View Full Version : Oil filter bypass

02-11-2011, 06:14:05 PM
This may seem like a stupid question to some of you, but what exactly is an oil filter bypass? What is the purpose of it ? And should it be removed for street use? Thanks.

02-11-2011, 06:24:40 PM
It sits under the oil filter on stock setups such that if there is too much restriction for the oil to pass through the filter (like at cold temps, or worse case, clogged filter) the bypass opens and the engine can run un filtered oil through it. Pressure is a restriction to flow which is why you see higher cold start oil PSI than what you see when the engine is running warm. Some people argue they'd rather have all of the oil filtered at all times no matter what... that sounds good but if the trade off is very little volume under certain conditions wouldn't you rather have full flow of unfiltered oil than a trickle of clean oil? I personally would not remove it on a car that's started in cold winter temps like mine are.... I don't drive old stuff much in the winter but I do start cars to move them around and I noticed something on a 327 that I have been running with no bypass... with fresh 10w30 in it and a good quality filter (AC Delco PF454) I had NO oil coming out of the rockers for the first 5 or so seconds of run time and then it took enough time after that to make me nervous to have any more than a trickle coming out...would a bypass have opened to drop the pressure and increase the volume of oil during that cold start? I have no idea but it might have

Rich Schmidt
02-11-2011, 06:54:43 PM
The adapter that bolts to the block that the oil filter spins onto is the bypass adapter. I dont use one on my high performance car. As bondo has stated it allows unfiltered oil to flow into the engine if the filter has too much restriction. During cold starts that is sually the case. Since cold starts are when the worst of the trash is in the bottom of the pan,it is the time when you need a filter the most. The only thing it really protects from is if the filter is totally clogged. The oil pressure guage fitting is located after the filter,so if you have good pressure there you have good oil flow into the engine. I was only using them with low restriction racing filters. I was pumping so much oil into the engine when it was running at high speeds that the oil pressure would drop when the pan was sucked dry. I now have a regualr delco short filter on my street car and it still makes plenty of oil pressure even cold and the pressure comes right up. I use straight 30W oil,not 20/50 which is better for this type of setup. On my race car the engine block is a 1965 427 casting that uses the old cansiter style filter. I have an adapter that uses a Ford filter and has no bypass. You cant put a bypass on the early blocks. I run a race filter and straight 30W on that too.

02-11-2011, 07:00:50 PM
Ahhh that answers my question, I was actively looking on Summit to see if there was any way to adapt one of the canister-era blocks to have a bypass...since I am running a 1966 327 with a spin on adapter.

Rich Schmidt
02-11-2011, 07:07:23 PM
I have a transdapt adapter,it is faitly cheap. It is a pipe nipple that thread into the block and the filter thread onto it. It has a flat plate with an O ring around the edge of it that seals to the block in the opening in the block. The plate fits semi tight over the threads on the niplle,but is actually pushed firmly in place when the filter is threaded on and the filter O ring presses against it and presses it into the block. As far as I know there are no adapters that allow for a bypass,and the stock canister setup never had a bypass either.

Here is what my big block early filter adapter looks like. I dont have any pics of the other one.

02-11-2011, 07:44:19 PM
OK. That all makes sense to me now. Thanks for answering so quick.

02-11-2011, 08:01:19 PM
I have mine blocked. Like Rick said the pressure reading is from after the filter so you can see what your engine is getting even if all the oil is pushed through the filter. I run the biggest filter I can find (K&N 3002) and pressure/flow hasn't been an issue. I wouldn't block the bypass on a mild street engine, especially not a daily driver that's prone to cold starts and run hard cold. My Camaro gets warmed up before it gets any kind of revs.

02-11-2011, 08:47:28 PM

The Bypass Valve on my K1500 was beat to death. There was no way it could have sealed. The previous owner had the engine rebuilt, but they used the OLD bypass valve, the rods and mains were thrashed by the time I got it. This is similar to mine.

The OEM unit can be modified with a 1/4" pipe plug, to eliminate the wafer/spring/retainer. A low buck way to filter 100% of your oil all the time.
Or you could buy one of these, some units have an O-ring to seal it to the block.

I would not block it if the weather dropped below 40*F on a consistant basis.
I live in Florida and block most of mine off. A low oil pressure warning system is a good idea if you do block it off, to be on the safe side.

Rich Schmidt
02-11-2011, 09:17:18 PM
That last one is the one I have on my 408 small block. With 30W Rotella the oil pressure shoots to 75 psi practically as soon as the starter stops spinning. I drive it to work,and cant let it warm up in my driveway. I drove out the other day when it was 3 degrees out,I was doing 2000 rpm pulling out of my driveway with the 3500 stall convertor. If I was going a lot of miles between oil changes I might worry,I have about 2000 miles on the current oil,and it wont be much longer until I change it. I would change it now,but I just swapped the oil filter 80 miles ago so I figure I will get my monies worth out of it. I had a medium length Moroso race filter,and it hit the header,so I went with a super short Delco. Seems towork fine.

02-11-2011, 09:18:06 PM
The bypass opens when the pressure differential is 5 lbs.

I blocked mine off, use WIX filters and 10W30 oil.