Subaru Impreza Tuner

Throttle body coolant bypass

Let's start with some facts:

1. Colder Intake temperatures produce more power
2. Heat soak is a problem for engines that reduce power output
3. Coolant, usually runs about 212F (100C) boiling
4. On modern engines, coolant runs through the throttle body keeping the butterfly valve from freezing during cold weather

The Mod:

This hot rod throttle body coolant bypass modification removes the hot "coolant" lines from the throttle body to keep IAT (intake air temperature) at a minimum. The lines are coupled together (or replaced with a single line) and the throttle body ports are capped off.

If you live in a climate that doesn't see freezing temperatures then you may consider this modification to help reduce IAT and possibly extended the ability to run the engine harder for longer periods of time.

Preliminary measurements saw the bypass coolant line after ignition was 52C (125F and climbing), vs the throttle body staying at ambient temps of ~29C (85F). The throttle body would otherwise be at the same temperature as the coolant lines. Eventually the whole intake system (intake pipe and intake manifold) will increase in temperature.

By removing the initial heating source for the throttle body, upstream and downstream parts should stay cooler for longer , it should provide extended play time before the eventual onset of heat soak.

If you're going to be driving, drive for sport :)

Alternative heat management topics may include: Heat shielding for intakes/exhaust, EGR delete.

Back to Subaru Impreza Tuner