2715E Lehman started overheating, check coolant level, down 3.5 gallons! Refilled and ran engine, no visible leaks, no coolant in bilge... Ran for 20 minutes and it dropped a half gallon... Ideas??
Any signs of coolant in the exhaust? If so, it's probably a heat exchanger leak. If not, check for signs of coolant in the oil or any excess steam while running.
Loss of coolant can be the main heat exchanger, the lube oil cooler if coolant cooled and a bad head gasket/cracked block. The later will show up in the oil level rising and turning milky. You can probably smell antifreeze in the exhaust if the exhangers are leaking.
Be very careful with this problem. It maybe a simple leakage issue but then again it could be internal and cost you your engine. If there is coolant in your oil then the oil will normally look greenish, and as said before, high on the stick. Do not run the engine further. Find a good mechanic and get it fixed right now.
Loss of coolant can be the main heat exchanger, the lube oil cooler if coolant cooled and a bad head gasket/cracked block. The later will show up in the oil level rising and turning milky. You can probably smell antifreeze in the exhaust if the exhangers are leaking.
David
Agree, these are the most likely culprits. Hold a rag over the exhaust for a minute. I would put this repair in the emergency category.