>One ignorant question about oil: I was told that 20-50wt oil for example
>has a viscocity of 20 when cool and 50 when hot. Surely this is not
>correct. Could someone explain how temp and viscosity are related if
>its not the obvious (ie the hotter the oil the lower the viscosity).
At cold temperatures, like winter in New Hampshire, say for example at 10
below, a single viscosity oil of 20 weight, will still flow. Starters will
turn over engines. The viscosity of single viscosity 50 weight oil in the
engine at 10 below be somewhere between honey and solidifying epoxy.
Starters will will not turn over engines.
If you drove your Land Rover to Alice Springs in December, 20 weight would
lubricate about as well as a very dry martini. 50 weight would keep things
nice and slippery.
If you were a very clever oil chemist you would invent a viscosity improver
that would keep a 20-50 weight oil thick in the Alice Springs summer and thin
in New Hampshire winters. Furthermore, either you or the oil company would
get rich. Guess who.
These temperature ranges can be exceeded by the normal operating engine
temperature conditions. For example, this evening on the way to a Bruins
hockey game, the Commonwealth of Massachusetts suceeded on bringing traffic
to a complete standstill in all lanes AND the shoulder. My Ford Escort
diesel, a car which is neither lbc nor inclined to overheat, started to
overheat because the electric fan did not come on. (Not surprising, it
hasn't worked in the last 190,000 miles.) However because I had faith in the
ability of my multi vis oil to cope with the temperature range from near
freezing to over 200 degrees F and keep everything lubricated. Eventually
the jam broke up and faster air flow cooled the engine back down. I
continued on to the Garden to see the Bruins beat Ottawa 5 to 4. Yea,
Bruins!
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