Filter bypass valve

[ProfPS]

Do filter bypass valves open when you start a cold engine? Not necessarily a winter start, but when started in the morning when the oil is at its thickest for the day. If so, since bypass' are set by psi and thicker oil increases psi, would a cold 5W-20 not open the bypass where a 5W-30 would at the same temperature?

 

[StevieC]

Usually no... Unless there is too much pressure from trying to send the oil through the media in the filter. a 20wt would not open the bypass as quickly as a 30wt at the same frigid temperature. The bypass is also there in the event the media plugged, so as to prevent oil starvation.

 

[Gary Allan]

Whenever your oil pump is in relief you're at some elevated PSID. It may or may not be at the bypass valve threshold. If the pump relief is not engaged, there is virtually no PSID across the media at cold start. While not indifferent to viscosity, the variance is compressed into a very small range. Like 2psid or less. All media is highly resistive to flow. It is only the back pressure of the rest of the engine that makes it a low differential. Loading will alter this view as the filter ages. Whatever impact the relief event produces, loading will make it more pronounced. Load will also allow PSID to linger beyond the end of the relief event. It will diminish as the viscosity decreases.

 

[sdan27]

How close is the relief valve on the engine set to as compared to the relief valve in the filter? I mean, it's probably not a set in stone value but how close are they generally?

 

[ProfPS]

Since the prevailing belief on BITOG is more filter material pleats is better, won't a filter with "the most" pleats increase psi until resistance is reduced as the oil heats and have a higher operating psi at the filter intake than one with less pleats?

 

[Gary Allan]

 Originally Posted By: sdan27

How close is the relief valve on the engine set to as compared to the relief valve in the filter? I mean, it's probably not a set in stone value but how close are they generally?

Typically they have no reason between them. Some Asian engines appear to require very specific bypass valve settings ..and most Euro's require very high bypass valve settings. ..but most bypass valve settings are set by the filter manufacturer and are somewhat generic. Wix is 8-11 normally ..as Purolator is something like 12-16. Pump relief settings can be anything. If you have a gauge, it's whatever it will usually hit on the first start of the day ..even if it's warm out. Whether you actually "relieve" any flow will depend on the volume and speed of the pump, and the viscosity of the oil (its temp).

 

[Gary Allan]

 Originally Posted By: ProfPS

Since the prevailing belief on BITOG is more filter material pleats is better, won't a filter with "the most" pleats increase psi until resistance is reduced as the oil heats and have a higher operating psi at the filter intake than one with less pleats?

I think that that prevailing belief is due to (probably) more square inches of media being compressed into a given area with more convolutions. They would be right. ..but I see no reason to equate any of that to any pressure component of merit. It's typically the pump relief event that creates the most frequent PSID situations. It's the inability to push X volume of Y viscosity oil through T engine. That divergence of flow produces the pressure differential. Pressure produced by the reduced flow through the engine ..and the maximum (or even exceeded due to too small a relief port for volume shunted) pressure applied. I would say that if the pleats do add up to more square inches of media ..and ..when compared to the identical media of the same density (call it whatever you want to mean resistance to flow) ..that the higher pleat count would probably produce less PSID than one with few pleats. Just keep in mind that any media doesn't want to naturally pass oil too easily.

 

[SuperBusa]

 Originally Posted By: ProfPS

Do filter bypass valves open when you start a cold engine? Not necessarily a winter start, but when started in the morning when the oil is at its thickest for the day. If so, since bypass' are set by psi and thicker oil increases psi, would a cold 5W-20 not open the bypass where a 5W-30 would at the same temperature?

It all depends on: 1) The oil viscosity. 2) The oil pump flow rate at start-up. 3) If the driver revs the engine up while the oil is cold. 4) The flow resistance of the filter's media, and how dirty/loaded it is. The oil pump does not necessary need to be in relief mode in order to produce a large enough delta P across the filter media to cause the bypass valve to open. For instance, if the filter was loaded up and had lots of restriction, the the bypass would open with hardly any pump flow through it, and the pump not in relief mode. If conditions in 1) through 4) above add up in the right direction, the filter's bypass valve could open way before pump relief mode is achieved.

 

[SuperBusa]

Forgot one for the "depends on" list: 5) What the filter's bypass valve is actually set to and starts to open at (psi).