Oil Pressure Relief Valve – 1967 H0-xxx-xxx Engine 1500 series – Part I

I never had studied the Oil Pressure Relief System. A young VW friend called to tell me about “some sort of oil pressure problem” he was having. As it turned out, it was unrelated to the Relief System. It was a blockage which trapped Crankcase Pressure

But I was prompted to look into the Oil Pressure Relief System. In communication with the local VW Engine Builder, Barry Blythe, he and I briefly discussed Oil Pressure. This prompted me to look for information in the common VW informational source—the Bentley Official Repair Manual. I also found a YouTube video where a person was having what he supposed to be an Oil Pressure Relief System problem. My interest only increased.

I turned to my parts bins and sorted the parts which related to this System. At this point, I had little information and the pile of parts on my work bench was without any semblance of order. I took the parts to Barry and we sorted and organized them. Some of the springs were distorted. We finally arrived (from my jumble of parts) at a coherent set both for the Oil Pressure Relief System and for the related Control System (for 1970 and later VW engines).

Now, at least, I could begin a study with the correct parts—or what I thought were the correct parts. Since I wanted to focus upon the 1967 H0- engine, I geared my efforts to learning about that particular year. I contacted David Brown in Pennsylvania, who maintains parts manuals and other pertinent VWaG and VWoA Literature.

Definition had begun!

Those early Volkswagen engineers used their math skills and slide rules to great advantage. Computer technology was, perhaps, not even a day-dream during their life-times. Engine cooling already was thought through and in common usage for internal combustion engines of all sorts. Air-cooled technology was in use in the fields of automotive, motorcycle and aircraft engines. It would be an interesting study to learn how such technology was used for other types of automotive air-cooled engines. That’s for you, my Readers, to delve into on your own.

But, we must concern ourselves here with what interests us of the 1967 Beetle Community the most—our 1967 H0- air-cooled Engines.

If you do not care to read the more technical aspects of this subject, skip to Part II (coming soon), where I outline the importance of maintaining the Oil Pressure Relief System in your 1967 Beetle.

I referred to Bentley’s Official Service Manual (Blue Cover) which treats 1966-1969 Beetles and Karmann Ghias. I like the 1986 Edition, which is more complete on the subject of Engine Lubrication than are the earlier Editions. This is important because earlier Editions lack some of the diagrams/depictions which the 1986 Edition features.

Please refer to Section 2, Engine, pp. 46-53.

John Muir, in his How To Keep Your Volkswgen Alive–A Manual of Step by Step Procedures for the Compleat (sic) Idiot, 1981 Edition, pp. 83-91, Oil Pressure, also throws light onto the subject.

Noting that H0-xxx-xxx engines (for 1967) do not begin with the part Number H0-000-000, David Brown says:

“H0 204 001 was the first 1500cc engine listed in my Parts Book as the beginning of production of the 1967, 1500 Beetle. There were 1500cc engines used in both the T-2 and the T-3 in earlier years. This might account for the large number (apparently) of 1500cc engines by the time the 1967 Beetle/Karmann Ghia came along in August of 1966.”

In this article, I am going to treat ONLY the H0- of the H Series of Engines (1967-1969 Beetle/Karmann Ghia).

Not only so, but I am limiting this study to engines beginning AFTER production had begun, which did Not include the first H0- engines installed into the new 1967 1500cc Beetle.

In fact, VW tells us (see the reference to the Blue Cover Bentley’s above), on page 50 that:

“In the 1500 engine, from chassis # 117 054 916 and engine # H0 225 117, (the) piston (plunger) of (the) oil pressure relief valve is modified. This new version of piston has an annular groove, which allows oil to pass directly to the sump, relieving pressure and lowering oil temperature”.

Chassis # 117 054 916/Engine # H0 225 117 (according to thesamba.com, Technical, VIN/Engines Codes) had a manufacturing date of Aug 15, 1966 and was a 44 bhp DIN.

Indeed, in going through my parts, I had discovered 3 different Pistons. Non-1500cc Pistons were simply straight-sided pistons while the reconfigured Piston for 1500cc Engines had the Annular Groove.

