My overheating problems.

[blackrose]

Not necessarily.

 

If it has an odd number of horizontal baffles, it will normally result in top and bottom connections being at opposite ends of the tank.

 

 

I see, I just assumed that straight baffles would be easier to make rather than curved ones.

[alan_fincher]

The pipe with the gearbox oil cooler attached should be the cooler return water.

So the other on the rusty elbow should be the hot inlet into the tank,and it looks as if it enters at the top.

So I think on available evidence we all agree it is plumbed up correctly!

 

(Of course Mike can check with the boat that has the identical installation that the "identical-ness" includes the way it is plumbed.

 

So if it is correctly plumbed, can anyone come up with any explanation that could ever make the bottom of the skin tank hotter than the top ??? :wacko:

[blackrose]

Certainly hope they are not vertical! If the entrance and exit are at opposite ends, that just (hopefully) means there is an even number of horizontal baffles.

 

 

Why not? You can have vertical baffles alternating from the top and bottom of the tank.

[alan_fincher]

Why not? You can have vertical baffles alternating from the top and bottom of the tank.

Because it would work far, far less efficiently,(and yes, I firmly disagree with Richard on this, I'm afraid). Effectively every other compartment instead of gravity assisting, you would be trying to defeat gravity, meaning you relied more of less solely on the pump, rather than any natural convection.

 

Your tank will, I'm very confident, have horizontal baffles, like in the picture I posted....

 

 

Any way time for this SAE to go to bed.

 

My one credential is that I have had a boat with an undersized and poorly designed skin tank, and worked to get the problem fully resolved. I therefore think I understand the issues quite well, including dismissing all kinds of other red herrings thrown at me until I finally conceded that the only true solution involved employing a welder!

[nicknorman]

Why not? You can have vertical baffles alternating from the top and bottom of the tank.

You could, but for all the reasons I thought I had explained, it would be very inefficient. Water would just bump along the top and thus you would lose a fair bit of the surface area for heat dump.

 

With the temperature differences between top and bottom you mention (and assuming you got it the wrong way round!), I don't think it can be restricted flow. If flow was low, the coolant would be leaving the tank quite cool since it would spend a long time in the tank losing heat. It would be the inlet that was getting too hot and possibly boiling.

Edited May 28, 2012 by nicknorman

[bizzard]

I'm convinced this is not a problem of restricted flow!

 

Do you think looking at the pictures it is plumbed the right way around, or the wrong way around.

 

A clue here, possibly....

 

(Picture from Ashby boats site).....

 

 

May be not identical engine, but an Isuzu with that top mounted gear box oil cooler, just the same. Note it also connects to the lower part of the tank, just like Mike's.

 

If Liverpool Boats got it wrong with Mike's then Ashby surely got it wrong with this one too.

 

I cn't see how the top connection can't be hotter than the bottom, I'm afraid - no explanation I can see at all as to how bottom could conceivably be hotter than the top.

Yes the shiny return pipe with the oil cooler on it should enter the engine lower down than the hot outlet,and on your photo i can just make out that it does. The hot outlet water is led out via the blue exhaust manifold heat exchanger header tank

[nicknorman]

 

Any way time for this SAE to go to bed.

 

Me too!

[alan_fincher]

You could certainly see the weld lines of the baffles on our skin tank - that was before it was spray foamed.

Sorry, I've not done it for a while, (honestly!), and I simply can't control myself......

 

Wouldn't spray-foaming also cover up any carefully applied "rivets" ?

 

(Goodnight!.....)

[blackrose]

You could, but for all the reasons I thought I had explained, it would be very inefficient. Water would just bump along the top and thus you would lose a fair bit of the surface area for heat dump.

 

No, you've misunderstood me - it couldn't bump along the top because the baffles connected to the top of the tank would force it to the bottom.

 

Edited May 28, 2012 by blackrose

[bizzard]

Nite folks.

[nicknorman]

Sorry, I've not done it for a while, (honestly!), and I simply can't control myself......

 

Wouldn't spray-foaming also cover up any carefully applied "rivets" ?

 

(Goodnight!.....)

 

You have been very good recently so I will allow you that one!

 

FWIW here is picture of our skin tank in build:

 

 

No, you've misunderstood me - it couldn't bump along the top because the baffles connected to the top of the tank would force it to the bottom.

 

Sigh - knew I should have gone to bed! Now consider the flow of water as a current the same diameter as the pipe bore (28mm?) and draw it flowing all round the baffles but staying as high as it can. The hot water has not nearly filled the tank, so a good bit of the surface area is doing nothing. True it will fill the chambers where the flow is downwards, but not upwards. Fluids at different temperatures in general don't like to mix so it is a mistake to consider the hot flow spreading out.

