Oil Filter Bypass Valve -- How Long Before It Opens?

[Xtrema]

Rumor has it that the standard oil filter bypass valve opens due to excessive filter backpressure way before you change your oil. This doesn't make much sense to me. Sure, it is possible, but surely it doesn't happen. Tell me it ain't so!

 

[OperaHouse]

You are right for the wrong reason. It is unusual for filters to go into bypass because the element is clogged. Most filters in a normally running engine can easly go more than 20,000 miles. Here is what you didn't expect. Filters often go into bypass when the engine is started and the oil is too thick to go through the filter media at the flow rate. If these things keep you up at night, buy a filter with the bypass valve at the top of the filter.

 

[Xtrema]

Well, that makes some sense, as the oil will be thicker at startup. Any idea which filters are bypassed at the top? The Motorcraft seems to have a spring valve at the top, but I always thought that was the anti-drainback valve.

 

[widman]

The anti-drainback valve is the rubber seal just inside the 5 to 8 small holes in the base. The Relief valve is what you normally see at the end of the long tube. certain filters combine both at the base (Fram-which is no good for other reasons, and Luberfiner are two I know of with the combo valves.) If you are using oil that is too thick for your climate, you ideally do not want this valve at the lowest position. The combo valves are excellent for horrizontal, diagonal, or hanging filters. But those mounted vertically with the base down would be better off with the top valve. Some filters do not have the bypass/relief valves at all, either because they were designed for engines with the valves built into the baseplate by the manufacturer o they are bypass filters that filter down to smaller partical sizes knowing that they are only carrying small percentage of the total oil and when they clog the oil just stays in the normal flow pattern.

 

[Xtrema]

Thank you. I'll check for non-combination valve on my Mobil 1 filter and my K&N filter. My filter is mounted vertically with the cup up, threads at top.