What weight oil to use

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Mar 7, 2003
New Jersey
Hello everyone. I am new to this site, just heard of it and visited it for the first time yesterday...and have since been wrapped up in all the available information. GREAT SITE!!!!! I don't know as much about oil and fuel that I should an I know that I have finally found a resource that will boost my knowledge level.

Anyway I have this question: I have a '66 Chevelle (big block, etc, etc.) The engine was rebuilt a number of years ago, very little milage was put on it, then into storage it went...and stayed there for a bunch of years...I am now getting back into the beast and bringing it back to life.

Back in the day when I was running this engine I was told by a buddy of mine (one that has been helping me with the vehicle) to run Penzoil 20W-50. Which I did. Now that I am geting this car back on the road
I am wondering what your opinions may be as to the weight of the oil.

Is this heavy?
Thanks for your help everyone
. Since it has been so long since I have had the car running I will try your suggestions, keeping an eye on the oil pressure.
If it was recently rebuilt, so the seals will be tight and good, why not run mobil1 15w-50?

Youll get an oil that flows well when cold (A 20W-50 isnt so good in that department), and will provide a superior protection when hot, surpassing any dino xw-50 that was ever out.

M1 15w-50 is designed for high power aplications...

20W-50 would be OK too, in that situation, since the car wouldnt be used too much, thats the only dino Id use (unless it is usually cold), as it ought to leave a better film after running. Synthetics usually leave a nice film, but I have heard that lighter dino oils tend to drop off the metal parts easier.

There are certainly a lot of knowledgeable folks that will be hapy to help you. I would probably not go with the 50 wt. I don't know what the manual recommends but I used to use a 40 wt in my 307. If you are planning on going with synthetic there is the Mobil 1 10W-30 or Amsoil 10W-30, or the 10W(?)-40. There is Mobil Delvac1 5W-40. Chevron Supreme and GTX seem to do well in the Non-syn oils.
I'd recommend something like Delo 400, 15w-40 to start out with and see how it does. In hot weather you might want to run 20w-50, but only if you have oil consumption or oil pressure problems.

Welcome CD! Nice car! I agree with the others, try out a 10w40 or 15w40 in that, and it will probably be just the right viscosity for you.
We were running Valvoline 20W-50 "Racing" oil in my dads '70 Chevelle SS396 Convertible for a few summers with a fresh 396. Last year, we dropped down to a 10W-40.

From reading this board, I am going to recommend that my Dad stick with 10W-40 or 15W-40 in the big block, and I am going to switch to 10W-40 in my 327 Chevy II.

I think 20W-50 is overkill, even for these old motors. However, I have used in in "summer cars" for years without any problems.
Just in case you haven't already, I'd certainly drain that old oil out of the crankcase (and refill) before trying to start it up.
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