1969 v-470-m twin Cummins

What can I say other than old “Heavy Iron” wins over “Marine Age” in this case……………………………. They just do not make them like they used to………….All is good..

Just so you understand that there is a natural expansion of coolant so you will see the level in the expansion tank rise as it warms and will naturally contract back when cool. I am unsure of the total volume of coolant in these engines but it would not surprise me to see 1-2quarts of change in volume. The rust thing says you have something going on that may or may not be related to the overheat if not the head gasket then my next place to look would be in the exhaust system.

If I was chasing this – I would be looking all through the raw water side of the system. My brother was chasing an issue on a Volvo he had (’80 vintage 60 series) and we had everything apart from the raw water pickup to the exhaust elbow. Tested component by component with garden hose. (this was almost every stop of our 2 week vacation). Finally on one of the hard lines between oil cooler and heat exchanger which would flow water volume of garden hose with no problem I dropped a 10mm socket to run through the tube. – It didn’t come out. Turns out there was a giant salt crystal that was slowing flow when the engine was run up over ~2000rpm.

Now if you are a hands on, DIY person it can be reasonable to keep old iron running. If you aren’t skilled in those areas then ripping the band-aid off quickly with a simple repower may well be far more economical. It doesn’t take too many trips at $100+/hr chasing these types of issues to add up to real money. The other part of hiring out work on stuff this old is there aren’t many techs that have any real experience on it. That means you pay for the learning curve.