1991 325iC - Throttle Body Coolant Delete

[mikerob97]

Not sure if this is too popular, but while replacing all of the coolant hoses on my newly acquired Cabriolet, I decided to delete the two small coolant lines to the throttle body - did the same mod on my E36 years ago.

There were three areas that modified to delete these lines. First, I drilled out the thermostat housing and taped for 1/4-18 NTP brass plug. Next, I also made a plate for the throttle body to cover the removed coolant line manifold. The last step was to plug the hole with cylinder head with a metric plug available through BMW. It was a few hours of work and removes two coolant lines that run under the intake manifold. I am a big fan of removing unnecessary stuff...

I have included a few pictures.

[hooken m]

i really like the idea of drilling the holes in the plate to cover the exposed area on the TB. i just removed mine and left it as is lol.

[dnguyen1963]

Why do you think BMW designed the coolant lines into the throttle body? You are lucky that you live in a warm climate. Doing that to a cold weather car is asking for a lot of trouble.

[mikerob97]

Not sure why BMW designed the coolant lines to flow adjacent to the throttle body. Do you know? What I can say is that I did the same mod to my 1986 when I lived in CT many years ago, I never noticed any adverse effects.

[dnguyen1963]

In cold climate, under certain conditions, the throttle plate can freeze leading to an unpleasant situation of not being to shut off the gas. That was why the coolant was piped into the throttle body.

[mikerob97]

Makes sense - probably similar to carburetor icing in aircraft - we used to use "Carb Heat" when descending due to pulling the throttle more closed and increasing the venturi effect - (ie pressure drop/decreasing temp) - never thought about it in a car, but I supposed it could happen. Thanks!

[95BMWIC]

Im not sure about the plate freezing..

But I do know the throttle body housing is heated for additional cold running drivability and fuel economy.

The air is warmed entering the engine in cold weather to reduce fuel condensation and improve mixture formulation.

All motronic models use this process and of course the coolant temp sensor to monitor engine temp to help ensure smooth running during engine warmup (This is done by adjusting the injector opening time).