 1 in the picture above) on the lower heater core hose. Gently pull the molded hose away from the heater core. Be careful a little coolant will most likely come out of the water box unless you are doing this mod after you have drained your radiator and coolant system. Have something like an oil pan to catch the coolant that will come out of the hose.

Now loosen the worm gear clamp on the last line connected to the intake manifold (the other end of the lower heater core hose). The intake manifold from the driver's side of the car should look like the picture below.

Now take the 5/8" radiator hose you purchased at the auto parts store, place a worm gear clamp on one end and connect in to the lower heater core, tighten the worm gear down. String the 5/8" hose over to the front of the water box, cut the hose to the proper length and place a worm gear clamp over the end. Fit the hose up on to the water box inlet and tighten down the worm gear. You've now just bypassed your intake manifold's coolant lines, congratulations you've earned yourself somewhere between 3.1% to 4.66% more horsepower (that's approximately 2.9 to 4.3 hp on a bone stock engine, more if you're done some other mods).

Your engine coolant may be a little lower (it shouldn't be if you have a reserve tank), just to be safe run the engine with the radiator cap off and check the level after your engine has reached its normal operating temperature and add a bit more water and anti-freeze (should only be as much as the 5/8" hose you used to bypass the intake manifold could hold).

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