Auxillary engine cooling system

[ChrisPy]

This last point made by Beta contradicts the earlier stated theory that an over propped engine will overheat.

I guess we should distinguish between an engine working hard under load and developing maximum power (and waste heat) at those revs, and an engine taking it easy turning a smaller prop and never developing much load.

The first condition produces maximum heat but it is not over-heating per se.

Most canal boats with modern high speed diesel engines probably operate within the second condition.

[soldthehouse]

Explain ?

 

I thought his skin tank was a "thin" one, about 9.5 square feet, and it clearly fully meets the needs most of the time, and doesn't fall far short even if pushed hard.

 

I don't understand the comment.

 

All received wisdom is that about 1" internal measurement is good for a canal boat skin tank.

 

That's how the better builders do it, and there is no advantage in making it thicker, and lots of potential disadvantages.

 

We had our crap 4" thick tank replaced with a 1" thick one of a much greater external area, and it completely cured all the problems of the original arrangement.

 

Incidentally ours was rebuilt on the outside of the swim, due to it being a much lesser task than putting it inside. It made no discernible difference to handling or fuel economy. This is always an option if adding a new one inside is going to be difficult, or there just isn't enough space to make it big enough.

Arnt forums great!! I dont obviously communicate that well I agree with you on most points so my scribblings must be badly written. Suffice to say my tank on my 34hp Petter is 2inches thick and 9sq feet inarea thats 4.5ft x2ft x 2" and I hope it works. thats as technical as I can get. I must learn to stay out of these conversations as my gut feelings which normally serve me well in real life rarely come over well on here

[WotEver]

I don't think anyone uses max revs and power more than a few seconds.

Not even when travelling upstream on a river?

 

That's a genuine question, I've never taken out boat onto a river, and I'm not sure she'd have the speed to cope if I were to try.

 

Tony

[soldthehouse]

not understood.

 

The only way any heat exchanging system (which is what a skin tank is) works is by exchanging heat from a hot fluid (the coolant) with the cold surroundings (canal water) through a barrier (the boat's skin). The only critical parameters are the differential temperature of the coolant againt the canal water and the surface area of the barrier. The volume of the tank has nothing to do with it, except that a bigger (thicker) tank may retain the coolant longer and therefore be at a slightly LOWER temperature.

As long as the coolant can circulate unobstructed, the tank can be as thin as you can make it, without requiring any increase in surface area.

Actually the standard LB skin tank on a widebeam (my memory says about 6sq.ft. area and 1" thick) works fine for most installations of 55 Isuzu engines, including mine, at well above tickover.

 

 

 

 

 

............ all this reminds me of flash steam systems for some reason - now that is something for Daniel to work on

As usual I bow to your obvious technical knowledge and I must learn to stay out of such conversations. [Longer version in reply to Alan}

 

Surface area is the important bit, it's where the cooling takes place. It shouldn't need to be increased just because you make the tank thinner. A thicker tank will slow down any overheating issues, just because there is more coolant to be (over)heated, but it will only be a delay to the inevitable. It'll also take more antifreeze!

 

I recently fitted a new external tank for a Barrus/Yanmar, the instruction book recommends IIRC about 40mm thick but I went for 30mm as it is an external tank. I don't know their basis for suggesting 40mm.

 

Fitting new tanks alongside an existing engine may seem straightforward, but getting a water(pressure)tight weld at the bottom/chine corner can be a real pig if you're working in an awkward space, leaning over an engine, etc., and don't get it spot on first time I have uncomfortable memories of sorting out someone else's failure in that department, some years ago, and would look carefully at access for a job like that before taking it on.

In Blackrose's case with a wider boat there may well be enough access to do the job comfortably.

 

Edit to add that the easy option in my book would be a heat exchanger in line with the existing system, and an electric raw water pump which can be switched on in times of stress.

 

Tim

I intend having an open header tank system on my boat running an unsealed system that can be drained and topped up on fast tidal runs, by the lesser member of the crew at short notice as a foolproof system but dont tell anyone else on here Tim..

[colin stone]

Perhaps I'm being a bit thick but I don't understand which coil I'm supposed to connect the Bowman heat exchanger to?

 

I have a twin coil calorifier. One coil is connected to the engine and the other coil was connected to the diesel heater which has now been taken out as it packed up. So in effect it is a spare coil but it is not connected directly to the engine.

 

If the Bowman heat echanger has 4 ports then I suppose I could connect it to both coils. Is that the idea?

