Bukh DV20 overheating cause?

[Babylon]

Academic question now really as not my boat, but the other day I was moored next to a guy with a 1982 DV20 which was overheating. He was new to boat ownership, had only recently bought the boat, and didn't appear technically-minded, but this is what I found:

• no seawater strainer fitted
• water was coming out of exhaust
• takeoff and return pipes to calorifier (which he said didn't work)

So what could have been the cause of overheating?

• thermostat failed or jammed due to raw-water debris?
• cooling chambers all clogged up?
• other cause?

Any answers won't help the guy now as he's gone home, but just curious.

 

[vyv_cox]

Scale is a common cause of overheating in this engine. The first place to look is the entry of water into the block, located behind the flywheel. It can be removed without removing the flywheel but it may be necessary to shorten an Allen key. This fitting commonly scales up, especially the older, perforated type.

Water coming from the exhaust is not necessarily a clue, as it may well be bypass water if the thermostat is faulty.

 

[Malish]

Scale is a common cause of overheating in this engine. The first place to look is the entry of water into the block, located behind the flywheel. It can be removed without removing the flywheel but it may be necessary to shorten an Allen key. This fitting commonly scales up, especially the older, perforated type.

Water coming from the exhaust is not necessarily a clue, as it may well be bypass water if the thermostat is faulty.

and check in the opposite direction too - my DV24 exhibited overheating a couple of times at the start of a season due to partial blockage of the other pipe within the 'poker' fitting, leading up to the themostat. Couldn't be seen, but rodding out with a bit of rigging or monel wire sorted it.

 

[Babylon]

Thanks both, interesting and not surprising given a 43yr old direct-cooled engine with several past owners.

Yes, I suspected the thermostat at least and suggested that he mention that when speaking to a marine engineer, but didn't have time to help him remove it to check and clean (as I had the tide to catch and a whole load of other time-critical things at the other end). I couldn't remember if there was a gasket etc to replace and didn't want to get involved in a messy, smelly job on a rather manky boat.

I must say I found the absence of a raw-water strainer surprising! Before I fitted a Beta 25 nearly 15yrs ago, my own boat originally had exactly the same DV20 of the same vintage, but that definitely had a strainer.

 

[LittleSister]

. . .
Yes, I suspected the thermostat at least . . .

A thermostat failure - if it meant the water was bypassing the engine (as Vyv mentions) could also explain why the calorifier wasn't working. (Though that could, of course, be something entirely separate.)

I must say I found the absence of a raw-water strainer surprising! . . .

The addition of a strainer would, I think, be a good idea, but I doubt the absence of one would be a direct or the whole cause of the problem.