What's thicker 40 or 20w50 SAE?
 

I think I've figured my oil psi issue. I had a problem with a lifter bore. After finding my pickup tube fell off, I've put it back on and I still have lower than normal, so until I get my 383 built I'd like to use 20w50 or 40. Which is thicker? I have to do a 200mile road trip in it and I want the PSI higher.

update...after reading about 12 web sites, I found a nice viscosity chart. Bottom line, 50 thickest, 20w50, 40, 10w40 etc. Test was rated at 212 degrees. Thing I noted, was at cold 100 degrees the viscosity differences is great, as temp rise that gap is drastically reduced. So 20w50 it is...

there you go. you answered your own question. My thing about 50w is that its alot thicker and i would think it would be harder for the motor to be lubricating properly. If it was me 40w would be the most i would go.

What oil are you currently running? IMO a 50 weight is too much for a 350 LT1. Stick with a 40 weight

I'd be tempted to go with the 20W-50, so there's a little more oil flow on the cold start-ups...

There would be less flow on cold starts with 20 W. 0 W will have the most flow on a cold start

Keep in mind I'm not talking about a normal condition, I just want to get buy until the time is right for me to drop in the 383. Right now at operating temps the psi drops to 20 at idle 10w40. Before it was 28-30 psi with 20w50. So 20w50 it is. Also, this setup has about 30k and 6yrs old. It was a stock rebuild H/C & boltons. I think its held up well.

I was amazed to find that Autozone had 50. I bought a few and may mix it in to get the psi I want. Also...Cold?! No stincking cold where I live in FL. It's hot, hotter, hot and cool.

Im a parts sales manager at Autozone, i'll explain to you how the Castrol company people explained to us about oil and multi-viscosity formulations.

First off, explaining oil "weight" or viscosity

Viscosity means a fluids ability to suspend particles within it. With oil, the HIGHER the number, the THICKER or "heavier" the oil's weight is. Most oils used these days are multi-viscosity oils. This means they have 2 diff. weights, that change based on demand. for example, a conventional motor oil that is 10W-30 will be a 30 weight oil while it sits cold or "under engine operating temperature" in your crankcase. The same oil will be a thinner, easier flowing 10 weight oil at or above normal operating temp., or the time when it is actually heated and circulating through your motor.

There are a lot of myths about oil, both conventional and synthetic. The people at Castrol periodically send us information or even conduct information classes which managers are allowed to attended to keep people informed about the product. One of the biggest is that on a factory engine, as the miles go up and the ware sets in, you should switch to a thicker or heavier oil. That is completely wrong to do. In fact doing that will strain your motor much more than help it. Factory (non-modified) engines and their components are built and tested with very specific weights and types of oil (to establish component tolerances) and no matter the amount of mileage on a motor, you should always try to match the factory specs as closely as possible, and maintain the oil properly (proper oil AND filter changes). As your motor goes up in mileage, switching to a synthetic oil, and a high mileage oil, are you best 2 options. (i.e. we have a regular customer who is a traveling saleman, has a 2002 ford F150, with over 330,000 miles on it. Has never had an internal engine issue EVER with the vehicle, and puts nothing but Mobil 1 High Mileage synthetic in his truck, same weight as it came from the factory with and he refuses to use anything else.)

Remember that when a performance engine is "built" the best thing you can do is to ask the assembler their suggestion for an oil type/weight (as they will best know the tolerances of the components), and than stick with the type/weight for the life of the engine.

There is much more were taught in our foundations courses about these things. Such as the switch from conventional to synthetic oil, and how (contrary to popular belief) if your engine is well maintained (newer engines only, the older teh motor the less tolerant teh seals are to expansion) you can switch back and forth all day without leaky seals (synthetic causes seals to shrink, conventional causes expansion). For what your asking, the stuff I said above should be enough to get you going with some oil wisdom.

All information above based off information received from oil producers and distributors through my time working at AZ.

If you choose to run the 50W go ahead but i think even a 5W-50 would be a better choice. I know Castrol Syntec comes in 5W-50

You have that backwards.

what do you guys think of 15-50? sorry to hijack

for? for a stock displacement LT/LS you want a thick 30 weight or a thin 40 weight at most unless you are really hurting for pressure or you are seeping from your pan (high mileage). There is no need to go above a 10W no matter where you live. When you get into strokers where the tolerances are greater then a thick oil like 20W 50 comes into play.

Here is some more accurate oil info as far as what is thicker and when-

http://www.upmpg.com/tech_articles/motoroil_viscosity/

As for the 15W-50 their is really no need to run that thick of an oil on a stock shortblock LT1 unless its shot. A 5W-40 would be a good choice for an engine with lower oil pressure at hot idle.

Excuse me, he's right I had it backwards. 10 hours of dealing with the idiotic general public and it being after midnight has my brain all fried, sorry for the slight misinformation, I tried to help D:

it will be a fresh 357

im runnning a straight 30wt right now... will be switching to 5w30 or 5w20 when it's broken in and it get cooler outside. no need for thick oils if you've got 45+psi all you're doing is wasting hp.

Your bearing clearances and oil pump will determine what oil you really need to run, your builder should be able to give you a good idea based off of your clearances. If its a fresh engine their is no reason it shouldn't run off of 5W-30/40 if it was machined right.

there's no "right" bearing clearances. you can run <.0020 on the mains if your builder knows what he's doing and you've got quality parts. running a motor "tight" like that has some hp benefits. then again you can run >.0035 with a hv pump and gain a little longevity but there's no "best" way to run a dual purpose motor or "best" oil.

I was referring to "right" as it being done correctly as in a good machine shop and machining equipment in comparison to just being slapped t/g with unknown clearances and non machined surfaces (ie having crank cut, mains honed...).

Every machine shop likes to do things a little different, but if something gets botched on the build you'll have oil pressure issue the whole (possibly short) life of the engine and may attempt to mask it by running thick oil.

20 psi at idle is more than enough hot.

Yea like he said above me. Gm only calls for 5-7psi at idle. So thats just barely above the redline. As long as your getting 10psi per 1000rpm, then your good.