I have this system you can mount it in any position it comes with the fittings and a smaller hose to put inside the tank so it can be mounted in just about any position
I used the oil port worked fine my old engine rattled on startup every time on the back passenger side tensioner as soon as the gauge goes up ...2 sec start up with no rattles I have been using this for 4years without any problems
The air in the tank when you first install it is enough air no need to add any more
As far as the sandwich adaptor I bought one it's in the box
Ever seen a sprinkler system turn on
Does the sprinkler closest to the supply of water
Spray first ...no they all equally spray at the same time so when the gauge goes up there is pressure on the whole engine if some oil galleys are empty the air in it will be easily pushed out way be for the oil pressure sending unit can be overcome it's like 5-7 psi I have heard this theory before it's just that half the engine can't have pressure and not the other half the oil will just flow fill up all the galleys then pressurize
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I have 60 psi build in the tank one quart