Oil viscosity

[firebird77clone]

My 01 Silverado calls for 5-30 oil, it was low and I'll change oil in a day or two, I put in a quart of 20-50.

Just what do the numbers mean, and would it damage the engine to run straight 20-50, as i have quite a bit.

Thank you

[34_40]

I wouldn't run 20w50 in a "newer" vehicle. Especially when you know it takes 5w30.
Save yourself a lot of trouble and do a simple google (bing) search on oil viscosity - there are pages and pages of info out there.

In the "old" days" the general rule of thumb was the higher the number the better. But that thick oil actually consumes horsepower!

Some new cars today actually use oil that is listed as 0w30 and 0w20! Again, I'd say do a simple search all the info is at your fingertips and also search API index, more good info.

[35WINDOW]

The 5W (the W stands for Winter) is the viscosity of that oil when cold, and the 30 is the viscosity of the Oil when it's at 212 degrees-

That being said, the "30" designation uses what is called "Viscosity Index Improvers" which is mostly Polymer based (which is a form of plastic)-part of the reason you change Oil (other than to get the trash out) is that with multi-grade Oils, the Polymer can shear leaving you with the lower number to protect your engine-

Now, when you say "straight" 20-50, there really is no such thing-a straight weight would be, say, a straight 30 weight (straight weight Oils do not have Viscosity Index Improvers)-they are graded by a "hydrocarbon chain" which is a molecule that consists primarily of hydrogen and carbon (there is more to that subject, but Ill keep it short here)-

A short Hydrocarbon chain would be a lower Base Weight (say a straight 10 weight), whereas a long hydrocarbon chain could be, say a 40 weight (the longer the hydrocarbon chain, the higher the number)-

It is absolutely ok to mix straight weight Oils, but I would not recommend blending multi-viscosity Oils (there are just too many Additive package differences)-hope this helps-

edit: Ooops! Looks like I've been tree'd-

[35WINDOW]

Btw, if you had, say, 4 Quarts of straight Grade Oil (2 of 20 weight, and 2 of 40 weight) and you mixed them together, you would end up with a straight 30 weight-

[Matthyj]

Newer vehicle have tighter clearences and roller cams, rockers etc so as I understand and like mentioned lower viscocity free's up horsepower. Combining different viscocities is suppose to be a no-no, however I will stick with I bet a motor can live a lot longer on mixed viscocity oil than none! You did what you had to do, now just change it when you can.

[34_40]

And like the "old-timers" used to say about oil pressure.. "some is better than none!"

[firebird77clone]

Ya, my thoughts exactly. Mixing in 1/5 volume of something similar you end up with something close... And oil pressure is good, at any viscosity.

[rspears]

Ya, my thoughts exactly. Mixing in 1/5 volume of something similar you end up with something close... And oil pressure is good, at any viscosity.

You've got three out of three (make it 4 of 4) telling you that blending straight weight oils is OK, but that blending multi-viscosity oils (your 1 in 5 volume) is not recommended, because the multi-vis oils have additives that may not play well together.

Like Matthyj says, you'd do well to change your oil sooner than later, even if your pressure is good.

[firebird77clone]

It occurs to me that I ask about viscosity every couple of years or so. I just can't seem to wrap my brain around it.

This mixing of oil was a short term fix only. I've been ignoring the blinking dash light (change oil) for too long. I was certain the risk of low oil outweighed any risk of lubrication reduction for a couple days, so I dumped it in.

There certainly seems to be something to this polymer shearing, as the pressure came up slightly after changing the oil.

It seems that even the simple tasks can teach us things. My first time changing oil on the lift: I've always been on the ground with jackstands. My nice clean oil catch can with the telescoping neck and oversized funnel, I figured this was going to be the easiest, cleanest oil change ever.

Nope.

Had the lift high enough to not have to duck (I'm six foot) and totally underestimated the initial lateral velocity of the oil stream...

SKEET

Right on my reasonable presentable boot.

