Coolant Flush - GM Engine Coolant Supplement ?? - Google Dec 30, 2007100,000 miles. The last coolant flush service was done by Saturn 5 or 6 years ago. This time I went to an independent shop, but I brought my Owners Manual along. While I was in the shop waiting room, I read in the Owners Manual on page 283, "Use GM Engine Coolant Supplement (sealer) (GM Part No. 3634621 with any complete coolant change". Cooling System Repair Guide - Auto Parts & Accessories The Northstar uses a coolant solution and GM coolant supplement (sealant) designed for use in aluminum engines. These engines use DEX-COOL® and GM coolant supplement (sealant) P/N 3634621 (or equivalent) specifically designed for use in aluminum engines. Failure to use the engine coolant supplement (sealant) and the approved coolant antifreeze could result in major engine damage.