Quote:
Originally Posted by Army
I'm still unsure whether that will always be the case
My copy of the FSM has been badly scanned - so it is hard to see - but have a look at this diagram which is on page 11
I understand that in the world of the ideal OM617 the oil filter housing is meant to behave as described in the FSM but I was thinking that in the real world it may (just MAY) behave differently.
The oil enters at arrow "a" as shown above - it goes through a "star valve" that's number 16 (you can hardly see that from the crappy scan though).
The star valve acts as a non return valve so the oil filter housing doesn't empty via this route when the oil pump (=> engine) is stopped.
The control valve (12) and the thermostat (11) would normally open to allow flow via "A" round the oil cooler and back to "B" at a temperature of about 95 degrees Celsius and higher.
If "A" is blocked then the oil should in principle flow upwards through the little gap next to the spring for parts 11 and 12 and into the coarse filter part of the of the filter element and back into the engine. If there is enough pressure the oil should also reach the fine filter part of the filter element above. I understand from the FSM that this gap is smaller than the normal route to the filter - the normal route is restricted as the flow is encouraged to flow via the cooler. I'm not sure about how big this gap is though as I haven't been able to get hold of the special tool to remove the thermostat housing to check.
I've been worried that if people just block off the flow at "A" the pressure relief valve could be fooled into thinking that there is a blockage in the filter as the flow is already restricted going into the filter (as described in the FSM and above). On an older car with less than ideal conditions in may (just MAY) cause the pressure relief valve to open and so you then get unfiltered oil flowing back into the engine.
That is why I think it is probably safest to either remove the thermostat if you block off "A" or alternatively just connect the two unions "A" and "B" together with a bit of pipe.
If you join the two unions "A" and "B" you can be assured that the filter housing is working as well as it should be albeit with a really crappy "oil cooler" (<= just a bit of pipe that runs down the side of the filter housing). |
I used the 617.952 manual.
The whole outer portion of the Oil Filter is exposed to the same amount of Oil Pressure.
With the exception that there is a spring loaded Valve at the bottom tube that extends from the Oil Filter Cap; when that spring tension is over come the Fine part of the Oil Filter also has Oil flowing though it but at a low flow rate due to a single less than 1/16" hole at the top of that tube that restricts the flow.
I am guessing that at Idle speeds no Oil is going through the fine bypass section of the Oil filter but have no way to tell if that is true or not.
The Bypass Valve reacts to a difference in pressure between the inside and the outside of the Filter.
Unlike a simple Pressure Relief Valve in normal use the Bypass Valve has Oil Pressure on both sides of the Valve; Oil pressure on the dirty Oil side and the clean Oil side.
The manual has the Bypass Valve opening at 3.5 bar (about 50psi) of differential pressure.
Yet when I put a test Gauge on my Engine and was getting 97 psi after first starting my Oil Filter Bypass Valve was not opening and given me dirty Oil during idle; because it had nearly the same Oil Pressure on both sides of the Valve.
So If you Oil Filter is OK I do not see any reason that a blocked Oil Cooler Outlet port would cause the Oil Filter Bypass Valve to open.