Oil thickness and grades

[mattysshop]

now i know this may seem like a silly question, but i have always gone by what the oil bottle said, and i was fine.. but recently some of my mates have brought up very good point, and now i'm just confused!!

take for example..

a 15w 50 and a 14w 40 oil..

15 meaning the cold start viscosity, and 50 meaning the operating temp viscosotiy, from what I have read, and people have said.. 15 is thicker than 50..as the 15 is used on a cold crank, thicker oil will create more oil pressure there for reaching the top of the motor quicker etc..

so why the hell would a 10w 40 (same SAE grades) be insanely thin and blow through rings and create massive valve train noise as if the oil was just tooooo thin?? If going by what the book says… the lower the number the thicker the viscosity right??

Just incase people were wondering Ambeint temp would be around 25-27deg C so both oils would be fine working in an average engine..both oils are same brand and both synthetic blend

Am I missing something here?? Physics proves that pretty much all liquids thin out as the temp increases...especially oils..

i'm just confused now with this over load on info...

Matty

[monkeymajik]

The smaller the number the thinner it is.

[mattysshop]

so oil defies physics and gets thicker when hot?? why is it that mechanics test drive a car befor a service, i always do it to as the oil is hot, and drains a hell of alot faster cos it's thin..

[mattysshop]

this is what i don't get..because that used to be what i thought.. then i realised it's not the case.. oil gets thinner when it's hot.. service a hot car takes you 5 mins.. service a cold car you can at least double that...

[crazy86]

Ok, let me start that i dont know the answer, and im not really sure what Im talking about, but i seem to remember reading that the second number is not "thickness", in the same manner at the first number, but it is more a number to signify the rate of change of the oils viscosity once heated up to a certain temp.

therefore a 20w 40 oil will change viscosity less than a 20w 50.

and a 15w 40 oil may have a similar "hot" viscosity to 20w 50

Then again, i could be completely wrong and leading everyone up the garden path http://www.ae86drivingclub.com.au/forums/emoticons/rolleyes.gif

[mattysshop]

on the back of most Penzoil bottles it says cold start viscosoty and operating temp viscosity, but yeh that would make sense a bit...

i know for a fact that a smoky engine running on 10w would benifit greatly running on a 20w.. so that to me means that the higher the first number the thicker the oil?

[monkeymajik]

Maybe i've read it all wrong too http://www.ae86drivingclub.com.au/forums/emoticons/sad.gif

I think crazy86 is right though, because the higher the second number the more protection you have in hotter environments.

The smaller the first number though the thinner it is. I am certain of that.

[crazy86]

yep ^^^matty

[mattysshop]

RIGHT!! good work fellas! the milkybars are on me! http://www.ae86drivingclub.com.au/forums/emoticons/smile.gif now that i've got that sorted.. i'm getting me some 25w50 http://www.ae86drivingclub.com.au/forums/emoticons/smile.gif

[Monk]

he he..

he..

I still dont get it http://www.ae86drivingclub.com.au/forums/emoticons/biggrin.gif http://www.ae86drivingclub.com.au/forums/emoticons/huh.gif http://www.ae86drivingclub.com.au/forums/emoticons/blink.gif

I know nothign about oils but from what i do know (which is nothing) the lower the number the thinner the oil.

5w (cold) means thinner, little protection.. but more performance
20w (cold) means thicker, good protections .. little performance gain?

thats what i was always told. i could be wrong but?

[twitch]

I think crazy 86 is on the right track, and oil gets thinner as it gets hotter. http://www.ae86drivingclub.com.au/forums/emoticons/biggrin.gif

[sic86]

lol, i see your point. But then there is synethetic and semi syn. Which last longer and heats up quicker etc.

Cheers

[ADRIAN]

Penrite make a type thats a straight 50 grade, you could try that to stop your car smoking, or disconnect the breather from the intake. http://www.ae86drivingclub.com.au/forums/emoticons/wink.gif

[sic86]

Penrite don't make a straight 50, Pennzoil do though

Cheers

[ADRIAN]

Originally posted by Alan@Jan 7 2006, 02:01 PM
Penrite don't make a straight 50, Pennzoil do though

Cheers
Ahh well there ya go then

Cheers

[hinricp]

sorry to hijack your thread but is it ok to mix oils ? As in gearbox oil ?

[mc68]

if you were mixing different grades then its a no no.

[sic86]

Originally posted by edison@Jan 7 2006, 02:52 PM
sorry to hijack your thread but is it ok to mix oils ? As in gearbox oil ?
It's not recommended but as long as it is the same grade and the same base (sythetic, mineral etc.) shouldn't be a problem

Cheers

[mumblezzz]

Originally posted by Alan@Jan 11 2006, 08:01 AM
Penrite don't make a straight 50, Pennzoil do though

Cheers
I used to use that shit in my hachi. Works great for those that dont run an oil cooler.

[mattysshop]

oil in the gear box?? i'm running a mix between 75% dextron III auto fluid, and 25% VMX 80.. when i change the oil in a few weeks i'm going to straight dex III.. sounds weird..but hey.. try it and you'll never go back sweet shifting gear box all day long!!

yeh i used pennzoil HD-50 in my gemini, used to chatter heaps on hot days..

the 86 doesn't blow smoke, but it used to running on penrite HPR 30.. swapped to a penzoil line up and tried numerous pennzoil even way thinner than the HPR 30 and the pennzoil didn't smoke at all..

[sic86]

I use Penrite 75/85w i think in the gearbox, can't remember. But i also use Nulon Gearbox/Diff Treatment aswell. Awesome stuff

Cheers

[Joel-AE86]

I use Fuchs Titan 40W70 in my front shocks http://www.ae86drivingclub.com.au/forums/emoticons/smile.gif

[RobertoX]

^^ are they very stiff? The oil in shocks is a pretty light machine oil I think.



After some googling:

viscosities (http://www.sizes.com/materls/engineOil.htm)

Good guide to oily bits (http://www.carbibles.com/engineoil_bible.html)

how they measure viscosity (http://www.carbibles.com/viscosity.html)


If you read each page in the order that I have posted here you will feel a bit better about being confused! http://www.ae86drivingclub.com.au/forums/emoticons/blink.gif

It seems that it is a little bit more complicated than just a cold viscosity and a hot viscosity. They are measured on a different scale, the cold at a low temp (starting at 0deg for 5W) and the hot at high temp (100degC). But as these are different things measured ("cranking viscosity" and "pumping viscosity") and hence use a different scale.

But accoding to the second link CRAZY86 is sort of correct in that the second number denotes the rate of change of the oil.... also it does get less viscous as it heats up and a higher number indicates a higher viscosity, its just that the two numbers in say 10W40 are not on the same scale.

so a 5W50 will be less viscous than a 10W50 but a 5W50 will change less than a 5W40 (lol I think)...