 

Right. The rubber hose connections in my pic are attached to the engine calorifier take off points and replace the connections to the calorifier coil, which are probably before the thermostat. The coil that was connected to your heater should be reconnected to the CH system as if it was another radiator, with a ball valve to adjust flow. The brazed brass connections are in the CH supply line from the CH heater. If in the return line, then hot water merely heats the heater first. A CH circ pump is used to circulate through the entire CH system and will pick up the heat from the exchanger - flow through the exchanger should be in opposite directions. One does not want to overcool the engine just after starting, so I delay switching on the CH pump until the engine has run for 15mins. This can be done manually of with a delay timer and relay.

 

Here is a diagram, but only 3 of 14 radiators shown.

 

Edited July 1, 2010 by colin stone

[GUMPY]

Edit to add that the easy option in my book would be a heat exchanger in line with the existing system, and an electric raw water pump which can be switched on in times of stress.

 

Its just to easy

KISS

See my posting #11

 

Mike if you want to come and look at what I've done give me a bell

[blackrose]

My opinion, given the use you make of the boat, is firmly "yes", as I think it's the only reliable solution to the problem, and shouldn't cost a fortune.

 

But as I say, your choice!

I'm going into the drydock on Saturday for blacking and have been quoted £500 for the steelwork. The quote from Uxbridge was about the same.

[blackrose]

Right. The rubber hose connections in my pic are attached to the engine calorifier take off points and replace the connections to the calorifier coil, which are probably before the thermostat. The coil that was connected to your heater should be reconnected to the CH system as if it was another radiator, with a ball valve to adjust flow. The brazed brass connections are in the CH supply line from the CH heater. If in the return line, then hot water merely heats the heater first. A CH circ pump is used to circulate through the entire CH system and will pick up the heat from the exchanger - flow through the exchanger should be in opposite directions. One does not want to overcool the engine just after starting, so I delay switching on the CH pump until the engine has run for 15mins. This can be done manually of with a delay timer and relay.

 

Here is a diagram, but only 3 of 14 radiators shown.

 

 

Thanks for that Colin. Contrary to what some here say, the heat exchanger system obviously works if both you and Julian have variations of the system on your boats.

 

In most canal situations my engine runs at just over 80C which is fine, so it's difficult for me to justify spending £500 on an additional skin tank when all I really need is a system which will dump a bit of heat on the occasions when I really need it.

 

Its just to easy

KISS

See my posting #11

 

Mike if you want to come and look at what I've done give me a bell

 

Thanks Julian. I'm just down at Winkwell now. I'll bring a picture on my phone and hopefully you can advise.

[nb Innisfree]

Not even when travelling upstream on a river?

 

That's a genuine question, I've never taken out boat onto a river, and I'm not sure she'd have the speed to cope if I were to try.

 

Tony

 

Max speed is dictated by the hull, even in deep water max revs and therefore max bhp just results in a slightly faster speed massive bow wave and lots of noise and unnecessary prop thrashing etc, far too manic. We find about 1800 to 2200 rpm is the most comfortable range for going upstream which equates to approx 60 to 75% of full output, 2400rpm (80%) is still ok but starting to get a bit hectic. It's a bit like taking your car on the motorway, if there were no speed limit you wouldn't thrash it at top speed, or would you?

Edited July 1, 2010 by nb Innisfree

[FadeToScarlet]

Max speed is dictated by the hull, even in deep water max revs and therefore max bhp just results in a slightly faster speed massive bow wave and lots of noise and unnecessary prop thrashing etc, far too manic. We find about 1800 to 2200 rpm is the most comfortable range for going upstream which equates to approx 60 to 75% of full output, 2400rpm (80%) is still ok but starting to get a bit hectic. It's a bit like taking your car on the motorway, if there were no speed limit you wouldn't thrash it at top speed, or would you?

 

Much the same observation for me, with my BMC 1.8-engined narrowboat.

 

I've never pushed the throttle all the way to the stop when the boat's in gear, but I suspect it will reach 2,800 rpm or so.

 

It will certainly cruise at normal speeds at 1800 rpm, and recently, when punching a 7-8 kph current when the river was in flood, sustained 2,200 rpm.

 

The engine's certainly overcooled with the system it's got, it never went above 55 degrees even after three hours at 2,200rpm. But then, the system was installed by Fox narrowboats, who are presumably used to the users of the boats they build going everywhere at full throttle

[Trilby Tim]

55bhp is about 41 kW. Since a diesel engine is only about 40 % efficient then for every 41 kW of mechanical power it delivers its creating 61 kW of heat which must be dumped somewhere. Standard domestic radiators are only rated at 1 or 2 kW each, so its easy to see why using the engine to heat the radiators isn't absorbing very much of your excess engine heat. Fitting a second skin tank would seem to me to be the best bet. Since there's a thermostat fitted to the engine then excess cooling capacity is never going to be a problem.

