It's also entirely possible that a piece of crud from the cooling system has partially obstructed the thermostat or some other point in the system when you drained it you might have loosened it up...its probably not a bad idea to take it out to inspect and replace it to eliminate it as the culprit as it is not a very expensive part to replace and can cause lots of heartache and damage if it fails.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz