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Old 12-06-2013, 19:08   #1
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Join Date: Aug 2011
Boat: Catalina
Posts: 57
BUKH DV8 Overheating... or is it ?

Hi folks,

I have a small single cylinder raw water cooled diesel that I think is overheating. There is no temp gauge, and when I tested the temp warning light, it didnt work.

SYMPTOMS:
  • "smells" hot
  • feels hot - block and flywheel are too hot to touch
  • water flow through the exhaust (and telltale from the syphon breaker) at what seems a reasonable rate/volume (how do i measure this - what should it be ?)
  • water flow through exhaust and telltale cycles from cool to luke warm
  • Engine otherwise seems to perform normally
  • No steam (im in a warm climate anyway so this may not mean anything)
SO FAR IVE CHECKED:
  • raw water through hull fitting and plumbing to pump - no fouling
  • raw water pumping from a bucket - it emptys a 5L bucket in about 30 seconds
  • thermostat - opens at about 70o C in the saucepan
  • VDO temp sender probe - closed circuit at about 85oC
The engine is only 2yrs/100 hours out of a complete 'factory' rebuild.


Is there anything else I should check before removing the exhaust elbow ?
When I do remove it, would should I be looking for ?

Thanks
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Old 16-06-2013, 16:50   #2
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Join Date: Jul 2012
Location: Auckland New Zealand
Boat: Farr 1020
Posts: 101
Re: BUKH DV8 Overheating... or is it ?

Check for any bluing of the exhaust bend where the bypass water injects into the exhaust bend. If any discolouration then check the bypass hose is not restricting the bypass flow to the exhaust on both sides of the thermostat housing.
The bypass allows flow through the system while the thermostat is still closed during warming up.
The pump throughput is OK at 10 litres per minute.
With the engine at normal running temp I measure the flow through the engine with a bucket and stop watch at the exhaust. The engine needs to be at about 2000 rpm and the exhaust temp should be 70 to 75 degrees C with a flow of about 8 litres per minute.
I check mine at the marina with the mooring lines attached and in forward drive at 2000 rpm so it is easy to lean over and catch the flow and I can hold my hand in the exhaust water flow (just)
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