Adjusting Oil pressure?

You don't actually adjust the oil pressure with the by-pass valve, just the maximum system pressure. In normal operation the by-pass valve should never open, it's a safely think more than anything else in case the filter plugs or you put gear oil into he crankcase causing ridicules pressure.

If your pressure is running low it's because your bearings are worn or you are using too thin and oil or both. Either way the immediate cure is thicker oil.

 

I'm not sure why they used 2...maybe the oil cooler is rated at a lower pressure and they are counting on pressure drop across the filter to keep the system at a safe pressure??? I've never seen 2 used before, but both diagrams you posted are for relief valves so they don't do anything except open at a pre-set pressure from what I can see.

 

oil weight issue,
agreed with all points made here, I have switched from 20-50 SWEPCO racing oil to straight 40 wt Kendall. Oil consumption is down. I live in No Calif. so the temps are faily the same all of the time.

 

The by-pass valves shown in the diagrams are single pressure type valves. They will open and regulate pressure to a pre-set value, normally right around 90-100 psi.

So for example if the engine is making 70 psi at redline when it’s cold the valve set pressure is at least 70 psi and will be completely closed at all pressures below 70. Many filters have a built in by-pass for safety reasons, but they too should be closed under normal operation. One of the by-pass valves could be not sealed and leaking, that would cause low system pressure. It’s rare, but it does happen. It might be worth popping it apart and giving it a quick clean, but I would start with an oil change to the factory recommended oil first.

The oil pump is sized to deliver the correct required oil volume at any given rpm so pressure goes up with rpm as flow rate goes up. Pumping extra oil through the by-pass would waste power and fuel and I don’t know of any engine manufactures willing to do that, at least not in the past 50-60 years. Also, if the system were designed this way you would see the pressure go straight up the by-pass pressure right at idle and remain constant at al rpms and temperatures and of course that is not what you see happen.

As for a rod bearing failure, in almost any engine you can spin 1 or maybe 2 rod bearings without seeing a very noticeable drop in oil pressure. The bearing issue I was referring to is normal wear which causes excess clearance in all the bearings resulting in a decrease of system pressure which is most noticeable in a warm engine at low rpm.

 

Well stated Mark,

This is how it works, the relief valve is really only there to keep the oil filter (and oil cooler) from exploding at startup with cold, thick oil.

I have seen relief valves become sticky or the bore that the little piston moves in become scored but it's not typical.

If you want to try and increase the setting (at your own risk) you can add a few appropriately sized washers behind the spring and see if it makes a difference. Once everything is warmed up it will probably be as before.

 

Bypass and pressure relief are two diffrent things. There are two, three, some times four relief valves on cars, that will only opeon when max. allowable pressure is reached, air cooled Porsche 911's have a relief valve and a bypass valve in the engine case, two seprate springs and pistons. There is a relief valve also in the spin oil filter and there is one in the eternal cooler oil line with the second thermastat in the right rear fender. One car, three relief valves and one bypass valve to maintain oil pressure and two oil thermastats.
The 400 also has a 'Pop off, relief valve' and a bypass valve, very normal two diffrent valves with two diffrent tasks.
Notice the wording for fig 3 'pressure regulating valve' fig 4 'relif valve' Ferrari used diffrent terms becouse they are diffrent valves with diffrent jobs. Or they got bored with word choices and wanted to mix it up?

 

oops, got my fig 3 and fig 4 reversed.

 

The different names are more an engineer geek thing than anything else, we’ve done stuff like that at every place I’ve ever worked. The one is called a by-pass because it literally connects the pump input to the output, by-passing the pump. The second valve is a relief valve because the over pressure oil is retuned to the sump, not the pump inlet as with the first valve. The effect is exactly the same since the pump inlet is clearly connected to the sump, but in the most technical sense they are doing something different.

 

Sounds like an improvement over original.

 

Al, I am glad you have found the oil line before it broke. I also am glad you started this discussion, in an effort to prove my point I found I did not have it all right.
There were many places to look but this site was very clear http://www.hillmanimages.com/912/manual9.htmlr on an engine designed with oil coolers having two oil valves.
Mark had it right that one valve opeons only when max. allowable pressure is reached.
Having been rebuilding these engines ( engines engineered with oil coolers) for longer than I should post, becouse it will just till every body how long I can have something wrong, I knew the springs for these two valves had diffrent rates and that the pistons were diffrent, they prefomed diffrent, tasks unfortunatly not the tasks I thought they were.
The second valve I knew opeoned at operating speed and stayed opeoned but not to regulate pressure but to make sure the engine had oil and pressure before the cooler (like during start up). So clearly outlined on the web.
So thank you Al for starting this discussion and Mark,Byod and Tim for pushing points to research, I hope all are wiser for it.
Fritz

 

The VW bi-pass valve shown in the link appears to be a different design than either of the ferrari valves. In the VW valve, oil pressure is supplied to both sided of the valve thru different paths, allowing the change in oil viscosity to change the valve operating pressure and bring the oil cooler on or off line much like a thermostat would....or in the case of the VW who's oil cooler is positioned such that it drains whent eh engine is not running, allows oil to go the the bearings first, then and only then to filling the cooler.

I don’t think the Ferrari valve is like that. I’ve got as 400i engine in pieces in the basement so I’ll have a look at one tonight to make sure there isn’t another port or flow path the diagram is omitting.

I had to take the "r" off the end of the link to make it work.
http://www.hillmanimages.com/912/manual9.html