Oil Flow Diagram
 

I'm looking to understand the oil flow in my 1996 M44. Is there a diagram available anywhere? I've searched and not found one.

Long story, I'm in the middle of changing my oil filter housing gasket and I broke off the bottom, front bolt. Two bolts evidently had corroded and were thin in the center. I failed to inspect them and one broke upon reassembly. I know this now from inspecting the remaining bolts. There is maybe 1mm protruding from the block, not enough to grab and drilling this out will be very difficult. I'm not sure I can get a drill down there.

However, this corner of the housing is very clean, no dark oil staining like other parts. It seems that very little oil gets to the bottom, front corner and I'm contemplating heresy - putting it back together with only the 5 remaining bolts. If my suspicions are correct, there should be very little to no leaking there. However, I'm not really sure where the oil is pumped to and from here.

Can anyone provide a diagram or some insight? Is oil pumped into the center of the filter or to the outside of the filter?

I believe the oil flowing into that filter housing is straight from the oil pump but I could be wrong since I didn't pay attention to the oil pump location when I had my pan off. Maybe someone else can chime in with exactly where the oil comes from that goes in the filter housing. I'm not sure if it runs through the crank first??? Don't know for sure...

John S

I believe that you are right.

I've attached 2 images, one of he block (with the offending broken bolt) and one of the housing.

I believe the oil comes from the pump out of the upper of the two small rectangular openings in the block. That aligns with a passage that leads to the outside of the filter. Oil flows through the filter and out the center, through the "bush" in the round opening. The oil pressure sensor is connected to the center passage, just before the bush.

There are spring loaded valves at the base of the housing where the passage from the pump comes up and in the bush that would only allow flow in that direction. There's also a spring loaded bypass valve in the bottom of the filter housing straight to the pressure sensor that would allow oil flow if the filter is clogged.

So, there should be little to no pressure or oil in the C shaped, larger part of where the housing meets the block. As you can see, there is very little oil indicated at the bottom of it (where my broken bolt is). The only access to this area is from the center of the filter, but the o-rings in the stem of the cap normally seal this off. I suspect the oil that has made it in there is from drips during 20 years and 240K of oil changes.

My plan is to put it back together with 5 bolts and hope for the best. It really can't leak much worse than the 300 miles per quart it was getting past the rock hard o-rings in the bush.

Have you tried knocking it round with a screw drive or cold chisel? Looking at it its worth a go just becareful not to damage the face if you do I'm sure a bit of rtv will seal it.

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I was actually able to cut a slot into the exposed part of the screw with a Dremel and a small cut off wheel and then back it out with a screw driver. I covered all the exposed oil passages with duct tape to keep debris out first.

The housing is back on, but I'm going to wait to put everything else back together until I change the motor mounts this weekend.

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Excellent choice to remove that bolt and do the job right. If you start taking short cuts they will bite you in the ass down the road.

Best, John S

Agreed, but I think if I had ended up backed into a corner, this would have been OK with just the 5 bolts.

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