Throttle body coolant bypass

KingKong · Dec 13, 2023

blanchard7684 said: ↑

Cool thread. I've often wondered about this very old school system on the Tundra.

Back in the day there was all sorts of thermostatically controlled devices not to mention carburetors sitting on hot cast iron intakes with a little spacer...

However at wot the carburetor system actually cools the incoming charge substantially through several thermodynamic mechanisms. JT effect and heat transfer from phase change in gasoline.

on this system with port fuel injection, the MAF measures the mass of air incoming and also the intake air temp. Combined with throttle position, cam position, crank position, and rpm, the ECU calculates the timing, phasor position, injector pulse width, and in general transmission shifting strategy.

So counterintuitively they routed engine coolant to the throttle body.

At wot throttle this system may not be adding as much heat as you'd think.

The throttle blade is basically parallel with throttle body. Air flowing over this is removing heat from the blade (at least until the two are the same temperature). There isn't much surface area for convection. Many other throttle body systems don't have this feature of a coolant passage. The throttle body temp rises and falls with engine temp.

So accounting for the heat transfer, there is heat transfer from the aluminum housing to the atmosphere. And then there is heat transfer to the internal air flow going through the aluminum housing/casing.

Looking at the inlet and outlet of the coolant flow it appears to be a very small area that gets the coolant flow.

So it doesn't look to me like there would be a huge convective heat transfer into the air flow.

It must be for something else...

Looking at other throttle bodies they don't have an electrical heater nor do they have engine coolant passages. But they do seem to have the throttle body machined differently and also positioned differently. Most non toyota throttle bodies seem to be thicker in many areas.

The Tundra and other toyota throttle bodies look to have a very small air gap when closed. No matter if the blade is brass or aluminum.

And the coolant passages seem to land right at where the air gap is positioned.

I'm thinking this is to maintain some dimensional integrity of the housing. For part load conditions under closed loop, this will ensure the throttle body will have a steady "orifice size" which then allows for less variation in air flow.

With engine at cold conditions or at wot the engine control regime is open loop and running off feed forward program based on maf flow and tps.
Click to expand...

I think you nailed it.

Jowett · Dec 15, 2023

reywcms · Dec 15, 2023

I can confirm cooler coolant temps by doing this I’ve mentioned this before

Jowett · Dec 19, 2023

In-line throttle body thermostat from a Lexus NX 200T. This shuts down coolant flow at 83C/181F. Great for cold climates. Part # 90916-03155

HulkSmurf14 · Dec 19, 2023

Jowett said: ↑

In-line throttle body thermostat from a Lexus NX 200T. This shuts down coolant flow at 83C/181F. Great for cold climates. Part # 90916-03155

Click to expand...

Badass!!

ZPhilip · Dec 19, 2023

Jowett said: ↑

In-line throttle body thermostat from a Lexus NX 200T. This shuts down coolant flow at 83C/181F. Great for cold climates. Part # 90916-03155

Click to expand...

This is interesting. How do we get one to shut down at say 70F?

Jowett · Dec 20, 2023

Something with a lower temperature will likely have to be custom.

Ponderosa_Pine · Dec 20, 2023

I’ve ran my coolant bypass in 0f and the throttle body is still very hot after it’s warmed up. No issues in that temp although I understand the concern of it getting stuck closed or open due to freezing. In a constant state of well below zero it likely makes sense to reattach the hoses for winter or use a sweet inline setup like posted above.

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