I also discovered pistons with not only the Annular Groove but which had a modified, beveled Groove. I verified that these latter Pistons were after-market parts designed for modified Engines using high oil pressure pumps and accompanying parts—designed particularly for racing engines, etc. Such modified annular grooved pistons are part of kits called “oil pressure booster kits”. These kits are unnecessary for the stock VW H0- Engines which most of us own.

The Single Oil Pressure Relief Valve for the 1967-1969 H0- Engine is located at the Crank Pulley End of the Engine (driver’s side, bottom—engine in the car)

The VW Part Numbers and Specifications for the New Oil Pressure Relief System Elements are as follows:

• 311 115 411 Oil Piston (alternate name is Plunger) [Bentley’s refers to these as piston/plunger] 113 115 421 Spring
  113 115 431 Plug
  N 013 817 1 Seal for Plug C 18mm id x 22 od ….The “C” denotes Copper. Aluminum originated with all of the other reproduction parts in engine gasket kits.
• Spring–Unloaded Length 62 – 64 mm
• Spring–Loaded Length 23.6 mm producing a spring pressure at this height of 17.1 lbs (7.75 kg)
• Diameter of the Piston—approximately 16mm

The Engine Case used in this exercise is H0-653-501. The Case is one which had been damaged beyond repair. I bead-blasted the Case Half which houses the Oil Pressure Relief Valve, in order to have a clean Case for demonstration purposes.

Cautionary Note: Never media-blast a viable VW Engine Case. Such cleaning measures are likely to damage the Case beyond use. As well, medium can infiltrate gallery recesses only to reappear during subsequent operation to damage important bearing surfaces. There are special cleaning solutions used in vats, or special pressure washers for cleaning VW Engine Cases. In my experiment, I knew that this Case never could be repaired for rebuilding.

Our Engineer Son, Kevin Salser, spent time calculating “pressures” based upon measurements provided by VW, David Brown, Barry Blythe and my own measurements of parts. He says–

“David Brown indicates that the specification for the Loaded Length of this Spring is 23.6 mm — producing a Spring Pressure, at this “height”, of 17.1 lbs (7.75 kg). Given that information and knowing the surface area of the Piston Face, we can calculate that any pressure above approximately 55psi will begin to move the Piston against the Spring Force. [i.e.—the Spring is compressed when it is installed by screwing the Bottom Plug into the port. This holds the Piston against the top of the Chamber. When the Engine is started, the Pumped Oil exerts pressure upon the face of the Piston which pushes the Piston downward against the compressed Spring–if the oil pressure exceeds about 55psi.]”

Kevin continues:

“The Piston Face Diameter is about 16mm, or about 0.630 inches. To calculate the surface area of the Piston Face, the formula is PI times the Radius Squared.

The Radius is half the diameter–about 0.315 inches. The surface area of the Piston Face is therefore about 3.1416 x 0.315 x 0.315, or about 0.312 square inches.

According to the specifications, the Spring is exerting about 17.1 lbs of force against the Piston. That means that the Oil has to push against the Piston Face with more force than 17.1 lbs to move the Piston against the Spring Force. Since the surface area of the Piston is about 0.312 square inches, the Oil must push downward with more than 17.1 lbs per 0.312 square inches. 17.1 pounds divided by 0.312 square inches is about 54.8 pounds per square inch– call it 55psi in round numbers.

Said another way, 55psi applied to 0.312 square inches is about 17.1 lbs. 55psi x 0.312 square inches = 17.16 lbs.

Keep in mind that the 55psi result is an approximate/nominal figure. Differences from one spring to another, or differences in Piston fit to the cylinder could cause the exact value to vary from one engine to the next.”

**The important thing to remember is that there are two opposing forces in play: the Spring is exerting pressure to hold the Piston to the top of the Chamber. The Pumped Cold Oil exerts pressure wanting to push the Piston downward.

David Brown adds: “The question of ‘how much oil pressure?’ is a moving target. Temperature, Oil Viscosity and Engine Wear greatly affect this.”

When the Cold Engine is started, the Piston is forced downward by the “thickened” Oil to divert most of the Oil away from the Oil Cooler. Remember—it takes somewhat in excess of 55psi to over-come the Spring Pressure. The “thickened” Oil provides the process by which this happens.

