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Old 04-14-2004, 10:36 AM
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Oil Viscosity And Bearing Clearance Relationships

Apart from temperature and climate, is there a rule of thumb for what viscosity of engine oil you would use depending on what your bearing clearances were, so that way, at least you couldn't go too thick or thin?

In Australia, we are told that 20w 50, and 20w 60 oils are the go, but it just seems too thick. Could this cause any problems due to bearing clearances not allowing such thick oil to flow? I have tried 30w, 40w, 50w mineral oils and am running the 20w 60 currently, but I can't tell the difference in any area between them all. Pressure is the same with all of them on my guage, and I haven't noticed any damaging effects on anything as yet.

It just gets confusing to choose, as some people run the mobil 1 10w30 synthetic, and that just feels too thin on the other hand. Would a thick viscosity oil cause excessive wear perhaps at startup, or due to the fact that it doesn't flow as freely to all areas of the engines internals?

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Old 04-14-2004, 04:13 PM
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The multi weights are the best of both worlds. You used to have to run thin oil when it was cold and thick oil when it was hot. With the multi weights the oil does all the work for you. The hotter the area you live in the bigger the high number. The colder the lower the low number. I use Kendal 20-50 year round in Seattle Washington. Our temperature ranges from 20F to around 90F and it works fine. The synthetics are great but a little pricey for a cheep skate like me.
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Old 04-14-2004, 05:45 PM
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I would never deam of putting anything as thick as 20-50 in my engines I generally run 0-30 or 5-30 year round which I have had great sucsess with. Think oils do horrible things such as being slow to circuate at start up which can sarve bearing extra I personally don't believe that there is any good reason to use anything thicker than 10w40 even if warm climates.
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Old 04-14-2004, 07:56 PM
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Viscosity is just one of the factors to think about. Too thick of an oil takes too long to get to the bearings on a cold start-up. Too thick of an oil robs horsepower. Today's oils are far better at lubricating than even those of 15 years ago. If your bearing clearances are not too loose, a good 10w-30 is as thick as you need. If your need something thicker, then your engine has some time on it or it was a little loose to begin with. In that case, thicker oil will help the pressure, but at the cost of some horsepower and cold start lubrication.
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Old 04-15-2004, 11:50 AM
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I was just in the store yesteday looking /buying Valvoline racing oil. I like to run 30wt util my engine is broken in. I was shocked to see they didn't have much 30wt (I bought the last 3 quarts), and they stocked more 40, 50, and 60wt Valvoline racing oil. I was thinkng to myself why in the world would anyone want oil that thick? I can't imagine what the oil pressure muct be like with that molases for oil in the pan. I run 10-30W synthetic oil after break in.

Royce
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Old 04-15-2004, 11:56 AM
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This is a little off topic, but I like to use the valvoline 60 WT to smear all over my bores and machined surfaces when the motor is waiting to get built. It sticks well, and will work as oil when the motor finally runs! Other than that I use 10w30 on my motors, sometimes 10w40 on a high miler. 20w50 or 60 is way too thick.

K
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Old 04-15-2004, 02:08 PM
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The heavier weights are usually stocked for the Harley guys with the older engines. Seems like they aren't happy with anything less than SAE 50.
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Old 04-15-2004, 03:18 PM
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You choose higher viscosities for higher loading, hence why many race cars use straight weight 50. Myself I use 5W50 all year round...but I do keep the cars plugged in at -40C.
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Old 04-15-2004, 03:34 PM
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Well race cars live in a little bit different a life than street cars they don't have to worry about start up wear and spend there entire life under high load. How ever there acually are alot of teams running with as thin as 0-20 these days to and are have very good success.
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Old 04-16-2004, 12:29 AM
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I use Kendal Nitro 70wt in my 56pan/shovel Harley. The factory recommends 65wt. The HD engine is almost completely a roller bearing engine except for a couple of bushings.
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