There is a check valve to prevent the oil passages from draining when the engine is off. Another valve opens to let oil bypass the filter if it becomes plugged. Dirty oil is better than no oil. Those valves can be inside the oil filter or can be part of the oil pump. Sometimes they make design changes, then find out the results weren't what they wanted, it added too much to the cost of manufacturing the engine, the supplier for that new pump raised the price, went out of business, couldn't keep up production, used inferior materials, or there were any number of other reasons they decided to go back to what worked well in the past. GM had one special oil filter in 1978 that only fit the one engine for that one year, in one model of car. You can't even buy that one from GM anymore. Only Fram still makes it.
There could also have been clearance issues near some body or suspension component. Chrysler came out with a smaller filter with their first front-wheel-drive cars but inside it was exactly the same as their larger filter. You could use either one but the larger one hit against the fuel pump on the front-wheel-drive cars.
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Monday, April 18th, 2011 AT 11:22 PM