 

On Sunday I flew 300km in my glider thanks to the fact that hot air in rising thermals doesn't mix with the surrounding slightly cooler air, and so routinely carried me up to 7000'.

Edited May 28, 2012 by nicknorman

[bizzard]

No, you've misunderstood me - it couldn't bump along the top because the baffles connected to the top of the tank would force it to the bottom.

 

Mornin all.I think the only time a configuration like that would be used would be on a base plate tank and the water is forced around by an engine driven Jabsco type pressure pump.

Edited May 28, 2012 by bizzard

[MtB]

Having only skimmed through the whole thread I note one crucial piece of data is missing, mainly because it is fiendishly difficult to obtain. The flow rate through the skin tank. Needs a flow meter in series with the skin tank to measure.

 

With this bit of data we can do the calcs and work out how much heat the skin tank is dumping, and compare this with the engine data (cooling requirements). My bet is the low skin tank flow/return temperature differential is caused by a stupidly low flow rate. If the flow rate is high this indicates missing baffles, if low this indicates a pipe restriction or underperforming water pump.

 

Is yer fanbelt nice and tight??!

 

Mike

 

 

(edited to correct spellin)

Edited May 29, 2012 by Mike the Boilerman

[David Mack]

No, you've misunderstood me - it couldn't bump along the top because the baffles connected to the top of the tank would force it to the bottom.

 

 

If it was like that how would you bleed air out of the tank, and how would you drain the coolant? Not a problem with horizontal baffles.

[alan_fincher]

My bet is the low skin tank flow/return temperature differential is caused by a stupidly low flow rate.

I'm sorry, Mike, but while I have previously seen people suggest similar, it completely goes against the facts.

 

If the flow rate is very low, then hot water entering the tank at the top will spend longer in the tank before it eventually finds its way to the bottom, for return back to the engine.

 

That means it spends longer on average against the cold outside of the tank, so will lose more temperature than if it were being pumped through faster.

 

Hence slow flow rate, if anything, results in a bigger temperature difference across the tank.

 

If you follow things through to the point where almost no flow is possible, because of a constriction or damaged pump, then the little bit of heat that does manage to get circulated to the top of the skin tank will all get dumped there, long before the water moves down very far, and water being returned to the engine will be fully cold.

 

Low flow rate, (or no flow rate!) simply means the heat is not getting taken away from the engine properly, but it also means that what little heat does make it to the skin tank, the skin tank can easily dump that small amount.

 

That's why I say firmly this is not an air-lock, constriction, pump failure or anything that means low or no flow. There is adequate flow here, because water is still hot when it is reaching the bottom of the tank. The problem is either too much heat being produced by an engine with a fault, or a skin tank not simply adequate to cool the correct amount of heat from an engine being worked that hard. That's my SAE's worth, anyway!

 

If it was like that how would you bleed air out of the tank, and how would you drain the coolant? Not a problem with horizontal baffles.

Obvious innit!?!

 

You simply crane the boat up fully at one end, and let it dangle down at the other, at which point the baffles will be horizontal, and it will drain out just fine.

Edited May 29, 2012 by alan_fincher

[blackrose]

 

Sigh - knew I should have gone to bed! Now consider the flow of water as a current the same diameter as the pipe bore (28mm?) and draw it flowing all round the baffles but staying as high as it can. The hot water has not nearly filled the tank, so a good bit of the surface area is doing nothing. True it will fill the chambers where the flow is downwards, but not upwards. Fluids at different temperatures in general don't like to mix so it is a mistake to consider the hot flow spreading out.

 

 

I think the pipe bore is more like 45mm, but anyway surely what you describe would also apply to some extent with horizontal baffles - the hot water staying at the top of the chambers and not mixing? Woudn't fluid mixing actually be enhanced through the increased turbulence of having to go up and down rather than just falling in a tank with horizontal baffles? In any case, I really don't think vertical baffles are such an outrageous idea.

 

If it was like that how would you bleed air out of the tank, and how would you drain the coolant? Not a problem with horizontal baffles.

 

You would have small notches cut at the top and bottom of each baffle before they are welded in. (I dare say you'd have to do the same thing to make sure no small amounts of air or coolant were trapped behind the baffles in a tank with horizontal baffles.)

Edited May 29, 2012 by blackrose

[Tony Brooks]

May I comment that is is not unknown for the water pump impeller to fall off its shaft. many are only a press fit.

 

Now, I do not think this is the case here because of the hot outlet temperature but I think I would be inclined to remove the inlet to the skin tank and hold the hose up with a hot engine so the thermostat is open (or a cold one if the stat is still removed) to stop the coolant draining (Put a pipe clamp on any hose from a remote header tank) and rev the engine. The amount of water flowing from the hose should give a fair idea about the engine water pump - no flow = faulty impeller.

