Remove Bypass?

[Ross1.8t]

I have a 99 1.8t vw passat with about 80k on it. I have been running the amsoil bmk-11 bypass for the last 5k or so.

I recently (after the bypass) installed dakota digital oil pressure and oil temp. gauges. With the bypass on I was getting 12-13 psi at hot idle (200oF). Now this past weekend I removed the bypass filter and got 20-21 psi hot idle. This is certainly a significant difference.

My question is is there anyway to reduce the flow to the bypass filter to cause less of a loss of oil pressure? How much of a drop in oil pressure do you think is safe for this engine? Keep in mind this is a sludge prone hot running turbo motor.

Thanks

 

[Ken2]

The BK-203 Filter mount assembly with restrictor has a .032" orifice. You could remove this, have it welded or silver soldered shut, and drill smaller.

At idle your oil pump is putting out the least possible volume of oil. Is your hot oil pressure any different at operating speed with the bypass filter and without? The idle pressure isn't that big a deal because there is no load on the engine and the turbo is spinning at minumum speed.


Ken

 

[Ross1.8t]

I probably should add that my hot oil pressure at 2k rpm was now 42 psi up from about 35 psi. What kind of surprised me though was that when I first started out on a cold engine my oil pressure was 95 psi driving about 45mph. I have never seem this high of an oil pressure with the bypass on. The highest cold pressure in the past has been about 75 psi with the bypass on. This is what has me most surprised and concerned.

 

[johnd]

The old rule of thumb about oil pressure is that an engine requires about 10 lb per 1000 rpm. It doesn't sound like anything to worry about. You still have adequate levels for operation. I'm surprised at the 75-90 lb cold figures. Usually the oil pump bypass will prevent pressures that high.

 

[canadiantim]

Ross1.8,

How is this particular bypass connected? The bmk-11 is simply a bypass canister-style, tapped in, leaving the original full flow in place I believe?

Where is the pressure reading being taken?

What viscosity oil are you using?

 

[Ross1.8t]

My setup is as follows:

At the location of where the factory oil pressure switch is I ran a hose to a remote mount where I have the factory pressure switch and the sending unit for my gauge. I also have a line going to the bypass oil filter from this mount, the bypass returns through the oil pan drain plug.

I am using Mobil 1 Truck and SUV 5w40. Earlier I was using GC, but I switched to a heavier oil to see if it made a difference in pressure. It didn't make any noticeable difference.

I'll look into a needle valve.

 

[canadiantim]

Your gauge might be showing a different pressure than the engine is actually getting due to the effect of the hose between the port and the sending unit. The pressure difference would likely be even more exhagerated when the bypass is bleeding pressure off this small line.

I've read of innaccurate readings (artificially lower) when the bypass and gauge are both teed off the pressure port without any hose length involved. Likely depends on engine design but worth taking a look at maybe?

It's likely a pain, but I'd be tempted to try a mechanical gauge teed at the sending port with and without the bypass just to see if there's really pressure that low at idle.

I also recall some other posts regarding low idle pressures on some VW engines in this forum. It was just the way they were based on my memory. Not sure if diesel or gas though. Wonder if some VW forums might have some expected "normal" pressures?

 

[canadiantim]

Gary, do you have any info/sources on the needle valve you mentioned?

 

[Gary Allan]

Get a chemical needle valve and plumb it to the outlet. Adjust until desired hot pressure is attained. If you've got that .032 restrictor in there (I thought that they had left an installation plug in the nipple since the hole is almost undetectable to the casual observing eye) I find it hard to believe that you're having this issue.

 

[Gary Allan]

canadiantim may be on to something. If your small hose is too long you can be overloading the supply. That is, the resistance of the hose when there's a dynamic flow through it could reduce the line pressure. Without the bypass filter involved...it's effectively dead headed and will read line pressure. Open the tap ..and even if the main line pressure is within "inches of water column" with or without the bypass filter attached ..the pressure at the remote sender can be reduced substantially.

Good job of detective work there, canadiantim

You can find all kinds of needle valves at McMaster Carr ..starting on page 381 Here You can also check at Grainger

 

[Ross1.8t]

Would I get more accurate oil pressure readings if I put a tee at the factory sending unit position with my oil pressure sending unit right there and a line going to the bypass? This would eliminate the small line going to the sending unit.

 

[Gary Allan]

IMO, yes. It should surely "close the gap" between indicated and actual.

 

[canadiantim]

The tee up close would be better but still may not be accurate.

The posts I'd read regarding this as well as either Frantz's or Motorguard's sites indicated that once you had teed off the sending port, you could not rely on it for an ACCURATE reading in some cases. It will show the pressure at the entry to the bypass filter, not necessarily the pressure within the oil system itself.

In theory the pressure port should be a hole in the side of "large pipe" with the oil pump/filter at one end and the engine oil passages/pressure regulator at the other.

Unfortunately, who knows where the designer stuck the pressure port within the oil system. If they only intended it for a pressure "switch" only, rather than a variable gauge, they might have it attached somewhere where it only sees a "buffered" pressure, like a port on the pressure regulator.

The pressure port could also be fed with only a very small internal passage since it is not intended to actually flow oil, only to build up pressure. This is fine for a gauge/switch but as soon as you steal some flow, it becomes inaccurate (particularly at low flow - idle conditions)

I would do some research on some VW sites to get an idea of what to expect for a pressure reading at the port. You can find lots of experiences with pressure readings if you seach under "oil pressure" as many people like to install gauges and then compare the results online as well a lot of people play with Turbos and post some thorough info of their learing experience/progress.

I too would be doing my homework if I saw readings as low as you have. Hopefully you may find you can leave everything as it is...

 

[Gary Allan]

The majority of contemorary vehicles tap the sendor/sensor right off/after the filter ..and is typically visible proof to the theory of the hole in the side of the big pipe. Older V8's used to tap in up higher in the block. Chevy liked near the distributor/cam. "Old" Oldsmobiles had it near the front of the block. They would probably get different readings that those same engines if they were tapped at the outlet of the filter.


The FSM (factory service manual) should have a transparent view of the lubrication system. It may be available somewhere on line. There may also be multiple places to tap into for line pressure readings. This would also offer other locations to plumb the bypass filter to.

 

[porcupine73]

When I put in my bypass filters, I considered trying to put a solenoid valve on the outlet so I could either manually stop the bypass flow with a toggle switch when at idle, or perhaps setting it up so that below a certain oil pressure gauge reading (say 15 psi) the solenoid valve closes to prevent bypass flow. Of course some hysteresis or a time delay would be needed if you wanted avoid potential chatter of the valve from opening/closing in rapid succession. I never did it because I couldn't find any reasonably priced solenoid valves that could handle more than maybe 180 deg. F. (other than steam valves but I couldn't figure out if they would work for engine oil).
-Louis

 

[msparks]

My question is why do you need more pressure at Idle? What's your pressure at speed?

You know there is a difference between pressure and flow, and I'm positive that your flow is not affected. If it were mine I wouldn't worry a bit unless my pressure at speed were affected, meaning that is was so low that you weren't getting any oil. I can bet your probably at at least 50psi at speed.