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 Post subject: Oil Pump Bypass Q?
PostPosted: Mon Oct 18, 2010 11:15 am 
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Location: Regina, SK
What is the bypass rating for these pumps?

I'm looking at different oil filters, and I've found some that fit, but they are 2.5 bar bypass vs 1 bar(stock), The sticky point is if the oil pump will just dump back into the sump before the filter goes into bypass, then that's no good... :lol:

So will our pumps force open a 2.5bar bypass or are they artificially limited below that?

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J. McBean: '98 Suzuki Swift 1.3L 16v SOHC 5sp+ "Mk5" Made in Canada
The Mini Rattler: '94 Suzuki Swift .993L 6v SOHC 5sp+ "Mk3" Made in Canada *The Winter Beater*
B. Berry: '90 Chevrolet Turbo Sprint 1.0L 6v SOHC 5sp+ "Mk2" Made in Japan

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 Post subject: Re: Oil Pump Bypass Q?
PostPosted: Mon Oct 18, 2010 2:14 pm 
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Location: Roumania
Filter bypass refers to the oil just going into the engine , instead of being filtered.
Pump dumpvalve is set a 5.5bars

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 Post subject: Re: Oil Pump Bypass Q?
PostPosted: Mon Oct 18, 2010 3:06 pm 
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I know, the stock filters are set to 1 bar, which isn't a whole lot of pressure before the filter goes into bypass and you end up with unfiltered oil getting shot through the engine.

I was looking up some filters for the GF's VW, when I noticed the thread was the same size, and I looked into the measurements and the filters should fit without issue. The only thing about them is that their bypasses are set for 2.5 Bar.

So the VW filters should work fine on our oil pumps.

The filters are for the VW AEG 2.0L.

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My cars:

J. McBean: '98 Suzuki Swift 1.3L 16v SOHC 5sp+ "Mk5" Made in Canada
The Mini Rattler: '94 Suzuki Swift .993L 6v SOHC 5sp+ "Mk3" Made in Canada *The Winter Beater*
B. Berry: '90 Chevrolet Turbo Sprint 1.0L 6v SOHC 5sp+ "Mk2" Made in Japan

I got 18MPG in a 3cyl with a 5 speed manual 4dr, '93 Metro! :yeahyeah


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 Post subject: Re: Oil Pump Bypass Q?
PostPosted: Mon Nov 01, 2010 10:47 pm 
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Location: Georgetown, Guyana
The issue that's not being addressed in this discussion is how restrictive the filter media is.

The filter bypass valve is there to allow oil flow to bypass the filter media in the event it clogs, restricting the flow of oil.

On a new filter, one should be able to safely assume that the filter media does not restrict the flow of oil appreciably, if this is the case, you should never develop enough pressure across the bypass valve to open it, allowing the unfiltered oil through.

Equally important is the flip side - if the filter media does clog enough to restrict flow - with a 2.5 bar bypass valve, will the pump build sufficient oil pressure at idle to open the bypass valve, so that oil circulates?

Which would you prefer - no oil circulating - or - unfiltered oil circulating?
Why not stick with the recommended filter and change both oil & filter regularly?

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 Post subject: Re: Oil Pump Bypass Q?
PostPosted: Tue Nov 02, 2010 12:05 am 
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Simplicity, and filter size.

1 bar filter: 14psi bypass

2.5 bar filter: 35psi bypass

Oil pump 5.5bar: 77psi

So even if the filter plugs, the oil pump still has 32psi of headroom to force the filters bypass open. I've had a filter hit bypass before at idle with these cars. I was flushing an engine, and it was a almost steady clunk/tap, scared me the first time I heard it, then I figured out what it was.

Couple it with the use of ever more effective filtration type of filter, with a smaller effective size, will increase pressure drop, and then add in better than the stock oil pump. I'd rather have a bit more pressure drop, and the difference in time for opening is minimal if any. For example, cracking the throttle open and revving the engine up will for example force the oil filter into bypass for a short period because of the pressure surge. I'd rather cut that opening time... I imagine that most of the oil pumps on these cars would have no problems creating a 14psi difference in pressure across the filter between idle and 5000rpm.

Along with the stronger filter construction that the higher bypass equipped filter will require. So I figure win/win along with the slightly larger filter, while still being narrow so to allow the use of it on the factory turbo cars.

