While the engineering term defining an oils range of operating temperature is called the viscosity index, the SAE grading system simplifies things slightly, offering a cold, and hot performance rating, typically depicted as "10W40" or a similar number. In plain terms, you can think of the "W" in this rating as "Winter", and the number prior to the W indicates the cold weather performance of the oil. The larger number after the W indicates the high temperature performance of the oil. So simplified, the lower the first number, the colder weather the oil will perform in, and the higher the second number, the better the oil will perform in high-heat and high-load situations.

Choosing the correct grade oil for your engine can be as simple as looking in the owner's manual, but more often depends on how and where you drive your car. In colder climates, a low first number in the oil grade will give you superior flow and protection during cold starts, but if you drive your Mopar aggressively you'll likely still need the protection of a higher second grade number. Conventional oils are limited, and generally synthetics will offer a wider spread, or wider viscosity index, for better all-temperature protection. Another consideration is the power it takes to move the oil through the engine. Since thicker oils take more power to pump, using the thinnest oil that gives adequate oil pressure can make more horsepower available to the rear tires.

Special Consideration For Flat-Tappet Camshafts
While we could dedicate an entire article to choosing the appropriate oil for an engine equipped with a flat-tappet camshaft, in this article we'll give you the basic information you need to protect your engine's cam and lifters. As engines have evolved over the years, so has oil technology, and so have the government regulations governing what additives can be added to engine oils. As a result, the amount of zinc and phosphorus in modern engine oils is often inadequate to properly protect a flat-tappet camshaft and lifters. For these reasons, you should pay special attention to the oil used during engine break-in, and also to the oil you run day to day in a flat-tappet cam equipped engine. Racing oils, such as Valvoline VR1, and synthetics, generally contain more of the necessary additives than off-the-shelf oils from your auto parts store, and for break-in we certainly recommend an additive like Comp Cam's break-in lube.

Realizing the need for higher zinc content in oil, manufacturers such as Brad Penn, Comp Cams, and Joe Gibbs Racing have developed "race only" oils that don't necessarily meet government regulations for street use, but do contain the additives needed to protect your flat-tappet camshaft. So if you want the ultimate protection for your solid or hydraulic flat-tappet camshaft, and you don't drive your car on public highways, one of these oils may be right for your application.

SOURCE
Valvoline
PO Box 14000
Lexington
KY  40512
800-832-6825
www.valvoline.com
Milodon Inc.
2250 Agate Court
Simi Valley
CA  93065
805-577-5950
www.milodon.com
Comp Cams
3406 Democrat Road
Memphis
TN  38118
800-999-0853
www.compcams.com
AMSOIL
925 Tower Ave.
Superior
WI  54880
800-777-8491
www.amsoil.com
Auto Performance Engines
1479 Berkley Rd.
Auburndale
FL  33823
863-967-8781