No decrease in oil pressure seen with Purolator Pure One

[quadrun1]

One of the cars I'm taking care of has an oil pressure gauge ('99 Camaro with the 3800 Series II V6) and I thought it would be interesting to compare the oil pressure of a Purolator Pure One compared to what was on there before, a regular STP oil filter.

I used the stock filter size for both (PF47 equivalents). These filters have no bypass but do have an anti-drainback valve.

With the Pure One, the oil pressure reads the same--60 psi at idle with a fully warm engine and hot oil.

 

[slalom44]

It is likely that the Camaro has its oil pressure sender located after the filter, so any changes in backpressure won't be noticed by the gauge regardless of what filter setup you have.

 

[Michael SR]

quote:

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Originally posted by slalom44:
It is likely that the Camaro has its oil pressure sender located after the filter, so any changes in backpressure won't be noticed by the gauge regardless of what filter setup you have.

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that makes no sense to me. if the sensor is after the filter, that's precisely when you'll see a difference. if it's before the filter, you'll always see whatever the pump's bypass valve allows (except for at idle and very low rpm).

i never did test what the bypass pressure is for the valve in the block. if it's only 5psi, you might see the same pressure on the lowish resolution stock gauge regardless of filter.

-michael

 

[slalom44]

An oil pump on most engines is driven off the camshaft. Oil flow is primarily based on engine RPM, but if the oil pressure exceeds the setting of the internal pressure relief valve, then that is the maximum pressure the entire engine gets. The bypass setting is typically quite high, and on cars with oil pressure gauges it's a little lower than the maximum pressure that the oil pressure gauge reads (assuming that the sender is post-filter). On my car, the pressure relief valve is at around 100 PSI.

Oil flow does not get reduced with added backpressure at the pump. If it did, then MichaelSR would be correct.

There is a pressure drop through the oil filter, and a pressure drop past the oil filter as it passes through the bearings, etc. Since the flow is the same regardless of backpressure in the filter (due to constant flow from the pump), then the oil pressure the sender (and therefore the gauge) sees is the same regardless of the filter. The only exception to this is when the total backpressure to the pump exceeds the pressure relief valve setting.

If the sender was placed before the filter, then it would read the combined backpressure contributed by both the engine and the filter.

I hope this makes sense, since I see a fair amount of misinterpretation of oil pressure readings because many people don't understand this.

 

[rpn453]

quote:

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Originally posted by slalom44:
An oil pump on most engines is driven off the camshaft. Oil flow is primarily based on engine RPM

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So are the oil pumps on most cars positive displacement pumps (approximately same flow at a given RPM for any pressure below that of the relief valve)? This is something I've never really known for sure. If so, then everything slalom44 said is correct as far as I know.

Slalom44: For a filter without a built in bypass, there would be an internal bypass at a lower setting in addition to the pump's internal pressure relief valve, wouldn't there? Of course, with a P.D. pump this wouldn't change the pressure after the filter either, whether open or closed. I'm just trying to determine the status of my non-verified assumptions about engines!

[ June 11, 2004, 07:22 PM: Message edited by: rpn453 ]

 

[Patman]

What about at full throttle though? At lower engine speeds I wouldn't expect you'd see much change, but at full throttle the PureONE would flow considerably less and you should see a noticeable difference on the pressure gauge. I have never noticed a difference in oil pressure at idle or normal driving between different filters, but I do notice a difference in oil pressure at full throttle between the K&N and lower flowing filters.

 

[rpn453]

quote:

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Originally posted by Patman:
I have never noticed a difference in oil pressure at idle or normal driving between different filters, but I do notice a difference in oil pressure at full throttle between the K&N and lower flowing filters.

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Maybe the pump's relief valve is opening up, or opening sooner, with the more restrictive filters at increased throttle. This valve would see pressure before the filter, and the decreased flow to the engine would reduce pressure after the filter.

