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AQAD40B overheating

Hi all,

I'm looking for some experienced advice or tips.

I have just recently taken on a job diagnosing an old AQAD40B that is overheating.

The owners bought the boat last year, It started overheating couple of months after.

The engine has no hour meter or maintenance history.

They had a mechanic who:

1: replaced thermostats
2: clean heat exchanger
3: replace end caps (heat exchanger)

Now I took over (unfortunately) and I have checked:

4: exhaust mixer elbow, removed it wasn't blocked, ran water through to check
5: sea strainer
6: G/B cooler
7: raw water pump and impeller
8: replaced drive belts (jcw pump pulley slipping)
9: ran the engine with raw water discharge hose removed to assess flow, seemed quite sufficient, flow increased with rpm.

I used a temp gun on sea trial, all temps on raw water circuit 25-30'c, jacket water gets up to operating temp and keeps climbing to 90'c+

I haven't checked the oil cooler or aftercooler yet as there is more work involved and the raw water temp and flow seemed satisfactory??

The jcw pump pulley spun quite freely when belts removed, didn't look like it was leaking from teltale, but how would I know if jcw pump is causing it to overheat?

Any advice or tips would be much appreciated.

Cheers!
 
I had a yard and fixed a number of heating problems not solved by other yards. The most common fix was cleaning the coolant side with a good descaler that removed rust. A lot of owners run water only and only add anti-freeze when trying to solve a heating problem. Or the anti-freeze is so old, the additives are all dead. Rust can build on the water jackets and passages, insulating the engine from the coolant. It builds temps until it's so hot it has to transfer heat and it overwhelms the system.
 
Aftercooler or Raw Water pump would be my next checks. Aftercooler is 2nd only to the Heat Exchanger for engine cooling. Air leak before the RW pump is another possibility. I assume that the hull and especially the prop are clean?
 
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