MPG Down With Oil Change

I'm certain that my mpg is down following the replacement of the original
mineral oil at 3000 miles with Amsoil 5w-30 in my 2007 Sonata, V6 engine.
I was wondering if this new oil effects the camshaft timing, as the timing
mechanism is powered by the engine oil pressure.
Should I put the original type back in when the oil change is due, whatever
it was.
Does anyone know what the original specification would be?
Nick

 

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

 

5W-20 is what is recommended on mine.

 

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


Happy New Year!
-

Bob