Although if you think you're over-propped anyway then reducing the prop might also help. You'll be doing a higher rpm for a given power, which means the water pump will be pumping harder. You also might be using less power for a given speed (if the prop's better matched the efficiency will go up) which would also help.

[colin stone]

55bhp is about 41 kW. Since a diesel engine is only about 40 % efficient then for every 41 kW of mechanical power it delivers its creating 61 kW of heat which must be dumped somewhere. Standard domestic radiators are only rated at 1 or 2 kW each, so its easy to see why using the engine to heat the radiators isn't absorbing very much of your excess engine heat. Fitting a second skin tank would seem to me to be the best bet. Since there's a thermostat fitted to the engine then excess cooling capacity is never going to be a problem.

 

Yes - but the CH cooling system is only an auxiliary system to take away excess heat over and above that managed by the current skin tank. Although in Aug 08, my 118kw motor was well cooled by 25kw worth of radiators. And it is a great system to have in the cooler months. It is also a very cost effective way of achieving additional cooling.

Edited July 2, 2010 by colin stone

[blackrose]

55bhp is about 41 kW. Since a diesel engine is only about 40 % efficient then for every 41 kW of mechanical power it delivers its creating 61 kW of heat which must be dumped somewhere. Standard domestic radiators are only rated at 1 or 2 kW each, so its easy to see why using the engine to heat the radiators isn't absorbing very much of your excess engine heat. Fitting a second skin tank would seem to me to be the best bet. Since there's a thermostat fitted to the engine then excess cooling capacity is never going to be a problem.

Although if you think you're over-propped anyway then reducing the prop might also help. You'll be doing a higher rpm for a given power, which means the water pump will be pumping harder. You also might be using less power for a given speed (if the prop's better matched the efficiency will go up) which would also help.

 

Since my skin tank is about 75% of its ideal size, I would guess that 75% of the 61kw of heat (or 46kw) is already dealt with.

 

That leaves 15kw of heat to dissipate through the rads. I have 4 rads which I believe are 2.5 kw each so we're not far off..

 

The engine's certainly overcooled with the system it's got, it never went above 55 degrees even after three hours at 2,200rpm. But then, the system was installed by Fox narrowboats, who are presumably used to the users of the boats they build going everywhere at full throttle

It sounds to me like your engine's not reaching it's correct operatiing temperature. Either that or the temp gauge isn't giving you an accurate reading?

Edited July 1, 2010 by blackrose

[nb Innisfree]

Since my skin tank is about 75% of its ideal size, I would guess that 75% of the 61kw of heat (or 46kw) is already dealt with.

 

That leaves 15kw of heat to dissipate through the rads. I have 4 rads which I believe are 2.5 kw each so we're not far off..

 

 

It sounds to me like your engine's not reaching it's correct operatiing temperature. Either that or the temp gauge isn't giving you an accurate reading?

 

Of that 15 kw a lot of it is lost through the exhaust and some through through external radiation from the block and exhaust so I would guess you are well within.

 

Much the same observation for me, with my BMC 1.8-engined narrowboat.

 

I've never pushed the throttle all the way to the stop when the boat's in gear, but I suspect it will reach 2,800 rpm or so.

 

It will certainly cruise at normal speeds at 1800 rpm, and recently, when punching a 7-8 kph current when the river was in flood, sustained 2,200 rpm.

 

The engine's certainly overcooled with the system it's got, it never went above 55 degrees even after three hours at 2,200rpm. But then, the system was installed by Fox narrowboats, who are presumably used to the users of the boats they build going everywhere at full throttle

 

I agree with Blackrose, sounds as if your thermostat is either knackered (failed in the open position) or the wrong temp range.

Edited July 1, 2010 by nb Innisfree

[Radio-Ga-Ga]

I didn't read every post in this topic so might have missed somthing, but I think we all know if you make an engine labour hard it produces more heat. increasing the capacity of the cooling system enough will dissipate it and it won't overheat, but the engine is still labouring. what I know about props could be written in large print on the back of a stamp, but whatever the load, prop or fairground ride if an engine is held at low rpm by its load with a wide throttle the load is too heavy. that doesn't mean that by reducing the load we have to race down the motorway at breakneck speed or have the kids flying off the roundabout. what it does mean is that by giving the engine a load that it is capable of driving at near to its maximum rpm it's less likely to be labouring at the lower speed you do intend to run it at.

