All PD oil pumps have a pressure relief on them. If not, they could literally destroy themselves or something in the oiling system for over pressure.
How often are filters in bypass mode?
- Thread starter ZZman
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It would depend on the flow rate through the filter at those oil temps/viscosity. Rev the engine high enough even with 0W-xx and the filter dP could hit bypass valve level. Oils with higher than 0W at the same temps would be more likely to open the filter's bypass valve. Best way to prevent filter bypassing when the engine is cold is to simply keep the revs down until the oil warms up.
Not sure what you're saying. With a PD oil pump, it puts out the same volume of flow vs RPM (if not in relief) regardless if the oiling system galleries are empty or completely full. The oil pressure doesn't come up until enough flow is sent into the oiling system to register oil pressure at the oil pressure sensor. Even in a totally empty new oil filter after an oil change, the flow from the pump at start-up is whatever the flow rate is at that start-up RPM, and that flow rate goes through the filter, same as it would be if the filter and galleries were completely full of oil. Nothing changes the flow vs RPM rate of the pump output except the pump itself relieving flow and pressure at the pump.
It would depend on the pump's pressure relief setting and how well it controls flow at high output pressure, combined with the filter's dP vs flow performance and the filter's bypass setting. Lots of combined factors. A filter could very well hit bypass dP before the oil pump cuts back output flow enough to keep the filter out of bypass. Just like Jim Allen's on the road testing showed, if you rev the engine high enough with cold oil, the filter dP would hit bypass dP and higher.
Yes, the other thing is the stock oil pressure sensor is mounted at the rear of the block at the top, mounted into the valley cover. Here is a diagram of the flow map. A clogged filter will cause a pressure drop at the sensor, before the bypass opens.
This is the kind of stuff some guys on GMs see when they end up removing/blocking the filter bypass valve that's located in the engine, then run thick oil and go race the car, lol. The filter bypass valve is mainly to protect the filter from damage due to high dP across the media and center tube, along with keeping adequate oil flow to the engine, and it also helps keep the pump from cutting back flow volume as quickly.Depends on the climate of course but anywhere other than hot, then bypass mode every cold start regardless of oil grade.
When you have a very high flow pump, even the bypass sometimes doesn't flow enough to prevent a crushed filter. It illustrates that a bypass is necessary even if a crushed filter is a very rare occurrence.
Oil filters typically have a pretty small diameter bypass valve opening, and are really meant to just bypass a small portion of the flow going through the filter. They aren't meant to take the majority of the flow, so on filters that are all sludged up and highly clogged, the filter can also be damaged if the bypass valve is relatively small. A super clogged filter with a small bypass valve opening could also put the pump in relief, or farther into relief which would cut oil flow to the engine.
1) Don't let the filter get too clogged, and 2) Keep the engine revs down until the oil warms up.
You mean the oil pump bypass (ie, pressure relief valve)? If the pump wasn't in pressure relief, you wouldn't see the oil pressure change if the filter was more restrictive when the OP sensor is after the oil filter. Some of the GM type oil pumps look to be in pressure relief at around 1000 RPM and above depending on oil viscosity, so if the OP above idle is seen to have decreased, then it could be a clogging oil filter making the pump go into pressure relief farther and cut back some flow. At idle with hot oil, the GM pumps shouldn't be in pressure relief with a good flowing filter, but a clogged filter could put the pump in relief even at idle, and then you would also see less OP at idle.Yes, the other thing is the stock oil pressure sensor is mounted at the rear of the block at the top, mounted into the valley cover. Here is a diagram of the flow map. A clogged filter will cause a pressure drop at the sensor, before the bypass opens.
If the entire oiling system was bone dry, including the oil filter, and the pump started flowing oil at X RPM at Y flow rate, when that oil hits the filter, it goes through the media at that same Y flow rate, and the resulting dP across the filter would only be a result of the oil viscosity and flow rate, regardless if the system downstream of the filter was full of oil or air.
The pump output pressure won't rise much until most of the oiling system is full filled with oil flow - the oil filter is much less flow restrictive than the oiling system. The oil pressure at the pump outlet with a dry filter and oiling system would only jump to whatever the resulting dP was caused by the flow going from the pump outlet to just after the oil filter - it would most likely be way lower than 60 PSI in that dry system start-up scenario unless maybe the oil was super thick like molasses, the filter was very restrictive and the engine RPM was way above start-up/idle speed and sending lots of flow. The oil filter won't see any more dP than whatever the viscosity and flow rate going through it will create.
As the oil flow keeps going past the filter and filling the oiling system, the pump outlet pressure would keep rising until the full pump pressure level is seen for a completely filled and pressurized system at that oil viscosity and flow rate. The pump could go into pressure relief during the short time period while the system becomes fully filled if the flow and viscosity is high enough. But the oil filter never sees any dP higher than what the viscosity and flow rate going through it would result in, regardless of what else is going on in the oiling system. Using appropriate "W" rated oil for the cold start-up conditions and keeping the engine revs low until the oil warms up will help keep the filter out of bypass.
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When the oil galleries are empty, all the oil pressure buildup you see is from the filter media. So between the time pressure exceeds the BP valve setting and full oil pressure is reached, there's full oil flow through the filter and BP valve. Once full pressure is reached, oil flow reduces as the relief valve opens, and that reduces the pressure differential across the filter media.
As explained in post 48, the dP across the filter is only based on the oil viscosity and flow going through the filter - regardless of what's going on past the filter. So the dP across the oil filter is the same regardless if the galleries after the filter are empty or full. Most engines have the OP sensor located after the filter, so you won't be able to see the OP due to the dP between the pump and filter outlet before the oiling system pressurizes (talking about an empty system to start with). By the time you see the OP even start rising, the oil has already went through the filter and started pressurizing the oiling system. If the filter and oiling system was full of oil, then you would basically see the OP caused by the whole pressurized oiling system come up almost instantly after startring the engine (no empty filter and galleries to fill).
If there was an OP sensor between the pump and filter (say just down stream of the pump), all the pressure you would see before the oiling system after the filter started filling with oil would be the dP of the main gallery between the pump and filter, plus the dP of the filter. If the filter only had a dP of 5 PSI at that viscosity and flow, then the OP sensor right after the pump might show 2 PSI for the main gallery plus 5 PSI for the filter = 7 PSI total. After the oil went past the filter and into the more restrictive oiling system, then you'd see the OP go from 7 PSI to whatever the full OP would be with the whole oiling system flowing oil, which would be much higher than 7 PSI.
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But the same thing is NOT going on when the galleries are full or empty, that's your fallacy. I didn't talk about what you see either, but about what is.
There's a rush of oil at first, and that rush goes through the filter, the rush stops when oil galleries are full and full pressure is reached, as now not all the oil pumped goes through the entire system. See your own first sentence above.
I'm NOT saying it's guaranteed that the oil filter is bypassing, it's just more likely.
I'm confused what the point of your reply is anyway?
How can there be a "rush" of oil flow when the pump is sending the same flow volume regardless if the galleries are empty or full, and the pump isn't in relief even after pressurizing the whole system? That's rhe senario I'm talking about. You must be assuming the pump hits pressure relief after the whole system pressurizes, and the pump cuts some flow.
At start-up RPM, the oil would have to be pretty cold/thick and the pump pretty high volume at low speed for it to hit pressure relief after fully pressurizing the whole system.
The filter will only bypass if the viscosity and flow rate are high enough to make the dP across the filter high enough to open the BPV. If the pump puts out enough flow at start-up RPM, and the oil is thick enough, the filter BPV could open even if the filter and galleries were already full of oil.
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