10-40 or 20-50?

[Spool]

You realize you will never hear unanimous agreement from gearheads on which is the "best" engine oil to run.  That's because a little true data is nearly always mixed with fixed opinion - sometimes more than a little.  In southern California and the greater Southwest, 10W-40 oil works really well in seasoned engines.  On a brand new engine or fresh rebuild with tight bearings and clearances, 10W-30 is a great choice.  If you reside in cooler climates, again 10W-30.  On the other hand, if your truck crawls the back roads of Mojave or the Sanoran desert, 15W-50 or 20W-50 becomes pretty attractive for a typical factory engine.  But, what about modified engines?  I run 5W-50 in my 355.  It's happy at 5,500 RPM.  The point is that there is no absolute when it comes to suitable lubrication other than the moving parts of the engine need to be adequately lubricated.  That's what oil does - for the most part pretty well no matter what you are running.  Albeit, the idea of 20W-50 "taking up the space" to prevent cam wear wavers on ludicrous.  Virtually any multi-vis or straight weight oil originally specified for an application will adequately lubricate the moving parts of the engine, including the camshaft and piston skirts - AS LONG AS the high pressure friction modifiers (for example ZDDP) are present in suitable quantity.  This is old news.  Where you might notice subtle differences in the performance of various oils in street machines is over consistently long distance commutes with steady throttle.  Lighter weight oils may provide measurable improvements in fuel mileage if all other variables are maintained constant.  Eat a few extra cheesburgers and an extra twelve pack of beer in one week or forget to air the tires and that could change.  Get the idea?  So, if you want to run 20W-50 in your engine, go right ahead.  It won't hurt anything.  It may cost a little more.  Will it function any better than the 10W-40 you have always used, probably not, unless you change it more often.  But then, you could accomplish the same result with the 10W-40 by changing it more often.... 

Just what you wanted to hear, another opinion.  Use what has always worked.  Why deviate from a proven routine?

Thank you BD. I've spent a bit last night and this morning looking into it further and as you say, I can't find anyone to agree on much. Lots of folks talk about 10/30 coming out of the manufacturer but other than that, no agreement.

The engine did run fine 10-40, if 20-50 is too thick in a Los Angeles temp where temps are now 50-70 and will soon be 70-90, than I'll have to go back to 10-40.

I'm just so confused as to why 2 different professionals, 1 I trust and 1 who is a salesman who say 20-50 in the truck.
The first is a high performance engine builder. The theory was, cam lobes will wear over time without the zinc, go 20-50.
The 2nd was a Saab mechanic who just sold my girlfriend a 2001 Saab, "says it takes 20-50 oil, just like your truck", insinuating that my truck should take 20-50.
Now I'm thinking the guy is quieting a 2001 Saab engine with thick oil.
The 3rd is a friend who drives a 59' f-100, It's a clean truck he's been working on for 10+plus years, he run's 20-50.
The 4th was a stranger a year ago, Jiffy Lube only had 20-50 and at the time I said no, I want 10-40, and they by-stander explained to me that it would be better.

Yet, when I go online, I see nothing of this.
Given my truck needs work, the engine is fine. I'm just trying to make the best move here to keep it fine as I learn more and fix more with my truck as I intend to carry this one with me all the way to passing it on.

At 8mpg, I wouldn't want to put more stress on the block with an unnecessary thick oil, even if it wouldn't hurt the block.
But in all, I remember switching from Synthetic Oils to Regular Oils because the truck was 44 yrs old.
Then adding Lucas additive to make up for the Zinc.
And now 20-50, which I'm thinking is a waste and I should just take this as an opportunity to drop the oil pan, change the gasket to stop a leak and call the 20-50 a loss when filling her back up with 10-40.

Frustrating to feel like you're doing the right thing to mess it up. Living and learning.

[bd]

Again, people have their opinions.  But, only the opinions based on observation, experience, first hand knowledge, and otherwise verified data are reliable.  Opinions based on "everybody knows" or "I read it in a magazine" or "that's what racers use" or "that's what I was taught" are generally centered around unexamined data and "fixed" on assumption.  Even professionals have their fixed opinions.  It's almost unavoidable when you consider the sheer number of things you have to know in order to get a product.  So, you fill in the gaps with what appears to be reasonable and hope for the best.  Eventually, it becomes "factual" in your thinking.  Essentially, the issue you face is opinion versus fixed opinion.  Opinion is earned.  Fixed opinion is baseless assumption.  Another significant point to consider is the environment and application to which an opinion relates.  They are not all the same.  Engines are not all the same.  The environments in which they are used are not all the same.  And then there are those who have the right idea based on the wrong reasoning.  Get the idea?  So, the real issue that you face when receiving data from an outside source is sorting opinion from fixed ideas, then determining which of the true data are relevant to your application.  Fortunately, with a little practice it's not difficult.

You haven't messed anything up!  Oil isn't a waste, it's necessary... so is ZDDP in non-roller cam applications and new engines.  In a near stock build, whether you use 10W-30, 10W-40, 20W-50 or __________ is largely personal preference with some consideration given to usage and specific circumstances.  None of these oils will harm or shorten the lifespan of an engine as long as they contain the appropriate concentration of ZDDP and are serviced at the OEM recommended intervals.  The general consensus on this forum is 10W-30 or 10W-40, but that is not absolute.  The only caveat, is that multi-vis oils generally contain higher detergent concentrations among other things than straight weight oils and will better control sediment and deposit formation for a healthier engine.  So, if you want to switch back to 10W-40 and need to drop the oil pan to change a leaking gasket, wait until the engine is due for its next scheduled LOF service. 

