Hi all.

I have a 4 cylinder 2 litre and am adding a remote oil filter and oil cooler circuit via a spin on adaptor attached to the stock oil filter console mount. But I noticed the oil filter bypass valve in the stock oil filter mount (circled in photo below) and now I’m concerned that, at high rpm, I’ll be bypassing the remote cooler/filter circuit. Does anyone know the bypass valve relief pressure setting? Knowing that would at least allow me to judge whether it’s an issue.

Click to view attachment

Good concern and already discussed here in the past. I believe it is very low pressure and yes, you can by-pass your external oil cooler with the spin adaptor.

Here is a thread on the subject:

http://www.914world.com/bbs2/index.php?showtopic=10227

Yes I’ve seen that thanks Montreal914.

Does anyone know the bypass valve relief pressure setting?


.

Looks like it is a couple of psi.

Read @ChrisFoley 's post #11 in this thread. I tend to trust the guy.

http://www.914world.com/bbs2/index.php?sho...295002&st=0

I hate chiming in on this because I don’t have an absolute numerical answer to provide.

Please look at the factory manual diagram closely.

The bypass in the oil filter console is only affected by differential pressure between the inlet and outlet of the oil filter.

Typical oil filters only drop 1-2 psi unless the filter is loaded & beginning to clog. So it should not be surprising to see the console bypass sized to a couple psi what ever that means. It just needs to be set high enough that it only opens when the oil filter is developing too much of a pressure drop from being clogged & too restrictive.

The factory manual doesn’t specify the pressure delta needed to operate this bypass internal to the oil filter console.

If you want an absolute answer, you’re probably going to have to do the math or build a test fixture.

Click to view attachment

Also keep in mind that most modern oil filters also have a built in bypass. So even if you’re going to try to go to a full flow system, you’ll have to choose the oil filter carefully to find one without a bypass internal to the filter itself.

Unless you’re doing something very unusual with the sizing of your oil pump, or running high viscosity oil (at operating temp), the spin on remote oil coolers are reasonably well proven. Again this assumes you aren’t using a crazy restrictive external oil cooler.

I believe every single ICE engine with bypass valves (most have both a flange mounted and oil filter mounted) bypasses some oil.

Mostly when cold.

No way of getting around this without a dedicated full flow system.

Thanks for the great responses everyone

If it’s truly only 3 PSI then I think it’s worth doing some modifications, as I think it will bypass at high rpm, right when the remote cooler is most needed. The stock bypass valve could be set at 3 PSI without concern, because it wasn’t bypassing the oil cooler when it bypassed. But now it does and that could be a problem.

My remote filter will be a Mann 940/81 which has a built in bypass valve set for 0.8 Bar (11.6 PSI). Most are higher than this. It makes me wonder about the stock bypass which is apparently about 3PSI.

I wonder if I set the stock filter bypass to say 10 or 15 PSI whether it would cause any issues for the pump. I normally see no more than 60 PSI on a cold start. Are they okay for say 80 PSI whilst warming up?

Anyway, to put some engineering into this mod, I’m considering measuring the pressure at the upstream side of the stock filter console, carefully getting the engine up to about 185 deg F whilst watching the pressure gauge and then carefully running up to redline whilst watching the gauge so I can see what sort of back pressure would be normal in the remote filter/cooler circuit. I’ve already got a pressure gauge mounted at the stock pressure switch location so I could just subtract that reading from the new gauge reading to get the remote circuit backpressure. That way I could choose a relief pressure for the stock bypass valve that bypasses only at pressures developed above redline AND at oil temperatures below 185 deg F. Then I’d be convinced the remote cooler would be doing its job when it’s needed.

Where in the world did you come up with 3 psi?

I appreciate the idea that you’re going to try to measure the pressure drop across the filter but I’d seriously suggest you look into the accuracy of the gauges you’re using to do the measurements. If you’re using conventional dash mounted pressure gauges, the measurement will be lost in the noise and inaccuracy of the gauges. As a mechanical engineer, I will tell you that if I were trying to do what you’re proposing, it would be done on the bench and the test would be done on the filter console only without bringing an bunch of other variables into the test.

If you’re that worried about bypassing the external cooler, you should be using a full flow cooler and should not be using a spin on adapter.

And why on earth would you want to send cold oil to cooler?

Montreal914 and Chris Foley said it’s “a couple of PSI” so I’ve taken 3PSI as a bypass valve setting. I can’t find any better information.