[Proper Job]

I agree with Blackrose, sounds as if your thermostat is either knackered (failed in the open position) or the wrong temp range.

IIRC, isn't Lucky Duck raw water cooled?

[RobinJ]

I didn't read every post in this topic so might have missed somthing, but I think we all know if you make an engine labour hard it produces more heat. increasing the capacity of the cooling system enough will dissipate it and it won't overheat, but the engine is still labouring. what I know about props could be written in large print on the back of a stamp, but whatever the load, prop or fairground ride if an engine is held at low rpm by its load with a wide throttle the load is too heavy. that doesn't mean that by reducing the load we have to race down the motorway at breakneck speed or have the kids flying off the roundabout. what it does mean is that by giving the engine a load that it is capable of driving at near to its maximum rpm it's less likely to be labouring at the lower speed you do intend to run it at.

Nothing is ever that simple!

What you have to remember is that when an engine is under heavy load the actual rpm may be lower than intended due to loading, so may not be burning the fuel fully and therefore producing less heat. Also as the water is probably going round slower, the amount of cooling is reduced, so it is possible that the cooling system will get hotter or cooler depending on all the variables.

There may be lags, I often notice when I have been cruising for a while and slow down, the header tank overflows for a few seconds as the temperature gauge goes up and then drops back again.

Increasing the capacity of a cooling system merely allows it to absorb short 'peaks' of heat better, but it creates more expansion problems and won't solve overheating per se, just postpone it.

[alan_fincher]

Increasing the capacity of a cooling system merely allows it to absorb short 'peaks' of heat better, but it creates more expansion problems and won't solve overheating per se, just postpone it.

And if you do have a cooling system with a much bigger volume than the norm, (perhaps because the skin tank is much too thick), once it has got far hotter than it should have done, it will actually take longer to get back down to a correct temperature, once the engine is producing less heat.

 

They can slow down the time taken for an engine to overheat, but also the time it takes to recover back to something more satisfactory.

 

The only things that really make a skin tank system work properly is an adequate area of cooling surface, and proper baffles to make sure the water uses as much of that surface as possible. (Assuming you have not done something obviously wrong, like reversing the flow and return connections to the engine, of course!).

 

 

IIRC, isn't Lucky Duck raw water cooled?

It is, I believe, unless the Ducks have had a skin tank fitted since.

 

This is where I get confused though....

 

Some "raw water cooled" canal boat engines don't actually pass canal water (and sludge!) around the engine itself, but retain a closed circuit passing through a heat exchanger, which then had the raw water pumped through it. (My old Perkins P3 worked this way).

 

You then have two water pumps, one circulating the closed circuit, (probably an "engine style one), and one circulating the raw water, (maybe a Jabsco one).

 

In such cases I would still expect the engine to retain a thermostat, so, however hard the water is running through the raw water circuit, I'd not expect to see the engine temperature down in the mid fifties.

 

I'd have thought when using raw water cooling on something like the B series engine, that would be more normal than straight direct cooling, (where you would have to take steps to protect the engine from frost damage).

 

Perhaps FTS could confirm exactly what cooling arrangements their BMC does have ?

[MoominPapa]

IIRC, isn't Lucky Duck raw water cooled?

Not any more; it has had a skin tank installed.

 

MP.

[Proper Job]

Not any more; it has had a skin tank installed.

 

MP.

In that case, I think James needs to check his thermostat?

[alan_fincher]

Not any more; it has had a skin tank installed.

 

MP.

In that case it either has no thermostat, or a stuck open thermostat, or is plumbed up wrong, or the temperature gauge and/or sender is quite knackered.

 

Pointing an IR thermometer at the thermostat housing will tell them if it's really at 55 degrees, or whether the measurement equipment is lying.

 

Thermostats specific to this engine are usually around 74 degrees or 82 degrees. If ine is in there, the temperature gauge should rise to those kind of numbers before any significant amount of heated water goes anywhere near their skin tank. (So skin tank size can't be relevant to not reaching thermostat temperature, can it ?).

 

I suspect thermostat is missing, stuck open, wrong type, or is put in upside down, (although the latter shouldn't be possible if it's an 1800, and has the "bypass" type, often fitted to these engines).

[RobinJ]

Some "raw water cooled" canal boat engines don't actually pass canal water (and sludge!) around the engine itself, but retain a closed circuit passing through a heat exchanger, which then had the raw water pumped through it. (My old Perkins P3 worked this way).

