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My daughter has a small, steel hulled, canal boat powered by a 4cyl Kubota marinised diesel.

I am used to tractor cooling systems but find this one visually impenetrable:-)

There is a header water jacket surrounding the exhaust manifold with the usual pressure relief filler cap. From that a flexible pipe takes cooling water to the top of a rectangular tank welded to a steel bulkhead inboard (I think) from the boat hull. A return pipe disappears below the generator and circulating pump. A further pipe connects to the engine block, said to be from the shower. The boat is fitted with a shower and I now think engine coolant is also routed through a heat exchanger for that?

The problem is that, following a coolant pipe leak, the engine overheats. With the filler cap off and engine running there is no apparent circulation, no emulsified oil or visible gas bubbles.

The impeller pump is not noisy or loose. I believe thermostats fail open rather than closed?

Is it likely that an air lock at the shower heat exchanger would prevent circulation? There is a bleed valve on top of the rectangular tank, no air, is there likely to be another at the shower?

Any other ideas?

Reply to
Tim Lamb
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An air lock in the shower heat exchanger would stop circulation in that circuit and give her cold showers, but not affect the engine temperature.

An air lock in the primary system would lead to overheating. This could be in the exhaust heat exchanger, the cooling tank or the pipework.

Another possibility is that there is a pump similar to the type that fits on the end of an electric drill, which have a rubber impeller shaped like a small water wheel inside a circular housing, with a belt driven pulley. the impeller on these tends to disintegrate with age and overheating, giving a lack of circulation.

The closest analogy would be a car system, with the skin tank (The water tank welded to the hull) replacing the car radiator, with an water jacket added round the exhaust to cool it and the shower circuit replacing the car saloon heater.

The problem with boat cooling circuits is that the pipework tends to have odd kinks in it, and so is very prone to airlocking. The tank welded to the bulkhead will also have a labyrinth inside it, which can't be seen from the outside. Try disconnecting the top pipe form is and filling it by using a hose connected to the bottom pipe. I have had some success by running the engine, all hoses connected, with no load at 1200

- 1500 rpm, with the filler cap open and keeping it topped up. Last time I did this, the cooling system swallowed a gallon of coolant before overflowing, starting at being apparently full. You may also find bleed screws on the flexible pipes at the higher points of the system.

If there's no bleed point on the shower heat exchanger, then you'll need to disconnect the return pipe until you get a flow of coolant with no bubbles in it coming out.

If the boat is in West London or thereabouts, I might be able to nip over and have a look.

Reply to
John Williamson

Also (It's annoying what comes to mind when I'm driving) If the rectangular tank (Heat exchanger) isn't attached directly to the hull, there will be a secondary water circuit drawing raw water into the heat exchanger from the canal, and the pump circulating this water may have failed, or the input through the hull may be blocked by debris such as water weed or a plastic bag.

Reply to
John Williamson

In message , John Williamson writes

There's kind!

It was at Kensal Town but she got a tow back to her mooring at St. Pancras.

I believe an engineer visit is booked for next week so we will see what that discovers. But thanks for your comments and offer. She is on a film job at Camden starting tomorrow so I have no idea of her availability.

I had rather hoped a shower air lock might be the cause as there were no reported symptoms prior to the pipe leak. Does the engine circulation pump do both jobs or is there a second dedicated pump?

She plans to check for a bleed valve on her next visit. Somewhere under the bed I'm told.

I am ashamed to know so little but last Wednesday was the first time I had seen the boat. We were there for an outing so unprepared for unbolting pumps and thermostats. I quickly decided that marine engineers must be incredibly agile!

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Reply to
Tim Lamb

Not that. The primary water is not circulating. The top hose barely gets warm with the engine overheated. Nothing is known about additional cooling pumps although that doesn't mean they don't exist!

Interesting what you say about the heat exchange to the canal. Can it be done passively for a small engine/boat? The rectangular tank is vertical whereas the hull is rounded and coming in to the stern at that point.

