# How to calculate vis@85C ?

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#### Ken4

Vis@40C = 80
Vis@100C = 14.5

Vis@85 = ??

Thanks.

quote:

Originally posted by Dr. T:
Ken, what's at 85?

Normal operating temperature of the oil in an engine (at least my Honda Prelude).

Ken, what's at 85?

Im testing out my new oil temp gauge on my 4cyl camry, seems to take a long time to reach 85C, about 30mins. I had guessed 10mins for the oil to be fully warm, but I was wrong. Im sure glad I installed this gauge.

9 mins = 60C
15 mins = 70C
20 mins = 75C
25 mins = 80C
30 mins = 85C

The water temp, on the other hand, heats up very fast and is fully warm in about 5mins. Oil Im using is BP Visco 7000 0w40. Strangely, oil temp doesnt seem to go up when I drive hard. I redlined twice, but oil temp seems to go down bcos of more cooling air. Oil temp rises quickly when you shut down the engine though.

I also installed a oil pressure gauge, starts out at 60psi when cold, then drops to 0psi @ idle after 15mins.

quote:

Originally posted by Ken4:
I also installed a oil pressure gauge, starts out at 60psi when cold, then drops to 0psi @ idle after 15mins.

Are you sure it's 0PSI? Maybe you meant 10PSI. My Prelude has 12PSI at idle.

It's 0psi when idling in 'D' with aircon on. If I switch off the aircon and put in 'N' it jumps to 5~10psi.

Ken:

O.K. I graphed it on Log paper.

I didn't use a drafting table or large sheet of log paper so the results are 5-10% off.

60C = 42 cSt.
70C = 32 cSt.
75C = 27 cSt.
80C = 23 cSt.
85C = 21 cSt.

I'd be interested in seeing water temp vs oil temperature and outside temperature. I would be willing to corrrelate/graph the data a little more accurately. Great information.

[ November 07, 2003, 09:12 AM: Message edited by: Al ]

quote:

Originally posted by Ken4:
Vis@40C = 80
Vis@100C = 14.5

Vis@85 = ??

Thanks.

you can't calculate that unless the oil's viscosity vs temp graph is perfectly linear (or a known function).

-michael

quote:

Originally posted by Michael SR:
]you can't calculate that unless the oil's viscosity vs temp graph is perfectly linear (or a known function).
-michael
No you just need two points and graph (which he provided) it on logpaper. That's what I did
You could solve it math wise. But this is quicker

quote:

Originally posted by Al:
I'd be interested in seeing water temp vs oil temperature and outside temperature.

Thanks Al! The outside temp was around 25C at night when I did the test. My water temp gauge is the stock oem one and doesnt have graduations. The water temp fully warms up pretty fast and just stays constant (around the middle of the gauge) no matter how hard I drive or whatever the outside temp is. I see no point charting water temp vs anything.

I tested my oil temp again today in the hot afternoon, outside temp around 31C. This is what came up:

6 mins = 60C
9 mins = 70C
13 mins = 80C
19 mins = 85C

The absolute max oil temp would go was 90C, and that is if Im going slowly uphill or slowly thru a shopping center basement carpark searching for a parking lot. Now I know why extensive idling is considered servere service. Normal city driving with lots of stop & go, around 85C. Highway driving, around 82.5C. The oil temp gauge is an awesome gauge for all you oil fanatics out there!

The oil pressure gauge isnt really so useful. Max oil pressure is around 70psi (cold), 60psi (hot). I only got it bcos when installing the 4-way-t-adapter for the oil temp sender, I had provision for the oil pressure sender, so I decided to get it over with at one go.

I don't get how you can solve it. Log paper or not. It's not possible. You only have 2 points. Every oil is different. You need to test the vis to know the real vis.
Honestly I don't even know 100% what log paper is. But I have an idea. Math is not my favorite subject (I'd rather stick the pencil in my jugular than sit at a desk punching numbers) but I have no problem doing it really. But hey if I go back to school in the next year or two it will probably be for engineering. Can't think of anything else.
Anyway this is not possible. Simple logic says so. You are basically saying all oils behave the same! That is not true.

Calculate this!

BS just like Mobils vis log chart.

[ November 07, 2003, 11:33 AM: Message edited by: Jason Troxell ]

I like to see detils on where the temp is taken and what the setup is

Also strange that the oil temp doesn't get beyond water temp. Information I have seen in the past showed that oil temp is greater than water temp even at the sump. I assume your water temp is 200 F or so that's where the midpoint of water gages are (in my experience) Be nice if you had an OBD II to hook up which showed the water temp

Jason Troxell-Trust me with two end points viscosity is linear on log paper. I'll explain later-'gotta go

[ November 07, 2003, 11:41 AM: Message edited by: Al ]

I don't understand the need to know the viscosity of an oil at 85C though. If you have an oil that is thicker at 100C, and then another which is thinner at 100C, chances are pretty strong that the thicker oil will still be thicker than the other one at 85C.

So if you're comparing oils, why worry about the spec at 85C at all? Or are you just wondering for curiosity sake?

Since water boils at 100C, I wonder how much moisture actually gets burned off if your oil temp is only 85C? I know there will be hot spots in the engine where the oil is hotter and can burn it off, but how effective is it if the overall average temp of the oil is colder?

That oil warmup seems about the same as mine. VDO electric guage. Drain plug sending unit.

quote:

Originally posted by Patman:
I don't understand the need to know the viscosity of an oil at 85C though. If you have an oil that is thicker at 100C, and then another which is thinner at 100C, chances are pretty strong that the thicker oil will still be thicker than the other one at 85C.

So if you're comparing oils, why worry about the spec at 85C at all? Or are you just wondering for curiosity sake?

Since water boils at 100C, I wonder how much moisture actually gets burned off if your oil temp is only 85C? I know there will be hot spots in the engine where the oil is hotter and can burn it off, but how effective is it if the overall average temp of the oil is colder?

Patman-he just want's to know what the viscosity of this oil at 85C bc that's where his oil temp is. So if that's the accurate temp of his oil he is running the equivalent of a high 50 wt oil compared to the 14.5 cSt (40 wt.) at 100C . He might just be better off with a 30 wt oil.

quote:

Originally posted by Al:
Jason Troxell-Trust me with two end points viscosity is linear on log paper. I'll explain later-'gotta go

Still don't believe it, but when you have a minute I'd at least consider evaluating it

Why have a test for the winter number too? You have 40 and 100C...CALCULATE IT

I think that calculator is BS too. Maybe for a single fluid with nothing in it, it might be ok. A motor oil with multi vis oils blended together combined with PPD, VII, and other additives, keep dreaming.

Cool calculator Jay!

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