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Old 01-29-2013, 05:08 PM
BogiesAnnex1 BogiesAnnex1 is offline
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Originally Posted by 71nova355 View Post
Hi, Hey I thought the bypass was only meant to happen cold untill the oil was warmmed up so it wouldnt have such a hard time trying to go through the filter? Are you guys talking about somthing else? not starting anything but id like to know.
Two different bypasses in different places for different reasons:

The bypass on the pump establishes maximum operating pressure. The bypass at the filter shunts oil around the filter if the flow through the filter isn't fast enough. In that case there is a back pressure which opens the bypass to allow unfiltered oil to proceed into the engine this does not affect operating pressure unless both the filter media and the relief valve fail.

The pump is really a relief valve, however, the stock designed oil pump rather than venting the excess oil back to the pan circulates (bypasses) it back to the inlet side of the pump. The down side of this is the oil gets hot (although that helps heat the cold oil). The up side is the factory doesn't have to design a system to absorb the energy from the oil to prevent splash when it would have returned to the sump. However, racers that run wet sumps (by rule) close the return route and open a vent to the pan while using a heavy perforated metal screen to absorb the energy from the oil and direct it into the sump without splash nor entraining it into the crankshaft assembly.

The filter bypass is a tougher deal if you need to be sure that only filtered oil flows into the engine. This requires more filter media area which leads to GM heavy duty truck filters that are about twice the length of the standard filter and suck up ground clearance. There are kits to mount these horizontally if the installation has the space. There are remote filters that require external plumbing to and from the engine, these often use two filters usually the large Ford spin on type. There's also a host of specialty screens that are designed to catch the larger chunks of broken parts.

To a large extent both relief/bypass valves are very sensitive to pressure that results from oil viscosity, so when the oil is cold these valves are almost always open. It actually takes some time for engine oil to warm up this is long after the coolant temp says the engine is warm; without some form of heat exchange this in cold weather is easily 3 to 4 times the distance it takes to indicate that the coolant is normalized. So if you rip on the throttle in this period you’re for sure pumping a lot of unfiltered oil into the engine. Many years ago the OEMs started running engine oil through a heat exchanger either within the radiator, as auto trans fluid does, or with an external unit like the Ford's cop cars. The point was severalfold in that this gets the engine fully warmed a lot faster which improves oil filtration, reduces sludge formation, reduces wear of rubbing parts, improves fuel mileage and greatly reduces emissions. It really turns out, that contrary to hot rodders dogma, the bigger problem with engine oil is getting it hot enough rather than needing to cool it. Cooling is a problem for very heavy duty applications and distance racing, for ordinary street functions not so much.


Last edited by BogiesAnnex1; 01-29-2013 at 05:19 PM.
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