Viscosity diff between synthetic and mineral oil?

[CarbonCrew]

I was browsing one of Dr. Haas' technical papers on the subject of mineral and synthetics viscosity differences at engine startup at ambient temperatures. Dr. Haas suggests that a 5w30 mineral oil has a higher viscosity of a 5w30 synthetic at startup. He explains that the waxes in the mineral oil will coalesce causing the oil to thicken and that synthetics lack these thickening agents.

Generally speaking, I know that synthetics have much greater viscosity indexes. However, I'm a bit confused as to how viscosities compare between the oil as they move through the temperature test range.

It is my understanding that both 5w30 mineral and synthetic oils should have very similar viscosities at -25, 40, and 100 C. However, Dr. Haas suggests that there will be differences in viscosity between the oils at 70 F. I would assume that the viscosity changes logarithmic vs. temperature. Am I correct to assume that the logarithmic scales of vis vs. temp. wildly different between synthetic and mineral oils?

Any insight on the subject would be greatly appreciated.

Thanks!

 

[RxxR]

OMG

What I know is that minerals do not have that good viscosity stability within the drain period compared to synthetics. But If we are talking about two fresh samples... Viscosity index of mineral oils is usually not higher than 160 and the same of synthetic oils starts from 170 this may give a thought that viscosity of mineral oils changes more within the temperature range. You can perform a simpe test with a kitchen freezer set to -30 C and two samples of 5w30: leave them there for 24 hours in two identical glasses filled by 1/4 and than take the glasses, set them on the same angle(like 60 degrees) and see which oil climbs to the edge first

 

[[RT] ProjUltraZ]

do an advanced search on Widman viscosity and all your answers are there

 

[stubbakatt]

Originally Posted By: RxxR
OMG

What I know is that minerals do not have that good viscosity stability within the drain period compared to synthetics. But If we are talking about two fresh samples... Viscosity index of mineral oils is usually not higher than 160 and the same of synthetic oils starts from 170 this may give a thought that viscosity of mineral oils changes more within the temperature range. You can perform a simpe test with a kitchen freezer set to -30 C and two samples of 5w30: leave them there for 24 hours in two identical glasses filled by 1/4 and than take the glasses, set them on the same angle(like 60 degrees) and see which oil climbs to the edge first

LOL, I can imagine the look on my wife's face if I put motor oil in the freezer.

 

[RxxR]

Originally Posted By: stubbakatt

LOL, I can imagine the look on my wife's face if I put motor oil in the freezer.

 

[Bluestream]

Originally Posted By: stubbakatt

LOL, I can imagine the look on my wife's face if I put motor oil in the freezer.


You never tell her stuff like that; just do it...

 

[JHZR2]

The reality is that an oil that is rated at n cSt at x degrees will have the same viscosity whether it is a syn or a conventional.

There are other characteristics pertaining to flow that also come into play.

 

[labman]

As I mentioned in another thread, I think the log of the viscosity of a base stock should be a straight line plotted against the reciprocal of the absolute temperature. However, again you add VII's, pour point depressents, other base stocks, non viscosity related additives, hype, and everything else going into a modern oil, it may not be the straight line. 2 oils with the same viscosities at 2 different temperatures, may not be the same at a temperature inbetween. So which flows better on start up, synthetic or conventional? Well which one? I have some 5w30 Pennzoil YB and M1 in my garage. Both have been there for months and likely are the same temperature as the M1 in th eoil pan of my truck.

As a crude measure of their viscosity, I took 2 paper cups and put marks on them at the same place. I then filled one with each to the mark. I then poured both back in at the the same time trying to keep things as equal as I could and let the cups set for a while. The amount left in the cup should depend on the viscosity. As near as I can tell, both are the same. I am sure there isn't enough difference to affect the flow on start up. Now last December when I changed from the Pennzoil to Mobil, I think the engine turned over faster in the cold. However, we are all very good at perceiving what we want to.

It does sound like if I believe in thin, I need to try harder to find somebody that stocks 0W-30. If I go to longer intervals, buying my oil out of town will be less of a hassle.

 

[mechtech2]

Carbon - It could go either way.
If it is really arctic cold out, then the synthetic should have an advantage.

 

[Captain_Klink]

basically, a synthetic 10w30 will have the cold properties of a conventional 5w30, at very low temp, like -25C.
5w20 conventional oils have excellent cold properties, even better than a synthetic 5w30, so in winter, i use a mix of 5w20 conv with 5w30 synthetic. in the heat of summer, it is mix of 10w30 synth with 5w30 conv. and in between times, mix of 5w30 synth and 5w30 conventional. it is not necessary to do this, the engine will still work well, but this is just a personal preference of mine. it is not really ever needed to buy synthetic 5w20, unless you wish to go for long oil changes. i prefer the cheaper conventional, and change the oil more frequently.