Oil Change Alert- Public Service Announcement

From what I read, the bypass valve opens quite often when the oil is cold. Looking at a typical high-end synthetic 0W20 oil datasheet, there is a 5x difference in oil viscosity between 40C and 100C, and around 770x difference between -35C and 100C (100C being the typical operating temp). If the spin-on filter's bypass pressure is higher than OEM, then there's a potential for oil starvation when cold (or even at high rpms when hot). If the filter's bypass pressure is lower than OEM, then the bypass valve will open more often, letting more unfiltered oil through.

 

You fools! I welded my drain plug closed.

 

When the bypass valve opens it is bypassing the filter. It is used to keep oil in the filter during engine shut down so oil is available upon start up. Don’t really know why this is important for spin ones while cartridges don’t have them at all. I believe the bypass opens based on pressure, not temperature or viscosity. I don’t think that would be normal operating procedures but I will look into it further. Thanks!

 

It is normal for the bypass to open when cold. The oil is thicker and pressures are higher. On engines at work on cold start the pressures are in the 70's and drop to the 30's when at operating temperature. The pressure also build when reving the engine so the bypass valve and oil pressure valve will keep those excessive pressures in check.

 

I think we are misinterpreting what the valve is there for.

 

What happens when you try to stuff a higher viscosity fluid through a media filter? Pressure. The higher the viscosity, the higher the pressure as a result of increased resistance. This means the bypass filter opens to control the pressure. This is normal cold operation of a filter bypass valve. Some engines even use the bypass as a way to control volume of oil flow.

 

Maybe some of you can help us answer the following questions. Before we get to them we need to understand the purpose of a filters anti drain back valve. I think they are in the filter to hold oil in the filter during periods when the engine is not operating so oil is available at start-up.

1. Only filters configured vertically, gasket pointed downward, or horizontally mounted filters would benefit from this valve feature.
2. Filters vertically situated with gasket facing upward wouldn’t use this feature.
3. Element filters, not spin on filters, don’t have these valves.

Why does it seem the ant drain valves are only applicable in limited situations?

 

The bypass valve is separate from the anti-drainback valve. The latter is used to keep oil in the filter during engine shutdown. I'm not sure if the OEM filter housing has an anti-drainback valve, because it's at the bottom of the engine. The OEM bypass valve is basically the spring-loaded center tube mount in the filter cartridge cup.

 

Yes, an antidrain back valve, if used, is to prevent the filter from draining after shutdown. The oil in the ports and filter will be drain back as a result of head pressure on the oil above the oil pump.

 

Don't confuse the anti-drainback valve with the bypass valve. On spin-on filters, the anti-drainback valve is the rubber flapper visible through the holes on the filter end. The bypass valve is the spring-loaded end cap on the far end of the filter center tube. The 2GR OEM bypass valve is built into the filter housing cap.

 

Roger that. Thanks