Through our extensive testing we have found that the Softail oil tank internal feed and return oil lines are not properly positioned in the tank. By constantly recirculating hot oil to be used as soon as it returns to the tank. By constantly recirculating only a portion of the oil, aeration occurs and results in loss of oil pressure and volume to the lower end. This also results in lack of oil to the pistons for lubrication and cooling which could cause piston damage. By installing a fitting in the left side of your oil tank and bridging the two ends of the tank together with a "T" fitting this problem will be corrected. We recommend this for any Evolution Softail motor larger than stock or models using a Softail style oil tank.