Throttle body coolant bypass

Many cars run engine coolant through the throttle body in order to warm it up so the throttle body doesn't get filled with ice due to a mix of cold temps, humidity, and condensation. This is done because car manufacturers cannot design a car to work for "most" people, they are expected to make cars that work in any condition.

Lucky for almost all of us, we don't live in subarctic locations... It's a no brainer for anyone living in the south.

The throttle body's purpose is to control the amount of air that goes into the engine. With 180-200 degree coolant running through it, we are essentially heating up the air moments before it goes into the engine.

Bypassing the throttle body is easy and should take about 5 minutes.

You will need a single 5/16" barb that looks like this (buy it from home depot):

Two small hose clamps (any auto parts store will carry these):

And finally, you'll need two 5/16" vacuum caps (I initially bought 3/8" and it was far too big):

Before you begin, make sure your car is cooled down, otherwise you risk getting burned if coolant splatters on you.

First, open the radiator cap in case it's pressurized.

Next, look at the throttle body. On the top is a black hose...

Using pliers, remove the clamp, then pull out the hose. You may need a rag in case there's coolant still in the hose.

Now do the same for the bottom left of the throttle body. This one can be difficult to get to. If you're unable to remove the hose from the left side of the throttle body, you may have to remove the intake accordion hose to get access.

Attach the two 5/16" vacuum caps to the throttle body where you removed the hoses. You may reuse the hose clamps to secure the vacuum caps in place.

Now dig behind the alternator and pull the lower coolant hose out..

Line up the bottom and top coolant hoses together, then cut the excess hose from the top coolant line using scissors.

Finally, secure the two hoses together using the 5/16" barb and hose clamps.

The result of this is that the intake air isn't going to be heated before entering the engine. You may find increase throttle response, and maybe slight horse power gains.

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User Comments

This is a very nice mod. Only problem is, if you ever go traveling for, say Christmas, up north, there would be a chance that it would freeze up on you. I'm not 100% sure the chance of that happening will warrant the risk of a frozen throttle body. Then again, I can see where this would be used, and I'd recommend it in warmer climates!
well jus to say i'm a new rx 8 driver so what can you tell me about my car i would like to know!
The engine bay is already hot enough there is little to worry about. In Florida the throttle body with coolant flowing gets so hot it'll burn the skin on touch. Better to get rid of it.
Worked very fast and easy... Still under warranty so i didnt cut the hose. Easy to put back if need be...
Its a nice easy mod to get more denser air in the engine. But I did notice a drop of MPG with this mod and it makes sense colder air = more fuel, warmer air = less fuel. Also the warmer air helps vaporize the fuel mixture. I was averaging 120-150 miles on a tank of gas with this mod. When I put it back to normal I can get 180-210, Considering gas is very expensive right now, and work has been cutting hours... I want the most MPG out of my rx8.
I have a 06 Mazda 6S would that work on mine Do to the fact that the plastic one that came with the car broke
Can we get more information on the MPG Change on this? Junirol's numbers are pretty drastic, if thats the case, might not be such a good thing for daily driving what so ever.
Had this mod on mine and I undid it and really notice no difference in the MPG. Maybe he was romping on it alot more ;c)
Do you think it would be possible to use a 5/16th 2-way barb with shutoff to select between by-pass and not? Something like this:
Actually, cooler air is denser and hence you should get better MPG rather than with hotter air. That's why the air intakes are routed to draw cold air..

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