 

[edwardh1]

purolater wrote me this:
PureOne filters meet the flow requirements of automotive applications. We
test our filters per SAE specification HS806 Chapter 1, and the standard
flow rate requirement that we follow states that the pressure differential
(between inlet and outlet) shall not exceed 3.0 psi at a flow rate of 3.0
gpm. On the PL30001 filters, flow restriction is 0.8 psi (avg) at 3.0 gpm.

 

[slalom44]

Patman's observations make sense. The engine's pressure releif valve is located at the pump and therefore you will see a difference in gauge pressure at full throttle with different filters if full throttle opens up the valve (which it probably does).

I've never seen an engine torn apart that doesn't use a filter with a bypass valve, so I can't comment on how the bypass settings work.

 

[quadrun1]

quote:

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Originally posted by Patman:
What about at full throttle though? At lower engine speeds I wouldn't expect you'd see much change, but at full throttle the PureONE would flow considerably less and you should see a noticeable difference on the pressure gauge. I have never noticed a difference in oil pressure at idle or normal driving between different filters, but I do notice a difference in oil pressure at full throttle between the K&N and lower flowing filters.

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Patman: Hmm, it's hard to tell, because the tick marks on the oil pressure gauge are so far apart... but it looks about the same. I'll take a closer look.

At idle with cold oil, oil pressure is slightly higher with the fresh Pure One filter.

edwardh1: Thanks for the info!

 

[Michael SR]

quote:

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Originally posted by slalom44:
Oil flow does not get reduced with added backpressure at the pump.

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i maintain this in incorrect.

assume no bypass in the oil filter, ok? if filter A is more restrictive than filter B, and the oil pump is the same with the same relief valve pressure in both cases, then the filter A scenario sees less oil flow through the engine. (the pressure differential across filter A is higher, but the feed pressure to it stays the same.)

the pump just cares what the pressure is at its outlet. if at 3000rpm it can pump 5gph per hour, and its bypass valve system can flow 4gph, then the engine will get anywhere between 1gph and 5gph of oil flow depending on how much you restrict at the filter. but all this time, the pump just sees its normal bypass pressure at its outlet (and i think most engines are probably a good bit less than the 100psi of yours), and the difference in flow is just how much goes through the bypass/relief valve itself. (so yes, the pump is pumping the same volume regardless, but it's not all making it through the engine.)

but this is all academic since the bypass valve for the filter, whether in the block mount or in the filter itself, means the pressure differential will never be really large.

-michael

 

[Michael SR]

quote:

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Originally posted by rpn453:
So are the oil pumps on most cars positive displacement pumps (approximately same flow at a given RPM for any pressure below that of the relief valve)?

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all the ones i've seen have been, yes. but, all the engines i've seen also hit bypass/relief valve pressure very early in the rpm band, so the system does not act as a positive displacement pump. that's why filter restriction matters (if there were no bypass for the filter).

-michael

 

[slalom44]

Originally posted by Michael SR:

quote:

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the pump just cares what the pressure is at its outlet. if at 3000rpm it can pump 5gph per hour, and its bypass valve system can flow 4gph, then the engine will get anywhere between 1gph and 5gph of oil flow depending on how much you restrict at the filter. but all this time, the pump just sees its normal bypass pressure at its outlet

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This is incorrect because the pump is a positive displacement pump. It pumps the same volume regardless of the backpressure (this is the definition of a positive displacement pump)as long as it doesn't hit the pressure that opens up the pressure relief valve.

As I stated before, the pressure relief setting is: [the maximum pressure measured by the pressure gauge]+[backpressure of the filter]. If your engine was hitting this very early in the RPM band as you suggest, then your pressure gauge would be reading its maximum pressure most of the time.

Granted, my car (Honda S2000)has a bypass setting higher than most cars, but I've seen plenty of cars that have oil pressure readings in excess of 65 PSI which means that the pressure relief valve is opening up at well over 70 psi.

