I changed my oil in my 2006 Sonata and used a Bosch OEM filter I bought over
the internet from a Hyundai dealer. It doesn't have the valve in the bottom
of the filter like the Hyundai filter did that I removed. An earlier post
said the valve kept the oil from draining out of the filter and causing loss
of oil to valve train on startup. I'm confused by this explanation since
the filter sits vertically on the engine and there is no way that the oil is
going to drain out of it.
The valve might be a bypass valve if the filter gets clogged, which is
usually what is in some filters.
It lets the oil "above" the filter in the engine passages drain back
into the filter and crankcase. True, the filter likely don't drain, but
it isn't impossible even with a vertical filter. You are familiar with
the principle called siphoning, right?
An anti-drainback valve is an essential part of a filter and I wouldn't
use a filter that lacked one or had an ineffective one (Fram).
Yep, Matt, I thought about the siphoning action but doubt that it would be a
problem. For years, as I said, the valve is a bypass valve, not an
anti-siphon valve. I can see that, in cold weather when the oil is more
viscous, the oil flow to the valve gallery would be reduced allowing the
lifters to not pump up fast enough and cause some clacking. That would be
The fact that the OEM Bosch filter doesn't have the valve (at least in a
visible location) is puzzling. I will be writing to Bosch to let them know
and get their input.
The mystery is solved! The key was 'silicone' valve. In my years working
for packaging companies, we had silicone vacuum or pressure release silicone
valves, which were nothing more than a little silicone flap that covered a
Well, I looked at my spare Bosch filters and, there it was, a silicone
gasket that was just below the holes around the periphery of the filter.
The oil is forced through these holes and, in the process, push the silicone
gasket away from the hole. The oil goes through the filter and out the
center hole back to the engine. When the oil tries to come back through the
filter down the center hole when you shut off the engine, it pushes the
silicone gasket against the holes and prevents reverse flow.
Thanks for pushing me to a solution, Matt. I guess it's never too late to
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