Another point of interest... part way down the propellor shaft is a cylindrical drum connected by two small pipes to the water circuit. Is that a thrust bearing, or?

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Reply to
Tim Lamb

It's likely the engine water pump has failed or there is a bad airlock, then. I take it the drive belt is intact and tight enough, and the pulley is secure on the shaft? If the alternator is charging, then both are probably okay, unless there are two belts.

I would expect the water pump impeller to be cast iron shrunk onto a steel shaft, but it may be plastic and have melted off the shaft.

No, you need to pump a fair bit of water through these systems to move the heat, so passive doesn't work. A 4 cylinder Kubota will be about 30 kilowatts output at the shaft, so you need to lose at least that through the cooling system at full throttle.

Without actually seeing it, I couldn't say. it may be the raw water pump for the cooling system. I've not seen a water cooled thrust bearing, but that's not to say they don't exist. there is a make of stern gland that requires a flow of water through it to protect the seal, but that's normally supplied through the propshaft and returned that way

Reply to
John Williamson

In message , John Williamson writes Snip.

OK John. I'll pass all this on to the owner and hope the engineer can sort it next week.

Now she has a proper mooring close to my other daughter, I may get to learn more about the boat. My total experience of canals and motor cruisers is a one week trip from Braunston to Oxford and back 44 years ago:-)

Thanks again for your kind advice. Enjoy the rest of the holiday.

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Reply to
Tim Lamb

In message , John Williamson writes

In our case it was a fish stuck in there.

Our current engine (the third) was previously in a canal boat. The recirculating water is driven by the engine pump on the fan belt. The seawater rubber-impeller pump is driven straight off a shaft extension on the engine.

It might be useful to know the make of engine and whether it is a standard installation or, more likely, something cobbled together.

Manuals can often be found. I had some for the previous Petter engines, and there are some online for my current Mitsubishi-Vetus.

Parts are more difficult. I was told that the Dutchman who hand made my heat exchanger had died, and that the replacement I needed was one of the only two spares left in the world. Of course, a good story often helps the supplier.

Reply to
Bill

In message , Bill writes

Edible?

I don't recall seeing anything like that. There is plenty of room either side of the engine but the drive belt/pump assembly is tight to the forward bulkhead. (nautical terms! I must have been watching Hornblower:-)

Definitely Kubota 4cyl diesel, no visible engine number. Obviously marinised. ISTR Kubota do a 25hp tractor diesel although I had thought that was 3 cyl.

Yes. I have passed that thought on.

Reply to
Tim Lamb

I believe thermostats fail open

Thermostats on engines normally fail closed.

Reply to
Mr Fuxit

In message , Mr Fuxit writes

Google has the jury out on that. It appears to depend on the age/type of stat. My experience is of the old bellows type which tended to fail open. Fail closed is certainly going to get your attention:-)

Pump impeller and thermostat are due to be checked/changed once the correct part is obtained. The first move is to bleed the shower calorifier and see if that makes any difference.

Reply to
Tim Lamb

FWIW Ive had an old van water pump impeller strip from its shaft. Pulley went round and round but water didn't circulate

Check where pipes are hot and where not to establish circulation...

Reply to
The Natural Philosopher

I once had that happen to me, but it failed open, the engine would go really cold on a fast trip, but the thermostatic fan would keep it controlled in traffic, when it would get hotter. I took the car in for service for something else, (I had no facilities nor time to do this myself) and I also told them that I wanted the thermostat replaced. They didn't, saying that the temp. controlled fine when they ran it in the workshop. Whatever. Six months later, it was back in for something else, and they told me when I picked it up that it needed a new 'stat. Needless to say, somebody else got the job.

Reply to
Davey

I'm 25 miles away! All these helpful suggestions are being relayed to the slightly ditzy blonde owner!

Reply to
Tim Lamb

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