MPG Down With Oil Change

Along with the oil change comes the change of seasons. If your local gas now has ethanol during the winter, your mileage will go down by about 2 mpg. I don't see how a change of oil would affect other components, but I'll let the engineers answer that one.

As for the original specs, RTFM. It's in there.

It's either coincidental or something else was done during the oil change. Was any other service performed? In particular, if they disconnected the battery for any reason, the ECU will have to reset all its parameters and that could affect your mileage. Also how many tankfuls have you gone through since the change? If it's only been one or two, it could easily be influenced by other factors.

I'm not an Amsoil fan, but I can't believe it has caused any change in your fuel mileage. I'd sooner think something else happened coincidentally.

I don't know if the VVT is open loop or closed loop, but either way I don't think the viscosity of the hot oil would vary enough between the OEM oil and the Amsoil to make any significant difference in the valve timing even if it is an open loop system.

Matt

Hey NickPike! Small world.

I really, really doubt it. Has your weather cooled down a lot since the oil change? I would suspect that, or the gas. -

Bob

Yes, if you live in the northern climes with seasonal blends this could well be your problem. I lose 3-4 MPG when PA switches to winter blend and it comes back nearly instantly in the spring. :-)

Matt

Powered by the engine oil pressure? That's not how it works Nick. The camshafts are turned by a chain off of the crankshaft. Even hydraulic lifters don't really "power" the valves via hydraulics.

Mike, I think Nick is talking about the CVVT cam advance mechanism. Some engines CVVT or VVT do work on oil pressure. Not sure about the Lambda engine! -

Bob

Mike, Nick is correct. He clearly said the camshaft timing was powered hydraulically and that is correct. Oil pressure is used to change the cam/valve timing. He didn't say that the valves were powered by engine oil pressure.

Matt

In that case, Nick has a good point.

It would be interesting to do a cam timing test with different oils. It could make a difference. Thinner oils could {theoretically} cause the cam timing to change less than intended. That could cause anything from an imperceptible fuel economy change to a fairly substantial change. -

Bob

Maybe, but more likely not. If the system is open loop and depends on a certain pressure to obtain a certain change in valve timing, then a change in viscosity might well change the RATE at which the change occurs, but the end amount of change will be the same. Think of a water line into a pressure storage tank. If you open the valve wide open, the pressure in the tank will equalize quickly with the line pressure. If you just barely crack the valve open, the pressure will take a long time to equalize, but it WILL equalize at the same pressure as the line with the valve wide open. Thicker oil is like the valve that is only partially open and thin oil like the valve that is fully open. The viscosity might well change the actuation rate, but the end pressure and thus change in valve timing will be the same.

Now if the transients are rapid and not time is provided for stabilization, then you might see the difference. I'm not familiar with the details of the Hyundai system to know if it is open loop or closed loop.

Hyundaitech, is the Hyundai VVT system open loop or is there a feedback mechanism for the amount of rotation of the cam with respect to the drive gear?

Matt

Wow - that got noticed by a few guys. My mistake indeed. Tunnel vision or something, but I never considered VVT. I just hate it when stuff like this happens...

Such is life... :-)

Matt

Well explained, and exactly what I was wondering. -

Bob

We'll let it slide this time Mike. We know you have holidays on the brain and all. ;)

Happy New Year! -

Bob