Sorry, I mustn’t have been clear. I want to measure the extra backpressure created by the entire remote filter/cooler loop attached to the standard filter console. That includes the hose, the hose fittings, the remote filter mount, the oil cooler and the remote filter. I’m also a mechanical engineer and done a fair bit of test work/condition monitoring in my life; I’m comfortable I can get the necessary accuracy to achieve a practical result. I mean, if it turns out it’s less than 5 PSI and hard to see the drop on the instruments, then it’s probably just a case of making sure the modified stock bypass valve is set to about 10 PSI and it will be all good. And yes the accuracy of these gauges is not awesome, but I can reverse the connection points and take the average to make sure the conclusions aren’t too far skewed.


Yes, that makes sense to me now. However, it was already installed by others. It cost me a fortune through a highly experienced VW shop that’s been trading for 50 years. I just spent a small fortune fixing all the poor workmanship, poor material selection and poor routing of all the hoses. I didn’t know about the filter bypass and nor was anything mentioned to me about the limitations of the system when I paid for the job to be done. It’s only when I worked on it myself that I noticed the filter bypass valve. I’m quite disappointed about the whole thing.

Anyway, moving forward, I'm happy to spend a bit of time and effort making it work better. I don’t really want to spend another small fortune redoing the whole thing again unless I have to.

The remote filter console has a built in thermostat that starts to open at 165 Deg F and is fully open at 180 deg F. When the oil is cold it will only go to the remote filter and back to the engine. It won’t go to the remote cooler until the oil temp is greater than 165.

Sweet - so let’s review the check valve. It works via differential pressure that is a function of the area of the check ball exposed on the filter supply side (which is smaller) and the area of the check ball that is behind the filter (which is larger).

The spring that is there is very low rate and basically exists only to keep the check ball in contact with the orifice during initial start up before oil travels through the filter media reaching the back side of the check ball.

So how exactly are you going to modify the check valve to adjust the pressure at which it operates since that is a function of the exposed ball areas on each side of the orifice?

Basically your options are plug it completely or design your own check valve by altering the ratio of exposed check ball areas.

Food for thought.

Sadly, the old saying "if you want something done right, you have to do it yourself" is almost always true...

Whenever I take a car in for factory warranty work, I ALWAYS have an envelope taped to the steering wheel addressed to "The technician working on this car".

Inside is a gift card to a nearby eating joint, Chilies, Outback, whatever.

And a note: 'Been in your shoes, HATE WP! Please accept this token of gratitude for your careful considerations with my vehicle".

This works SOOOO freaking good!

Thanks Hawk!
I'd never thought about it before, modifying that will be almost untestable.

Every modification I've ever done (or seen!) to these was to plug them off which is GRAVY to do.

No one has said "lets increase the bypass pressure point".

It's always been "plug that crap OFF".

To modify the check valve relief pressure, change the spring rate. Ie a heavier spring to increase the relief pressure.

When the valve is closed, the effective area of the valve is the area of the hole on which the ball seats. The edges of the ball that are larger than the hole have the same pressure on both sides, which cancels each other out. So it’s just the hole diameter that’s used in the [pressure=force/area] formula.

The spring will dictate the [force], the [area] is calculated as mentioned anbove, and that allows calculation of relief [pressure]. I know there are other factors when the valve opens eg pressure drop on opposite sides of the ball when oil flows through the valve, but I don’t think that sort of accuracy is needed here. I’m more concerned about opening pressure.

That’s brilliant!

I want to make sure I don’t create an excess pressure issue for the stock oil pump but I also want to make sure whatever I do works. A stronger spring will compensate for the extra backpressure of the remote filter/cooling circuit. I’m a bit concerned about blocking it completely, but maybe I shouldn’t be? I’ve used 5/8” full flow fittings and hose, and the cooler and remote filter mount use -10 ORB (5/8” O-ring sealed) fittings. I’m just not sure whether that setup will result in peak backpressure with hot oil of eg 5 PSI (ie in the the remote circuit) or something much larger.

If you are going to ignore the annular sealing area effects completely, then why not measure the check valve spring force directly and get the answer you originally were seeking?

Can I insert just a couple basic questions here?