But, as the Engine and Engine Oil begin to heat during the combustion process, the Oil “thins” and the Piston moves ever closer to the Barrier, again sending most of the Oil to the Oil Cooler to be cooled. The “thinner” the Oil, the less force it takes to pump it through the Oil Cooler. And, the easier it is for the Spring to regain control over the pumped Oil by exerting force against the Piston—pushing it upward against the Barrier.

I have labeled this hand-drawing of the front of the Engine Case showing the journey of the Oil from the Pump using 1a through 1d to show where the Oil is going when the Engine/Engine Oil is hot—based upon the fact that the Piston is pressed against the Barrier by the force of the Spring.

1a—The Piston, at Hot Engine, is pushed by the Spring to the Barrier. The Oil goes to 1b- the Oil Pressure Switch, the Oil Cooler and then to the Crankshaft and Cam Bearings.

1b—Most of the Oil is going to the Oil Cooler where it is cooled, then pumped through all Crankshaft Bearings and Cam Bearings before returning to the Oil Sump.

1c—directs pumped Oil (from the Oil Pump Gallery) to both front Crankshaft and Cam Bearings through a shared side opening in the Pump Gallery.

1d—is closed when the Piston is at the Barrier. 1d is opened when, at Cold Engine, the Piston is forced downward by the Cold Oil, which then bleeds around the Annular Groove into the Cam Housing and thence to the Oil Sump.

Cold/Thick Oil pumped straight through the Oil Cooler can damage the cells of the Cooler.

David Brown reports:

“In my “Fabulous Failures Collection” I had a Beetle Oil Cooler that was ballooned so much that the flat Oil Cooler passages were almost round and there was no space between them for the cooling air. I had a hard time removing the Fan Housing.”

By diverting most of that Cold Oil, the Oil Cooler is spared the excessive pressure which otherwise could damage it to the point of splitting the cells.

I agree with Kevin when he says:

“This leads me to believe that the engineers….designed the Oil Pressure Relief Valve to never bypass Oil from the Oil Cooler except in cold/warm-up conditions to speed warm-up and to protect the Oil Cooler from excessive pressure, or perhaps in an over-rev situation where a pressure spike might blow out the Oil Cooler.” (and/or Oil Cooler Seals)

David Brown emphasizes that operating pressures depend upon oil viscosities. He says:

“At cold start and perhaps 2,000 RPM, with 30wt Oil, the Pressure might be 50-60 psi. But, according to Volkswagen, once operating temperature has been achieved, at 2500 RPMs (approximating 40 mph), Oil Pressure would be about 28psi.”

Remembering that at operating temperature, the Oil has “thinned” and is nowhere near the critical 55+psi needed to depress the Piston, the Oil definitely is going to be continually pumped through the Oil Cooler, then through Bearing Surfaces and finally into the Sump.

In the circuit is the Oil Pressure Switch. It has an operating range given by Volkswagen as 2.1 to 6.3psi, according to information which David Brown gleaned from his sources. David emphasizes that operating pressures depend upon oil viscosities.

David continues:

“’Normal’ Oil Pressure at Idle and at Operating Temperature should be enough to keep the Green Speedometer Warning Light off–perhaps 5-10psi.”

I ended my investigation by removing all of the front Gallery Plugs so that I could, by shining a light through them, trace the passages. It was a fun experiment, but all good things must come to an end. Now—I must find space to store yet another box of experimental goodies.

Notes:

My thanks to Barry Blythe of Blythe Enterprises. Barry took time, on several occasions, to explain parts, their dimensions and their functions

David Brown researched his Parts and Operations Literature to obtain important information regarding this subject. Besides his wealth of personal experience, I really appreciate David for having saved so much Volkswagen Literature. His willingness to discuss this subject gave me confidence to continue the discussion.

Our son, Kevin Salser, talked me through the pressure aspects of the Oil Pressure Relief System. He researched OnLine to gather information which helped to cement vital factors for the Article. He critiqued photos, drawings and other information which I provided. He was willing to explain, in layman’s terms, aspects which I had a difficult time grasping.

My wife, Neva, spent a LOT of time processing endless photos. She is so patient!