Dual relief oiling system. How it works.

[Juanito84]

[ozzo]

I installed a vdo for oil pressure.
After 30 min driving
Idle 1 bar or 15 psi
3000 rpm 3 bar or 45 psi

Even increasing rpm pressure does not go higher than 3.5 bar warm engine.

Looks good or idle pressure is to high?
This is a european 1978 as 1600 case.... probably the pressure control bleed off is already increased because i m getting this reading with 15/40 mineral oil and 30mm pump.

[mbw65bug]

I don't think many ppl wanna read this old thread again, but I really wanna share my experience;

I decided to use 32mm pump.
My case is AS.
I enlarged the relief hole to control the pressure from 5 to 10mm.
I put 20-50 oil into the motor.
The temperature is 5℃, so 41℉.

When I started the motor, the pressure was around 3bar at 1500rpm, and even after kept idling for a half of a hour, it remained at same. VDO oil temperature gauge hadnt moved.
I revved it to 4000rpm immoderately after I started it, and the pressure was slightly less than 5bar throughout the reving, which exactly I had expected when I measured the rate of the spring of the oil pressure relief valve. So, it was great.

What was not great is I can't open the relief valve of the oil cooler. It's supposed to open more than 6bar. The pressure hardly go beyond 6 unless I recklessly rev it.

I think I enlarged the relief hole a bit too much. I hope someone can learn from my failure and figure out the ideal size for 32mm pump.

[grandpanystrom61]

wonderful thread, read it all, and still have the same question as I did not find the 1600 DP mexico AS41 engine produced in aug 1973.

I have the front control valve with the rear relief valve, pulley end.
Now the control valve has a short spring with a solid plunger, and with mild force I can screw the plug back in against the spring tension.

Now that relief plunger is got the grove in it, and has a much longer spring, and it takes a lot of force against the plug against the spring to get the threads started so I can screw it in until seated tight.

I found all this out as I was putting the temp. sensor in place of the plug at the relief valve, pulley end.

Sensor is to big for oil drain plug location, so I used the relief valve port ???? good idea or very bad one........

Would it be better located at the control valve location ?

I found out I have no oil cooler on the engine, a bypass plate was installed on the motor when fan shroud was changed, but some one just looped the a hose on the ports.

So have the smaller external oil cooler on order, will mount an the backside of the fan shroud area where those oil ports are.

What about these relief valves... mine are flat on one side and cupped on the other side......so does flat side go in first, cup side rides on the spring ?

Or does the flat side ride on the spring and the cup side faces upward when putting it into the case ?????



Help me........

[ALB]

Don't mount a cooler to the back side of the shroud- you're preheating the cooling air! Think about it- it's counterproductive- you want the air as cool as possible as it enters the fan shroud so it can carry away the most heat (that's it's purpose). The hotter the air going in the shroud the less heat it takes out (and the hotter the engine gets). Get the proper factory cooler and put it on the engine- not only is it simpler (no hoses to mess with and leak) and more compact, with the pre-doghouse shroud the cooler is needed inside to keep air pressure (and temps) even from side to side. The cooler is needed to balance the side to side airflow in the earlier shroud- without it, temps will be substantially higher on 1 side. And if it has a doghouse shroud, same thing-
get the proper cooler and all the relevant sheetmetal installed. Remember that everything is engineered to work together. And the flat part goes in first with the cupped end against the spring.

Hope this helps. Al
_________________
On a lifelong mission to prove (much to my wife's dismay) that Immaturity is Forever!!

[Drewmon]

[PT Racing]

Excellent diagrams and explanation of the oil system. Do you have similar information for and engine that uses a CB Performance dry sump oil pump set up. In this set up a separate oil cooler is used. On my race engines the original oil coolers are removed and I believe the blanking plate blocks the oil path used for the stock cooler. As I am new to VW engines, I am trying to educate myself.

[Ohio Tom]

9 pages of comments.
Thought I'd throw mine out there.

As one who has College level hydraulics and work with Hydraulics almost every day, I have a few observations:

The oil cooler valve seeks to bypass the cooler to prevent excessive head pressure created by the cooler when oil is cold.
You can call it a "relief" valve, but it's not really relieving the oil, Rather it' is bypassing the cooler.

"some" oil is always flowing thru the cooler. Once warmed up, all of the oil flows thru the cooler as long as pressure is not excessive.

The pressure control valve (a true relief valve) is factory calibrated at 42psi.
It is closed until pressure pushes it open. Pressure only pushes it open just enough to maintain 42psi. It doesn't go from zero, to 100%. It's always floating like the lid on a pressure cooker.

The 5mm relief port into the case was fine for a stock motor running 4,500rpm.

In All of the Hi-Po builds I do, I open up the 5mm dump port on the pressure control (relief) valve. This prevents the skyrocket oil pressure when cold.

A number of companies make pressure relief oil pump covers. they are nice because they just dump the oil right back to the pump inlet so there is not a drain-back issue.
Makes running a 30mm pump a good proposition.

Most high-strung drag motors want 70-80psi oil pressure.
A modification to the stock relief valve, and a 30mm oil pump are the only way to get there.

Now, most drag motors don't get a warmup cycle, so the oil is cold and you are lined up to do a 7,500rpm burnout.

This is where you NEED and external relief so as to keep oil pressure constant hot or cold.

[mark tucker]

yup