Auxillary engine cooling system

[alan_fincher]

I would not argue against any of the above except to say that the calorifier does warm up quicker and hotter when running on one skin tank. This might, however, be more to do with the make of motor (Lister) because this effect was not apparant on my previous boat which was Beta Marine powered to which I also added an additional skin tank

 

I added the bypass circuit after much wondering why the calorifier was not getting hot.

 

Ditchdabbler

Does the calorifier take off come before the thermostat, (and hence bypass the engine thermostat ?).

 

If it didn't I could see what you are describing come into play.....

 

However, from my understanding it is usual to feed the calorifier from before the engine stat, not after it, (even though this can slow the rate at which a cold engine will heat, as the calorifier circuit is running even with the stat closed). Done that way, I'd expect any potential over-cooling by the skin tanks to result in the stat closing, but at that point the calorifier would continue to heat.

[Naughty Cal]

I'll go with Robin J on this one......

 

90 deg C is not excessively hot, especially for a diesel. The primary cooling circuit on the engine is pressurised so will be capable of running in excess of 100 deg.

 

The only issue will be lub oil temperature may effect the oil pressure but modern lubricant can easily cope with this.

 

If the temp flattens out at 90 deg, I think you're worrying about a problem that doesn't exist and en-curing unnecessary expenditure.

 

One thing that you need to be mindful of is that the calorifier temperature will get up to near the engine temp after long continued running.

 

Tend to agree. O longer runs our Volvo runs at 90 degrees. No adverse effects.

[n.b.Goldie]

Does the calorifier take off come before the thermostat, (and hence bypass the engine thermostat ?).

 

If it didn't I could see what you are describing come into play.....

 

However, from my understanding it is usual to feed the calorifier from before the engine stat, not after it, (even though this can slow the rate at which a cold engine will heat, as the calorifier circuit is running even with the stat closed). Done that way, I'd expect any potential over-cooling by the skin tanks to result in the stat closing, but at that point the calorifier would continue to heat.

 

The calorifer take off is before the thermosat and again I would not argue against the above. I did replace the 74 deg thermostat with an 88deg model which made only a small difference to calorifier heat-up, the major improvement being achieved with the bypass circuit.

 

I cannot explain it I just know it happens. My previous Beta Marine was not affected by the additional skin tank, the calorifier heating up just as quick.

 

Ditchdabbler

[blackrose]

I normally am very happy with most of the technical stuff Robin posts.

 

However on the subject of "thick skin tank is better than thin", I disagree most strongly, I'm afraid.

 

Thick is bad, and making the water stay in the skin tank longer is no good, if, as Tim says, you have far more of it.

 

There is every evidence to me, (assuming all other things are equal), that in a "thick tank", the water can chose to pass up the inside surface, (not water cooled) and stay away from the cooling surface on the outside of the boat.

 

Also a thick skin tank tends to result in more coolant in total than normal expansion arrangements on many engines can cope with, so it ends up getting expelled.

 

A thin skin tank will agitae the water more, so far more of it is likely to pass near to the cooled surface

 

I suspect it's a non-issue here though, as it's highly unlikely that Mike's Liverpool boat has anything radically different from the LB norm. My guess is it's well enough designed in terms of thickness and baffles, but given it's a wide wide-beam, and Mike does heavy river work in it, it just ain't big enough.

 

I'd bite the bullet, and have another one added.

 

I can't see why a particular Isuzu engine should be more prone to overheating than another. It's usually just basic maths about the cooling surface you need, and Mike sounds to have enough for most normal use, but just be on the margin.

 

I'd argue that if you have (say) an 80 degree stat, then the tank should never need to get hotter than the temp at which the stat opens. Since we upgraded our skin tank, the temperature guage never goes higher than the 82 degree stat we now have fitted.

 

Remind us Mike, how big is your tank. Without doing the math's, I'd say it needed to be an absolute minimum of (say) 12 square feet, (e.g. 6 feet long, 2 foot high), possibly even more. I'm guessing it isn't!

 

My skin tank is approximately 9.5 ft2 when it really should be more like 14 ft 2. It's about an inch thick.

 

This was the message I received from a forum member who used to work for HMI:

 

"The 4LE1 isuzu 55 was prone to overheating and possible failure of the cylinder head gasket especially in the boat hire fleets where the holiday operator had limited knowledge of the engine.

Investigations by HM Isuzu could not link the problem to one particular boat builder but it became apparant that the problem was only effecting the isuzu 55 and no other engines in the isuzu range.

 

From your post on the forum it is obvious that you allready take particular attention of your engine temperature during prolonged use and moderate the engine speed to suit and that is really all you can do.

