oil pressure and variable valve control

[thedawk]

What oil properties make a difference in a valve timing control systems? According to the service manual for my car, "the intake camshaft pulley position is regulated by oil pressure, which is controlled by the valve timing control solenoid valve." The manufacturer recommends 10W-30 up to 20W-50 oil depending on ambient temps. So my question is what difference would it make in a valve timing control system using different weight oil. What if I used a 5W-20 oil as opposed to 20W-50? Thanks for any input.

 

[Steve S]

What does the mfg recommend? Why would you use a 05w/20?

 

[thedawk]

The manufacturer recomends 10w-30 up to 20w-50. I'm not saying I want to use 5w-20, I'm just asking what effect would it have on the variable valve system that utilizes oil pressure. This is for a 94 year model car so 5w-20 wasn't really available back then.

 

[Gary Allan]

I think he's more curious about how the engine "knows" how much flow is required to advance the cam (I assume that we're actually talking about variable cam advance/retard and not true variable valve timing here) and that one could imagine that this would be somewhat dependent upon oil viscosity.

I could think of a few ways that I would regulate a given fluid circuit to provide a stable pressure ..but I have no idea how the engine manufacturers do it. I don't know if they have true variable cam advance or "two state" cam advance/retard. That would be simple ..you would just have a solenoid that ran in conjunction with a fixed orifice (constant flow) port. You would also have a pressure regulator that would maintain a constant pressure. When you wanted to advance the cam ..the solenoid would open and the cam would advance.

I'm sure that there is a far more sophisticated system employed. Keep in mind that although an oil pump is a positive displacement pump ..that doesn't mean that every part of the oil system is going to get a fixed portion of the flow. Otherwise you would never have a stuck lifter.

 

[nel]

I don't know what kind of car thedawk has. 20W50 makes me think it's European. On the BMWs with VANOS (1992+), there's a single helical gear that's in one position or another--which results in a 12.5 degree change in intake cam advance in the midrange. I'm fairly certain that oil pressure is just used to move the helical gear, and the system is not continuously variable--unlike the newest BMW designs.

I don't know the nominal oil pressure needed for the VVT mechanism. It's possible that if you go thin enough that the VVT may not index properly.

See BMW Vanos description and
Variable Valve Timing for more info.