In all auto parts stores and suppliers, replacement bypass valves are sold, mainly for GM. They are very cheap. I never understood what is going on with that. How do you even know the valve is bad? Or is it just people buying valves for maintenance reasons, like changing an air filter every so often? There is a bubble test on here showing a leaking bypass valve clearly. It seems a big unknown here because efficiency would be useless to talk about with leaking filter parts.
In block bypass valves
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Never messed with any GM bypass valves but the ones I have experience with, the pressure relief valve inside the Cummins filter head assembly generally don't fail.
Easy enough to remove & clean out & measure spring stretch specs after a head gasket blows & creates a milkshake though.
Easy enough to remove & clean out & measure spring stretch specs after a head gasket blows & creates a milkshake though.
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Leaks in filter media typically do not leak 100%. Bypass valves do not leak 100%. A few percent here or there is nothing to worry about.
Replace the bypass valve when rebuilding engine. The biggest issue with in block/mount bypass valves is that they sludge/varnish up on poorly maintained engines, which leads to other problems.
You can usually source an oil filter with a bypass valve if you worry about the OE valve failing closed. I don't worry about leaks but do worry that it could also fail fully open.
My favorite is the fools that eliminate the bypass valve, use a non-bypass valve equipped filter, and either balloon the filter or blow it off the engine mount. Good times with fools out there building engines!
Replace the bypass valve when rebuilding engine. The biggest issue with in block/mount bypass valves is that they sludge/varnish up on poorly maintained engines, which leads to other problems.
You can usually source an oil filter with a bypass valve if you worry about the OE valve failing closed. I don't worry about leaks but do worry that it could also fail fully open.
My favorite is the fools that eliminate the bypass valve, use a non-bypass valve equipped filter, and either balloon the filter or blow it off the engine mount. Good times with fools out there building engines!
Maybe it's for people who want to change the bypass pressure 
I don't think bypass failure is common in those cars.
I don't think bypass failure is common in those cars.
That was more my point of posting, how do we even know if they leak, as they are in there forever most of the time. The bubble point test showed a leaking valve on a filter so this is where the question comes from. An AC new one is like $6, but I never even thought about replacing one and I have had GM's with it. Maybe the valve is leaking the whole time, and there goes the "efficiency."Maybe it's for people who want to change the bypass pressure
I don't think bypass failure is common in those cars.
The in-block filter bypass valve on GM engines is pressed in, so not real easy to replace, especially when doing it under the car. Here's how it's done. Greasymechtech will like this after seeing his bypass valve removal comment - lol.
Regualar oil changes to keep the engine guts clean is the best thing to do, as we all know.
Regualar oil changes to keep the engine guts clean is the best thing to do, as we all know.
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