FL5 Throttle Body Coolant Bypass

[blueroadster]

I never really understood the need to pump coolant through the throttle body so it is time to eliminate it. Here is the parts diagram for the FL5 (throttle body coolant hoses are parts 1, 2, and 3):

Parts 1 and 2 in the above diagram connect to the throttle body barbs (E-15-12):

The hard pipe (To E-8-2 in the first diagram) has an 8mm OD for the coolant hose connections:

8mm = 0.315" so 5/16" or 3.125" ID end plugs can be used to cap off the coolant hose connections on the thermostat case (i.e., where parts 1 and 3 connect in the first diagram). End plugs can also be added to the throttle body barbs to cap them off.

 

[blueroadster]

The other barb connections on the hard pipe (To E-8-2 in the first post, first diagram) are for the breather tube in this diagram:

The hard pipe can be removed if you are using an aftermarket catch can connecting between the valve cover and intake pipe connection. If your car is tuned to run off of the MAP sensor only, then you can plug the connection in the inlet pipe and put a breather filter on the valve cover to vent to atmosphere instead of recycling.

 

[HKSpeed]

I used 5/16 caps my FL2. I capped off the lines at the water pump/thermostat housing.

 

[blueroadster]

Thanks and cool...Would you happen to know the routing and purpose for this hose on the FL2?

 

[J_D]

1. It is highly unlikely there are any performance benefits from doing this. Heat soak from he throttle into the charge air is negligible
2. If you live anywhere near freezing temperatures do not even consider this. The throttle body is heated to prevent icing over during cold weather.

 

[blueroadster]

1. It is highly unlikely there are any performance benefits from doing this. Heat soak from he throttle into the charge air is negligible
2. If you live anywhere near freezing temperatures do not even consider this. The throttle body is heated to prevent icing over during cold weather.

Thanks for the reply and I would like to better understand your point. If I cold start my car in freezing temperatures, the coolant is as cold as everything else during initial startup. As the engine warms, there is no need for hot coolant to be constantly pumped through the throttle body itself.

 

[J_D]

No worries! From my understanding moisture in the air can crystallize if it encounters a cold surface. Ever parked a cold car in a humid garage ?

It can build up slowly until it becomes a problem

 

[NSXavier]

I never really understood the need to pump coolant through the throttle body so it is time to eliminate it.

as another has already mentioned, it’s to prevent the throttle blade from icing over and becoming mechanically stuck. Before there was the ETCS, cable driven throttles used idle air control valves to manage air post throttle plate. These IAC valves also had coolant running through it to prevent icing of the valve, and to warm the throttle body to prevent icing. Running without to coolant lines in the throttle body is fine if you’re in a climate that rarely sees freezing temps.

Back when I had my NSX, I converted the throttle body to a cable driven from an ETCS and decided to omit the the water lines running to it because I didn’t feel like doing the plumbing. Long story short, cold morning, after about 20 minutes of driving my idle speed was at 2k rpm. Had to use a heat gun on the throttle body to get it back down.

I don’t see too many performance benefits with the mod; would be nice to use logR to compare air temps before and after the mod…

 

[HKSpeed]

Thanks and cool...Would you happen to know the routing and purpose for this hose on the FL2?

That hose and its plumbing is stock. I did not modify it. It connects the upper and lower sections of the thermostat/water pump housing. I wonder if those connections are used on turbo engines.

I got the idea after reading this thread. I live in Southern California. I don't ever worry about freezing temperatures. ? I bought these caps and clamps.

 

[blueroadster]

as another has already mentioned, it’s to prevent the throttle blade from icing over and becoming mechanically stuck. Before there was the ETCS, cable driven throttles used idle air control valves to manage air post throttle plate. These IAC valves also had coolant running through it to prevent icing of the valve, and to warm the throttle body to prevent icing. Running without to coolant lines in the throttle body is fine if you’re in a climate that rarely sees freezing temps.

Back when I had my NSX, I converted the throttle body to a cable driven from an ETCS and decided to omit the the water lines running to it because I didn’t feel like doing the plumbing. Long story short, cold morning, after about 20 minutes of driving my idle speed was at 2k rpm. Had to use a heat gun on the throttle body to get it back down.

I don’t see too many performance benefits with the mod; would be nice to use logR to compare air temps before and after the mod…

Thanks and makes sense. I am going to bypass the throttle body coolant line as I don't drive the FL5 in the Winter when temps dip below freezing.

In my situation, there is really no need to heat up the throttle body to the temperature of the coolant itself. I think that is actually counterproductive when dealing with Summer heat. Granted thermal transfer from the throttle body should be minimal, but in an idle situation with low airflow it does not seem to be beneficial to have a hot ass throttle body affecting IATs.

 

[blueroadster]

That hose and its plumbing is stock. I did not modify it. It connects the upper and lower sections of the thermostat/water pump housing. I wonder if those connections are used on turbo engines.

I got the idea after reading this thread. I live in Southern California. I don't ever worry about freezing temperatures. ? I bought these caps and clamps.

Cool and thanks...I'll have to look at the hose on the FL5 the next time I remove the intake. It does however make since that those barbs may be used for the coolant lines to the turbo.

 

[AZCWTypeR]

My 1st car was an MGB, which didn't have carb or intake manifold heat. The throttles (dual carbs) would often ice open at highway speeds in 35-40F weather. They were cable operated, so flooring and releasing the gas pedal usually cleared the ice.

I doubt the FL5 throttle actuator clears ice as forcefully as a pull cable.

Air going through a restriction (throttle body), cools and moisture precipitates. This is how the ice forms. Ambient air was above freezing in my carb icing experience. I never had icing problems below 30F to well below zero F.

 

[blueroadster]

Will skip modifying. Does not seem worth doing for a street car.

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