Oil filter bypass

[westex39]

I've been wondering about this for sometime. Why is there such a concern about a oil filter going into bypass on a cold start up? Seems to me that this may not be a problem since all the oil that had gone through the filter the last time the car was driven would have been filtered. How dirty could the oil get just sitting in the oil pan until the next time the engine is started? If the oil bypasses until the oil gets warm what could this hurt since the oil was as clean as the filter could get it during the last engine use? doesn't seem that there could be that much contaminate build up during that short time until the oil filter began filtering all the oil again.
Can someone enlighten me further?

Thanks

 

[Pablo]

Maybe I ain't thinking about this right

(still early on the left coast!)- But when your bypass "valve" opens the previously collected crud (pcc?) on the dirty side of the oil filter can be swept into the oil stream....

 

[westex39]

Pablo,

I did think of that. However, In my case (GM 5.3L engine) the bypass valve is built into the block. According to a schematic I found somewhere, If the bypass opens the oil goes directly to the engine. It does not go through the filter at all. Some engines donot have this type setup with the built in bypass valve. This would cause the oil to go through the filter. I have found that some filters have the bypass valve in the top and some have it in the bottom. I would think that the one in the top would be the best setup by not allowing the oil to go past the dirty filter element to get to the bottom mounted bypass valve.

Regards,

westex