20W50 would be better, but the 15-40 is OK. Since all multi-viscosity oils stay at their minimum weight rating all the time, and only lubricate like heavier oils at higher temperatures, the 15-40 is only half as thick as the straight 30 weight the original specifications reccomend. That will result in somewhat lower oil pressure, particularly if the engine in question has some bearing wear. It will probably lubricate OK, but expect to experience lower than usual oil pressure.
Jerry

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