Overheating marine diesel
As I mentioned on an earlier post, while trolling a few weeks ago my aux engine overheated. Fortunately the engine was idling and it seemed like no damage was done. I went through the cooling system to try and find the source of the problem. given that it only overheated while idling and not during full throttle, i suspect something in the heat exchanger system. If it was in the fresh water (engine) circuit, the opposite would be more likely - overheating at higher RPMs.
I made sure the raw water screen was clear and then checked that the raw water pump impeller hadn't lost an impeller. No problems were found.
I knew that this engine still had it's original thermostat, so although it was counter-intuitive to the symptoms, i decide to replace it anyway.
Replacement from Lordco. No way was i gonna pay Westerbeke prices. I brought in the old one and they were able to match it up. The original is a British Leyland part.
Although I replaced the thermostat, i had no faith that this was actually the problem so I next went to the heat exchanger. It's in a bad spot on this engine, and unfortunately you have to pull the entire manifold to remove it, so I serviced it without pulling it, although it was very awkward. The copper tube under the fresh water reservoir is the heat exchanger.
To clean out the heat exchanger you have to pull the rubber cap off the end. It's held in place by a large hose clamp.
The inside of the heat exchanger; someone has given it a good wallop. The copper is very soft. I was very surprised when i pulled off the copper and a chunk of zinc rolled out. I had checked the engine's pencil zincs just a few months ago and they were fine. The base of this zinc had dissolved and the remaining chunk was rolling around in here, blocking at least a few channels.
Not only that, but some channels were plugged by bits of shell. The red arrows point to plugged channels. You can just make out the fragments in the picture. Between the zinc and these clogs, I suspect the heat exchanger was down about 1/4-1/3 capacity
Two months ago, this pencil zinc appeared fine. From now on I'm replacing them every 6 months regardless what they look like; zincs are cheap. This was new last October
Reaming out the channels with a length of clothes hanger wire.
After cleaning out the channels (and straightening out that dent. I'm surprised it didn't leak), I decided to replace the zinc in the transmission heat exchanger.
No problem here, but of course there is much less copper to protect.
I didn't get a chance to put it all back together but I'm gonna try tomorrow. I'm pretty certain I've discovered the source of overheating. I do wish that the engineers had built more capacity into the system but you gotta work with what you got. It's this aftermarket Westerbeke bolt-on heat exchanger system that has caused pretty much all the troubles I've had with this engine: heat exchanger clogs and raw water pump problems.
One modification I have to do is in the electrical - this old system has no key switch and you start the engine with a push button. Once the engine starts the generator supplies power to gauges and the alarm system which is obviously not working. But with that arrangement there is no alarm test; there isn't that buzzing you get with most boats before the engine starts or when you first shut it down. I'm gonna rewire it with a keyswitch so i can hear that the low oil pressure and high temp alarm are working. There is too much going on with a sailboat to be having to watch engine gauges all the time.
I made sure the raw water screen was clear and then checked that the raw water pump impeller hadn't lost an impeller. No problems were found.
I knew that this engine still had it's original thermostat, so although it was counter-intuitive to the symptoms, i decide to replace it anyway.
Replacement from Lordco. No way was i gonna pay Westerbeke prices. I brought in the old one and they were able to match it up. The original is a British Leyland part.
Although I replaced the thermostat, i had no faith that this was actually the problem so I next went to the heat exchanger. It's in a bad spot on this engine, and unfortunately you have to pull the entire manifold to remove it, so I serviced it without pulling it, although it was very awkward. The copper tube under the fresh water reservoir is the heat exchanger.
To clean out the heat exchanger you have to pull the rubber cap off the end. It's held in place by a large hose clamp.
The inside of the heat exchanger; someone has given it a good wallop. The copper is very soft. I was very surprised when i pulled off the copper and a chunk of zinc rolled out. I had checked the engine's pencil zincs just a few months ago and they were fine. The base of this zinc had dissolved and the remaining chunk was rolling around in here, blocking at least a few channels.
Not only that, but some channels were plugged by bits of shell. The red arrows point to plugged channels. You can just make out the fragments in the picture. Between the zinc and these clogs, I suspect the heat exchanger was down about 1/4-1/3 capacity
Two months ago, this pencil zinc appeared fine. From now on I'm replacing them every 6 months regardless what they look like; zincs are cheap. This was new last October
Reaming out the channels with a length of clothes hanger wire.
After cleaning out the channels (and straightening out that dent. I'm surprised it didn't leak), I decided to replace the zinc in the transmission heat exchanger.
No problem here, but of course there is much less copper to protect.
I didn't get a chance to put it all back together but I'm gonna try tomorrow. I'm pretty certain I've discovered the source of overheating. I do wish that the engineers had built more capacity into the system but you gotta work with what you got. It's this aftermarket Westerbeke bolt-on heat exchanger system that has caused pretty much all the troubles I've had with this engine: heat exchanger clogs and raw water pump problems.
One modification I have to do is in the electrical - this old system has no key switch and you start the engine with a push button. Once the engine starts the generator supplies power to gauges and the alarm system which is obviously not working. But with that arrangement there is no alarm test; there isn't that buzzing you get with most boats before the engine starts or when you first shut it down. I'm gonna rewire it with a keyswitch so i can hear that the low oil pressure and high temp alarm are working. There is too much going on with a sailboat to be having to watch engine gauges all the time.
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