@ ~250K, car was burning one quart every 400 miles. Did two Marvel Mystery Oil piston soaks and now it burns one quart every 800 miles. Same driving conditions: 600 miles around town driving plus 1000 miles mostly 80mph highway driving, with lots of big elevation changes (high speed coasting/high vacuum.) Another benefit of the MMO soak is that the oil stays cleaner longer. Before it would turn black in 400 miles. Now, with almost 2000 miles since the last change, the oil is still pretty clean looking.

Previous owner allowed the car to overheat due to bad head gasket. My guess is that the rings got carboned up and the MMO freed them up.

First soak was for 24 hours: Pulled plugs, set the pistons to about the same height, and poured MMO through a funnel into each chamber 'till it was lapping at the spark plug holes. After the soak sucked as much of the MMO I could with a turkey baster, restarted the car, and drove for about ten miles. Took about 45 seconds of cranking to get it to start.

Second soak was 48 hours: same thing, except halfway through turned the engine over by hand a few times, lined up the pistons, and refilled with MMO. Drove another ten miles and changed the oil and filter.

 

Interesting, never heard of that before.