oil

[devans]

Many thanks guys, i always use fully synthetic and will therefore use up what i have first. Always used mobil 1 but for some reason the service used valvoline!!! I want to ensure i continue with mobil 1 so will use what i have, thanks for the technical info,
David

 

[Mark Elder]

ORIGINAL: Richard Hamilton

Sorry Paul, but i think you have got that the wrong way round. Both 0W-40 ant 5W-40 have nominally the same viscosity when hot. 5W is thicker than 0W when cold.

Hi Richard,
So, is the "5W" part of the rating measured on a different scale from the "40" part? - because obviously the oil must be less viscous at high temperature. This has always confused me about oil ratings. But like you I have always understood the "W" part to be the Winter viscosity.

Or does "-40" means "minus 40"?!

Mark

 

[Richard_Hamilton]

The first number is the viscosity at 40 degrees C, and the second is at 100 degrees C.

The "0W", "5W" and "40" are in fact ranges. When comparing viscosities of oils, it is best to compare the kinematic viscosities in CentiStokes, which is a true value for the oil's thickness.

Hopefully this chart will make it a bit clearer:

 

[Richard_Hamilton]

Here is a table I made some while ago from oil datasheets. You can see that because "0W" and "5W" are ranges that overlap, you can get a 5W oil that is actually thinner than a 0W at 40C.

 

[paulus]

Richard,

You're right, I hadn't understood the oil ratings correctly.
However, after your last post I think I understand !

Your last chart shows what I expected, that all of the oils have higher viscosity cold than hot - which I guess most people would intuitively think is right - hot oil is "runnier" (to use the technical term !).
I'd therefore (incorrectly) assumed that the lower rating must indicate the hot viscosity. From what you've explained & shown in chart in your first post, the rating for hot & cold viscosity is totally different - even if the viscosity is still measured with the same Cst units.

Its good to learn something new every day !

Paul
2004 996 C2 40th Anniversary

 

[Mark Elder]

Very interesting. In that case you really can't compare between brands on viscosity - only within the Castrol brand (the only brand with more than 1 oil in the table) is there any relationship between the viscosity and the ratings.

I'd be interested to see the viscosity figures for Mobil 1 5W-40 if anyone has them to compare with the 0W-40, but only out of "interest" - I'm not sure that I'll do anything different![8|]

 

[Richard_Hamilton]

I got the info in the table from datasheets on the Opie Oils site, and from manufacturers sites. You are right, it is very difficult to compare brands. Mobil 1 0W-40 is thicker than a Castrol 5W-40 in both hot and cold ranges.

 

[devans]

omg, I didn't realize my post would get so technical. You guys certainly know your stuff. It will take a little longer to sink in with me but thanks all the same.

 

[thirteeneast]

@ 6k I would be changing the oil not topping up?.

5w-40w

I use Miller or Fuch from Opie.

 

[tim92gts]

If the cars got a few miles on i'd be contemplating a 10W-50, i use Millers full synthetic.
Tim
'02 C2 Cab 60k miles

 

[andyjwhit]

Hi guys, thanks, are you saying you change oil every 6K, including filter? Thought service schedule was up to 12K?

Had never heard of Miller but had a quick look and seems decent enough

Bst

Andy

 

[thirteeneast]

Hi Andy,

For what it costs yes, I change my oil every year or 6k.

Mine actually only does 3k-4k before I change the oil.

I would never leave it till 12k. I don't think its cost effective.

 

[andyjwhit]

Hi Thirteeneast, thanks for the comments,

how many miles has your 996 done? Mine has 118K on the clock. I do about 12K a year so I could change oil twice a year at 6K. When you say cost effective are you refering to engine blow up then??

Would have thought modern synthetic oil would still be doing a good job at 12K, some modern service intervals go up to 18K?? I guess if you are only doing 3K a year then oil would require changing due to lack of use, if you see what I mean.

Bst

Andy

 

[thirteeneast]

I don't think fully synthetic oils do a good job for consumers at all, If they did cylinder scoring on cars under 100k would not be such a common fault.

In fact my heads a mess with Fully synthetic oil

I change my oil regular mainly because its the same cost as a tank of gas and could save me a bill of £££££.

It doesn't take long and is the single most important part of your car I don't let any of my cars do more than 6k before an oil change.
Not even the banger I use for work it just makes no sense.
If theres anything wrong your going to pick up on it 6k earlier.

Just my choice of course but a small price to pay in grand scheme of running a Porsche. (or any car)

Mine has 54k on the clock and gets used every weekend problem is the millage/use is split across three cars so therefore is less on all.

 

[andyjwhit]

Possible that synthetic oils dont go a good job, I guess if you only used mineral oil scoring might appear earlier, or possibly later? We run a fleet of old mercs and use semi synthetic..we have a 300D with 470K miles on it...agree small price to pay guess its a bit load dependent so 6K change makes sense...nice problem to have three cars!

Bst

Andy

 

[Richard_Hamilton]

I wouldn't worry about bore scoring on a 3.4. It is pretty much unheard of.

I would say use an approved 5W-40 synthetic, and change it every 6000 miles, and you won't go far wrong.