What were VW thinking when they made the dual-relief case?

[Jon]

In the single reduced case they did it all with one piston, before the oil gallery.  Then in 1970 they added another valve to regulate the pressure AFTER the gallery, I have all my life believed that that was an improvement. But I can't seem to find any other engine constructed that way, most regulate directly at the pump. In the field of hydraulics the story is different, where the regulator is usually after the "consumers". But hydraulics are considered a "closed" system and a engine is considered "open" due to the controlled leaks in all the bearings.
The trend today is to block of the valves and introduce a regulator in front of the main gallery, to gain more consistent oil pressure?? Are we going backwards or were they (vw) completely lost?

Please, would someone enlighten me, what were they trying to fix?

[Lee.C]

Hmmmm interesting.....

I look forward to hearing some "Engine-builder's" ideas on this 

[modnrod]

Please, would someone enlighten me, what were they trying to fix?

Using incorrect oil viscosity in a single-relief case can cause all sorts of problems, both immediate and in the long-term.
Maybe they were trying to "idiot-proof" it! 

[Jon]

So that makes the vw engine more idiot proof than say a chevy 350?
Are you thinking about the valve getting stuck open?
 

[Torben Alstrup]

Can´t say for sure, but IMHO the reason must be that in an ACVW or any aircooled engine, the oil carries a larger part of the cooling than in a water colled engine. That also means that the oil temperature and thereby the viscosity varies a lot more than in a water cooled. In order to get the most even oil pressure/supply to the bearings the second relief valve was added.
If you look at a WBX case, they went back to sgl. relief. And my theses hold water 

T

[Lee.C]

Can´t say for sure, but IMHO the reason must be that in an ACVW or any aircooled engine, the oil carries a larger part of the cooling than in a water colled engine. That also means that the oil temperature and thereby the viscosity varies a lot more than in a water cooled. In order to get the most even oil pressure/supply to the bearings the second relief valve was added.
If you look at a WBX case, they went back to sgl. relief. And my theses hold water 

T

I was hoping you might drop in...... Interesting thoughts 

[Cheesepanzer]

I suspect it was designed to improve cooling.  The first dual-relief case was 1970, I believe.  Emissions equipment was becoming more advanced, gasoline was changing, all for cleaner air.  These changes were driving up engine temps to improve emissions.  Oil temp is key in our engines, so....

[glenn]

My understanding is the one toward the crank pulley is the oil bypass valve and prevents excessive oil pressure from blowing out the oil cooler and seals. The one toward the flywheel is the oil control valve and bleeds off excessive oil pressure to the case protesting the bearings and lifters.

They serve different purposes.

[Jon]

Can´t say for sure, but IMHO the reason must be that in an ACVW or any aircooled engine, the oil carries a larger part of the cooling than in a water colled engine. That also means that the oil temperature and thereby the viscosity varies a lot more than in a water cooled. In order to get the most even oil pressure/supply to the bearings the second relief valve was added.
If you look at a WBX case, they went back to sgl. relief. And my theses hold water 

T

Thats quite interesting, sounds plausibel with the wbx and all. The pressure valve in the wbx is just doing one job I guess, regulating pressure and nothing more. Or is it also routing to the oil cooler?

The heat aspect is interesting as the pressure regulated early on (before the main gallery or outside the case) is done with relatively cool oil that has higher resistance to flow into the main gallery. As the oil passes down the gallery it picks up heat and looses pressure, or am I wrong? That would mean a post gallery regulator would ensure you regulate on the thinnest/warmest oil... But is the result a more even pressure?

[Jon]

My understanding is the one toward the crank pulley is the oil bypass valve and prevents excessive oil pressure from blowing out the oil cooler and seals. The one toward the flywheel is the oil control valve and bleeds off excessive oil pressure to the case protesting the bearings and lifters.

They serve different purposes.

For sure, but didn't the first one do it all in the first version? What did they gain in you eyes by changing it?

[modnrod]

So that makes the vw engine more idiot proof than say a chevy 350?
Are you thinking about the valve getting stuck open?
 

VW possibly didn't want to develop a reputation for being an oil leaking little motor that didn't last long.
Real engines MUST take 20W50 surely? 

[Torben Alstrup]

Well, the above answer was the short version. To explain it completely would require taking a lot into consideration.