 

You then have two water pumps, one circulating the closed circuit, (probably an "engine style one), and one circulating the raw water, (maybe a Jabsco one).

 

In such cases I would still expect the engine to retain a thermostat, so, however hard the water is running through the raw water circuit, I'd not expect to see the engine temperature down in the mid fifties.

 

I'd have thought when using raw water cooling on something like the B series engine, that would be more normal than straight direct cooling, (where you would have to take steps to protect the engine from frost damage).

 

Perhaps FTS could confirm exactly what cooling arrangements their BMC does have ?

I think in my time I've seen all variations! Including both water pumps working with only a skin tank and raw water going through the skin tank!

When I put raw water on mine, it was to keep the gearbox cool! Now I've got the engine oil cooler, its relieving some of the engine heat too!

[FadeToScarlet]

I love how the forum as a whole knows rather a lot about my boat and its problems!

 

It sounds to me like your engine's not reaching it's correct operatiing temperature. Either that or the temp gauge isn't giving you an accurate reading?

 

Yes, there is no thermostat due to the previous raw-water cooled nature of the cooling. There is a debate as to whether it matters or not, though; Alnwick is very firmly of the opinion that it doesn't.

 

I could fit a thermostat, as the housing is there, I'd just have to drain the coolant, I think, in order to do it.

 

In that case it either has no thermostat, or a stuck open thermostat, or is plumbed up wrong, or the temperature gauge and/or sender is quite knackered.

 

Pointing an IR thermometer at the thermostat housing will tell them if it's really at 55 degrees, or whether the measurement equipment is lying.

 

Thermostats specific to this engine are usually around 74 degrees or 82 degrees. If ine is in there, the temperature gauge should rise to those kind of numbers before any significant amount of heated water goes anywhere near their skin tank. (So skin tank size can't be relevant to not reaching thermostat temperature, can it ?).

 

I suspect thermostat is missing, stuck open, wrong type, or is put in upside down, (although the latter shouldn't be possible if it's an 1800, and has the "bypass" type, often fitted to these engines).

 

IIRC, isn't Lucky Duck raw water cooled?

 

It doesn't have a thermostat currently fitted, as it never had one in it's indirect raw water days (as in, water sucked in through inadequate mudbox by Jabsco impeller pump, circulated through heat exchanger, then expelled into exhaust) although it could have.

 

As I mentioned, I'm in two minds whether to fit a thermostat or not. Even running hard on the river, the engine doesn't get near to temperature, according to the gauge.

 

It certainly would have no hope of getting anywhere near whilst at canal speeds.

 

I suppose I'd better borrow an IR thermometer! I used to have great fun, back when I was 15 and working at Safeway, taking an IR thermometer outside on my lunchbreak and, whilst wearing a hi-vis jacket, pointing it at passing cars.

[Radio-Ga-Ga]

Nothing is ever that simple!

What you have to remember is that when an engine is under heavy load the actual rpm may be lower than intended due to loading, so may not be burning the fuel fully and therefore producing less heat. Also as the water is probably going round slower, the amount of cooling is reduced, so it is possible that the cooling system will get hotter or cooler depending on all the variables.

There may be lags, I often notice when I have been cruising for a while and slow down, the header tank overflows for a few seconds as the temperature gauge goes up and then drops back again.

Increasing the capacity of a cooling system merely allows it to absorb short 'peaks' of heat better, but it creates more expansion problems and won't solve overheating per se, just postpone it.

 

Is this intended as a joke?

 

If this post is serious it's so ridiculous the only response it deserves is to say, if you post on any subject requiring mechanical aptitude I suggest you limit yourself to the fitting of door knobs.

 

But no it can't be, so yes very funny, realy made me giggle,

[RLWP]

Is this intended as a joke?

 

If this post is serious it's so ridiculous the only response it deserves is to say, if you post on any subject requiring mechanical aptitude I suggest you limit yourself to the fitting of door knobs.

 

But no it can't be, so yes very funny, realy made me giggle,

 

It's not completely ridiculous though, is it?

 

If you have overloaded a diesel engine so that the governor cannot maintain the speed you set the throttle for, it will overfuel. You can see this effect as unburnt fuel coming out the exhaust as black smoke. In the combustion process, unburnt fuel gets heated up, lowering the temperature of the charge in the cylinder, and robbing the engine of power

 

Whether that makes a scrap of difference to the coolant temperature is a whole different question

 

Richard