Well, it WAS reasonably presentable.

I grabbed the oil catch funnel and repositioned it, but then it started dripping, and the funnel wasn't big enough to catch both streams..

Anyway, sufficient to say it made a mess.

But it's all done, the boot will never be the same, but the pressure is slightly up, and the slight lifter tick at start up went away.

Changing oil... Good idea for everything but your boots.

[fraso]

My 01 Silverado calls for 5-30 oil, it was low and I'll change oil in a day or two, I put in a quart of 20-50.

If you were just at the low mark of the dipstick, you could have easily went a couple more days without any problem. The danger with not enough oil is that the sump level isn't always high enough to keep air from getting sucked into the pickup.

Just what do the numbers mean?

As explained by others, the first part of the viscosity (20W) is the cold viscosity and it means that that your oil has the viscosity of a 20W-weight (W means Winter) oil. That is:

• maximum Cranking Viscosity of 9500 cp @ -15°C and
• maximum Pumping Viscosity of 60,000 cp @ -20°C

The second part of the viscosity (50) is the hot viscosity. It means that it has the viscosity of a 50-weight oil. That is,

• Kinematic viscosity between 16.3 and <21.9 cSt @ 100°C and
• HTHS of at least 3.7 cP

Your 20W-50 flows like a SAE 20W oil when it's cold and like a SAE 50 when it's hot. See SAE Viscosity Grades for Engine Oils for more information.

Would it damage the engine to run straight 20-50, as i have quite a bit.

Engines depend on flow for lubrication and pressure is characteristic of flow and viscosity. Using too thick of an oil means that the relief valve will end up recirculating more oil back to the sump. It's better to stick with the recommended viscosity but, if you really want to use up your stash of 20W-50, you could add 1 qt every oil change.

[Bob Parmenter]

You guys have made my day! First clone, sorry it's at your expense but envisioning you chasing the cascading oil stream without total success, the way you told the story on yourself, gave me a good laugh. Humor is it's best when the audience can relate..............

Second, as an ex-oil "expert" it's amazing to see just about every response in a thread be so accurate for a change.....especially the understanding of "w" not standing for weight.........35, you've got your poop together man! For decades (that's weird to say in a way), that error has been like finger nails on a chalk board to me. You guys all get an atta-boy. Even fraso bringing up the idea of flow/viscosity/oil pressure boarders on higher level understanding. The only additional thing I'd love to see is the end of referring to viscosity grade as weight.........but that's a minor thing by comparison.

A brief (also meaning incomplete) discussion about the correct advice about being cautious when mixing different brands and grades of oil. The "safe" advice is to say no for all the reasons noted above. The real world practical version is that what started this thread is a comparatively low risk scenario. Additive incompatibility most often will lead to the additives dropping out of solution so while not ideal, it won't destroy the engine in typical light duty driving, especially if the operator changes oil on a routine, reasonable interval. Your engine will survive fine on an oil with no additives, it just won't be as well served for the wide range of possible operating conditions it may be subjected to. Again, that's not a blanket endorsement of mixing, but know that it's also very unlikely that mixing will be catastrophic. Well.................except when it is.........

When I got the late model Mustang a couple years ago one of the things I learned was Ford insisted on ONLY 5w-50 grade synthetic. Not going to go into the discussion on the pros and cons of synthetic versus conventional, or the stuff about "voiding" warrantees and blah blah. Why would Ford be so insistent on such a wide spread grading? It took some digging because Ford doesn't offer any easily reached answers...............probably because they operate from the not altogether incorrect assumption that the vast majority of consumers either don't care or aren't informed well enough to understand the reasoning. Turns out that their variable valve timing system is highly dependent on oil viscosity grade, and to ensure proper operation across the wide possible range of conditions that their cars might be subjected to the safe thing for them to insist on was the 5w-50. So, there is one example of the complexity of newer engine operation management systems changing how we have to evaluate applications.