To start with the last first. VW NEVER recommended 20w/50 on this side of the Alps. That´s something the community adapted from the racing world, where the engines were, - and are to a certain extend, built with larger tolerances so that there was room for a little expansion and less drag. In order to compensate for that and have a fatter oil film 20w/50 oil was/is widely used. In a street engine, even one with a liter output of about 70 hp/l and a 7000ish red line, (Perhaps even more than that) there is no need to build with larger tolerances to overcome these problems. 2 reasons : 1. Today we have really good oils that carries a lot more than the general oils did just 20 years ago. 2. Today we are generally much better at controlling the oil/case temps than earlier. So again, no need.
Also, in stockish engines with no external thermostat, you will soon develop a temperature problem if you run too high a viscosity, especially if nothing is done. The reason is that the oil pressure relief valve(s) act like a thermostat. IF you use a fat oil you will not notice much when driving around town. Once you get on the motorway you will notice that the oil temps climbs nice and steady, and keeps climbing to unacceptable levels, even at relatively low speeds where a stock engine should/could handle the load with no problems. (Assuming the trim and air supply is as should be) The reason is that the engine "thinks" that it is half cold, because the viscosity is high, so the relief valve is open and the system bypasses the oil instead of routing it to the cooler.
That is the very simple reason as to why 50% of all the guys that runs 20w/50 oil in their old cars have problems when going fast over longer distances.
Now, switching to a lighter viscosity will help the relief system to do its job as supposed to, and suddenly the engine does not overheat at regular freway speeds anymore.
On engines with external thermostats and coolers this problem hardly exists because then the thermostat is temperature controlled and forces the oil through the cooler when it gets warm enough.

Then there is the drag of fatter oil and big oil pumps. I did some testing on a 2 l. type 4 some years ago, where I tried using a 30 mm pump with 20w/50 Castrol (deliberately chose that one as that is what people generally think is good) also a 26 mm pump. and the same pumps with 15w/40 Shell Rimula with a shot of ZDDPlus. The difference was even "worse" than I expected on this low reving engine with peak hp at 5000 rpm
Note, this engine has otherwise stock oil system.

30 mm pump and Castrol 20w/50,  101 hp @ 5050 and 170 Nm peak torque @ 3540 rpm.
26 mm pump and Castrol 20W/50, 103 hp @ 5100 and 173 Nm peak torque @ 3600 rpm.
30 mm pump and Rimula 15w/40,  104 hp @ 5100 and 174 Nm peak torque @ 3600 rpm.
26 mm pump and Rimula 15w/40,  107 hp @ 5170 and 177 Nm peak torque @ 3650 rpm.

As you can see there is a significant difference depending on which set up is used. A 6 hp difference in drag at 5000 rpm is A LOT. Think of how much the oil pressure relief system has to work extra to compensate in the "worst" set up contra the "softest" set up. this engine resided in a buggy with huge rear tyres. But even with those the power gain was definitely noticeable when you drove the car.

Now, wrt the dual relief question.
I do not buy the "heating up" answer throught the case to be a motive for altering the oil system to dual relief. The reason is that the oil is warm already, so to speak. It either comes directly from the sump/pump or it comes from the cooler, and it happens so fast that there is very little time to pick up temperatures from the case before it reaches the bearings or the lifters and subsequently the cylinderheads.
Still IMO, it is most likely not the total answer, the main reason is that with the dual relief system you now have larger oil passages and a larger oil pump. This ensures superior oil supply to the bearings at all times. But the pressure/volume is actually too large when the engine is cold and also at higher rpm. When the engine/oil is cold the main bleed relief is at the pressure plunger at the pulley, as it is adjusting the amount of oil going to the cooler. The resistance is high, so the oil gets bypassed directly into the oil gallery and excessive pressure get routed back into the sump by the front relief plunger and also the pressure relief in the back of the case.
when the oil gets warm the rear relief plunger closes the bypass and sends the oil through the cooler and then down into the oil gallery. At this stage the volume is relatively high because the oil floats well since it is warm. Now the volume is higher than what is actually needed for the bearings etc so now the front plunger bleeds the excessive volume back to the sump.

