O.K....but the owners manual doesn't say that. Mine doesn't anyway; it calls for 5w30 from below 0F - "and above" (shows over 100F on a thermometer) and as "thick" as 10w30 from 0F - "and above"

So GM isn't saying that it's appropriate (or required) for your temp ranges.

I guess what I'm trying to understand is this: you said that your car has "stable" oil pressure w/75k miles, that you're in it for the long haul. I guess it seems that you're implying that the 20/50 you chose is what you think is required "for the long haul"...yes? No? If yes, then I'd point out the results from my truck, that 20/50 is definitely not a requirement for a long engine life. Same goes for Diff oil...the same truck has only had 75w90 synthetic in it's diff for all those miles and all that boat towing.

 

How bout the casual thought of base weight of the oil stock and how long it takes to circulate WELL in any motor? Wouldn't that outweigh (or at least equal) any benefit of the 50 (vs 40) in hotter conditions?

I even tried the 0w-40 Mobil Euro blend for this reason. Then, I found the base weight wasn't really "thinner" than 5w-30. I'm pretty sure (w/o looking) that 20w-50 has a base weight heavier than 5w or 10w base stocks.

Obviously, GM had something in mind when they sent "the fleet" of Corvettes out with THAT weight versus the heavier stuff -- even when MOST owners would have similar/same use as you. It's rare for any owner to drive in the cold crap.

 

GM had plenty in mind and it was corporate fuel economy and emissions. Those are the things that brought on the gearing in the 2's the 4+3 and the 226 fan on temps. It also brought us the L98 TPI and over 100 less HP than a C3 or a C5. The C4 was built when they were learning how to balance smog and performance and stole performance for mileage so they could sell many more trucks that made them a bunch more per unit than cars did. Lighter weight oil was all about cold start and the first few bagged samples taken that weighed in large into the emissions profile they had to meet. To understand the engineering and decisions made you need to transport back in time to the tools they had to work with and the demands placed on them to understand the decisions.

I managed the rebuild for the engine shop that did the B2K cars and have seen what is inside well over 400 C4s and robust is not the word that comes to mind. 2 bolt mains cast crank cast pistons light duty timing chains low tension valve springs dished intake vales that are begging to deform. They are not the C3 LT1(how that designation got reused I will never understand) forged crank and rods with quality pistons and 4 bolt block along with the 375 HP that was not a problem then. Once the tight new part fuzz wears off by 75k they are into more performance oriented clearances of 0.0022 to 0.0025 on bearings pistons looser timing chain with some wear etc. 20w-50 has a good deal more sticktion to leave a film of oil for cold start at the expense of a tiny bit more fuel to do it that I don't care about more than I do about the oil film on parts. Some people complain about their engine needing 8 or 10 turns to start and I consider it a feature to get oiling system started lubing everything before the start... go figure.. I come from seeing how they were built rather than the myths in a service manual.

 

Thanks for all the replies some great information.
I am still curious about the comment in Post 16 about not using Synthetic Brake Fluid. I could understand if it was Directed at "Silicone Dot 5" but why Synthetic Dot 3 or 4?
Barrier

 

Okay...but they're still recommending 5w30, today...so it's not just a "back then" thing.


Yet somehow they last...



Nor was it in the '90's. The C4 LT1 made more power than than the LT-1. What do forged cranks, 4 bolts and forged pistons have to do with oil, wear and life? ALL SBC use forged rods, FYI.



Myths? How about the results I've gotten with my truck? No "myth" there...that's real life/real world results and it starts on the first compression!


.

 

I read in a post about brakes I think it was, to not use synthetic or maybe it was silicone brake fluid but pretty sure it said synthetic, something to do with abs if I remember right. In my 94 coupe LT1 engine with 104000 miles I have just started useing Mobile 1 10/w40 high mileage,starts like 1st turn,better oil pressure on gauge by 10 lbs. or so cold and hot, a warm weather car.No ticking when cold or hot instant pressure on gauge. Seems to have slowed down an oil leak that drips about 3-4 drops down left side of engine by filter.

 

Thanks,Peter.
It was the Silicone that was not recommended.
Silicone, Dot5 was used because it was not Hydroscopic (did not absorb water) which common Ethylene-Glycol based fluid did. Silicone fluid will not destroy paint if spilled on it as does Glycol based fluid.
They did find other problems though, it would hold moisture in suspension trapping it in the system and causing small water pockets. This would cause difficulty in bleeding off air and possible rust in wheel cylinders etc. It is best left for Show Cars or rarely driven cars since it lasts Forever and does not absorb moisture while stored.
Harley switched to it for a few years in the early 2000s then switched back. It also caused problems when mixed with the conventional alcohol Ethylene-Glycol based systems
I have only seen positive results for Synthetic based fluids.
Barrier

 

It wasn't a myth in a service manual that's been my driving force. There's a lot of feedback in places like "BobIsTheOilGuy". Plus, my build isn't exactly standard (with a 4-bolt block, Scat 9000 crank, and Wiseco pistons (1/16" rings).

My build has everything forged except the crank. I would have done the crank (forged) too had it not been for EVERYONE suggesting it was overkill in the HP range of my build. (At least it's a bit strong Scat 9000).

