M50 throttle body heating- why is it designed like this???

[genphreak]

Has anyone any experience with the throttle body thermostat? It mounts into the airbox and regulates coolant flow through the Throttle Body housing to allow for the outside air being cold.

I'm talking about this thing: Part #13541730682

It is item 10 in the realoem context diagram (below). Apparently it stops the Throttle Body icing up

I think this is faulty on my M50 as the TB is boiling hot (can't even touch the TB) once th car is at temperature. Locally, temperatures here do not get cold enough for this feature to be needed as we never get anywhere near freezing here unless I got to the mountains.

This thread was helpful: (thanks Ryan and Bill R.)
http://www.bimmernut.com/forum/showt...+%22air+box%22

Occasionally the engine backfires into the intake manifold when starting- especially if the car is started whilst still warm. This usually blows a hose off the intake and pumps grey smoke everywhere under the hood.

Lots of hoses were cracked up originally, so I have been chasing intake leaks as the motor was running very badly when I got the car. There were lots of split-ends and broken connectors like the one that seals the ICV hose to the intake manifold. The TB boot was even split and there was plenty of signs of previous dodgy vacuum fixes (like cable ties over split hoses).

Origianlly I checked fuel pressure, plugs and changed the oil and coolant. There is no coolant in the oil or oil in the radiator, no smoke at any time- even on hard kick down when it is running shittily. The cooling system works as it should and pressurises fine. Now I have changed most of the hoses and connectors, but it still doesn't run right. The motor bogs down under throttle and idles very slowly. It is is often quite rough- especially once it is at temperature.

However, just to keep this home troubleshooter on his toes, occasionally the engine runs really well.

The rough running when warm I think is a hint about the TB. The occasional backfire into the manifold at warm startup (it doesn't at any other time, such as under load) has led me to think I should try bypassing the coolant from the TB altogether. I figure a boiling intake can't help her much.

Searching online for similar troubles others might have had, it became clear that this issue is not common amongst M50 owners. However this strange plumbing is common to M50 powered e36 and e34s.

Anyhow... surely super-heating the TB can be avoided altogether? The reason I ask as opposed to just do, is that realoem shows no thermostat on the airbox on ealry M50s. On these 89-90 model cars the hot coolant is seemingly piped straight form the head to the TB all the time... which seems , but makes me think bypassing coolant from the TB is a bad thing to do- and I'd like to be able to go to the mountains without getting the throttle plate stuck.

Any thoughts would be greatly appreciated before I give this a go... Thanks in advance, Nic

[Paul in NZ]

why cant you just conect the two hoses together with a short peice of copper pipe

[attack eagle]

well it certainly couldn't hurt to try it with the hoses bypassed.

If you found a second unit in a junk yard, you could simply put that one "dead" in to the TB, and pull the current one out so it could not affect air temps while remaining connected.

I know many people with various vehicles that have bypassed TB cooling with no ill effects, even in winter.

[Paul in NZ]

whats this about an e39????

[genphreak]

why cant you just conect the two hoses together with a short peice of copper pipe

Thanks Paul- nice to know your comments.

I'm bypassing it now. Have pulled the ICV and its hoses they look okay though, but am checking everything else I can get to also.

I wonder if it could have a broken valve or something more sinister. I think the backfire only happens when the engine is started warm (not cold, not hot) but I can't be 100%.

I am having trouble believing the thermostat could be the problem as the TB must remain hot on the earlier cars- ie the ones that don't have the TB thermostat in the air cleaner.

Thanks for your comments too Adrian, if people do this where you are it should be fine in balmy Oz...

I'll let y'all know how it goes!

[genphreak]

whats this about an e39????

No idea Paul- I'm talking about a '90 e34...

Just buttoned her up. She idles fine, just went for a drive. She wasn't perfect, but was not running like a dog. Have to do 50km now, will get that done and then let you know how it pans out.

Wish me luck... now I know why these cars beat so many people! Monkey arms, cut hands- it is a pig working on the plumbing under that manifold. Still- at least it isn't an M60 or an M70!!


Nick

[Paul in NZ]

in your sig you say
WTB: e39 engine wiring, Airbag steering column, Manual conversion