What you suggest depends entirely on the source of the pressure. If the pump is a centrifugal pump, like in a central heating system, then the flow is proportional to the resistance in the system, as you suggest. So adding a filter into your central heating is an additional resistance, so the flow would be lower. (Or adding a “high flow” filter, with a low pressure drop would increase flow).
The oil system in the car is different though. The oil pump is a gear pump, which delivers a fixed volume irrespective of system resistance. So the oil filter doesn’t affect flow, whether it’s “high flow” or not.
The only thing that affects the flowrate is the speed of the pump - rev the engine and the pump turns faster. It’s still a positive displacement pump though.
[quote=“timangus, post:40, topic:115442”]
Many years ago, when I was a BMW bike dealer, we were under cut on price by pattern oil filters, until people realised that the saving was done at the expense of not having a pressure relief valve. When engines went bang people learnt their lesson.[/quote]
That’s what happens with a positive displacement pump - it pumps a constant rate, so if there’s a restriction in the system then the pressure rises to allow the fluid to pass. The pressure can exceed the strength of the system, so you get a leak, usually at a joint, but sometimes catastrophically. Usually though, oil pumps have a spring loaded relief valve integral to their body which allows the oil to recirculate around the pump when the discharge pressure gets too high. Tha Mazda has this, surprised the BMW didn’t.
Do some ( more expensive/oem) oil filters have pressure relief valves and other (cheap) filters, designed to work on the same engine, not though.
It does seem like a very big difference.
[quote]Do some ( more expensive/oem) oil filters have pressure relief valves and other (cheap) filters, designed to work on the same engine, not though.
It does seem like a very big difference[/quote]
I’ve had a think about this.
So the relief valve in the pump is primarily to protect the pump from smashing itself to bits if the discharge is blocked. It just results in oil circulating around the pump bot none going forward.
If the oil filter blocks then no oil goes to the engine, resulting in failure. So the oil filter (or some!) has a relief valve which allows oil to bypass the filter and still feed the engine, albeit unfiltered, preventing engine damage.
So having thought about it, it makes perfect sense for the genuine BMW filter to have a relief (bypass) valve, in addition to the pump’s own!
Incidentally, I always use the genuine mazda filter. This is the one made in Japan and supplied by mx5parts, not the uk-dealer supplied filters which are different and made in Europe. Oddly, the mazda removal tool only fits the Japanese one. I have no idea if either include a bypass valve.
Blimey, I didn’t think that an oil filter could be so complex, I’ve just bought a budget filter from MX5 parts for my mk3, its for my impending first oil change attempt, I assume these filters are all good
Don’t worry about it, I’ve used all makes of filters in my time on the cars, currently got the K&N on my NC and they recommend a VW approved filter on my SEAT daily, I went with a Mann filter.
The pressure relief valve in the oil pump is to regulate maximum oil pressure as engine speed rises.
I cut a “European” Mazda oil filter open a good few years ago, it had a pressure relief valve in it. I’m sure I put the photos on the forum. They may still be here if you search.
They are quite simple devices. The only real way you are going to get “high” flow is for the filtration media to be more “porous”, so either bigger holes, more filter area, either by more media in the same space (which does not necessarily equate to more flow, or a physically bigger filter. While oils have become much thinner, I would not in the least be surprised if there was some partial bypass of the filter media when cold and the oil at it’s thickest on start up. Far more dangerous to have no oil that oil that is a bit “dirty.”
Indeed it will regulate the pressure, agreed. But the pressure has increased because the flowrate has increased, as the flowrate is proportional to the rpm. I think we’re saying the same thing though
Yes, the Japanese one I got from MX5parts has this on the website description -
“Please note that these are not the European sourced Genuine Mazda filters that are actually made by Mahle which have a “9A” on the end of the part number.”
