5w-40 vs 15w-40 startup smoke

[ModMech]

A 5w40 oil will be heavier at startup than at operating temperature. So, it's not a component in startup smoke.

Ralph

That's backwards...

15W-40 is THICKER, relatively speaking at 32*F than 5W-40. The number in front of the "w" indicates the equivelant "winter" weight, meaning weight when tested COLD.

If is also THE weight of the oil itself (except in some synthetics). Therefore, 15W-40 is 15 Wt oil at -40*F, 40*F, 140*F and 240*F; BUT "multi weight" oils add "viscosity improvers" (VI for short) to "thicken" the oil as it warms to counter act oils natural tendancy to thin as it warms. It doesn't do ANYTHING in terms of actual lubrication, only thickening to prevent collapse of the boundry layer.

 

[Gale Hawkins]

Ralph do you follow what JohnG posted. This was confusing to me for a long time too.

Not sure why but some think motor oil usage is a "bad" thing. The thinner the oil the less start up damage an engine will have.:thumbsup:

 

[RalphVa]

The original poster doesn't mention whether he's using dino or synthetic. Synthetics likely get the vis range via more or less polymerization, etc., NOT by use of more or less additives. If it's dino oils, they get the vis range higher or lower by using what's called "viscosity index improvers".

Doesn't matter re startup smoke. Yes, 15w40 will be heavier on startup than a 5w40, but BOTH of them are heavier on startup than at operating temperature. What probably causes startup smoke is a tiny (I do mean TINY) bit of oil leaks by pistons that are probably in the down stroke on shutdown such that the pressure in the combustion chamber cause a TINY bit of oil to seep upward. This oil is then partly burned to cause smoke on startup. Can't see why 15w40 would be any less prone to this that 5w40, because they're both 40w at operating temperature when the engine is shut down.

I get a tad of startup smoke on my 4010 every time I start it up. I use 0w30 synthetic in it and don't worry about a little bit of smoke. It normally uses no measurable amount of oil between changes at once/year.

My 2010 VW TDI has 5w30 Castrol SLX oil in it. It's all that VW will allow during the warranty. After 3 years, I'll switch to 0w30 Mobil 1 ESP that is 507 certified if I can find it. Pep Boys has 5w30 Mobil 1 ESP; I hear.

I was using 0w30 in our 1983 240D for the last approximately 30k miles on it. Got about 1 mpg better mileage on it vs. 5w40.

Ralph

 

[grandv8]

a W does designate that it is a winter rated oil, but 15w-40 doesnt mean that it acts as a 15 weight cold
multi-weights are not understood all so well. The oil is a 40 regardless, the 5 or 15 just signifies the viscosity index

Oil Grade Maximum Viscosity (cp)
0W 6200@-35C
5W 6600@-30C
10W 7000@-25C
15W 7000@-20C
20W 9500@-15C
25W 13000@-10C

a lower number indicates better cold pumpability, on the flip side Vi's also make the oil less stable, so its a give take relationship. The multi weight oil is really a base weight ie 30 or 40 or 50, then they add viscosity improvers to make it pump through an engine faster at under operating temperatures to ensure better start up and cold lubrication properties

 

[Gale Hawkins]

K7LN thanks for your post. I has similiar questions but did not have time to do any digging today.

 

[ModMech]

Not to be a horse's @55, butt....

a W does designate that it is a winter rated oil, but 15w-40 doesnt mean that it acts as a 15 weight cold

The "w" in 5W or 15W can be infered to mean either Winter or Weight, as in Winter rating or oil Weight, either is technically accurate. As for 15w-40 not meaning that it acts as a 15 weight cold, that is 100% wrong.

multi-weights are not understood all so well.

Well, there IS some confusion about them yes. Lots of people don't really understand why there are multi-weight oils, how they came about or what they actually do.

The oil is a 40 regardless, the 5 or 15 just signifies the viscosity index

Completely, 100% backwards.

a lower number indicates better cold pumpability, on the flip side Vi's also make the oil less stable, so its a give take relationship.

That is correct, assuming we are meaning that "Vi's" is Viscosity Improvers and not Viscosity Index.

The multi weight oil is really a base weight

That much is true, but it is the LOWER number that is the weight of the base stock oil and not the higher number.

 

[grandv8]

sorry but I think you gents need to come on over to bob is the oil guy forum, mabye get a better understanding of multiweights.

 

[Gale Hawkins]

Bob sure knows a lot about oil.

 

[grandv8]

lol I guess we dont see eye to eye but hey at least this thread is good for a laugh in the oil forums.

First of what I said about a 5w-40 isnt entirely true a 5w-40 really has to split It has a Pour Point Depressant and a Viscosity Improver. A 5 grade does NOT exist.
One way to tell how good of a base stock it is, is to look at HT/HS. HT/HS is High Temperature, High Shear viscosity. Basically worst case scenario. 40 grade is split, which no other grade is.
0W40, 5W40, and 10W40 is required to have a minimum HT/HS of 2.9cP @ 320F.
Thats the same minimum as a 30 GRADE.
15W40, 20W40, 25W40, and STRAIGHT 40 has to have minimum 3.7cP @ 320F.
Answer me this, how does a 5w-40 in your thinking have a cP of 2.9 first find me a oil rated 5 weight straight second show it with A cP of even close in the 2.9, it cant its far to light. Second notice my statement on 15w-40 it has the same HT as a straight grade 40 hmmmmmm why would they have the same, so the 15w-40 has more of a Pour Point Depressant rather than Viscosity Improver. Its a common sense thing we used to run straight grade but with the introduction of multi-viscosity oils, cold weather pumbability has dramatically improved. Your saying they are taking a 40 sae straight off of the shelf to put a 5 weight in its place oh but with improvers to simulate a 40 weight at operating temperature..... So lets see we are designing an oil do I take a 40 or truley in the case of a 5w-40 a 30 weight and add both Pour depressants and Viscosity Improvers to make it flow better or do I start with this light weight mineral oil and add ridiculous amounts of improvers to try to simulate a 40 ? Where does the engine spend most of its time start up or operating temperatures, which is more likely to shear out of grade a 5 or a 30 hmmmm
heck even take a 15w-40 lets say its a 15 base grade, wow putting atf a straight 20 is heavier than my 15w-40 sorry not buying it, but I wish you the best apparently we do not see eye to eye but I am not here to argue oil, i spend most of my time on BITOGF anyhow, I just thought I would share more lubrication experience here but what does an Oil Tribologist compare to a 50 year engineer......

 

[grandv8]

not hard to understand at all reread it 40's are split

0w-40, 5w-40 and 10w-40 are actually closer to a 30 on base then they add both Pour Point Depressants and Viscosity Improvers to make it fit, hence why I said that the 15w-40 is more shear stable then the 5w-40.......

15w-40, 20w-40 and sae 40 are a 40 with Pour point Depressants. That's why 40 is split.

Excessive viscosity improvers or Pour Point Depressants aren't a good thing that's why its so hard to to create super spreads like say 5w-50 because of the required brew it creates an inherent instability in the oil.

Now It is still possible to make good spread spectrum oils, but the add packs have to be well researched and spot on. Rotella T-6 is a good example here its a great 5w-40.

Yes I was vague by using the term VI as a generic additive rather the ppd, vi or vii. But I felt that was excessive techno bable for here I apologize for being to simplistic on that accord.
Thank you for your response much appreciated