doing the 'throttle body coolant bypass' thing


Staff member
Blingnoring said:
I was thinking about doing the ' throttle body coolant bypass' thing its not that expensive. does it make a difference where its worth doing?
most t-stats work by by having a thermo reactive wax that starts to expand at a set temperature , then over about 10F-20F it continues to expand,and allow heated coolant to flow to the radiator, thus the t-stat will remain closed until its rated temperature range is reached and it will open wider up to its fully open position over about a 2-5 minute time frame



Here, the dyno shows a 6.3 horsepower and 7.1 ft/lbs torque difference between having coolant run through the throttle body and bypassing it, with an average gain of 5.6 horsepower and 6.8 ft/lbs torque. I made the first test after driving the car for approximately 15 minutes. I monitored Coolant Temp and Intake Air Temp while making the run. At the beginning of the baseline run, the coolant was at 178F, intake air was at 80F, and the throttle body itself had a surface temperature of 102F. After bypassing, I again brought the car to temperature and repeated the test. This time, the coolant was at 180F, intake air was 80F and the throttle body was at 82F. To make sure the runs were accurate, I set the cruise on the dyno to 70mph in 6th and let the car run for about 6 minutes. After this time, the throttle body had reached 100F. I let the car cool to 185F coolant temp, and 88F intake air temp. Running the car again with these elevated heat readings yielded another .2 horsepower and -.2 ft/lbs torque compared to before heat soaking the engine. Check out the Dynojet Race Routine between the stock vehicle, the stock throttle body coolant routing and bypassing the throttle body coolant.


This procedure is considered a "free modification."
After doing this myself on my engine (88' 350 TPI) I noticed a difference in the throttle response right away, as far as horsepower, well I've heard you may get 5 additional HP out of this.

From what I have read GM incorporated this into the throttle body to prevent any kind of freezing of the TB valve in extreme cold conditions by having water from the cooling system run through it.

This heats up the throttle body quite a bit (just try touching the "Tuned Port Injection" plate after a long drive) and from what I understand there is a possibility that the incoming air may be warmed slightly.

You want the air going into your intake system as cool as possible I've heard, cooler air has more density, that's all I know.

There are two ways to do this, both have the same results, I will cover both in this article and you can decide which is to your liking.

NOTE: If you live in an area where extreme cold conditions exist I would not recommend this procedure.


The above diagram shows the "quick" method using a hard tube (approx. 5\8") to connect the existing hoses using clamps.

This takes little time to do, however if you are a stickler for details as I am this looks like a quicky job. ... index.html

I simply got a new piece of 5/8" hose with a built in (90 degree) elbow, and ran it from the black plastic heater control valve/diverter and down to the intake manifold outlet this took about 10" of hose to do and looks much better!
NOTE: Place the elbow end of the new hose at the intake outlet.

Now after you have everything back togther take you car out for nice long drive and when you get back, open the hood and feel the TB, it's cool to the touch!


always measure carefully before you buy parts to be certain but you generally need a double 5/8" hose barb ... 178-xx.htm
You can leave the water outlets on the TB open if you wish, or do what I did!

I got some new 5/8" hose and from the left side TB water outlet ran the hose over past the battery through the fender and down under the battery tray , attached a small pickup funnel to the end of the hose and mounted it to the fender support bracket facing forward for maximum air pick up.

Then another piece of 5\8" hose from the right side TB water outlet ran next to the upper radiator hose, down next to the radiator and under the car, pointing rearward.

What this does basically is "air cools" the TB housing while your driving, I don't have the air volume specs if there is any to take in the first place, it's just an idea I had and I decided to try it.



keep in mind with some aftermarket efi intakes the throttle body coolant component of the IAC throttle body housing must be removed to allow the t-stat housing to fit

there are some mods that bring noticeable results , and don,t take a great deal of work, btw if you have a 1985-86 corvette swapping to a CRANE cam #114132 and doing a throttle body by-pass with a good tune-up especially if you swap to a 3.54:1 or 3.73:1 rear gear really wakes up an early TPI corvette, that crane cams a very good match to the stock TPI power band, and an easy and fairly cheap 35-40 hp upgrade

Here, the dyno shows a 6.3 horsepower and 7.1 ft/lbs torque difference between having coolant run through the throttle body and bypassing it, with an average gain of 5.6 horsepower and 6.8 ft/lbs torque.

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solid fixture here in the forum
i did the coolant bypass on my lt1, however it was in combination with cutting my air lid, k&n filter, 1000cfm maf housing and an airfoil. all in all the car seemed to get quicker, so theres power to be had from freeing up even the later redesigned intake structure.


Well-Known Member
I recently did the throttle bypass thing and used a molded hose with a 90 deg. bend already in it. Trimmed it to fit, very clean and easy way to do it. I got it from AutoZone and the part number is E80402.


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solid fixture here in the forum
i just moved the hose that fed he throttle body to where the other hose runs under the injector cover on the pass side, didnt need any extra hoses or anything, just used a fresh worm clamp