FLYN930

Can anyone explain the function of the vacuum thermo-valve that is installed on top of the oil breather and feeds the vacuum advance mechanism on the distributor?

I am helping a friend tune his '87 930, and this valve does not seem to do anything on his car. It appears to be closed at all times. I would expect to see the valve open while the engine is cold, and after reaching a certain temperature it should close. This would have the effect of advancing the timing to aid cold startup. Is this how it is supposed to function or am I missing something?

Thanks in advance,

Brian

sand_man

BUMP! I'd like to know too - just out of curiosity. I'll be running Electromotive crank fired ignition, so I won't really be using this "valve", I just wonder how it works.

NSXTC

I tested mine...It seems to be closed when cold. I then threw the valve in hot water and blew through it using a hose. Sure enough, it's open when hot.

But can someone explain the logic?

nathanUK '81 930 G50

Guys, does it control the advance when on vacuum or the retard when on boost ? My euro car has two hoses going to the dizzy.

NSXTC

I think I got my vac hose reversed. My has the dizzy with two vac hoses. I think the proper way is for the red hose to go to the advance (bottom of the dizzy diaphram or closest to the engine) and the black to the retard (top of dizzy diaphram or furthest to the rear of the car). Does any one have a pic of their dizzy w/ two hoses?

A930Rocket

Here you go...

NSXTC

Thank you...hmm...that's how I have mine and I thought I had it reversed. So the red line is advance? Which from the dizzy goes to the thermo valve, then from the thermo valve to the TB?

Handy930

The valve controls the retard on the dizzy on cold start up. On cold start the vacuum allows advance only. When the valve opens with the warmed engine the retard side of the vacuum diaphram retards the advance. I think it just eliminates any vacuum effect and the engine timing becomes strictly mechanical.

NSXTC

Thanks Handy,

I think the confusing part for me was where the red line is plugged in from the pic above. This is actually the retard part of the dizzy whereas I thought this was the advance pot. Now this is starting to make sense.

On my CA emissioned 930, the advance (black hose) pot is then connected to an electronic thermo switch (there's actually two located on the left on top of the BPV) then to the TB. So when the engine is warmed, the electronic thermo switch closes preventing advance. Then the thermo valve opens and allows retard?

I've since removed all my emission stuff including decel, AAR, AAV, and Thermo switch. I can just vent the advance pot to atmosphere?