INTERESTING: Wrong Oil = Poor Economy ?

[BETTER THAN A WRX]

Hi, I am still investigating why my T4 is getting bad economy.
The O2 sensor operates 9 times in 10 sec's @ 2000rpm, so
seems fine.
Got new plugs, clean filter, speedo is fine, no dragging brakes etc....

But; last time it was serviced (not at nissan) it got 20W50 put into it.
Now from reading abit about hydraulic lifters (which SR20's have), I have discovered that pumped up lifters can cause valves to stay open
for slightly longer duration.
Now too viscous an oil can cause the lifters to pump up when cold,
so I am wondering of this would have a significant effect on the compression ratio, and hence economy/power.

Has anyone come across this before?
Does it sound reasonable?

Later

[howard_w13]

20w50?!? Is that what the owner's manual recommends in New Zealand?
Far as I know the SR20DE should use either 5w30 or 10w30. Not sure about oil with that viscosity could effect fuel efficiency.

[BETTER THAN A WRX]

No, the manuals are all pretty much the same.

Manuals/catalogues here recommend 10W30, but have been
told by a much that 5W30 is also good.

I just went to a generic jap import(car) mechanic to get a
filter and oil change, I asked what oil he was going to
use and he said that 20W50 was fine.

I think the problem is that many mechs just buy huge barrels
of generic oil to do most cars, so of course he is going to say it
is right.

The car is due for a fluid change, so I am going to REPCO in
the weekend, to get some engine flush and some nice 10W30.

Will see what difference it makes.

Later