914/6 conversion - help! No oil pressure!

[AlexJ]

Hello everybody, (it's "conversion" not "conversation" - I cannot edit the title.)
I am finishing a 914/6 conversion and I am having problems with the oil pressure - green light doesn't go off.

Here are the facts:
- Engine has been working fine on a testing bench, connected to a normal oil tank (from a 911)

- we installed a front air cooler
- I installed a specific oil tank from Patrick Motorsport and the correspondent oil filter console.

Here is a bad schematic Of what is installed:

[AlexJ]

After I filled 5 liters of oil and run it a couple of minutes, here are the facts:

- when we start the engine, the light goesn't go off (green light)
- we unscrew the fuel pressure switch on top of the engine, started the engine and noir oil comes out from the thread of the switch
- we filled some oil through the oil breather on top of the engine (around 2 liters) and light still on and no oil out of the pressure switch hole.
- when we filled with the first two 5 liters, the oil tank stick level, indicates around 1/3 RS of the level.
- when we filled the Engine with the extra 2 liters through the engine breather, the level at the oil tank increased to more than a half...

Can anyone help on finding the possible reason for this situation?

[Dave at Pelican Parts]

Some 911 engines (late SC?) have oil sump covers that can go on in more than one orientation. At least one of those orientations can block the oil pick-up inside the crankcase. I am not sure it would cause your symptoms, though.

I know that the Six originally took about 9 quarts of oil. Not sure if the PMS tank holds more than that or not, but the cooler lines and such certainly hold some. So you might not have enough oil, but that shouldn't result in a lack of oil pressure or flow.

How sure are you of the plumbing? It sounds kind of like the oil is completely bypassing the engine. If the cooler outlet is in the high-pressure circuit, then you're just dumping all of that back into the oil tank and not sending it through the engine at all!

Here is a diagram of the system with no external cooler in it:


Pay attention to the arrows. You can see that the cooler itself is indeed in the high-pressure circuit, after the pump and before the bearings. The line going in the bottom is a bit of a "red herring", it doesn't carry any oil to the cooler itself.

--DD

[AlexJ]

Hi Dave,
Many thanks for your comments.

I forgot to say that the engine is a 2 liter 130hp.
The strange thing about it is that the engine has been running on a test bench perfectly!
On my bench I have the circuit exactly how it is on the diagram Dave posted.
The fuel tank in car is slightly different: the oil filter and console is lower and it has the supposed outlet to feed the oil pump under the oil filter. On the face downward, at the lowest point, it has another connection to receive the line coming from the engine cooler...
Very similar to this:

[AlexJ]

What we did in fact, was "cutting" the line coming from the engine oil cooler and direct the oil flow to the front cooler and back again to the lower connector on the tank.

Dave, I will check the position of the oil sump cover but I suspect it is on the right position because the engine already run on the bench - and it had oil pressure!

[Dave at Pelican Parts]

I still think you may have the cooler in wrong. Eliminate that from the setup, and get the plumbing exactly the same as it is on the bench. If you have oil pressure at that point, then you know the problem is in the cooler setup.

--DD

[AlexJ]

Got it Dave!
Thermostat was not correctly assembled.
Thank you for your help!
All the best!

[porschetub]

Why did you add a cooler with a small engine like the 2 litre,they are fine without one ,my engine is a 2.2 and runs great oil temp.
The oil capacity for a stock 914/6 is 7 litres ,however I believe the PMS tank is larger and you will have to allow for your extra oil lines and cooler,so you may find you will have to settle on say 8-9 litres.
I run 7.5 litres because I have large diameter oil lines and my engines fine with that.
Best to contact PMS about what size your tank is as its important to get this right,911 motors do not like being run with too much oil in the tank.
Good luck.

[mepstein]

It won't matter how much the oil tank holds, the total oil volume is different now that lines and a cooler were added. You will probably need about 10 quarts total +\-

[AlexJ]

Thank you all for your comments.
Car is already working fine with the correct oil pressure.

[AlexJ]

Originally Posted by porschetub

Why did you add a cooler with a small engine like the 2 litre,they are fine without one ,my engine is a 2.2 and runs great oil temp.

Future owner wants to take the car for the track sometimes, so extra cooling had to be added.

[mb911]

Just want you to know it is plumbed wrong. Scavange side goes to front oil cooler. The bottom fitting goes directly to engine oil cooler fitting which is actually just a feed and not cooled in that location

[Coloradocurt]

Originally Posted by mb911

Just want you to know it is plumbed wrong. Scavange side goes to front oil cooler. The bottom fitting goes directly to engine oil cooler fitting which is actually just a feed and not cooled in that location

Absolutely correct..............with a minor correction.
Scavenge side goes to the thermostat before the front oil cooler.

[mb911]

Originally Posted by Coloradocurt

Absolutely correct..............with a minor correction.
Scavenge side goes to the thermostat before the front oil cooler.

Yup I just assumed everyone knew that my bad

[BoxsterGT]

Inquiring minds want to know......

What size fittings are on this custom oil tank? M26 or M30?

M30 would be my preference. I may just have to buy one for my Six project.

Len

[mb911]

Originally Posted by BoxsterGT

Inquiring minds want to know......

What size fittings are on this custom oil tank? M26 or M30?

M30 would be my preference. I may just have to buy one for my Six project.

Len

My fittings are 26mm but could weld in 30mm if you can source one. I just got a new batch of laser cut blanks for the tanks which make them even nicer.

[JimmyT]

I make weld bungs that are used in the restoration or aluminum, tube-frame prototype racers.
They fit either 25mm or 1" aluminum tube or can be welded into tanks with a 1-3/16" diameter hole.

Material: Aluminum, 6061
Thread: M30x1.5
Finish: Ra 12µm (As machined)
Weight: 32.38 grams

The price is $31.18 each.
Shipping within the US is by choice of USPS Priority ($7.15) or Parcel Post ($3.00).

[mb911]

That might be a good option..

[mb911]

Originally Posted by BoxsterGT

Inquiring minds want to know......

What size fittings are on this custom oil tank? M26 or M30?

M30 would be my preference. I may just have to buy one for my Six project.

Len

Len,

I received a few fittings from Jimmy and they are wonderful.. So now I can make a tank with 30mm fittings.

[porschetub]

Originally Posted by mepstein

It won't matter how much the oil tank holds, the total oil volume is different now that lines and a cooler were added. You will probably need about 10 quarts total +\-

Was just stating the 914/6 holds 7 litres not "about 9 litres '',well aware the pipework ,cooler and hoses will add to that,cheers.