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Unread 05-13-2009, 04:38 PM   #1
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Default Viscosity of oil?

Since higher viscosity oil covers everything in the engine better than lower viscosity, why doesn't everyone use high viscosity oil? In other words, what are the disadvantages of using high viscosity oil?

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Unread 05-13-2009, 04:55 PM   #2
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Winter + High Viscosity Oil = Not Happy Engine.
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Unread 05-13-2009, 05:31 PM   #3
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Originally Posted by SgtSpike View Post
Since higher viscosity oil covers everything in the engine better than lower viscosity, why doesn't everyone use high viscosity oil? In other words, what are the disadvantages of using high viscosity oil?
Thats not true... It doesnt cover things better. Coverage is the same...

What does happen though, is it has a higher film thickness, thus providing more of a "cushon" between parts. Believe it or not, most parts like bearings and journals do not ever touch in the engine. This is because there is a layer of pressurized oil between them. This layer is crucial to the operation of the engine. Without it the motor will over heat, and practically weld its self shut.

Oil that is too thick, does provide a thicker barrier between parts, but the problem is getting it there. Trying to make your tiny little oil pump flow thick oil in a gap thats only a few thousandths of a inch wide is difficult.

And on another note, your oil playes a second part to engine operation. Heat control. Oil helps regulate the heat produced by the engine. The thinner the oil, the better it flows, so the faster it can pass its heat away from the engine in the oil cooler. The thicker, the less flow, thus less heat transfer.

And also, thicker oil is harder to pump. The harder it is to pump, the more work the engine must do, robbing precious power. Its just not very efficient to use higher viscosity lubricants than what the engine was designed for...

And as legoman stated, in cold weather it would be a nightmare if your running heavy oil. Since heat effects viscosity, climate has some influence on what oil to use. In very high temps, its ok to run a slightly thicker oil, and vice versa for colder climates. But over all, most engines have an oil spec that covers these things. Unless you know what your doing, and have a reason too, i wouldnt run anything but what the manufacturer specifies for viscosity.

But i will say, ALWAYS sue synthetic!!! (that will be a whole other discussion....)
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Unread 05-13-2009, 05:40 PM   #4
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full synthetic :drool: And thanks pbasil1 for that great explaination. I was going to try and explain it as well but Im not so good at it sometimes lol. At least not on the internet
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Unread 05-13-2009, 06:13 PM   #5
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Good answer by pbasil1

I'll just a couple of things as well.

High viscosity oil in a cold engine, being much thicker and thus harder to push through the small oil passages, takes longer to get to the parts it must protect. It's not uncommon for an engine to runs several seconds with no oil to the the bearings. If the oil is very thick it could take nearly a minute to get oil to the moving parts.

Also it takes more effort on your starter to crank over an engine with thick oil on the parts.

Thick oil also takes longer to drain back down into the oil pan and at high PRM the oil can be pumped up into the top end of the engine faster than it can drain down. Possibly causing the oil pump to run out of oil to pump.

Engines designed today have much better tolerances in manufacturing than those of he 50's & 60's and multi-viscosity oils are available now to maintain bearing/journal clearance without resorting to thick oil.

And to add, before multi-viscosity oils were available, the manufacturer had to specify an oil thick enough to lubricate when hot, but was hindered by the thicker oil when cold. Those engine had a hard life and it was not uncommon for them to need an overhaul by 100,000 miles. Now we see engine with much higher mileage before overhaul thanks to multi-viscosity oils & fuel injection.
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Unread 05-13-2009, 06:47 PM   #6
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full synthetic :drool: And thanks pbasil1 for that great explaination. I was going to try and explain it as well but Im not so good at it sometimes lol. At least not on the internet
lol, I think I'm FINALLY going full-synthetic this time around...I've run out of reasons not to. lol
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Unread 05-13-2009, 07:26 PM   #7
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lol, I think I'm FINALLY going full-synthetic this time around...I've run out of reasons not to. lol
It could be in my head but I swear the engine had more get up and go after too lol.
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Unread 05-13-2009, 10:04 PM   #8
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There is ABSOLUTELY no reason not to run synthetic. It is better in every way shape and form than any mineral oil. Period. Even a cheaper synthetic will out perform a mineral based in almost every test.

Synthetics hold up astronomically better in high heat environments than minerals. Plus the additives that can be used in synthetics help to have much lower friction, and better cleaning properties, to help reduce "sludge" and carbon build up... Just watch them brag on any Penzoil platinum commercial.... And all these better features of synthetics also allow you to use the oil longer. It outlasts mineral based oils by more than double in most cases. In my daily driver i can safely change the oil every 9-10k miles with mobile 1 (synthetic) Where as with something like castrol GTX (mineral based), i wouldnt want to go over 4-5k mi every oil change.

Ill even throw in my recommendation, if you just need a good affordable daily driver oil, run mobile 1. You cant go wrong....

For you high performance guys, there is no all in one oil for you. Engine design, stress levels, and over all goals has too much to play when choosing the right oil, so i suggest finding what most other people use and have good results with, with your similar setup engine.


And to top it all off. oil filters play a huge role in this aswell.... So ill just make this easy. If you want to read on, here is a huge explination and comparison of everyday filter found at your local parts store... This guy knows his oil, and has helped us guys out in the supra community tremendously... Im sure all the info can be used for just about any car...

http://www.supramania.com/forums/showthread.php?t=42763
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Unread 05-13-2009, 10:29 PM   #9
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yeah I actually have a cheap oil filter on my nice new mobil 1 oil lol. I shouldnt have cheaped out but I did, and I will still change mine out every 3k miles or so.
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Unread 05-13-2009, 10:42 PM   #10
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That article was very informative - thanks. I usually just buy the Wix filters from O'Reilly's. (Though now I'll have to buy them somewhere else lol)

So Mobil 1 w/ wix filter should be fine, for my car (daily driver, though I tend to drive a bit heavy-footed lol)?
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