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Bmc Overheating

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Hi all, any help and advice would be so much appreciated.

 I've been running my BMC 1.5 narrow-boat engine for six months now and I've serviced and replaced quite a few parts...Glow plugs/lift pump/water pump/ thermostat 82 degree Celsius  ect.

It has been starting and running well for the most part but the calorifier the cooling system it is linked to has never produced any hot water. During my last cruse the engine stated to overheat  running over 100 degrees which has not been a problem in cooler weather before now. 

My first thought was there must be a blocked pipe in the calorifier loop system but having just taken it all apart it all seems to be free flowing.


First off can someone tell me what temperature the engine should run at during  say a steady 1500 rpm?

Is the calorifier essentially the engines radiator?

Is the engine water pump (brand new) powerful enough to circulate the coolant through the whole system...or do I need an additional pump for the calorifier?

Is the thermostat supposed to kick in at 82 degrees and then allow circulation of the coolant?

Any advice or answers to these questions would be really great

Thank you



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Mine runs steady 88. Sounds like you got an air lock that stops the flow of water. The heat exchanger on mine is the highest point of the system. When refilling mine I use a big plastic bottle to provide a large head of pressure to force any air out

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Oh and no, your hot water isn’t a cooling aid. It’s plumbed to the engines primary circuit that circulates in the heat exchanger. That bit cools the exhaust and the engine coolant before taking heat away down your exhaust. Providing that is you have the usual set up

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You say it's a narrowboat set up but you don't have a skin tank which is unusual as most are keel cooled in some way.  So I'm assuming you are raw water cooled and normally have a flow of water out of the exhaust?

Have you checked the raw water filter isn't blocked?  Some raw water narrowboats had a mudbox instead of a filter, they were harder to block.  And the raw water pump impellor is intact?  There are other checks but these would be my first.

As for no hot water, that could be an air lock but first check if there is any water in the engine?  (Be careful if it's still hot).

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My similar problem was an airlock. I think it was Cheesey that suggested to me buying one of those point and read thermometers and by taking readings along the whole system I found the air lock. Mine was at a joint in the hose so I replaced the connector with one that has an air bleed  screw. 

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You will still get water from the exhaust even if it’s keel cooled as this normally has a take off from the raw water pump.  Disconnect the feed hose from the Calorifier and run a hose pipe through the system back to the header tank to bleed the system, if you have a keel cooler repeat the procedure on this also. It sounds like an airlock somewhere in the system and the engine water pump cannot always push this through.  It should run around 85 degrees.  It took me nearly 2 days to bleed mine after the engine had been out.  

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