- If you're removing the oil filter and replacing it with a sandwich plate...why would oil go through the bypass, given same psi on both sides of the ball with, as noted, a larger surface area on its back side; and

- Even if it does go through the bypass, whether fully or even slightly, why do you care? You could remove the checkball and spring entirely and the oil is still flowing from the inlet to the outlet.

And...discuss.

EDIT: Here's where you shold be focusing your energies:

http://www.914world.com/bbs2/index.php?showtopic=236133
https://tangerineracing.com/shop/ols/produc...re-relief-valve

I don’t want to answer for OP but my understanding is he is worried about bypassing his external oil cooler and overheating. Operating oil pressure hasn’t been part of this conversation.

I view this discussion as largely theoretical. Unless the external oil cooler and plumbing is stupid restrictive the bypass in the oil filter console is a non issue.

On the other hand, if you do have a HIGHLY restrictive external cooler and hose assembly, the last thing in the world that you ought to be doing is plugging or increasing the relief pressure of the oil filter console bypass.

That situation of high external oil cooler restriction, is basically the same limitation of oil flow as a plugged & restricted oil filter. This can cause bearing damage due to loss of pressure and flow at the bearings. Which of course, is why the automotive engineers that designed the system put the oil console relief valve in there in the first place (ie to ensure oil gets to the bearings). This is why I initially suggested that the oiling diagram be looked at closely.

I suggest it's a non-issue. But if you're that worried about it then stop using those cheesy cheap-ass sandwich adapters and use one of Chris' good bespoke ones:

https://tangerineracing.com/shop/ols/produc...-oil-cooler-kit

And now we’re back to the post #8 in the thread

That’s an option. My first preference was to ask whether someone knows the spec. I can only do this work in my driveway and we’ve had 40 deg C days, thunderstorms etc. plus I’m leaving on a 1,200 km trip in the morning so I need it together and running now. I’m going to the Bathurst 12 hour this weekend. Disassembling and measuring needs to wait a few weeks.

Because it’s not the same PSI on both sides. That’s the issue here. The pressure difference between the upstream side of the valve and downstream side increases because of all the backpressure in the hoses, remote filter mount, cooler and fittings that are now positioned between the upstream and downstream sides of the valve.



Because bypassing the valve bypasses the remote filter and the oil cooler. I don’t want it doing that when cooling is needed. I installed a remote cooler so it would cool the oil, not bypass.


Haven’t looked at these yet.

I looked at those two links and they’re not relevant. They’re considering the engine pressure relief valve, not the oil filter bypass valve.

Because I’ve never seen this option! I’ll check it out.

The oil filter bypass valve piqued my interest so I bought a second hand filter console and just did a quick test on the bypass pressure using compressed air. It started bypassing at about 12 PSI and peaked at about 16 PSI with a lot of air flow going through. (Refer next post before using these values!)

Conclusion: if the remote oil filter and/or remote oil cooler circuit has more than 12 PSI pressure drop at highway cruising rpm or hill climbing rpm, then the remote circuit will start bypassing and the performance of those remote components will start to diminish. And, if the pressure drop is upwards of 14 PSI, then the remote circuit will probably not be effective during those cruising/hill climbing rpm just when it’s needed. Of course that assumes the oil is up to full operating temperature.

My guess is that the pressure drop won’t go near 12 PSI if the remote circuit hoses and fittings are generously sized and oil is warmed up. The next stop for me is to measure the pressure differential in the remote circuit at high rpm with oil temp over 190 deg F. If that’s e.g. only 5PSI, then it proves theres absolutely nothing to worry about.


Click to view attachment

The above pressure readings were measured using the bottom 1/3 of a leak down tester pressure gauge so accuracy is a question mark on this method. So I thought I’d verify using a different method.

I just used electronic kitchen scales to measure the force required to crack open the valve (0.45 kg) and to fully open the valve (0.85 kg). I then used vernier calipers to measure the valve seat inner diameter (11.1 mm). If you do the calculations you get 6.6 PSI to crack open the valve and 12.5 PSI to fully open the valve. Quite a lot different to the air pressure readings.

I’ll have to do the actual pressure test on the valve again with improved accuracy as the two methods should somewhat verify each other.

Interesting data points.

Food for thought on the differences between measurement methods.

Air is a compressible fluid and will behave somewhat differently than oil which is incompressible.

Likewise measuring the spring force was done using a solid incompressible probe of some sort and will be different than what compressible air does.

Very cool that you’re getting some data points.

