At operating temp 5w30 and 10w30 are the same viscosity...

 

6 or 12 Cs is NOT a wide spread in viscosity..if it was you would see a significant rise in oil pressure at 210,but you won't.

 

On the chart, 6 to 12 just seems significant.....I mean the whole chart scale basically covers 4 to 18 cSt for 5 to 50 weight oil. I never was much into mathematics but 6 to 12 is a 200% increase or double. Maybe semantics come into play.

 

200% of what? Now give the percentage spread at 32F and you will see the point that I am trying to make. I don't know if my perception of feel is more sensitive but with cold oil I can feel the difference in my fingers and pouring through a funnel....Why shouldn’t I?

 

Yes, it is significant. For example, think of an air-cooled Harley that uses 50- or 60-weight, and then think of how well it would work to dump 10- or 20-weight in it. Run it up to operating temp, then drive it all day in 100 degree heat. It would not be a happy motorcycle.

 

Not the same if Harley's are designed for 50 wt. with 250 degree operating temperature why would you want to DECREASE viscosity??
The viscosity drop off curve above 210 degrees is extreme...the viscosity/temperature curve is not linear. This same analogy would be like putting sewing machine oil in your jeep, we are on different wave lengths here!

 

You wouldn't...that's my point. You said there is no significant difference in viscosity between different weights at operating temp, and I'm saying that there is.

 

That's what I was questioning......because the chart indicates that 10 and 40 are not "close to the same viscosity" at 210-212F

12 is double of 6.....and viscosity charts must have some kind of standardization, I would think......at least a little more scientific than ones fingers feeling oil on a dipstick.

That's also what I was thinking.......10 and 40 would have significantly different viscosity's at operating temp, not close to the same vis at operating temp. The charts seem to show a significant difference.

 

It appears my new jeep was mostly T'd off about wanting its oil changed. I took off the old filter(thought it was Purolator due to it being yellow but saw no branding). At any rate with the CarQuest 85515 filter and the T6 5w40 (couldn't find 0W40 locally) the pressure at warm idle (650 rpm) is now around 10. 2000 rpm is nearly 40. What a relief !!! I was shaking in my shoes concerning a potential cylinder head and bearing replacement.

Changed ATF, considered doing filter as well but changed my mind due to the ATF I took out being pretty ugly. I will run a few miles and then change the ATF again along with filter. Besides by then it should be warmer it's only 33 here today and my garage isn't heated. If it NEEDED done now I'd do it, but it doesn't.

Thanks everyone! I learned a lot about oil and will watch pressure to be certain I don't need to back down to a 5W30. Now to start searching on other stuff

 

Glad to hear it!

 

Hey Mr. belvedere, how about one more for your sig......

brake - part that stops something
break - broken

 

I like it!

 

If it runs well I'm glad. One guy here is running with 4 PSI, but beware that the minimum spec in any 4.0 is 13 PSI at hot idle. Was this done with the in-dash gauge or verified with a mechanical test unit?

 

Yes awesome sig

 

There's going to be a quiz later, isn't there.