BMC 1.5 overheating....

[NickRobinson]

My neighbour in Glenarm turned back today with an overheating BMC 1.5

Two days ago he tells me he had engine oil in tge bilge after 8hrs motoring but not obvious where from. N ow stopped, he thinks.

Heat exchanger today needed one litre topup and gets hot but no smell of exhaust products, bubbles or oil. Raw exit pipe from exchanger stone cold though exchanger too hot to hold.

Flow to exhaust described as normal, he's rodded the stack with wire.

Over to you-

 

[Caer Urfa]

My neighbour in Glenarm turned back today with an overheating BMC 1.5

Two days ago he tells me he had engine oil in tge bilge after 8hrs motoring but not obvious where from. N ow stopped, he thinks.

Heat exchanger today needed one litre topup and gets hot but no smell of exhaust products, bubbles or oil. Raw exit pipe from exchanger stone cold though exchanger too hot to hold.

Flow to exhaust described as normal, he's rodded the stack with wire.

Over to you-

I would start with the basics as many a time I have found the raw water inlet has blocked, poke say a plastic grease pipe (6mm bore) down from the filter so you know it must be 'out the bottom',
Many a time I have found blocked seaweed or even a small plastic bag is enough to reduce the water intake resulting in the engine overheating.

Mike

 

[Tranona]

Water out the back suggests nothing wrong with the raw water side so it must be in the heat exchanger, or the fresh water not circulating properly. Is the fresh water pump belt driven?

 

[NickRobinson]

Water out the back suggests nothing wrong with the raw water side so it must be in the heat exchanger, or the fresh water not circulating properly. Is the fresh water pump belt driven?

Yes, but fresh side seems to be circulating as exchanger exterior warming well- top and bottom hoses hot/warm

 

[maxi77]

The dear old BMC B series like many engines of that period often needs a good radflush treatment. The waterways in the block get clogged and hot spots develop causing the coolant to boil hence the need to top up the fresh water frequently. Also the water pumps can wear and the water may not be circulation fast enough. Thornycroft used to be able to supply new water pumps but with the number in canal boat and running old tractors alternative supplies may be available, though there are two types.

Also after the radflush you will need to backflush the engine with clean water so you need to be alongside with a water standpipe. It is amazing the impact a £2 bottle of radflush can have.

 

[Tranona]

Yes, but fresh side seems to be circulating as exchanger exterior warming well- top and bottom hoses hot/warm

Yes, but that does not mean it is circulating the block and head causing the overheating of the fresh water.

 

[Puggy]

Having just wrestled with a problem with similar symptoms, I found that the heat exchanger was clogged with silt/gunk. I took it off and spent a long time carefully hosing it out until not more silt was coming out. I think that running the engine slowly causes the thermostat to stay shut and the lack of water circulation causes it to silt up around the pipe stack. Open the throttle, thermostat opens but the heat exchanger can't cool the water... Worth a look.

P

 

[NickRobinson]

Thanks all- I've passed these on-

 

[Pasarell]

I had a similar problem with my BMC 1.5 / Thornycroft T90 engine a couple of months ago.
Water coming out the back seemed fine and also checked flow at each point around the engine which also seemed fine. Removed thermostat in case it was causing the problem. Then assumed it was the heat exchanger blocked but that also fine. Jumped to the conclusion the fresh water pump must be worn so replaced it. Problem unchanged so then bypassed the raw water pump with an electric one and the problem went away. After much time and expense realised the raw water flow was not sufficient despite looking OK. The solution was to polish the worn face of the raw water pump (I had changed the impeller long before). It had worn a groove of about 0.5mm which was obviously allowing enough water past that the cooling effect was reduced. Now the engine runs at a perfect temperature again.
Maybe the difference with you is that I didn't lose any oil or need to top up the fresh water tank.