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John Southcombe

Hi I have a cooling problem I have renovated a 37 foot narrowboat with a 1.5 BMC diesel the temperature does strange things it takes a very long time to warm up goes to 80 drops to 40 and sometimes does not cool but overheats. so there's the symptoms.
The engine cooling circuit seems strange it has a bowman manifold that has been disconnected from the water supply. it has twin keel tanks the R/H tank is the inlet for the existing bmc water pumpthe left hand tank has a Jabsco pump attached I first thought this was pulling water out of the engine from the thermostat but it is no its pumping water into the thermostat the back of the cylinder head had an outlet on that is feeding a header tank this tank splits and returns the water back to the keel tanks.
firstly is the BMC water pump man enough to circulate both skin tanks they each hold 40 litres.
would it be better to put the jabsco inline the the engine pump the help delivery.
Thirdly has anyone got a layout they can share with me. Overheated twice now damaged an impeller and think I may have cooked the head need to sort this out I believe it has had some tinkering with by the previous owner. The boat was stood idle for a couple of years and is now back to her former glory apart from the engine problem.

Asked by: john southcombe  | 8.08am, Sunday 20 November

WW says:

Hi John
Its not normal for anyone to wait this long for some sort of answer, but the array of symptoms you describe are a touch confusing. I know, its like trying to describe a spiral staircase while not moving your hands! The capacity of the skin tanks looks huge at 80 litres in total and the methods used sound strange. You may have put your finger on the root of your problem when you say a former owner has "tinkered" with it.
Perhaps it will help if I briefly set out how I piped the cooling of my last BMC 1.5 with tank cooling.
The thermostat housing is connected to the water cooled manifold/header tank (tube stack removed) with a 30mm hose, and the outlet of the manifold/header tank is connected directly to the top connection of the skin tank, again with 30mm radiator hose. The bottom connection of the skin tank is connected directly to the engine inlet pipe again using the same size hose.
This method has served me well on several previous boats using 1.5 and 1.8 engines. The engines normal water pump is quite sufficient to drive the water round the system. If your engine has overheated in the past you may an overcooling problem since the thermostat is often damaged and stuck open when this happens.
Best of luck.

Mike Jordan  | 10.41AM, Tuesday 22 November

It sounds much more complicated than a normal set up; could it have been altered from a heat exchanger system using raw water pumped by the Jabsco?
I think you have two problems.
If the engine takes a very long time to warm up it sounds as though the thermostat is not working or may have been removed. Unbolt the housing and have a look inside.
The jabsco pump is pumping water the wrong way. It should be pumping the water from the thermostat housing into the top of a tank, which will assist the engine pump which might struggle if the tanks have restricted flow.
If the skin tanks have not been flushed out for a while, there could be a build up of crud which will not help matters.

Rupert Smedley  | 6.46PM, Wednesday 23 November

Your proposals sound fine, let us know if the head is damaged and how you get on.
Good luck!

Rupert Smedley  | 9.52AM, Thursday 24 November

Readers say:

Thank you for your help.
80 litres of cooling does seem too much it cost £80 in anti freeze alone. The thermostat is operational and okay. This weekend I intend to remove the cylinder head as I think it is cracked and causing the head to boil. I will then re pipe the system I have another water cooled manifold so will change this in the process. I would guess that at some point on skin tank cooled the engine and one cooled the currently dis connected bowman manifold.The pipe work is 1" but the outlets at the skin tanks are 3/4 so there is restriction here. I intend to pipe the jabsco in line prior to the engine water pump to help boost flow. Does any one see any problems doing so.
Once again thanks quite new to boating but have met many great people

john southcombe  | 7.43PM, Wednesday 23 November

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