[MoominPapa]

One thing I'd try is to arrange some way to bleed the top of the skin tank. It's quite possible for air/gas to collect there, and because the flow is into the tank at the top, it won't get removed by the flow of the coolant. If the top 20% of the skin tank is full of air, the heat transfer capacity is reduced by 20%.

 

This happens to a small extent in Melalecua. There is a bleed pipe from the skin tank to the header tank, but it's only 15mm and long, and it sometimes takes a bit of time before the air gurgles out. It quite often happens when the engine stops and you can see by the level reduction in the header tank that about a litre of air has accumulated. That makes a sensible difference to the engine temperature.

 

On Melaleuca I think the air is coming in past the water pump seals. That's less likely on a modern engine with a pressurised cooling system. If you do have even a small head gasket leak, that will produce enough gas to cause this effect in a big way.

 

MP.

[RobinJ]

How do I check the coolant pump?

 

The plumbing between engine and skin tank is the same as any other Liverpool Boat as far as I know.

 

How would anyone know if their skin tank was baffled unless they were there during the build?

Ah!, Liverpool, I guess it won't have baffles then.

You can somtimes see the welds in the tank, but I double checked using a coat hanger!

 

What are the systems, sudden overheating after a short time - most likely air lock or some sort of blockage.

Takes a long time, but slowly heats up and suddenly boils - likely skin tank insufficient cooling (lack of baffles)

[alan_fincher]

Takes a long time, but slowly heats up and suddenly boils - likely skin tank insufficient cooling (lack of baffles)

Or, of course, has baffles, but simply not big enough to sustain prolonged use of the engine on higher power settings.....

 

Are relatively modern LB boats known to come without baffles in the tank, then ? I'd have thought they built enough to get that bit of the design right ?

[Athy]

Pardon my higgerance, but what is the purpose of these baffles? Our boat has a keel-cooled engine so I assume that it has a skin tank (and therefore baffles).

[RobinJ]

Or, of course, has baffles, but simply not big enough to sustain prolonged use of the engine on higher power settings.....

 

Are relatively modern LB boats known to come without baffles in the tank, then ? I'd have thought they built enough to get that bit of the design right ?

There were a lot of changes to Liverpool at various times, but I have seen earlier and later boats than mine and none had baffles when they were built.

Having said that they do tend to be quite large on the bigger boats, over 40' they generally are as big as 9 sq ft.

Ones fitted with BMC, Beta and Isuzu have had problems especially on the river for long periods, as the whole skin tank heats up over about 4 hours.

 

I know its contraversial, and I agree to some extent that flow rate is not important, but there are times when the heat generated and the low flow causes a local heat spot which will boil an engine!

Example, big jumper on prop, engine gets hot - throttle back and engine boils; if instead - put in neutral, rev engine, cools down!

[RLWP]

Pardon my higgerance, but what is the purpose of these baffles? Our boat has a keel-cooled engine so I assume that it has a skin tank (and therefore baffles).

 

The purpose is to turn the skin tank from a simple box into a long series of square section pipes. The hot water has to travel further through the box whilst up against the cold surface - the hull of the boat. It may look like a box of hot water, in reality it's a long square pipe with some 180 degree bends in it.

 

I do love this image of gentle convection currents wafting the hot water up to cower in the corners. In reality, this is a massively turbulent system and convection will be negligible

 

Mike - temperature measurements, flow check as Tony suggests, inspect header tank as Bizzard suggests - report back

 

Richard

[bizzard]

There is an experiment that could be carried out quite cheaply.

If mike gets hold of say a second hand car radiator from a breakers yard ''complete with 12v cooling fan''and with the same size pipe stubs on it as the existing hoses and adds it into the circuit with an extra bit of hose and clips,Connect the fan up to the battery with croc clips and go for a trip,turning the fan on and of to discover the differences.

 

But first i'd carry out all the engine head gasket checks and so on.

As Tony Brooks mentioned the water pump can be checked but like he says,and in my 45 years in the motor trade only once have i had a pump impeller come off and that was on a petrol engined Cavalier which had been very severely overheated,run for many miles with no water,the impeller had cracked and broken off.

And don't forget Mikes boat is a little over propped,by how much we don't know,i don't think.

I have one of those powerful 12v radiator cooling fans on its frame from a Volvo 340 if you can make use of it Mike but no radiator i'm afraid.

[LEO]

Pardon my higgerance, but what is the purpose of these baffles? Our boat has a keel-cooled engine so I assume that it has a skin tank (and therefore baffles).

 

Hi,

 

Hopefully the baffles produces a more convulated path for the water to follow meaning that it has more exposure to cooling surfaces.

 

My experience of cooling/overheating in these circumstances found that water was flowing through the cooler too quickly and an adjustemnt of pump pulley size overcame the problem.

 

Best of Luck.

 

Leo