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i have an 89S4. Just changed the J hose on the bottom of the coolant expansion tank. There is a small hose that connects to the expansion tank just below the cap. It’s on the firewall side. What does it connect to? Also, the round item just below the left of the tank above the brake sensor wires has a nipple on the end facing the firewall. What does it connect to.? I traced it and it connects to the oil filler neck and via a Y close goes under the intake. Is this something that’s a part of the air pump system? Should I cap it off?
That hose by the expansion cap is the overflow. It connects to nothing. When the pressure reaches the caps maximum it will release excess fluid and and any air in the system. A good sealing cap is a most important part of a 928's cooling system. Well...for any car for that matter.
The other thing is part of the fuel tank venting system. Not sure how it goes on your model. You should be able to find a vacuum diagram here somewhere.
Yes, it is part of the Fuel tank vent system, only operates under certain conditions controlled by the ECU's on your 89 MY.
The "nipple" facing the Firewall on that vacuum diaphragm requires a constant vacuum source from the intake (non-variable) it is needed to Open the valve inside that modulator (engine running), the larger hose going to the "Y" at the oil-filler neck should go to another plastic modulator first, that is controlled by the ECU's, (has a two pin plug) and sits (or should sit) just below the top Radiator hose on top of the block above the water pump.
When Hot and not under load, the valve is opened and tank fumes are vented into the intake (via that "Y" connection) along w/ Crank case venting.
Thanks. I was looking at Dewayne’s top end refresh and it appears it connects under the intake. PO left a lot of things unconnected. If I can’t get to it as it is now, I’ll have to wait until the winter. I plan to do a top end refresh when the snow falls.
if I’m wrong about where it connects please let me know
If I don’t hook that up right away, are there any issues I’m creating? I drove from Memphis to DC and didn’t notice any loss of performance. It’ll be Jan or so before I do the top end refresh.
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