Intermittent Overheating

Attention all you experts out there: here's my story:

I recently purchased a 1982 C&C 27 Mark IV with the original Atomic 4 engine. The boat is sailed in salt water. The compression is reasonably good and, after a few problems with stalling that a tune-up seems to have resolved, it starts and runs well. The engine was rebuilt in 1994, and has been freshwater cooled from that time.

However, after a couple of outings, the engine overheated badly, and we had to be towed back to harbour. The mechanics took the cooling system apart and replaced the exhaust riser (which was badly rusted), the fresh water pump and impeller. They also boiled out the heat exchanger.

Shortly after that, I took the boat out. It takes about 30-40 minutes for me to get out of the harbour, and the engine ran fine. It also ran fine getting me into the destination harbour. But on the way home, the engine was clearly overheating again. A mechanic came and worked on it for several hours, and it seemed to be running fine. The next day I left the harbour on my return voyage, and the engine worked fine, but on my approach to my home harbour, it overheated again. Again, the mechanic worked on the engine, and it seemed to run fine. On a subsequent sail, I ran it twice, about 40 minutes each time, and then the third time it overheated, and I had to call for help.

I have noticed three things that might be of some diagnostic importance. First, on startup, the engine exhaust spewed out a white plume of water with small white particles, which I am guessing is a result of salt buildup. Second, the water exiting the exhaust comes in very irregular spurts. You can hear it building up before it shoots out. Third, when I start the engine after a couple of successful runs, there is very little if any water exiting the exhaust; there is only or mostly steam, and the engine subsequently overheats.

Although the mechanics don't seem to consider it likely (and I am no mechanic), I think the problem is in the raw water cooling system. The inlet has been checked and is clear, but somewhere along the way there is insufficient flow, and the salt buildup from evaporating raw water is blocking the system.

So who's right here, and what should I do? I've spent a considerable chunk of change so far with unsatisfactory results.

Thanks.

Lee

[Marian Claire]

Not an expert, especially on fresh water systems, but here is my two cents. I would defiantly check the raw water side. You do not need to be a mechanic to do a step by step connection to connection inspection and flow check. The batching, water coming out in spurts not a steady stream, my be normal but the absence of flow is not. Sounds like something is moving and blocking the flow then dropping out of the way. Good luck Dan S/V Marian Claire

[keelcooler]

No coolant loss, must be in your raw water system. New pump,new riser, cleaned out exchange, what's left? Confirm the repaired items are working and check flow from raw water intake down the line to water trap.

With your bad overheat and no flow events, check the inner wall of rubber exhaust hoses for collapse along with heat damaged water trap.

As Dan said, it could be a incensing intermittent flow blockage that requires troubleshooting at time of occurrence.

[Dave Neptune]

Lee, as stated above it sounds as if you have a intermittant problem. The pump usually either works fine or starts getting weaker slowly until it fails not from time to time. Check the integrity of the intake line they do break down on the inside and can colapse (suck shut) and restrict the volume available to the pump. You may also have something floating in the line causing an intermittant restriction.
Also if it were on the exhaust side it is unlikely that it would be an intermittant poroblem.

Dave Neptune

[Administrator]

Lost vanes on the raw water impeller are notorious for problems like this. On edge, no problem. On side, near-total blockage.

Bill

Thank you to those who replied to my request for advice on the intermittent overheating problem. I'm sorry that I didn't do this sooner, but work has been extremely busy over the last few weeks, and I haven't had time to worry about a problem engine.

Today I went over to the boat and started it up for the first time in about a month. The usual plume of whitish water came out of the exhaust, but this time there was a slight petroleum sheen as well, something I had not noticed before. The sheen did seem to disappear after a few minutes running. Is this an indication of a larger problem, or am I just being paranoid?

I ran the engine in neutral for about 15 minutes, and then for another 20 minutes or so under load, with no evidence of overheating.

I have another question as well (please forgive my naivete -- I told you I am no mechanic!). The fresh water pump is electric, is it not? I forgot to mention in my original post that the batteries have died, and I suspect, but cannot yet substantiate, that the generator may not be functioning properly. Could this result in the fresh water pump not working to capacity, or am I grasping at straws? I will attempt to charge the batteries tomorrow, and should know then if they are the problem. I does deem unlikely to me that both of the batteries would go bad at the same time, but as I told you...

Thanks again for you help.

Lee

[roadnsky]

Originally Posted by sharqui

The usual plume of whitish water came out of the exhaust, but this time there was a slight petroleum sheen as well, something I had not noticed before. The sheen did seem to disappear after a few minutes running. Is this an indication of a larger problem, or am I just being paranoid?

Lee-
The "sheen" is normal. Remember it's water AND exhaust gas mixing.
If it's a LOT or you actually see oil, then you'd investigate.
How do your plugs look?

I have another question as well (please forgive my naivete -- I told you I am no mechanic!). The fresh water pump is electric, is it not?

No, the water pump isn't electric. It's mechanically driven by the engine.

Roadnsky, the plugs appear to be fine. They were checked by the mechanic the last time he worked on the engine,in late August, and the engine has been run only a couple of times since.

Lee

[Ericson32]

This fall I pulled my raw water pump to rebuild it. In the process, I found a piece of rubber impeller lodge in the elbow of the exhaust side of the pump. I too had an intermitant overheating problem - I think it is now solved. I have no idea how long the piece was lodged there since all the impellers I changed were intact. I plan to remove the hoses and check the other elbows in the water system to insure there aren't more pieces elsewhere. A little digging and a good flashlight work wonders!

[67c&ccorv]

[QUOTE=Ericson32;17545]This fall I pulled my raw water pump to rebuild it. In the process, I found a piece of rubber impeller lodge in the elbow of the exhaust side of the pump. I too had an intermitant overheating problem - I think it is now solved. I have no idea how long the piece was lodged there since all the impellers I changed were intact. I plan to remove the hoses and check the other elbows in the water system to insure there aren't more pieces elsewhere. A little digging and a good flashlight work wonders![/QUOTE]

A little digging, a good flashlight and a mirror work wonders!

[CalebD]

Could a sticky thermostat cause this delayed overheating?