throttle body coolant chamber

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Robert Bondi
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throttle body coolant chamber

Post by Robert Bondi »

Anybody got opinions on bypassing and how it affects driveability, idle, etc...?

I'm building up a new engine based on the M30B34 block. I just noticed the coolant port isn't available to feed the throttle body w/o drilling and tapping the blind boss. As the 3.5L FAQ confirmed, the two main options are don't plumb the throttle body or tee off the heater hose leaving the cyl head rear.

Searching the archives shows all kinds of different opinions ranging from no difference to heater doesn't work the same to car runs hotter....
Robert
77 530i
77 Euro 528
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John in Simi Valley
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Post by John in Simi Valley »

On my 1980 528i, the water line from the block began to leak. At the time I didn't have another little hose of proper length so I just capped it off at the block. Have not noticed any differences. I suspect being a German design, the heater is more for cold weather function than warm. If I'm correct, it shouldn't be an issue for me, being in California.
You are in New Mexico, high altitude may play a factor especially in your cold winters. Answer from me is I'm not sure with snow on the ground.

However you have another option. Freeze plugs are brass and solder up or braze easily. Port a plug with an inch long brass tube versus drill & tap the cast iron. This freeze plug method is easy if the engine is on a stand. In the car is more difficult.
John Savage
1980 528i 5-Speed
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Mike W.
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Post by Mike W. »

I ran into that some years back when I put a late 3.3 in my E12. I did the drill and tap route, and damn, that cast iron is hard, I had to drill larger than I expected and tested the limit of the tap. But in retrospect, I wouldn't bother. The casting in the throttle body is fragile enough I've heard of guys having it rot out and just bypassing it, without issues. And B34s in E28s ran just fine with out it.

FWIW, it's a bolt thread, not a pipe thread, it uses the gasket to seal not the threads.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
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Robert Bondi
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Location: Austin, TX

Post by Robert Bondi »

Thanks, guys.

Given my new engine is all nice and almost ready to go, I'm not going
to do any drilling or tapping in the block. I'm either going to skip plumbing
the TB or tee off that heater hose leaving the cylinder head. At least the tee off option is reversible with multiple hoses available. It looks like a 3/4" barb
on the straight-through for the heater and a 5/16" diameter barb for the TB would work pretty well.
Robert
77 530i
77 Euro 528
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