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

[Seabird]

Bill, your words were prophetic!

Got to Sebring Saturday afternoon. Found Shane in the usual spot on the paddock. And began to unpack. Registration and Tech with Chin was a breeze. We were set for a nice day at the track. Little did we know there were gremlins laying in wait for us.

(IMG:http://www.914world.com/bbs2/uploads_offsite/dl.dropboxusercontent.com-16683-1402434139.1.jpg)

The long and short of temperatures was with the distraction of what was to come with oil pressures we got very little data on the cooling and the cooler bypass blank off kit. Between the rusty relief valve that was in the motor when purchased and a still unknown oil pressure issue I was not able to enjoy even half a session. We will try again in two weeks though so stay posted.

Sunday morning after the drivers meeting there was an open track warm up session which I was going to use to get in the grove before my evaluation session (first time running with Chin.) I could not even complete a warm up lap before my oil pressure dropped to the floor!!

As I idled in and through the pits pressure came back. 65-70 psi at idle. I thought maybe there was an air pocket in the cooler circuit and now its gone; head out and keep an eye on it. Nope, I got as far as Bishops Bend this time and the pressure disappeared. Idled in and hoped I did not do any serious damage.

A discussion among the friends on hand and we decided to check the pressure relief spring assembly. What we found was shocking to say the least.

(IMG:http://www.914world.com/bbs2/uploads_offsite/dl.dropboxusercontent.com-16683-1402434140.2.jpg)

Yep that is a rusty and scored piston and spring. If you have not inspected your oil pressure relief system in a while now is the time.

Our best guess of what was happening was that with the high oil pressures the engine was making the relief valve was fully extending and getting jammed open. A little jostling around and it would release. I had a new Weltmister high pressure kit on hand so that was swapped in. Ran a session with the fresh Weltmister piston and the rusty spring. Started to see ugly pressure drops after a few laps so I returned to the pits.

At this point we decided to test out the Foley blank off sleeve and piston. Very nice fit and finish. (I did not photograph it but I'll pull it out in the next day or two and post a picture here.) Ran a few more laps before the oil pressure light came on. At this point we were starting to suspect something else was causing the pressure drop off issue. The oil was hot but not hot enough to cause the massive pressure losses so soon.

For the four session we played around with some shrouding to block off hot exhaust wash from the headers entering the cooler. No significant change to oil temps. Pressure drop caused me to come in after 11 mins on track (IMG:style_emoticons/default/stromberg.gif)

Fifth and final session I decided to take it easy take a Sunday drive; it had not blown up yet might as well relax a bit and enjoy what was left of the day. More of the same. Got 16 mins in this time.

A big thanks to Shane and my friend Mike for coming out and lending a hand!! As usual Chris Foley's support and advice has been wonderful.

We have a few areas were I am going to look for the problems. Hopefully the gremlin will get sorted for the next track weekend. Stay tuned.

Miguel