Going from 10W40 to something thinner???

[Komrade]

All of these are multi-grade oils, hence the 5W-30, 10W-30, etc.
At cold cranking temperature the oils are different viscosities, the higher the number, the thicker the oil. At operating temperature, they all function as a 30 or 40 weight oil.

The closer the cold oil is in viscosity to the operating temperature oil (even though it functions as a 30 weight, its still really thin when hot), the better. It makes it easier for the oil to flow to all parts of the engine after startup.

As for rumors that the heavier oil 'sticks' more on to the parts after engine shutoff, that is untrue. The oil, thinned by heat, will flow back to the pan just the same whether its 0W-30 or 20W-30.

Use a thinner oil.

 

[jorton]

Some opinions or tales make engine lube interesting.

Originally Posted By: ethangsmith

Getting back to the oil, I've always been told "Engines wear to the weight of oil being used."


I used to believe that.

Another one: "Thick oil causes more friction"

Originally Posted By: Komrade
heavier oil 'sticks' more on to the parts after engine shutoff, that is untrue.


Which are fact? Fiction?

 

[d00df00d]

Originally Posted By: jorton
Another one: "Thick oil causes more friction"

It might be better to use the term "parasitic drag." Thicker oil doesn't cause more metal-to-metal friction, but it does generate more resistance.

Think about how your engine would run if it had molasses being pumped through it instead of motor oil, and I think you'll see the point.

 

[TFB1]

Originally Posted By: addyguy
If this vehicle were mine, I'd use a 10W-30 HDEO like Rotella, Delvac...etc...

You'll be 'stepping down' just a bit to a thick 10W-30, and have a good solid add-pack for the engine. Not to expensive, either.

This may well be the best choice, but "supposedly" a 0w-30 or 5W-30 will give better mileage while the engine is warming up, still I doubt the extra cost of a 0W-30 would be off set by fuel savings... Don't be disappointed if changing to a thinner oil doesn't yield a noticeable mileage improvement...

 

[ethangsmith]

That's a good point- What would be an advantage of going to a lighter weight oil? I always figured it would be for economy.

 

[d00df00d]

Originally Posted By: ethangsmith
That's a good point- What would be an advantage of going to a lighter weight oil? I always figured it would be for economy.

Theoretically...

- Better flow and pumpability on a cold start year-round
- Better cooling: fewer hot spots, lower internal temps, lower oil temps, less time with the coolant thermostat open
- Reduced drag: more fuel economy, freer revving, possibly more power

In reality, the first one is the only one you're pretty much guaranteed to see. The second one is pretty reliable but may or may not be noticeable. The last one probably won't be noticeable.

 

[addyguy]

Economy, and easier cold-weahter starting, if the car is winter-driven.

Even though a 10W-30 and a 10W-40 are both '10W' oils, the 10W-30 will have lower cold-cranking values, as it is thinner.

 

[ethangsmith]

The car does not get driven in the winter, however I do start it once a week to drive moisture out and keep the seals good. During the winter, on a cold start, I get horrendous lifter clatter until the car warms up. At that point, the oil seems waaaaay too thick.

 

[TFB1]

Originally Posted By: ethangsmith
The car does not get driven in the winter, however I do start it once a week to drive moisture out and keep the seals good. During the winter, on a cold start, I get horrendous lifter clatter until the car warms up. At that point, the oil seems waaaaay too thick.


You'd be far better off not starting it as all, I have a '69 Fairlane Cobra that sets all winter without starting... Come spring I charge the battery(cable removed for storage), dump a ounce or so of gas down the carb and fire it up... After checking tires and am sure nothing is leaking, I'm ridin'...