How to choose oil viscosity

[Tom Kirkham]

Interesting article on how to choose oil viscosity for your engine...

http://grassrootsmotorsports.com/art...lippery-slope/

[82ACAUTOCRAFT]

Very good article!

[Bob In Ct]

Most Cobra guys are of the belief that thicker is always better. I'm convinced that if Castrol were to offer a 30W-60 most would switch to it.

For me, getting 60 PSI while using a 5W30 Synthetic is the best of all worlds. Plenty of pressure and oil flow to move the heat. I would also have to think that the lighter oil would put less stess on the distributor gears.

Bob

[madmaxx]

wow i was told by valvoline to never mix viscosities. a 10w30 and 10w40 will not act like a 10w35 but part of the oil will act like a 10w30 and part like 10w40, he went on to say you are better off mixing brands rather than viscosity.

who knows? I do agree way way way too many use 20w50 because they think they have a "race" car. 10W30 is about the sweat spot or what Roush recommends in their $20k crate engines which comes with a two year warranty.

[SoTxButler]

Good article...looks like a change is in order.

[ERA Chas]

Originally Posted by Bob In Ct

Most Cobra guys are of the belief that thicker is always better. I'm convinced that if Castrol were to offer a 30W-60 most would switch to it.

For me, getting 60 PSI while using a 5W30 Synthetic is the best of all worlds. Plenty of pressure and oil flow to move the heat. I would also have to think that the lighter oil would put less stess on the distributor gears.

Bob

X 2. ...and less ring drag and crank windage.

[Ralphy]

I've also read the less variation in weights. The longer an oil holds up. With that being said, the statement about Roush recomending 10w 30. It should hold up longer.

[olddog]

Heavy oils have given hydraulic lifters a bad name. If your lifters pump up at high rpm, going to a lighter oil will buy you more rpms.

[tcrist]

Originally Posted by olddog

Heavy oils have given hydraulic lifters a bad name. If your lifters pump up at high rpm, going to a lighter oil will buy you more rpms.

So is this why they went to multi weight oil in the first place? If that is the case why would you need it in an every day motor that never gets above lets say, 3500 RPM. (I have a 2006 Chevy Silverado that very seldom does).

I am not trying to be a smart a$$. I am from the old school and don't understand what was wrong with the standard old school 30 weight oil. It was used for many years with no issues (at least for me anyway).

[Bob In Ct]

A straight 30 would not be doing a very good job at start-up, especially in a cooler climate.

Bob

[Gunner]

Engines in the 1960s typically needed rebuilding around 75-80k.* Engines today can typically run over 100k without even a tune-up, and close to double that before mechanical or smog failure forces rebuilding. I'd say that answers the single-weight question.

* Yes, you could keep driving them for 50k after that, if you didn't mind the mileage hit, oil burning and smoke.

[tcrist]

Ok, works for me. Thanks for all of the info.

[Ronbo]

Quote from article:

"This is precisely why multi-viscosity oils were developed. These products have different viscosities at different temperatures; as an example, a 10W30 oil has the viscosity of a 10 weight at 0 degrees Fahrenheit and that of a 30 weight at 212 F"

Ummm, WRONG!!! (I guess all that runny, hot oil just seemed thinner to me!)

I do agree with most of the rest of the article...

Here's one for you: I wonder how many of these blown dist. gears are in engines running 50 weight as apposed to 30 weight?

[Bob In Ct]

Ron:
You're missing it. 10W-30 means the viscosity is equivalent to what a 10 weight would be at 0 degrees and equivalent to what a 30 weight would be at 212 degrees. The 10w-30 does get thinner as it gets hotter, but at a lesser rate than a straight weight oil would. Even 30 weight oil is pretty watery at 212 degrees.

Bob

[Ronbo]

My bad, the way it's worded it sounded like it was thinner when cold.

My other point being the effect the 50 weight stuff has on your oil pump, as opposed to the almost non-existant engine failures from 30 weight. Viscosity has little to do with film strength.

[cavinbill115]

Viscosity refers to the array of a liquid. Motor oil bendability is rated according to standards set by the Society of Automotive Engineers (SAE). Higher numbers announce a thicker oil. Oil rated for low temperatures are adumbrated by a "W" afterward the bendability appraisement (SAE 10W). Oil rated for top temperatures are artlessly adumbrated by amount (SAE 30). Choosing the actual oil bendability will assure your engine from accident and save you from cher aliment in the future.

[Dominik]

Does that mean I can run a "straight" 5W (or other?) when my ambient temperature is around the 75F mark day in day out?

How can the second number (after the "W") be determined depending on local ambient temperatures?

Few of us drive a Cobra in 60 deg F or less.

[bobcowan]

No, you can't, even if you could find one. Even when outside temps are 75*, the oil still gets hot. An oil with base viscosity of 5 would get pretty thin when it gets hot.

If you have good tight tolerances and using modern engine building techniques, you might be able to drop down to a 0W-20 oil - which is recommended for a lot of small modern engines.

The second number has more to do with engine temps than ambient temps. RPM's heat oil, so if you're just cruising the streets the oil won't get that hot. But running on the track lap after lap, it will.

I drive my car in temps below 60 pretty regularly. Did that on Sat for a couple of hours. Below 50 is less common. Depending on where I'm going and what I'm doing, I've driven in the 20's.

[dcdoug]

So for those of you with vintage 427FE motors, how many of you are not running 20w50 and is there a compelling reason to switch. Seems like the lighter weight when cold might be a good thing for those occasional drives in a cold climate (the ones that ERAChas tells me I shouldn't do...)

[Dominik]

Hi Bob,
okay I assumed the straight W rating takes heating up during operation into account.

Let's hear if we can use another than 20W50 for our FEs.