Car eats oil - oil change interval?

You obviously have never poured 10-40 and 10-30 when it is -20F outside. If you
had you would have noticed that there is a significant visible difference in
viscosity no matter what the API might say. At that temperature, it makes a
noticeable difference in engine cranking also.

-jim

 

I shouldn't have used that example, because the wider the spread in
viscosity, the more likely you are to find the oil behaving wrong,
especially with non-synthetics. I never use oil with a 30 weight
'spread' anymore. 10W-30 seems to be just fine for Summer driving, so
10W-30 in Summer and 5W-30 in Winter (if the engine isn't worn) is
probably the best way to go for normal driving.

 

That's simply not true.

 

Why because you read it in a book?

 

No, because that's basically the DEFINITION of the API rating. If
there's a huge difference in cold pour characteristics, then the oil
really isn't meeting its API rating. Which, to be fair, is entirely
possible especially for bargain oils, and high viscosity spread oils.

 

So the answer is yes you just read about it. You didn't read very well. The cold
pour rating is not for -20F. When it is -20 there is a noticeable difference.


-jim

 

Ask the manufacturer for a plot of viscosity versus temperature.

The various API ratings require the viscosity to be in a certain range
over a certain temperature range. But once you exceed the rated
temperature range, all bets are off.

If you buy an API SL grade oil marked "10W-30", you know according to the
standard that it will be a 10 weight (7Pa) oil at -25'C and that it will be
a 30 weight (2.9mPa) oil at 150C. But you have no idea what the oil is
going to do outside of those two points. And when things get really cold
and really hot, the viscosity improvers get weird sometimes.
--scott

 

Its actually pretty close to -20F, as a matter of fact. Something like
-15F, -12F. Not far off, certainly no more than 8-10 degrees F. If you'd
said they differed a lot at -40F, then it might have been a more
believable statement. For sufficiently cheap and crappy oils.

 

Thank you, Einstein. But I can't afford more frequent oil changes cuz
I sent all my $$ to yer motha so she can buy you a new pocket
protector.