Okay, I just used a brand new gauge with 0-15 PSI scale to measure bypass pressure with air using a leak down tester.

Bypass starts to open: 6 PSI but flow is just seeping through
Bypass fully open: 10 PSI with significant flow

These values are very similar to the values I calculated using kitchen scales so I have a high confidence that the values are ballpark within say plus or minus 1 PSI.

Click to view attachment

Next step is to fit the two pressure tappings into the oil cooler lines and measure the differential pressure. Hopefully it’s less than 6 PSI at peak engine rpm.

Click to view attachment

Referring back to the above comment, I’m interested to know whether you have a feel for whether the external oil filter/cooler circuit is likely to represent more than 6 PSI pressure drop at redline. It’s a genuine question because I don’t have a feel for the quantum of pressure drop at all. I spent 20 years in the water industry doing a lot of pressure drop calculations on large pump systems (e.g up to 5,000 gallons per second) but that’s on cold water, not on hot viscous liquid through tiny hoses and fittings!

Comments have been made in this thread that there shouldn’t be more than a couple of PSI drop over the filter, so that leaves say 4 PSI for the remainder of the circuit. That’s not much, but maybe the flow velocities are very low??

You’re in uncharted territory as far as I know.

I certainly have not done the data collection and in general I’m not a fan of external coolers and trying to keep oil at 180F so I have that built in bias.

Here is a Samba thread on flow volumes for a T1 engine with a 26mm pump has oil flow volumes in the 6-7 GPM range that seem plausible to what I have previously seen published for Small Block Chevy circle track engines that want filters rated for 10 GPM.

Samba
https://www.thesamba.com/vw/forum/viewtopic.php?t=166608

Chevy
https://www.chevrolet.com/content/dam/chevr...NAL-2-13-23.pdf

I know this doesn’t answer your question about pressure drop across the external cooler and plumbing but may help with the magnitude of flow rate.

Interesting side note: at 100C oil can be lower viscosity than water. Might be interesting to use your pressure drop calculations and see what your prediction is vs what you measure.

Yes it’s helpful thanks Superhawk.

I did some calcs and it tells me I should expect about 7 PSI pressure drop at 5,000 rpm considering only the hoses.
I haven’t calculated the pressure drop through the filter, the fittings, the oil cooler.
I’d say it backs up the thinking that there’s cause for concern and that oil pressure drop measurements would be a good idea.

Food for thought

If you look at histograms of average vehicle speed, engine speed, and vehicle acceleration you will find that the amount of time an engine spends at 5000 rpm is trivial. It is out beyond 3 standard deviations.

Full on racing is different. Occasional autocross and track events would only skew that distribution minimally. The reality is engines don’t operate at 5000 rpm much at all despite what we think as enthusiasts.

Likewise at 5000 rpm the engine fan is providing the bulk of cooling. Not the oil cooler.

The worst case for cooling is when engine speed (ie fan speed) is low and load is high. This is usually in town at idle or when repeatedly accelerating away from traffic lights. On the highway, where aerodynamic loading becomes significant, you’ll find that your engine speeds are more like 3000-3500 rpm.

So ask yourself why would you be concerned if the external oil cooler had some minor bypass at 5000 rpm?

Yes all very pertinent considerations.

However, for my rig the oil temp gets hottest when cruising on the highway and I’m not changing the fan so that pretty much leaves an oil cooler as the alternative.

At 68 MPH, the engine’s doing 4,200 rpm. Being an auto, it drops into second gear on significant inclines and then it’s up to the driver whether to sit on e.g. about 5000 rpm at 55 MPH or something less. There are plenty of long hills like that over here and whilst I agree it’s going to represent a small percentage of driving time, it’s in my opinion the most important time for the cooler to be doing its job at best possible efficiency. The last thing I want at that time is for the cooler to be bypassed. And yes, I probably wouldn’t be too concerned about the bypass slightly cracking at 6 PSI at 5,000 rpm (I rarely push it that hard), but if it’s 8 PSI at 4,000 or 9 PSI AT 4,500 then that is something I’d like to fix! The calculation said I’ve already got 7 PSI without considering fittings so I think it’s heading that way.

Wow! There’s so much going on in that one statement.

The only thing I can do is cheer you on with the data acquisition and testing!

I’m truly impressed at what you’ve measured thus far. Will be curious to see what you come up with measuring the pressure drop across the operating system.