[bedwards]

Oil is a very controversial topic. So for an opinion. I have searched far and wide on the internet forums for guidance. In the new stuff I am running the 5w-20 or what ever the book calls for.
In my old flat tappet engines including the 1985 305 Chevy I am running 15w-40 regular diesel oil. Even with the reformulated oils, this should get the zinc that you need for a flat tappet cam. I have never had an engine failure in the forty something years I have been riding or driving.
The marine engines I have call for 25w-40 and at least one is nothing but a marine 4.3 Chevy Vortec V6. They do operate at extreme rpms more than your car will.
Do some research on the forums and draw your own conclusions.
BTW I am in Alabama

bedwards

[Spool]

BD, Bedwards,

Thank you so much guys. This really helps.

It's only been day 2 and I can feel the pick-up in the truck is a little slower.
Also, BD, I think I may let this 20-50 slowly drip out the pan as usual, and then fix that gasket. Usually about 3 months.
When I replace the gasket, maybe I'll try the 15-40 that Bedwards mentioned in his 85' if I can opt out of Lucas additive by using it.

Through-out my research I saw that in colder climates, people would use a thinner oil in the winter season. (Eg. 5-30 or 0-30)
No need for that here in Los Angeles, but does a thinner oil help cold starts?

Really appreciate the in-depth responses guys.

Best,
-Thomas

[Kren420]

I notice a little improvement using 5W-30 in winter over 10W-30, not much though, could even be in my head.  I live in Alberta so temps get quite chilly in the winter.

[Dr_Snooz]

I'll just point out that every vehicle comes with an owner's manual that recommends a specific type and weight of oil. The guys who create that manual are great engineers with hard data based on testing and vast experience to support their conclusions. I'd say let that be your starting point and deviate from that as your circumstances dictate.

And...

Has anyone ever wrecked a flat-tappet cam or valve by using a non-ZDDP oil? I've never heard of it and suspect it's an urban legend.

[Irish_Alley]

honestly, i dont think you will be able to feel what oil you have, it might just be a placebo effect. ive always ran 10-40 no matter what the temp is and the motor has lasted 10+ years and has had a hard life. it was in my first square when i was in my younger 20s. blew a transmission and differential in my 86 pulled it out and its been in my mud truck since turning 40+ tires. even my buddy (who i got the motor from) is shocked its still going strong.

would you be able to run 20-50 in yours? from the wide range of opinions and no facts i would say yes. if someone ran 20-50 then a 100 miles later their engine blew i think you would hear about it

[Dr_Snooz]

10-40 used to be what everyone ran. Now you can't find it anywhere. What's up with that?

[Stewart G Griffin]

10-40 used to be what everyone ran. Now you can't find it anywhere. What's up with that?

Probably because most newer cars don't require it?

[Stewart G Griffin]

Anyways, why did 50 WT oil come about anyways?

[bedwards]

As you can see, there is a lot of overlap   

[bd]

So, there you have it.  A recommended viscosity chart directly from GM!

[Stewart G Griffin]

My thoughts on oil:

1) i briefly used 20W-50 (royal purple) in the cavalier;  The oil pressure gauge was reading low, so after a little reading and after someone suggested i use a thicker oil, i decided to go with the 50.  (You have to remember that chevy initially recommended 5W-30 for this engine)   i stopped using the 50W after a few months and the oil pressure seemed normal after that.  i think something may have been wrong with the gauge.


2)  As far as the whole ZDDP thing;  i believe that if you are running stock valve springs, with a stock or not so wild cam, then you do not need any additional ZDDP.  That being said, when i was running the 305 and 350, i used Redline synthetic 10W-30 which DID have the recommended ZDDP levels which i think are 1500ppm and above?   My logic was that it was only a little more expensive than regular oil and this way i wouldn't have anything to worry about just in case you really DO need more ZDDP if you are running flat lifters.

3) Now that i've joined the 21st century and have roller lifters , i use Mobil 1 synthetic for the extra protection.  Again, it's only a little bit more than regular oil, so why not get the best protection?   Even though with roller lifters, you can pretty much use any oil and not worry about ZDDP additives.

[bedwards]

Interesting it says not to use the 5w-20 for continuous high speed driving.

[Spool]

Update/Partial Conclusion.

Weather is funky these past 7-8 years I've lived in Los Angeles. Warmer overall to say the least, but still chilly in the winter.

Been running 20-50 in the 73 C20 for about 2 weeks.
-Runs smooth.
-Cold 50degree mornings, takes a cold start a bit longer. Maybe the oil is too thick on a cold start?

Fast forward 2 weeks to today.
-Runs smooth.
-Quick starts at 70degrees.
-But I notice the oil pressure is at 60psi on start, 45 in drive, 30-35psi on idle.

Drive it 15 minutes, park it. Come back 30minutes later, start her up and the oil pressure is 45psi on start 30 in drive and 15-20 psi on idle.
The second scenario being what I'm used to in the truck.

Starting to think, when it's time for an oil change, I'll go back to 10-40 and return to 20-50 next winter.