 

The engineering manager and sales manager at HM isuzu tetbury made a decision that changing the engine completely from 4LE1 to the new model 4LE2 was the only option they had to overcome the problem and that decision was approved."

 

 

I'll go with Robin J on this one......

 

90 deg C is not excessively hot, especially for a diesel. The primary cooling circuit on the engine is pressurised so will be capable of running in excess of 100 deg.

 

The only issue will be lub oil temperature may effect the oil pressure but modern lubricant can easily cope with this.

 

If the temp flattens out at 90 deg, I think you're worrying about a problem that doesn't exist and en-curing unnecessary expenditure.

 

One thing that you need to be mindful of is that the calorifier temperature will get up to near the engine temp after long continued running.

 

On a hot day running above 1600rpm against the current my engine could easily reach 100 deg C. It doesn't because I don't let it.

 

Do you know the the temperature of the coolant as it returns to the motor from the skin tank? It should be at least 20 degC cooler than the motor and if you have a PRM gearbox with oil cooler connected to the motor cooling circuit, the temp. should not exceed 70c for significant periods (according to my PRM manual).

 

I fitted one of these inline temperature sender housings with matched sender and gauge and can now monitor what is happening to the water temp at outflow and return.

 

The housing and sender/gauge sets are available from Car builder Solutions and is inserted in the return pipe from the skin tank.

 

Monitoring the temperature persuaded me to have an additional skin tank fitted to which I fitted a bypass circuit to enable it to be switched in and out as required (winter and summer / canal or river settings!)

 

Ditchdabbler

 

I took some readings with an IR thermometer but just measured the gearbox itself and the cool pipe from the bottom of the skin tank to the gearbox heat exchanger. The temperatures were fine - about 70 & 80 deg C if I remember rightly. I also checked various areas of the skin tank with the temp gauge to make sure it was giving me an accurate reading.

Edited June 30, 2010 by blackrose

[GUMPY]

We've been round this buoy before!!! The simplest method, and probably cheapest, would be to fit a bowman tube heat exchanger into the main central heating pipe out of the ch boiler/heater and connect it to the engine calorifier connections. Then the whole CH circuit is heated up by the engine, including calorifier.

If TRVs are fitted, then opening them fully will make them operate all the time. I used radiator engine cooling in August 08 after I got an airlock in the keel coolers. Boat jumbles should provide a suitable heat exchanger for around £50 - I think mine is actually an oil heat exchanger. In cooler times of the year, a nice warm boat from the engine is brilliant.

 

New 12kw heat exchangers are available from Bowman for about £90 you wont need the brass type if you are not running seawater.

[blackrose]

We've been round this buoy before!!! The simplest method, and probably cheapest, would be to fit a bowman tube heat exchanger into the main central heating pipe out of the ch boiler/heater and connect it to the engine calorifier connections. Then the whole CH circuit is heated up by the engine, including calorifier.

 

 

If TRVs are fitted, then opening them fully will make them operate all the time. I used radiator engine cooling in August 08 after I got an airlock in the keel coolers. Boat jumbles should provide a suitable heat exchanger for around £50 - I think mine is actually an oil heat exchanger. In cooler times of the year, a nice warm boat from the engine is brilliant.

 

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?

[alan_fincher]

My skin tank is approximately 9.5 ft2 when it really should be more like 14 ft 2. It's about an inch thick.

 

I think you have probably answered your own question there.

 

9.5 square feet is probably adequate for a 55 HP engine if never worked too hard, but definitely marginal if you do.

 

As I think you have already conceded, LB have skimped on this area, even if the design is basically a good one.

 

If you pottered around the ditches, I'd say live with it, or maybe try some of these half-hearted work-arounds.

 

But as you try motoring yourself up the Thames and into Limehouse, if it were me, I think I'd be finding the money for the extra tank. (Particularly as you are often on your own, I think....)

[blackrose]

I think you have probably answered your own question there.

 

9.5 square feet is probably adequate for a 55 HP engine if never worked too hard, but definitely marginal if you do.

 

As I think you have already conceded, LB have skimped on this area, even if the design is basically a good one.

 

If you pottered around the ditches, I'd say live with it, or maybe try some of these half-hearted work-arounds.

 

But as you try motoring yourself up the Thames and into Limehouse, if it were me, I think I'd be finding the money for the extra tank. (Particularly as you are often on your own, I think....)

 

But I have plenty of unused heat radiating capacity in the boat, so if I can get it working by means of a circulation pump, heat exchanger and a bit of plumbing, then why not use a work-around?

