Hydraulic lifters hates additives if I must say from personal experiences. The problem is not with synthetic oil or not. If the engine is heavily sludged, the lifters would be affected.
If the oil level is low, high speed driving would have a problem with oil pressure as there is insufficient oil for the pump to work. Likewise if the engine is heavily sludged, the stariner would be partially cloggged and this would result in oil flow problem whereby the pump is not able to work fast enough to provide sufficient oil for lubrication.
Since the oil pan is cracked, you need to either repair or replace it. While ther, check the oil strainer for blockages.
Thursday, August 30th, 2012 AT 8:11 PM