[oldyeller]

I run 10w30 in the pick up and then what ever is recommended in the other vehicles. I had found on a 87 pontiac 6000 with a 2.5l l4 that if we ran 10w30 it would use a quart of oil in 3k mi but if we went back to 5w30 like was recommended it wouldn't use a drop. it had 218k on the speedo when we had to tear into it because the plastic crank sensor broke off in side the motor (didn't want it geting into the oil pump) and decided to put new bearings and rings because of the high mileage. we should have left the bearings alone, they had hardly any wear. it suprised the hell out of us. needless to say we will stay with castrol.
Also found on some of the new motors, if a person runs to thick of oil it will gum up the inside real bad. Have seen a few gernade because the pump couldn't move any oil. My theory is that the new motors run a little cooler and don't allow the oil to reach it's temp to do the cleaning part. haven't done much research on this though..

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72 LWB Fleetside C10 Custom 350/350
97 GMC Yukon 4X4 SLT
Anna, Texas