I have 2000 Mazda 626 with high rewing V6...Aprox 4000 RPM at 80MPH. It redlines at 7000RPM and I like to hit it from time to time. So far I used M1 5W-30, 10W-30 and currently GC 0W-30. I like to run oil for 10K. Recently I started thinking about M1 0W-20. What do you guys think would be PROS or CONS of using this oil in this type of engine? Or should I stay with thicker GC? You can see my two analysis results here : http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=3;t=000864 here is more info about engine: Specs - 2.5V6 - 28psi @1000rpm, 49-71psi @3000rpm Also engine architecture(mine is 2.5 V6): Engineering Data Mean Piston Speed - V6 Engines - all-alloy DOHC 24V 60-degree V6 configuration - Split Crankcase - as 911 flat-6 offers increased rigidity over traditional bearing-cap solutions for high-rpm capability (7800rpm 2.0V6) and low NVH (winning 1992 German engine award) - Bearings - 4-bolt Mains, with a further pair of bolts at each bearing section. Key journals & bearings are oversized regarding width. Bearings are triple-layer heavy duty - Crankshaft - Forged, nitrided, triple-lapped, mirror-finished - Piston Squirters - Upper bearing journals contain piston oil-squirters to aid cooling - Exhaust-Valves - Stainless steel & sodium cooled - Pistons - Lightweight to reduce reciprocating mass, piston skirts are moly coated to reduce friction - Head Gaskets - Stainless steel is used, with torque-to-yield bolts - Stroke - Very short stroke creates low crank angles & low rod/bearing loads Engine Dynamic Stress Levels o Mean Piston Speed, MPS - 2.5V6 MPS = 0.167 * 2.92 * 7000 = 3170 ft/min at 7000rpm - 2.0I4 MPS = 0.167 * 3.62 * 6500 = 3929 ft/min at 6500rpm - F1 engine MPS = 4519 ft/min at 16,400rpm - As a benchmark, MPS - under 3,500 ft/min - Good reliability - 3,500-4,000 ft/min - Stressing - over 4,000 ft/min - Very short lived o Bore & Stroke - 2.0 Bore*Stroke of 83x92mm (3.62" long stroke) - 2.5 Bore*Stroke of 84.5x74.2mm (just 2.92" stroke) - For comparison F1 engines have 70x42mm (1.65" stroke) o Ring Loadings Top-rings must balance high-rpm capability and wear, a thin ring allows high-rpm capability, too thin and wear becomes an issue. With reduced crank angles from a short stroke ring wear is reduced. A 1.5mm ring is beneficial over a 1.0mm ring for high-rpm. Maximum-Piston-Acceleration (MPA): 2.5 top-ring - 1.49mm/0.06" - MPA Permitted = 77,000ft/sec^2 - MPA Experienced = 51,354ft/sec^2 at 7000rpm 2.0 top-ring - 1.17mm/0.046" - MPA Permitted = 105,000ft/sec^2 - MPA Experienced = 70,157ft/sec^2 - The BMW M5 in comparison experiences MPA of 90,000ft/sec^2 on a 1.5mm ring. Lighter rings create reduced accelerative forces, reduced ring/piston interface overheating and reduced hammering of the piston-ring-groove. Too light and ring longevity is adversely affected. MPA = (rpm^2 * stroke"/2189)*(1/2A), A = ratio between rod-length-between-centres to stroke. 2.0 rod-centre-dist = 135mm; stroke = 92.0mm; A = 1.47 - MPS-2.0 = (6500^2*3.62/2189)*(1.2*1.47) = 51,354 ft/sec^2 2.5 rod-centre-dist = 138mm; stroke = 74.2mm; A = 1.87 - MPS-2.5 = (7500^2*2.92/2189)*(1.2*1.87) = 70,157 ft/sec^2 Both the 2.5V6 & 2.0I4 engines are engineered for longevity. The 2.5 engine is likely to be the longer lived engine subject to identical maintenance to the 2.0 engine. Mazda V6 engines are assembled entirely by robots, not humans, at the Osaka engine plant in Japan alongside Rotary engines. Ford bench testing, with very minor changes, showed the V6 to be capable of continuous running at 8900rpm - well beyond redline 7500rpm. SAE paper "SAE920677" covers detailed design of the engine.