After getting my new engine all dialed in I need to change the oil in it. I have searched these boards but havent found an actual "oil" thread so I am posting this.

What weight oil should I be using 10w40 or 20w/50? This car will be driven to cruise-ins and see some track time. The farthest the car will de driven is probably 20 miles one way. Right now I have 10w/40 in it and my oil prsseure is at 80 at startup then once the car warms up it goes to about 60 at 3000 rpms and maybe 20-25 at idle.

Your recommendations are greatly appreciated.

Thanks, Erik

10/30 synthetic would be good, hope youre not using regular oil, as synthetic will hold up much better with high temps.

I have had three different people, one engine builder, tell me that they are not sold on synthetic oils anymore. I am not sure why but thats what they have said.

Why 10w/30over 10w/40??

Thanks, Erik

Who built your engine? What are it's bearing clearences? We use to run 50wt in old worn, high mileage engines to compensate for loose bearing clearences. Same thing if a new engine clearences were on the loose side. This helped keep oil pressure up and allowed for oil protection if the engine was run on the hot side.

Typically though builders don't like using excessive clearences and tend to lean toward the tight side. That means not needing 40wt or 50wt oil, even in a performance build.

Multi grades poliferate these days, 10w-30 for example, the 10w is the oils viscosity in winter or extreme cold weather, the "w" actually stands for winter. The 30 is the viscosity of the oil at operating temps... Before multi grades, you ran different oil depending on the season or had cold weather starting problems or low oil pressure during the summer depending on what was in the crankcase.

New cars today and actually since the early 80's have been using 5w-30 for better fuel economy and a larger operating temp range... As for synthetic vs dino oil, there are some old school holdouts but for the most part synthetic has become accepted as a better product. Synthetic is capable of lasting longer without breaking down and is able to suspend more corosive gases than dino oil.

For more than you ever wanted to know about motor oil check this out... http://www.biologydaily.com/biology/Motor_oil

As for a recomendation for your engine, ask the builder or person that is garanteeing it and run what they recomend. IMO unless it has loose clearences 10w-30 is what I'd use unless you lived and drive in 110 deg temps every day.

yeah um i don't care what the heck anyone is saying .. the best oil is synthetic period if your engine is burning (or leaking) a bunch of oil than dont use synthetic its to expensive to throw out the tail pipe. As far as weight of oil is concerned .. if your engine is near new .. not leaking too much ... not burning too much .. just a normal oil usage i would recommend a 10w40 is most climates in the United States and Canada ..it is good in the cold and hot (primarily because it is synthetic the oil won't thicken in the cold too much and won't turn into water in the summer heat)

btw don't skimp on the oil filter either K&N makes a nice one that is easy to remove if you have headers

I have used Valvoline 10w/30 for break in and for the normal oil changes thereafter. The 'synthetic/dino' argument will go on for years. It is one of those that can never be won. I have never had problems during the winter or summer with Valvoline but the answer to your question will have to be yours. If you wait until the argument is decided you will be so old and grey it won't matter anymore.

I'd use 10W30 and I'm using the same in Mobil 1 in my truck BBC. Haven't noticed anything different compared to when it was dino.

All my vehicles, except my go-to-work car & truck, 2005 BMW 325Cic, use 10W30 dino.

Now I am more confused then ever. I just got off the phone with Beck Racing Engines, Shafiroff Racing Egnines and Nelson Racing Engines and every one of them told me something different. One said 10w/30 and the other said 20w/50. I understand everybody builds there engines with different tolerences but I dont see how different the weight of oil can be.

I will stick with the middle oil and run 10w/40 unless somebody can change my mind. Also two of three said no to Synthetic Oils.

Thanks for your help and I will keep reading the posts and hopefully come up with a concensus on what to use.

Thanks, Erik

The synthetic vs. regular oil thing is very confusing. ALL the cam companies I talked to said they do not recoomend synthetic oil. A lot of engine builders do not suggest it either.

If you talk to the oil companies they will tell you it's the best thing going. I use it 100% of the time in my 2000 GMC (Mobil 1). I have a hard time deciding for my hot rod engines. I have run some on synthetic and some without.

To help you choose a weight is fairly simple, choose the oil that gives you the oil pressure you want hot and cold. I stay away from 20-50, I normally run either straight 30 or 10-30 in my hot rod engines. 20-50 always seems to have the oil pressure too high (even more so when cold).

Erik - who built your engine? Ask them, not other racing engine shops. Racing engines are purpose built and depending on the application the bearing spec's will vary... Race engines may get the oil changed after every run or at the end of every day and synthetic may get too expensive under those conditions. Also who at these shops did you talk too? I doubt the engine builders themselves, I bet the phones are answered by an office person hired to do that or the oldest guy in the shop who may have old school on the brain. There's nothing wrong with dino oil other than it's a resource that isn't renewable and doesn't have the life span of synthetic. If your car sits for long periods of time or doesn't get properly warmed up by driving it for about 20 minutes each time you start it there is benefits to synthetic... This is science now not what someone learned 30 years ago and has etched in stone.

As for the different viscosity ratings of oil it explains it in that link I posted. The viscosity index is a measure of how much an oils viscosity (thickness) changes when heat is applied to it. A 40 or 50 is going to stand up to more heat than a 20 or 30. The 50 is not going to flow as well at lower temps as a 30 would. Viscosity is measured by heating oil and timing how long it takes to run through a specifically sized hole. Imagine using too thick of an oil at operating temps and your oil pump has a hard time pushing it through the bearing and oil passages through out the block, you might not get enough volume of oil and this could cause problems. Same thing the other direction, too thin and the oil pump can't keep the pressure up.

If you've run 10w-40 and have good pressure and such, I doubt you'll run into problems. If the outside temps don't get above 100 you might actually see a slight performance increase with 10w-30 or 5w-30 but that's about it...

While we're talking engine oils, what ever happen to the big push for products like Slick 50, etc?
Many of these products, when they first came out, made it sound as if engines will never wear out because of the way the products "coat" the metals. Haven't seen or heard much from those guys in a while. Any thoughts on this? Anyone using that stuff?

FYI, none of those places are going to give away the latest and greatest information to whoever calls them, with a possible exception to Reher Morrison.

20/50 is old school and you wont find it in any class racing engines that actually qualify.

I run 10w30 Mobile 1 synthetic. My engine is on its 5th season now and i DO NOT take it easy on it either. LOL

Thicker oil costs power, its harder to pump through your engine and that power comes straight from the crank. If your bearing clearances aren't set up intentionally loose, I'd use thinner over thicker oil.

Thanks everybody for the responses!!

I broke the motor in with 10/40 and have really good oil pressure. I will stick with that for now and maybe try the synthetic blend and see how it runs.

I appreciate everything and this board is freakin' awesome.

Thanks, Erik

I'm breaking my motor in with 20W-50 Vavoline VR-1.....it runs high pressure, but I don't have any problems....if I do it again, I'll go with a lighter weight(maybe 15-40 if you could find it). BUT, when It is fully broken in, somehwere over 3K miles, I'm going to run mobil 1 15W-50, it'll be easier on the engine and pressure.

one thing you could do is run 4 quarts of VR1 20-50, and one quart of mobil 1 5W-30(mobil 1 is supposed to be able to blend with ANY other oils), to "dilute" it a bit. the little bit of Mobil 1 won't hurt anything and would probably keep it cleaner than 5 quarts of dino oil.