I used the standard 30w for break-in...then started with 10w-40 for the first 5k miles. It didn't make it to 5k before I started concerning myself with the heat of a new engine...and summer. I swapped to 20w-50 in the first summer. I ran the heavier stuff for the next year and a half.

That's when I considered synthetic -- which the builder suggested was OK after decent break-in mileage. Since 5w-30 is what I run in my other cars AND since it was coming up on my second winter, I loaded some in.

First thing I noticed was how much faster it would spin up. Seemed like the difference between a 40-lb FW and a lighter one! You know...I always wondered if heavier oil might generate more compression/hp until that day. Since then...and after some reading on the type of forum suggested, I'm not so convinced that heavier oil is "better".

(Plus, the combination of 20w-50 and a HP oil pump may be the reason my valve covers seep a bit. IIRC, I was hitting mid 70s (PSI) for pressure. Maybe 80? I also noted there's not a ton of oil heading up to those covers (after seeing vids of a 350 SBC running w/o the covers mounted).

When an engine gets wound up, is lighter or heavier oil going to create more resistance on the parts? I'd think heavier...in terms of the mass flying around.

Bottom-line is I can see/think of several reason why heavier DIDN'T seem "better" though I USED to be of that mindset. It's just as hard to make the jump to 5w30. So, I decided to ride the middle return to the 10w-40.

It's hard to say there's a "right" answer for anyone/everyone. Like most, I don't run the car in cold extremes so 5w-30 doesn't seem "necessary". But, that spin-up showed me it might make more power.

I also used some lighter, thinner ring packs....like cars are running now. (Mine are 1/16" ring Wiseco pistons) With thinner rings, I'd think thinner oil might make more sense? You know...for the mass of the oil being moved like I suggested above. Of course, that's not an issue for C4's. I assume thinner ring packs weren't leveraged until later generations.

Do LTx cars also have 5/64" rings? Or...is that when they moved to the thinner 1/16" design...and started 5w-30 oil?

Of course newer motors can run even thinner rings -- like 1mm.

 

I live in Mesa AZ and I use 15W-50 Mobil 1. I chose this oil for one reason only heat. Today I did some spirited driving and my engine oil temps were around 215. Summer time temps run over 250 degrees. I've hit 280-300 degrees so the thicker oil is my choice. My Z06 gets 10W-30 MOBIL 1 which is thicker than 5W but my overall temps are much lower as the LS motor is superior.
I use Valvoline 75W-90 in all my differentials and add a little bottle of AC Delco additive.

 

I find this sentence interesting; My LS engine (LS2) and my LT1 ran about the same temps in the same conditions. 5w30 synthetic in both. I wonder if your 50 wt oil increases oil temps due to increased friction?

 

You are in fantasy land there were thousands of 375 HP 350 cars built in a C3..

 

Who knows? With the ambient temps now in the 70's my L98 oil temp stayed below 220 even at higher rpm's. If the oil was causing friction as you suggested then the temperature would reflect it. This great great weather is why I live here.

 

Say what? Let examine this and find out who is really in fantasy land; You DO realize that the C3's "375 HP" engine was rated differently than the C4's engines...don't you? And as a consequence the actual hp is pretty similar between the C3's most powerful small block and the LT1...right?

Here is some fantasy for you...straight from GM.

GM hp/tq comparison

Since I know you like to dismiss what the GM engineers who built the car say, here are a couple independent results that show the actual power to be virtually identical...

Vette magazine results referenced

SUPER CHEVY article


.

 

So a thread about diff fluid has digressed to oil...then HP fights. Is this a theme lately? Especially between the two of you? What's the deal?

I posted a winded-thesis w/o a comment while you two bicker. I guess it's time to leave you two alone and not address what you say any more?

I think we ALL know that the older 375hp cars were about the same as C4 LT1s. And, we know the higher 400+ were a little better. What does that have to do with oil or manufacturing quality/technique?

I wouldn't consider power the issue. If I listed (what I think) the reasons for doubling longevity of V8's today, power wouldn't be on the list. Newer cars make more power and last longer.

No point in actually thinking about (and posting) what I think contributed because it will get ignored anyway.

Have fun with the nonsense war!

 

I think it's just as likely the cooling system is what's better.

And, btw, I wouldn't discount the possibility that heavier oil COULD raise temps for the reason Tom posted. More friction/work for the motor to "slosh" through the thicker oil...

 

Exactly. That's what I was trying to get at (I even said that about "forged" parts). I didn't comment to your long winded post because...I agreed with it. I read it, and thought, "yep, Greg covered that and nothing more really needs to be said". So I didn't say anything. Next time, I'll post an

 

Thanks for all the responses. I suppose I'll go with the 75W90.
Maybe try the 75W140 next time.
As for the other 15 replies:
My '68 427 390 with 3.55 and close ratio 4spd was pretty quick if I didn't sell it 47 years ago I could find out if it was faster then the LT1 or not. How do you think a'69 350 350 3.36 wide ratio 4spd would compare? Had one of those as well.
Barrier

 

http://www.roadandtrack.com/new-cars...-corvette-lt1/

 

Not sure that that link was supposed to show. Cool read though!

 

Driver's race, assuming modern tires on both.


The '69 would get beat by a '90's LT1 stick.

However...I'd bet that both the older cars would provide a way more sensational experience through the 1/4 mile.