Some of you guys are wondering about the pressure building up in the fluid chamber of the M90.
Have to take into account there are some changes done to the M90 over the years. All 1997-2003 are not the same, ya we know about the external extra vacuum "tree" on the outside of the 1997's, but there were some internal changes many may not know of.
Lets start with the breather nut.
If you have the breather nut, it must always stay on your snout. The snout shaft is one thing that has changed inside these M90's over the years. If there is a breather nut, then you have a vented snout shaft. Where there is a hole drilled on the y axis of the shaft. The x axis is drilled clear though the center, up to the y axis hole. This vents pressure out of the oil chamber, and the breather nut contains the fluid filled vapor and only releases vapor.
If you open your snout fill/drain plug on a non vented snout shaft, you can get a little "pufft" of air/pressure coming out of the fluid chamber. Thats normal. The blower could be removed, off the car for weeks, and still get this effect cold or hot. It does not mean your seals on the rotor shafts, behind the drive gears are bad, leaking boost into the oil chamber.
You can also get the "pufft" sound of pressure being released on a vented snout shaft style M90. This can mean that the vent hole in the shaft is clogged, or the breather nut is damaged, or clogged. Either way...normal, not a big deal if it does happen.
Vendors selling M.P.S. and include the little black Christmas tree plug should note when they do sell these, they are only to be used on a M90 with a non vented snout shaft.
How can you tell which snout shaft you have?
If you have a breather on your snout now, then keep on using it. You have a vented snout shaft. If you have a plastic Christmas tree looking plug, keep on using that, you can run a snout breather if you want, but wont do you any good. Running the plastic Christmas plug on a vented snout shaft can cause fluid vapors to leak out, and get flung by the spinning shaft.
If your car does not have a plug at all, run what you want, or remove the snout shaft from the snout and see if you have the holes drilled from the side, meaning you have a vented snout shaft.
Why did Eaton change this?
Good question Jason, why thank you Jason. Probably there was no gains or problems having a vented style vs. a non vented style. You can also figure the price difference between the two types was a big one, considering there is another hole to drill on the vented style, plus it needs a special nut vs. no extra hole, and a plastic plug.
In this picture you can see the changes. Top shaft is a NON vented snout shaft, bottom shaft IS a VENTED snout shaft. Note the hole circled in red, there is your vent to the out side.
If you have bad seals behind your rotor drive gears you can tell by a few ways. Not in boost loss, but in fluid loss. If your low on fluid, and the pulley of the supercharger is clean and dry,(meaning the snout seal is not bad) and the under side of the supercharger is clean and dry, (meaning the seal between the snout and rotor assembly is good) then its inside where the fluid is leaking.
It can, and will go out of the seals that are located behind the drive gears of the rotor assembly and on into the LIM and used inside the engine. If the fluid is continued to be ran like this, low, and for quite some time, it will go well past the stage of coming out looking like nasty tea, or bad coffee colored as many of us have seen, and will end up looking like this:
Running the fluid low, will cause bearing failure, and seals to burn up.
Hope this information clears some things up, and answers a few questions along the way.
~F~