OK. Dunce's hat on. Thanks Mark!
OK, so returning to 'Stuff you may or may not want to know about your lubrication system' let's have a look at the Lubrication
First up though let's just clear something up. THERE IS NO SUCH THING AS 'SUCK'
. OK, having got that out of the way we'll move on and I will use the term freely while explaining what is going on in the lubrication circuit but in fact all that is happening when the pump is working is creating a low pressure area and crankcase pressure is forcing the oil into the pump but using the term 'Suck' is easier.
Allright, having got that out of the way let's look at the sump spacer.
In this first picture you can see the orifice into which the pick up strainer is inserted and bolted to the spacer flange.[You must be registered and logged in to see this image.]
Oil is 'Sucked' up through this by the pump and gets there through this orifice in the top of the spacer.[You must be registered and logged in to see this image.]
The reason why this gallery is larger than the others is simple. As noted above the only thing pushing the oil into the pump is the comparatively feeble crankcase pressure. Once it has passed through the pump it is actually being mechanically forced so it will flow easily through a more restrictive gallery.
Once the oil has passed through the pump it descends again, under pressure, through the middle of the three holes at the front of the spacer.[You must be registered and logged in to see this image.]
From here It passes along a gallery that contains the oil pressure relief valve which lives under the big, hexagonal, domed nut visible here.[You must be registered and logged in to see this image.]
The lubrication system is basically a series of tubes, (The bearings.) with leaky plugs in, (The shaft journals that run in them.). The purpose of the oil pressure relief valve is to ensure that the oil pressure does not get too high as this is both wasteful of energy and can be dangerous to the integrity of the bearings. When the oil is cold and thick this can be particularly problematic so the relief valve has a set 'Crack Pressure' when it will open and dump excess oil and pressure back into the sump via a hole in the casting. It's a simple spring loaded plunger that is unseated and lifts, exposing the gallery, when the pressure gets too high. It's virtually foolproof.
Once the now pressure regulated oil is past the OPRV it passes on to the oil filter. It enters the outer part of the filter from this gallery.[You must be registered and logged in to see this image.]
And then exits through the threaded hole the filter has that screws onto the central boss.[You must be registered and logged in to see this image.]
Now from there there are a couple of ways that things can happen but since we are talking STELVIO
we are talking 8V motor which is substantially different to the 2VPC motor that preceeded it. This is because on those motors there was only ONE oil pump and the oil temperature was governed by a thermostat that lived under this plug in the spacer.[You must be registered and logged in to see this image.]
From there the oil was either sent through the cooler via the exit and return ports in the front of the spacer[You must be registered and logged in to see this image.][You must be registered and logged in to see this image.]
if the oil was hot enough or simply directed to the delivery side.
On the 8V there is no thermostat and the oil cooler is on a different circuit. Those ports are simply blocked off and all
the lubricating oil is delivered to the bearings, (And under piston sprays, they too are fed off the high pressure lubrication circuit.) either directly up into a gallery in the block from the third orifice.[You must be registered and logged in to see this image.]
Or, at the rear of the motor, through the brass coloured pipe that runs from front to rear on the spacer.[You must be registered and logged in to see this image.]
Allof the galleries in the spacer have to be drilled and then their outer, non functional ends, plugged with welch plugs. As you can see the spacer is festooned with them. It's quite a complex piece of manufacturing.[You must be registered and logged in to see this image.][You must be registered and logged in to see this image.][You must be registered and logged in to see this image.][You must be registered and logged in to see this image.]
Anyway, now you've seen how it all works I hope it's easier to see why, when that wretched gasket splits and gets squeezed out the gap it leaves on the 'Suction' side of the pump will allow air to rush in which it is far more willing to do than oil. When that happens delivery is compromised and the situation gets worse the hotter she engine gets and the thinner the oil becomes. Eventually not enough gets delivered to fill the reservoirs for the cam chain tensioner plungers and they can't work so you get rattles. By then things are pretty dire and the cam bearings which are fed from the same circuit, (The oil for the cam boxes travels up two of the cylinder studs.) are probably only getting very marginal lubrication. Luckily the cams only run at half crank speed but even so........
Quite simply, if you have any doubts? Replace the spacer gasket with one of the good ones. It may save you a whole heap of heartache!
Here endeth the lesson.