Remember that the lower oil viscosity number is the viscosity cold and the higher is the hot viscosity. STpaulguy is right----stick with a 5 wt oil for good oil supply at cold temps on starting. If you were burning oil I might suggest a 5-40 oil but you are not. The knock would bother me. Is it lifter knock which sounds like lots of individual tic ticking? Or is it a knock---knock sound with time in between. The latter might be a bad sleeve bearing on one of the pistons. Oil would not help that condition.

For your 1999 CHEVROLET MALIBU 3.1L 6-cyl You would need:

5 Quarts of SAE 5W-30 Signature Series 100% Synthetic Motor Oil (ASLQT)

1 Absolute Efficiency Oil Filter (EA15K29)

Stick with 5W-30. It has better flowability at cold start and that means less cold start wear. Cold start is defined as an engine that hasn't run for at least 3 hrs. And it has the same hot viscosity

Do NOT use a lousy AC DELCO paper filter! Use a MOBIL ONE SYNTHETIC FILTER< and PENNZOIL ULTRA OIL with DEXOS ratings on it, or MOBIL ONE 0W-30 oil! Do NOT worry about THICKNESS! PENNZOIL ULTRA gives a 15 year 500k mile WARRANTY against engine troubles! Be SURE to STOP using that DELCO paper filter, and use either MOBIL ONE or FRAM 10x filter instead! ALSO toss out the DELCO PLUGS and use BOSCH or DENSO iridium plugs! LESS carbon footprint, MORE power more ECONOMY and LONGER cleaner oil changes! PENNZOIL OILS are SUPERIOR to most domestic oils, but ONLy in the higher end ratings. ULTRA OIL is FANTASTIC and you cannot beat the warranty you earn by using it! 500K MILES! DO NOT get duped by DELCO items! Gm makes most of them in mexico for higher profit margins! BOSCH and DENSO make REAL plugs that burn MORE fuel MORE COMPLETELY! In this way your CONVERTER and exhaust will last FOUR TIMES LONGER and you save gas as well! POWER WASH engine and also take #20-40 to ANY oil change center and have your IDLE AIR CONTROL VALVE and THROTTLE BODY cleaned up with AMSOIL or SEAFOAM! This will insure you get a proper AIR/FUEL mixture around town, with NO stalling or wasted fuel! GOOD LUCK! Expect to get to 350 k miles! The PUSH ROD, TWO VALVE GM engines are at least very stable if not very fuel efficient! <
I own a 1999 Chevy Malibu LS. It has the 3100 SFI V6 with 207,711 miles on the original engine. I have always used Pennzoil yellow bottle 5W-30 it's whole life and a ac-Delco filter every 3,000 miles. It's getting into the 90's here in Virginia and I'm worried that the oil is too thin. I checked the dipstick and I wiped the oil on my fingers, and it just kinda run down my finger. I think it's too thin for this old worn out engine. The manual says I can use 10W-30, but isn't that the same viscosity at operating temp? The engine does have a "knocking noise" that gets worse when I tried high mileage 5W-30! The engine doesn't burn any oil. I don't have an oil pressure guage, just a light. And it has never come on. What do you guys suggest? Does 10W-30 "break down" as easy as 5W-30 in hot weather? Or should I just stick with 5W-30 until it blows up? I want to try to make it to 300,000 miles. I believe i can do it, becuase it still has plenty of power and is in good shape. So sorry this is so long!! Just want to make sure you guys have all the details! Thanks!!