 

[Michael SR]

you're saying the same thing i am saying, the difference being you are ignoring the possibility of the pump being at bypass.

my point of view is almost always aggressive use or racing, otherwise why should i really care that much about oil pressure? if all i did was cruise the highways at 2000rpm, the engine will live fine whether it sees 40psi, 20psi, or 60psi. so when i think of filter restriction problems, my mind immediately jumps to WOT use. hence my point of view.

at what rpm do you see maximum oil pressure? my vette sees it by 2500rpm, and my jetta by 3000rpm. for the jetta, this means i'm at bypass/max pressure the whole time i'm on the highway. in terms of percentage of mileage, that's probably 80%, if not more.

-michael

 

[ZR2RANDO]

Something else to add, just because a pump is a positive displacement pump does not mean it is a 100% efficient pump at all. Real pumps (as opposed to "ideal" pumps like in textbooks) will have some efficiency loss as the backpressure is increased due to restrictions to flow like obstructions or high viscosity oil..
It will have some leakage due to imperfect internal seals/vanes etc. The pressure relief at the pump is not just protecting the motor from excess pump pressures, it is also protecting the pump from any severe backpressure that could possibly occurr (which probably would be a very distant secondary issue if that kind of backpressure DID occur..).
Just having pressure gauges is only part of the info (granted a big part..), the only way to see how the filter is really performing is to have flow meters as well as pressure gauges. The pressure gauges can be misleading by themselves sometimes. Unless you change pumps, higher pressure indicated can be showing less flow.

 

[Brian Barnhart]

quote:

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Unless you change pumps, higher pressure indicated can be showing less flow.

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With a perfect positive displacement pump, this would only be true when measuring the pressure before the filter when the oil pump is bypassing. With a less than perfect positive displacement pump, this could be true in certain other situations as well.

If the oil pressure gauge is after the filter, greater pressure (under identical conditions) would always indicate more flow.

Edit:
After further review, my last sentence seems too broad. A decrease in engine clearances could increase pressure without increasing flow. Likewise an obstruction in the engine could also increase pressure without increasing flow, and, if severe enough, could show increased pressure at a reduced flow rate.

Under normal conditions on a given engine however, an increase in pressure indicates increased flow if the pressure gauge is after the filter. For example, with different oil filters and the same oil at the same oil temperature, the filter showing the greatest pressure would be flowing more oil.

[ June 15, 2004, 08:56 AM: Message edited by: Brian Barnhart ]

 

[ZR2RANDO]

Under normal conditions on a given engine however, an increase in pressure indicates increased flow if the pressure gauge is after the filter. For example, with different oil filters and the same oil at the same oil temperature, the filter showing the greatest pressure would be flowing more oil.

True, because a less restrictive filter would cause less pressure drop across the filter..

[ June 15, 2004, 09:45 AM: Message edited by: ZR2RANDO ]

 

[Brian Barnhart]

Actually, I believe it’s the pressure/flow relationship in the engine after the filter. For a given engine restriction (after the filter), more absolute pressure (after the filter) means more fluid is flowing, regardless of the pump’s characteristics or oil filter used (assuming a fixed set of conditions, including oil viscosity, temperature, engine RPM, etc.)

 

[Ken2]

My Toyota V8 has the oil pressure sender on the filter housing, but I don't know if it's the inlet or the outlet.

That engine is putting out full oil pressure at about 2000 rpm. Any more rpm up to the 5200 rpm redline only causes the oil pump's pressure relief valve to open wider.


Ken

 

[Chevy Guy]

quote:

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Originally posted by Patman:
What about at full throttle though? At lower engine speeds I wouldn't expect you'd see much change, but at full throttle the PureONE would flow considerably less and you should see a noticeable difference on the pressure gauge.

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In an enigne or flow and pressure are unrelated. Pressure is determined soley on the clearances of the oil passages in the engine combined with the bypass valve setting. Flow is realtively low in an engine, its not like water flowing out of a hose.