The WBX does not need the second bleed relief as much because it has a heat exchanger, which means that the oil reaches operating temperature fast (As soon a the water temp is up the oil temp is too) Also the WBX and most of the type 4 cases have a slightly different oil system. They bleed excessive oil right back to the oil pick up, which again aids in supply stability, but also aids in quicker oil warm up Also the supply to the lifters are larger, which means less resistance so the difference in oil pressure from the main gallery to the outer lifter is minimized. - This is also why we perform the HVX mods to engines that are high rpm, high power, and especially those which run sustained high rpm to ensure adequate lubrication at all times.

Hope this helps.

T

[modnrod]

I could have said that.......

Well said Torben!

[Jon]

Thanks for a awesome answer Torben, I think you have described why VW needed a upgraded relief system. But I still can't quite grasp why they didn't just enlarged the solution they already had.
But for sure, with the wrong viscosity you might end up dumping most of your oil straight back to the sump on a cold engine with the old system.

excessive pressure get routed back into the sump by the front relief plunger and also the pressure relief in the back of the case

I thought there were only one way back to sump? Or am I misreading you?

[Eddie DVK]

Cool Info Torben,
Do you also have oil presure readings from those test at idle and maybe 5000RPM.

Regards Edgar

[jamiep_jamiep]

By the way VW did make a single relief version of the late case with the larger passages etc. in fact it has the case mouldings for the second relief but not machined. I have one kicking about somewhere.

[Torben Alstrup]

Thanks for a awesome answer Torben, I think you have described why VW needed a upgraded relief system. But I still can't quite grasp why they didn't just enlarged the solution they already had.
But for sure, with the wrong viscosity you might end up dumping most of your oil straight back to the sump on a cold engine with the old system.

excessive pressure get routed back into the sump by the front relief plunger and also the pressure relief in the back of the case

I thought there were only one way back to sump? Or am I misreading you?

T

No there are two passages back to the sump. The front one is rather small, only about 4,5 mm if memory serves.

Eddie, The oil pressure at 5000 rpm was just over 4,8 bar @ 80 degree C. with the heavy weight and just under 4,5 bar with the lighter weight oil with the 26 mm pump. With the 30 mm pump it wqs almost 5,5 bar. No need for that.
At idle there was 0,3 bar difference from highest to lowest. But who needs 1,5 bar at 800 rpm idle warm (?)
T

[Martin S.]

Interesting discussion. It would be so cool to get one of the air cooled VW engineers on here who designed the system and hear him explain it. It was only 40 years ago so these guys are probably still around...

[Jon]

Thanks for a awesome answer Torben, I think you have described why VW needed a upgraded relief system. But I still can't quite grasp why they didn't just enlarged the solution they already had.
But for sure, with the wrong viscosity you might end up dumping most of your oil straight back to the sump on a cold engine with the old system.

excessive pressure get routed back into the sump by the front relief plunger and also the pressure relief in the back of the case

I thought there were only one way back to sump? Or am I misreading you?

T

No there are two passages back to the sump. The front one is rather small, only about 4,5 mm if memory serves.

I was just looking at my cases, and I can find only one overflow pressure passage, near the flywheel. Sure there are bleed passages beneath both valves, to prevent hydraulic locking of the valves.  But they are not regulating pressure.

[Stripped66]

Interesting discussion. It would be so cool to get one of the air cooled VW engineers on here who designed the system and hear him explain it. It was only 40 years ago so these guys are probably still around...

It would probably sound like this:

"Let me zhink...ja, I remember. Our project manager vanted zee oiling zystem redesigned. Vee came upf witz an elegant dry-zump (vich was later adopted in zee Porsche 911), but zee bean-counters told us "NEIN!!! Zhu teuer!!! Das ist nicht akzeptabel!". Project manager said, "vell...change sumpfthing". Sooo, vee add doohickey over here (shrugs shoulders while pointing to flywheel end of case)."

(the above account was created from my limited memory of my high school German language class, and my trusty German-to-moron translator)

Joking aside, most great designs are thwarted by the accounting department, and we're left wondering what the engineers were thinking when it likely was a compromise loosely resembling the design they really wanted. Though I do like Torben's explanation I find the design of the Type 4 oiling system perplexing in light of how we perceive the deficiencies of the Type 1 design.

[Martin S.]

Haha, when I said that when my wife was in earshot, she said she'd like to meet the guy who designed the seats and kill him