Correct 1.8T oil filter/bypass pressure question

[akhristov]

Hi guys,

I made an interesting discovery about most aftermarket oil filters for the Audi/Volkswagen 1.8T engine: their bypass valve specification is different from OEM. How would this affect the engine?

I wrote a long post on PassatWorld about it, here's the link: http://www.passatworld.com/forums/showthread.php?t=309623. I know people here know way more about oil filters and specifications, so I want to know what you guys think/suggest.

Thanks in advance for all your replies!

Alex.

 

[labman]

A lower bypass means under some conditions you will get good flow but some unfiltered oil. A higher bypass means less dirt, but less flow. I doubt it makes much difference unless you run thicker oils. I also wonder how much science goes into setting a bypass spec. I suspect they come from a place not easy to access sitting down.

 

[Gary Allan]

Most of the Euro's run 30+lbs for a bypass setting. The media are typically mesh reinforced to withstand the much higher potential for differential pressure.

Here's the WIX for the 1.8T

Part Number: 51393
UPC Number: 765809513938
Principal Application: Audi (71-06), Volkswagen (96-09), Lotus (71-74)
All Applications
Style: Spin-On Lube Filter
Service: Lube
Type: Full Flow
Media: Paper
Height: 4.820
Outer Diameter Top: 3.020
Outer Diameter Bottom: Closed
Thread Size: 3/4-16
By-Pass Valve Setting-PSI: 33
Anti-Drain Back Valve: Yes
Burst Pressure-PSI: 410
Max Flow Rate: 7-9 GPM
Nominal Micron Rating: 21

Gasket Diameters
Number O.D. I.D. Thk.
Attached 2.800 2.450 0.230

 

[akhristov]

For what it's worth, the 1.8T uses a VW 502.00 spec oil, which is usually 5W-40.

 

[Gary Allan]

The reason, that may not be applicable in all offerings of the engine in all markets, is that there's a tendency for the Euro's to build based on operation at nearly 100% continuous output. It's not like an American higher performance chassis that may or may not be setup to run at near WOT indefinitely. Most lessor passenger cars don't have the power density to worry about it and their sumps/cooling systems/etc. aren't going to be taxed at sensible limits of being able to safely drive them.

The Euro's tend to build to this limit and typically spec heavier oils to enable this sustained operation. This is not always the case in the US market, but we're also (typically and in the recent past) NOT doing Euro length OCI's.

Oils are still of such limited VI that viscosity requirements at this sustained continuous output level necessitate compromises during the cold start and through the warm up process.


Hence you may have a peak pressure limit of 100PSI at the pump, but will see 125PSI on the gauge at start up. The pump relief can't shunt enough fluid to keep it down to 100PSI.

The difference is seen by (across) the filter. Once out of relief, the filter's relative resistance is nil except for the effects of loading. Those will be variable based on visc/volume, but are generally minor.

 

[akhristov]

So what would happen if I was using a filter with the wrong bypass valve setting?

 

[Gary Allan]

If you use a filter with an 8-16lb bypass during some conditions you can have unfiltered oil. In the case of someone using 5w-40 and over peaking their pressure limit during a cold start, the entire time the pressure is in excess of the relief limit the filter is likely to be in excess of 8-16lbs of differential. If the mismatch between visc, volume, and ambient temp is too great ..and your daily drive is too short, your engine can have the majority of its life with poorly filtered oil.

The co-benefit is that the filter can sustain substantial loading without bypassing. As engines cleaned up, OCI's could be extended.

The Euro's tend to factor just about everything. The exception (perhaps) being the American consumer.