Mr Hammond

Skip to the pictures if you already know what this does and why you want to do it.

First mod I did the day I bought my 1G RDX. This is an easy five-minute mod popular on K-series Honda engines with coolant flowing through the throttle body. I’ve seen discussion here about doing it, but mostly questions on how and never any RDX-specific explanations or pictures.

Why would you do this? As you probably know, this platform suffers from high intake air temps and heat soak. That means less dense air which means less power or even worse, knock, which triggers the knock control, which pulls timing, which means less power. So any way to lower intake temps is a good thing. There are many ways to do this. This happens to be a very cheap, and easy way, and the results reflect the ease and cheapness.

The coolant doesn’t actually cool the throttle body, but heats it up. The idea, in theory, is it keeps the throttle plate from sticking in extremely cold climates. This mod has been done countless times around the country without issues. I live in the mid-Atlantic region of the US. Our winters are pretty mild compared to up north. We see in the single digits rarely, teens and twenties are usually the coldest. Never had an issue.

What you’re actually doing is bypassing the coolant from entering the throttle body. Any part of the intake tract that you can cool down is helpful. Couple this with a thermal intake manifold gasket and you’ll see consistent 10 degree-ish cooler intake temps. It’s not so much that this adds power as it makes it so you’re not losing power, which definitely happens in the summer, especially in boosted engines.

Do this mod when your engine is cold and the coolant system is not as pressurized.

TOOLS NEEDED: Flat screw driver to pop the engine cover off. 90 degree pliers or your preferred pliers to squeeze Honda hose clips. Pliers to help loosen and remove hoses.

PARTS NEEDED: (2) ⅝” vacuum caps to plug the throttle body ports; maybe some coolant if you’re low, but you won’t lose much doing this cold.

First thing you’re going to do is remove the engine cover. Then you’re going to remove #4 in the picture below:



Then you’re going to remove the end of #5 in the picture below from the throttle body and attach it to pipe in the picture above that #4 was connected to. This now loops the coolant as if it was still flowing through the throttle body.



Place the vacuum caps onto the two exposed throttle body coolant tubes. Check your coolant level in the overflow bottle while you’re doing this mod. Add if low. If you do this cold, you’re not really going to lose any coolant. Put the engine cover back on and you’re done.

Here’s what it looks like when you’re done. The removed hose is sitting on my intercooler in the first pic:

josiahmgillespie

Good write up and glad I saw this. I’m in SoCal and the summers here have been killing my car. I’m always trying to find better and better ways too cool my engine and turbo system.

When I did this mod it was much easier for me to remove the intercooler and then move the hoses. Also, I used 3/8 vacuum caps not 5/8. Glad I bought the variety pack. When I disconnected the hoses, I was losing coolant pretty quickly. I used a ziplock bag underneath to catch all the excess that was draining down my engine and onto my garage floor. Put everything back together and all good now.

Ive been doing some soft/offroading and overlanding with my RDX so this is a much needed mod if it will help reduce heat soak for when I’m hitting the trails.