Simon's take on: 'Mess Under the Intake'

[spanish pants]

There´s a little purple question mark on the throttle body diagram. What does this get plugged with?
The throttle body on mine is plugged with a little rubber cap that is currently held together with electrical tape. I´ve looked on real oem for what originally goes there but with no luck.
Anyone know?

[freeride53]

Great thread Simon, I'm about to tackle this over my break in the next few weeks!

[trigtm]

A note on bleeding. I think the main problem is that the reservoir is not thr highest point in the system as with most cars. If you have the car on an incline for final bleeding, it will help alot.

I've been bleeding my car several tiems now and have had an issue to get it to take mroe coolant. Once I completly topped off the reservoir, it seems to be at the right level but the heat is only barely warm so I'm sure I have more bleeding to do.

[TimKninja]

BUMP. This is the most useful thread on the M42 Forum, and Ill b e using it a lot next weekend, thanks Simon!!!!

[Simon S]

Cool.
Thanks.
You're welcome.
Glad to be of help.

[gearheadE30]

Someone asked about the bypass and how it works- it is actually a second thermostat. When the coolant is cold, it allows everything to flow. When it gets hot and the pressure rises, and the solenoid controlling flow into the heater core is shut, this thermostat opens and allows coolant to flow around the heater core, thus bypassing it and reducing pressure on that solenoid, whose manifold is the part that is known to fail. the bypass causes a *slight* decrease in heating capacity but I doubt you'd be able to tell the difference. The coolant will still flow through the path of least resistance, and when the solenoid on the core is open, it's flow volume is an order of magnitude larger than the bypass.

as for the leak to the back of the block, if your bypass from the black plastic tube to the side of the head is leaking, the castings on the block will make the coolant flow to the rear. Mine did this. Also, head gaskets can leak coolant, so I'd check that. There is also a coolant port on the back of the head iirc; it goes to the heater. That said, I might be confusing it with an M20. Also check that your coolant block drain is tight (19mm bolt on the side of the block, under the exhaust manifold).

[Simon S]

Someone asked about the bypass and how it works- it is actually a second thermostat. When the coolant is cold, it allows everything to flow. When it gets hot and the pressure rises, and the solenoid controlling flow into the heater core is shut, this thermostat opens and allows coolant to flow around the heater core, thus bypassing it and reducing pressure on that solenoid, whose manifold is the part that is known to fail. the bypass causes a *slight* decrease in heating capacity but I doubt you'd be able to tell the difference. The coolant will still flow through the path of least resistance, and when the solenoid on the core is open, it's flow volume is an order of magnitude larger than the bypass.

Excellent! Thank you for sharing this knowledge. Greatly appreciated.

[Chuck C]

The only purpose of the bypass valve installed during the coolant system recall campaign is to cut off flow of coolant to the heater core in case of elevated coolant temperature--period. When the coolant reaches a certain temp, the valve closes, and when the coolant temp drops to a certain point, the valve opens (maybe); there is no halfway operation. This recall was designed to shield BMW from lawsuits over ruptured heater cores. If a car has compromised components in the cooling system

[Chuck C]

wouldn't it be better to replace those components instead of putting a Band-Aid on them?

[Roysneon]

So the main point of taking this stuff out and bypassing everything is to reduce failure points? I got my engine from a parts car that ran 'as far as I know'. I'm leaning toward leaving it all alone as long as the hoses look to be in good condition.

Basically, I understand what you're doing, I just need clarification as to why this is such a common procedure.

[roguetoaster]

Yes, this cleans up the under intake area, making it less prone to failures/leaks in future. On my previous 318 I did the conversion, on my current on I left it alone as everything is in good shape.

[AndrewBird]

Most cars also have a lot of cracked/broken hoses after being on the road for so long and it is easier and cheaper to just eliminate them rather then replace them.

[Ryann]

The idea that hardware store doodads and driveway engineering can somehow out-smart the Germans seems hilarious to me. If you'd like to bypass the TB heaters you can do so with the existing factory hoses.

Simply replace what's leaking, leave what's not, and enjoy the factory drivable experience.

[AndrewBird]

You have too much faith in German engineering. There is a reason they are known for over-engineering things and doing things more complicated then needed.

[kimmerkaze]

Just a quick note on cheap aftermarket plastic coolant tubes:

I got one for a wicked deal I couldn't pass up but found the usual fitment issues. The part that goes into the block with the o-ring sits crooked so maybe 1/4 of the tube (front portion relative to engine) is seated at best during initial fitment.

What I did was dremel off some material off the back of the 2 mounts with the brass inserts. I had to dremel off more on the front mounting 'lug' (the circle/1st datum mount) and less on the rearward lug (the slot/2nd datum mount). This makes the tube rotate more CCW (as viewed from top), which will eliminate the 'rearside' gap on the tube inlet to block and make the tube flange sit flush to block.

Haven't had any leak issues whatsoever so if you want to save $ just keep in mind you'll have to invest some time reworking the part.