Oil pressure relief, oil cooler, and accusump interaction Options

[Seabird]

Good morning everyone. I am in the process of upgrading my oil system. This is on my dedicated track 914. The upgrades include remote oil cooler, accusump, and CB Maxi oil pump.

In my research for installing the accusump it seems like there are two places that are recommended, in the cooler return line with a check valve and direct to the block. I did not want to use the sandwich plate adapter so I opted for the block option. Simpler with less seals to fail.

As I looked into the workings of the type IV oil system I found a potential problem with both these locations; the oil relief valve on the front of the engine. VW used this valve to bypass the cooler when the oil is thick. But this also means the cooler is bypassed when the oil pressure is high. Does the use of an oil accumulator negate the oil cooler system by maintaining oil pressure?

While on the straights the pump could potentially make 50-60 psi of oil pressure. (the 30mm pump that was in the engine produces those pressures much of a 20 min session) At those oil pressures the cooler will be bypassed based on what I know of the relief valve (bypassing cooler at 60psi, partially open at 35 psi, and sealed at 12psi). The accusump will also build up to that pressure. When I go to brakes and the revs drop the accusump will start pushing back and keep the pressure up till the differential is corrected. If I am back on to the next straight in that time then the pump starts building the pressure again.

Options:

1. Am I making a mountain out of a mole hill? Leave it alone.

2. Plug that relief valve so it stays closed and let the oil cooler thermostat bypass the oil when its cold. This is a pre 76 case so there is the secondary relief valve by cylinder 1. Might be able just to invert the piston so the bypass grove is below the bypass passages.

3. There is also the high pressure pistons sold by pelican parts and others. Does this just shift the bypass window to a higher pressure range?

I would love to hear people's thoughts on this.

Miguel

[ChrisFoley]

I've been doing a little noodling on this, and even machined into a crankcase to see inside the relief bore.
I'll post pics when I have an opportunity.
One interesting bit of evidence is a wear pattern in the bore from the spring which shows where the piston resided most of the time.
It was typically being pushed down by the oil pressure far enough to expose the cooler bypass opening.

Simply increasing the pressure resistance by using a longer piston/spring only moves the problem to a higher pressure but does nothing to solve the basic problem of oil bypassing the cooler at operating rpm.

However, there appears to be a simple "drop-in" solution which I can test in the next week or two.
My solution replaces the pressure relief piston and spring, but not with just a different piston/spring.
I plan to make a sleeve which blocks off the cooler bypass circuit, but not the sump return circuit.
The sleeve will hold a smaller diameter piston/spring designed to bypass anything more than about 60psi back to the sump.
That way the cooler will always get oil flow but never see pressure above 60psi.

[Seabird]

I've been doing a little noodling on this, and even machined into a crankcase to see inside the relief bore.
I'll post pics when I have an opportunity.
One interesting bit of evidence is a wear pattern in the bore from the spring which shows where the piston resided most of the time.
It was typically being pushed down by the oil pressure far enough to expose the cooler bypass opening.

Simply increasing the pressure resistance by using a longer piston/spring only moves the problem to a higher pressure but does nothing to solve the basic problem of oil bypassing the cooler at operating rpm.

However, there appears to be a simple "drop-in" solution which I can test in the next week or two.
My solution replaces the pressure relief piston and spring, but not with just a different piston/spring.
I plan to make a sleeve which blocks off the cooler bypass circuit, but not the sump return circuit.
The sleeve will hold a smaller diameter piston/spring designed to bypass anything more than about 60psi back to the sump.
That way the cooler will always get oil flow but never see pressure above 60psi.

Great Chris! Let us know how it goes. Put me down for one when you get it worked out.

Miguel