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My cars:

J. McBean: '98 Suzuki Swift 1.3L 16v SOHC 5sp+ "Mk5" Made in Canada
The Mini Rattler: '94 Suzuki Swift .993L 6v SOHC 5sp+ "Mk3" Made in Canada *The Winter Beater*
B. Berry: '90 Chevrolet Turbo Sprint 1.0L 6v SOHC 5sp+ "Mk2" Made in Japan

I got 18MPG in a 3cyl with a 5 speed manual 4dr, '93 Metro! :yeahyeah


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 Post subject: Re: Oil Pump Bypass Q?
PostPosted: Wed Nov 03, 2010 8:30 am 
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I wish it were that it simple - but it ain't.

Very simplified - the oil pump has a maximum delivery volume and pressure - and it will deliver maximum volume at minimum pressure. If you restrict the free flow, the volume delivered decreases and the pressure increases (to the point of restriction).

Let's complicate things a little now, by adding viscosity in to the picture - a trochoidal pump such as we are dealing with, can only be used to pump liquids within a narrow range of viscosity, too thin, and it leaks past the rotor lobs and end faces, too thick and it doesn't flow, and the viscosity of motor oil changes dramatically within the range of temperatures that a car engine experiences.

So - what we have here - is an oil circulating system, that needs to be able to cope with the relatively viscous oil with the engine is first started, and also, the much thinner oil with the engine is up to operating temperature.

On a cold start, at idle - you'll see 50~60 psi, but at operating temperature that drops to 20~25 psi - and that difference is caused by nothing other than the change in viscosity of the oil - it flows more freely, so a greater volume circulates and the pressure drops. Yes - the pump IS capable of delivering more - both volume & pressure - but it needs more rpms to do it.

At operating temperature and 3000 rpm, the pump will deliver enough volume to raise the pressure to 50~60 psi - but - that pressure rise occurs only because the flow of oil through the engine isn't changing signicantly.

Let's now go back to an operating temperature, idle rpm condition - and the point that I was making in my previous post - how much volume can the pump deliver, given the rpm at which it is rotating, and the viscosity of the oil - all we know, is that it is enough to create a 20~25 psi delivery pressure, given the volume of oil flowing through the engine's bearings.

Now - let's add your clogged filter - can the pump deliver enough volume at a large enough head to force the bypass valve open - AND - once it has forced the bypass valve open, the restriction of the bypass valve becomes the limiting factor that dictates what volume of oil flows.

Is that reduced flow adequate to ensure (1) an adequate flow of oil to the crankshaft and it's bearings, and (2) enough pressure to reach the upper areas of the engine.

I've already stated my opinion, you're entitled to yours - you use what filter you choose, it's your engine.

I've just completed a rebuild on my G13B - worn rings & bores were the problem - crank journals were in mint condition, no sign of wear from any unfiltered oil reaching them...

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 Post subject: Re: Oil Pump Bypass Q?
PostPosted: Wed Nov 03, 2010 6:40 pm 
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Location: columbus, ohio
there has been no mention of the spring operated pressure valve in the oil pump's body, either. looking at the castings on the back of an oil pump, it looks like any oil pressure above the relief valve's operating point gets shot back to the sump. i thought that i had read in a manual one time that the relief valve operates around 55 psi (may have been for the g10.)

in a case where the relief valve does operate below the 2.5 bar pressure that has been arbitrarily set for the oil filter bypass valve on the non-stock filter, it would never operate. oil flow would still be nil due to the fact that the relief valve in the pump would dump the developed pressure at a point below the filter's bypass rating.

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 Post subject: Re: Oil Pump Bypass Q?
PostPosted: Mon Nov 08, 2010 8:40 pm 
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Location: Georgetown, Guyana
That seems to be the actual subject of the OP's question, and the second post (which describes it as the "pump dumpvalve") indicates, incorrectly, that it opens at 5.5 bar (roughly 77 psi) - based on the FSM, you are correct, it starts to open at 56psi.


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 Post subject: Re: Oil Pump Bypass Q?
PostPosted: Wed May 11, 2011 1:18 pm 
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Location: Trinidad, W.I.
Bump for some great info in this thread!

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