I rebuilt a cummins 5.9L (Komatso branded) and refilled the rad with a 50/50 of glycol/water. After running for a couple days the engine started running hot (210 deg F) I had installed a new thermostat so I initally thought it may be factory defective so I drained the coolant so I could pull it out. Once the coolandtwas out and in a pail I could see a pile of gelled coolant in the top of the rad, as well as in the pail. Current outdoor temps are 80 - 95 deg F daily so it's not cold weather geling. The rad was washed out when the engine was out. Anyone know why coolant would gel in hot weather? Could a slight amount of residue of degreser cause coolant to gel? When Cummins rebuilds heads they coat the inside of the head with some chemical so they do not rust while sitting on the shelf, could this cause gelling of the coolant? I have rebuilt hundreds of diesel engines and have never experianced this. The gel seems to contain a high degree of silicon, and I took a sample to send out for analysis. I also flushed the coolant system with straight water and refilled. We will see what happens I guess.
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