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Strange Coolant Expansion Tank


DavidPeckham

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hi all, got a strange set up with my coolant expansion tank (photo below) it's welded on to the corner of the gas locker and is not sealed.  Anyone seen one like this before? sure there must have been some kind of pressurised cap on there at some point but not sure what to do with it. Cheers for any help, as ever.

Brian

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Calcutt did something similar on their hire boats but not in the gas tank.

Pressurisation is normally only required when the engine is working really hard that produces so much heat the coolant would boil on internal hotspots like the injector boss and valve seats. For canal work I very much doubt it is ever needed and suspect that for summer river work it will be the same. Certainly I never got the Calcutt boats I hired to show any signs of overheating or localised internal boiling.

I suspect this is is an older boat and the expansion volume that tank provides is far superior to the   manifold type header tanks of the day (Bowman/Polar).  Don't do anything apart from enjoy boating unless you find coolant being ejected when under high power but with a temperature at or not much above normal. Only then considerer pressurising the system.

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Great, relieved to know it's not having any adverse effect on cooling  - all seems ok (though I do have to top up fairly regularly) and I do have one of those petrol tank caps so will shove that in and keep an eye on it.

Cheers all!

Brian

 

 

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1 hour ago, DavidPeckham said:

Great, relieved to know it's not having any adverse effect on cooling  - all seems ok (though I do have to top up fairly regularly) and I do have one of those petrol tank caps so will shove that in and keep an eye on it.

Cheers all!

Brian

 

 

Hoe far do you top it up to. I would leave at lest two inches of clearance above the coolant on a tank cooled boat. If you fill it fuller then expansing coolant will just         overflow. Fill it full just once, run for several hours until its nice and hot. Allow to go cold. Whatever the level is then only top up to that level.

If the level then keeps dropping you have a leak on the system somewhere.

 

 

Edited by Tony Brooks
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58 minutes ago, artleknock said:

The boat I hired from Fox had an open box on the bulkhead next to the door. The guy that showed me around told me to keep an eye on it and if the level fell to throw a drop of water in, anything will do, even river water.

that sounds very unprofessional from fox, you would think they would have left some water/antifreeze mix on board.

Neil

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You’ll be surprised how much expansion you’ll get. The previous advice is good, fill it, run it hard for several hours until it is overflowing then let it cool and mark the level a little below this.

if you are still topping up then you have a leak. A popular place for a leak is where the tank is connected to the engine.

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The header tank on my boat is quite a large one (holds over 5 litres apparently) welded to the top left corner of the cockpit (or whatever the open bit on a trad is called) then routed out to the top of the boat by a piece of plastic waste pipe into a fake chimney fitting.

Made seeing when the engine was getting a bit hot (pre skin tank) easy as the coolant expanded into the fitting - also made some interesting gurgling sounds just before the coolant appeared.  Since the new skin tank was fitted that little bit of entertainment had disappeared :)

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Hi all, bit more info on this in case it helps anyone - seems,  as everyone has suggested that all will run fine without pressurising  but I've been told that the reason I'm losing coolant is because some is evaporating when hot and also that a little pressure over the system helps hold the boiling point of the water higher and then cooling runs a bit more efficiently.

Cheers

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Both are true to some extent, but the effects are small.  Covering, but not sealing,  the hole will practically eliminate evaporation.   Pressurising the cooling system will increase its tendency to leak, especially if it has antifreeze as that is rather good at escaping. If it works and  you are not having to put a lot of coolant in  then just cover the hole and don't worry.  If  it ain't broke, it doesn't need fixing.

 

N

 

 

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20 hours ago, DavidPeckham said:

Hi all, bit more info on this in case it helps anyone - seems,  as everyone has suggested that all will run fine without pressurising  but I've been told that the reason I'm losing coolant is because some is evaporating when hot and also that a little pressure over the system helps hold the boiling point of the water higher and then cooling runs a bit more efficiently.

Cheers

I told you about why the system is pressurised in answer #2 and do not think it has anything to do with cooling efficiency as such. It just allows the vehicle manufacture to fit a smaller radiator and a lower flow rate water pump. It also allows the engine to run at a higher temperature without localised boiling under high loads and thus allow more heat from the fuel to be converted to power. this makes the engine more efficient, not the cooling system.

I do not believe that evaporation over even an 8 hour cruise would result in a noticeable reduction in coolant level. I notice on your photo that the filler appears to have a large bore pipe  hanging down inside the tank. That does not seem right to me because it reduces the coolant volume the tank can hold. It is also likely to trap air between the bottom of that pipe the top of the tank. Air expands far more than water when heated so maybe the trapped air is expanding and blowing some water out of the filler hole.

If that is not happening then I would suggest that you have a small leak somewhere that may be evaporating so you can not see it when the engine is running.

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  • 7 months later...

Hi all, many thanks for replies to this, finally got round to running  the engine for a substantial amount of time - looks like the answer was  semi-pressurise with a plastic temporary petrol tank cap, been doing 6-8 hours a day and  not losing any coolant at all.

 

Cheers!

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