 I've had my boat now for about 5 years. And in that time, I've tried to maintain her as best I could. However in the last year or so, I've learned more than ever.
It was last summer and while on my way to the Chicago Air and Water Show running full speed ahead when all of the sudden the boat veered to the right and I heard a bad sound. It was the warning buzzer coming from below the dash. Now, I'm normally very attentive to what the gages are doing but at the time I had been standing on the seat keeping watch on the water ahead vs what the boat engines were doing.
As I was raising the engine hatch steam came pouring out at me. Yes, I had overheated the engine and it was turned off. In trying to asses the problem I shut down the other engine to quite things down. I wasn't able to just turn it over with the turn of the key. It's main shutdown system had turned off the engine automatically. The engine wasn't glowing red or anything but none the less, it was very hot! There were water like burn marks on the exhaust manifold from the antifreeze. I had found that the breaker switch inside the boat was tripped and wouldn't switch back to on.
Being that it was such a nice calm day and that I was only about ¾ of the way to where I was on my way to, I had to learn how to drive the boat only on one engine. I never thought it would be so easy! By using the Raymarine Autopilot, I was able to just set the heading and hit auto. The boat did all the work. I just sat back and toughed out the ride.
Depending on which engine is out, you really only need to have the engine rudders about 9-11 degrees over to keep it going straight. Stopping isn't quite so easy. It's best to just shift back to neutral and let the boat coast to a stop. Otherwise if you reverse, the boat wants to turn around. And if you are close to shore, a seawall or a dock, you could be slamming your bow into something.
Later that night once the engine had cooled all the way or most of the way back down, I was able to start and run the engine. Not ever on plane or anything, just to verify that the engine still ran and for maneuvering in tight spaces.
After some careful testing, trial and error, I had determined that the exhaust manifold had cracked from the overheat which was causing the closed loop coolant (antifreeze) to escape through the turbo. This meant that after refilling the cooling system tank and 20-30 minutes of run time, that the engine would begin to get too warm again having bled out all it's coolant. Lucky for me, the engine oil during all my multiple attempts to get the engine to seal and keep the water inside, never milkshaked the engine. That's when you get oil and water mixed together and churned up enough to make a grey foam if it's water, or a shamrock shake if it's antifreeze and oil.
This spring, my cousin and I replaced the exhaust manifold with a new cummins oem part, changed all the gaskets, checked the torque specs, and changed and topped off the oil and coolant levels. Surprisingly enough the engine ran fantastic all summer long. The only issue we've really been dealing with since is that it's been running at hot engine temperatures. Or rather hotter than I prefer to see on my gages.
The engine which was overheated last summer has run great, while running at wide open throttle, the temps only seem to get to about 190 or 195 and maybe 200 at the very top end.. The problem has been with the other engine. The port engine which has never seemed to have had a problem. It on the other hand runs hot. At about 2200 rpm it runs right at 200 degrees and up when you go faster which 203 is the max allowed temperature and 205 is overheating.
 Anytime I push the engines to full throttle or above 2200 rpm the engine temp needles seem to just keep getting higher. I've been searching for options or reasons for the higher engine temperatures. I settled on an idea that the antifreeze was simply worn out. Since the engine that overheated had gotten a fresh batch of antifreeze in the spring with the exhaust manifold, and was running just fine temperature wise. The port engine on the other hand which had fresh oil, new filters, new raw water impellers, but not fresh antifreeze still seemed to run too hot for my taste. Since I've had this boat for 5+ years, the antifreeze had never been changed in the port engine.
So last weekend I set out to change the thermostat in the engine (starboard) which had overheated last summer since the last time I went out. It seemed that the thermostat was stuck wide open which made the engiene seem to run like an ice cube. This made it smoke, and get worse gas mileage but this was a welcome sight considering the high temperatures I'd been seeing all summer. When I first went there last weekend I only had a single gallon of concentrated Peak antifreeze for each engine thinking each engine only held 2.4 gallons. I used one gallon in the starboard engine only to find that to fill the engine it took 5.6 gallons of coolant. Needless to say, the mixture is not nearly 50/50 as it should be (remember this for later).
The port engine got a full flush, 5 times with straight water before I finally drained it, bought 2 more gallons and put in 3 gallons of antifreeze and 2.6 gallons of water. So with a 55/45 mix of antifreeze/water this engine is now running cooler than the engine with the single 20% mix of antifreeze.
So with that data in, it would appear that the heat transfer properties of antifreeze does wear out over time, has a direct correlation to how hot the engines run, and if the mix is too low, the engine will run hotter than it could with the proper mix of coolant. And on top of all that, water does not have the same cooling properties as antifreeze. Or better yet have the same heat transfer abilities as antifreeze.
My goal is to have both engines running at the same temperature at any and all similar speeds and conditions again. Diesels need to run hot. But not too hot. 185 - 195 degrees is perfect in my book cause you'd be able to see that they're running below the red 200 degree mark and be able to know when it's going past that red indication point.
More data to follow in the coming months...
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