I'm not sure about the six cylinder Magnums. I've heard that there are problems with the V6 engines used in the early Chargers, 300's and all Magnums due to oil passages in the block and water passages in the heads being too small. The result is if oil changes are neglected so that sludge forms or good corrosion inhibiter is not kept in the cooling system, they are prone to engine failure. The only problems that I've heard of in the Hemi's is valve seats falling out of the heads if they are overheated. If your SXT has been neglected, I would suggest flushing out both the cooling system and the oil system really well, and put in fresh antifreeze and fresh oil to clean things out.