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  DIY: Throttle body coolant bypass
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| Jason |
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Site Admin
Joined: 30 Oct 2006
Posts: 184
Location: North America
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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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| david8 |
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Joined: 17 Jul 2008
Posts: 47
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| So I am not living in the south, I live in Canada but i do not drive my RX8 in the winter, the coldest it will be driven in is about -10 Celsius (14 Fahrenheit). If I do this to my RX8 will it affect me in colder conditions? |
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| Jason |
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Site Admin
Joined: 30 Oct 2006
Posts: 184
Location: North America
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If you keep your car in a garage, it will likely not hurt you.
Something else you can consider is instead of cutting the lines, you can add a valve in the mix so you can prevent coolant when you want to.
Personally, I don't think there's enough condensation and stuff to freeze the throttle body inside manifold, but I've never lived in areas that cold to know first hand. For all I know I'm just talking out my ass here.  So I don't know if this is something manufacturers do just in case, or if it's really common. |
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| david8 |
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Joined: 17 Jul 2008
Posts: 47
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| So if i put a valve on just one side of the throttle body it would be less work than cutting and splicing the two ends back together. Do you think it would cause any problems to have the coolant in the lines not circulating? |
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| Jason |
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Site Admin
Joined: 30 Oct 2006
Posts: 184
Location: North America
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none that i can see. i haven't had coolant going through those items in years now. you could also open it up once in a while if you wanted.
the only question with this route is which way the coolant flows. You might end up needing to block it off on both sides. |
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| david8 |
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Joined: 17 Jul 2008
Posts: 47
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| Right, thanks. Unfortunately I wont be doing this anytime soon i have to wait for winter to end before i can try it out. |
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