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.I never realized the oil pumps bypass too. Is this built into all vehicle oil pumps?
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.I never realized the oil pumps bypass too. Is this built into all vehicle oil pumps?
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.Here is a chart that goes to -20 C. At Bitog we discuss oils at operating at 8 to 16 cSt. Even at 0 F ( -18 C), a 0w40 would be at 1800 cSt, but probably not high enough to open the bypass. Would have the other oils opened the bypass? Maybe. This is why it drives me nuts when people say as long as it starts, it’s OK.
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.The're a large flow of oil until the system reached stable pressure, at max pressure the oil isn't filling any galleries so flow is actually less
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.3. No, as long as an appropriate filter is used, a filter should never bypass unless it's clogged. This is true even when the oil is cold and thick, since the oil pump will reduce flow enough to limit pressure drop across the filter.
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.There's a recent big discussion about the LS oil pumps. The info shows that they are basically in pressure relief not far above idle, and the relief valve is essentially controlling the pressure throughout the engine RPM range. That explains why on GM engines with this oil pump, that a severally clogged oil filter could show a decrease in oil pressure, because the pump is basically always in pressure relief above ~1000 RPM.
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.
![]()
![]()
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.Consider the case where oil pressure is only built up in the filter and in the oil passages between the pump and filter, and the passages downstream of the filter are still unpressurized. If the pump pressure rises to 60 psi, all of that pressure will be dropped across the oil filter and those short oil passages. If the filter makes up 50% of that total restriction, the dP across it will be 30 psi. It's as if the rest of the engine downstream of the filter doesn't exist yet.
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.
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).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.
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.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?
It's actually the oil flow volume going through the filter (and the viscosity of the oil) that creates the dP across the media and bypass valve. Just because an engine has "high oil pressure" doesn't mean it has a high flowing oil pump ... it all depends on the exact design of the oiling system and how flow restrictive the engine's oiling system is.Interesting. I was thinking about my LFX engine which is known to have high oil pressure, up to like 90psi, but the PF63 filter it uses has a BPV rated at 22psi. But I see you're point, its not the pressure in the system that counts, its the pressure across the filter.
Who knows, probably fairly often. Too bad the base end bypass valves design is not as much a thing as it used to be.We often worry about dirt holding /clogging or filtering efficiency. But how often does a normal vehicle filter actually go into bypass mode?
1. Has 0w oils reduced bypass in cold weather?
2. Does a high pressure oil pump automatically mean more bypass occurs?
3. Does bypass ever occur in warm to hot weather if filter isn't clogged?
4. Does running a heavier oil automatically increase bypass events?
5. How long does bypass usually last?
Those tests weren't very good.Let's put the bench racing theory aside and look at some real data!
A long-time member here (Jim Allen) did some actual filter BP event testing. It was more than a decade ago. He ran 10w-30 lube and a normal FF filter on his 5.4L F150. He used some fairly accurate equipment in a special filter base mounted to the engine, IIRC. He was able to measure the actual dP across the filter.
(note ... these threads are from the old platform, so some of the quotes are hard to discern and take a bit of deductive reading)
Here are a few of his dP threads:
Differential Pressure Testing Update
Nothing much to report on currently. Thus far, I have data for the setup I am running now ( P1 w/10W30 MC Super Duty CJ-4/SM) at 12K miles but I am still collecting filters for new-state testing, which won't start until I have finished the 15K interval on the MC oil I am currently running. I...bobistheoilguy.comDifferential Pressure Gauge Installed
Well, I got my differential pressure gauges installed. Works fine. Instead of buying a single gauge, I just hooked up two Isspro stepper type pressure gauges with senders on either side of the filter using a Pareto base. As you can see by the pics, I am using all the ports on the base now. The...bobistheoilguy.comDifferential Pressure Data, Pure 1 & Motorcraft
Hopefully nobody got too blue in the face waiting for this. A lot of data to go through, a busy schedule and other priorities... what can I say? Background: I installed a differential pressure test setup on my F150HD (5.4L 3V Modular V8). Mine is a two gauge setup with senders on either side...bobistheoilguy.com
Overall, the results were very telling. His filter would only go into BP when it was a cold start and he revved the engine up quickly. And that was with 10w-30. I later talked with him and he could rarely ever get the xW-20 grades to go into BP; they are thin enough that they flow really well. In "normal" use, especially with thinner lubes, the filter hardly ever goes into BP mode. And when it goes into BP, it's just a blip for a second or so; it's not a long event by any means. The only time it would do so frequently is if the filter were neglected to a point of blinding off (hardly a condition a BITOGer would ever experience, given their anal-retentive nature to over maintain things ....)
Who knows, probably fairly often. Too bad the base end bypass valves design is not as much a thing as it used to be.
Another fix for old Chevrolet engines is use a #9100 filter from a 6.6L Duramax.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.
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.