Edited June 30, 2010 by blackrose

[Radio-Ga-Ga]

It seems to have gone unnoticed that you mentioned the engine is over propped, that in itself could be a significant part of the overheating problem.

[blackrose]

It seems to have gone unnoticed that you mentioned the engine is over propped, that in itself could be a significant part of the overheating problem.

 

I thought over-propping reduced available engine revs? My engine only revs to 2000rpm in gear (2700 in neutral).

[Radio-Ga-Ga]

I thought over-propping reduced available engine revs? My engine only revs to 2000rpm in gear (2700 in neutral).

The engine revs are reduced because the engine is overloaded, like continualy driving your car uphill in too high a gear, it's likely to oveheat, and that added to the skin tank being possibly just adequate.

 

I know its nice to have a good cruising speed at low revs, but modern engines should realy be propped so they can achieve full rpm, or at least close to it.

[ChrisPy]

Mike,

If the right side of your engine bay is free of obstructions it should not be too difficult for a competent welder to fit a second cooling tank.

Your boat is wider than mine, and we have the same engine. I reckon I could easily get down beside the engine to fit a tank say 3ft long on the right side.

All it requires is to pre-fabricate a thin tank with pipe nozzles installed, with no front (outer) face, and no bottom, and thin enough to allow it to be 'bashed' into a curve to match the boat during installation (say use 20mm x 5mm flat bar for the surround strip. If it is fully pre-fabricated, all the installation welds should be easily accessible for welding and for visual inspection. The back (inner) face will be fillet welded to the base plate of the boat, and the side and top strips will be fillet welded to the vertical plate of the boat.

I would estimate 4hrs for a welder, cost about £250 including the material.

Ask the welder to clean the installation welds with a grinder and dye test for pinholes before you let him go.

Repair the blacking at the welds on the first occasion when you can use the tide to allow the boat to dry out.

I agree that all this may be avoided if you change the prop, but only because over-propping forces the engine to produce maximum power at any given revs, so the heat output will be at it's potential maximum.

Any ideas about cooling your boat through the radiators seems to me to be a non-starter, you are talking about serious amounts of heat that need to be dissipated!

Good luck.

[alan_fincher]

But I have plenty of unused heat radiating capacity in the boat, so if I can get it working by means of a circulation pump, heat exchanger and a bit of plumbing, then why not use a work-around?

Your choice, but I think you'll be pissing around for ever.

 

Do you really want corking hot radiators on a mid summers day, when you don't have to ?

 

Your original post said.....

 

Should I just bite the bullet and get a second skin tank...........

 

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!

[GUMPY]

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 exchanger has 4 ports then I suppose I could connect it to both coils. Is that the idea?

 

The bottom pipes connect to the engine in circuit with the send to the skin tank then the end pipes connect in line in the central heating circuit

When you need the cooling you switch on the central heating pump and that pumps water through the exchanger extracting heat from the engine cooling circuit and then on to the rads.

If you imagine it as a secondary boiler connected in the heating circuit that may help.

You will never get enough transfer from the calorifier coil to cool the engine.

Edited July 1, 2010 by idleness

[RLWP]

Your choice, but I think you'll be pissing around for ever.

 

Do you really want corking hot radiators on a mid summers day, when you don't have to ?

 

Your original post said.....

 

 

 

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 endorse this view.

 

For instance, you could extend the pipes from the engine to the skin tank up unto the roof and then fit several hundred feet of 2" copper pipes on the roof. Why haven't you tried that?

 

Because it may or may not work, and it's not really a practical solution

 

Talk to a welder about having a second skin tank fitted Mike

 

 

Richard

[soldthehouse]

Mike, Ive just picked up on you saying somewhere way back that your skin tank is about an inch thick. I thought the usual thickness was about two inches, this could be pivotal stuff, I await other opinions.

[WotEver]

Mike, Ive just picked up on you saying somewhere way back that your skin tank is about an inch thick. I thought the usual thickness was about two inches, this could be pivotal stuff, I await other opinions.

I believe we established earlier in this thread that 1" thick is ideal, and that thicker tanks are less efficient (despite them being common - mine is also about 2" thick).

 

Tony

[soldthehouse]

I believe we established earlier in this thread that 1" thick is ideal, and that thicker tanks are less efficient (despite them being common - mine is also about 2" thick).

 

Tony

I suppose thinner still would be even better if the area was increased disproportionately, but where do you stop!! There are so many variables I suppose the op question is oversimplistic to answer accurately and any set up will be a compromise if the operating conditions vary dramatically.

 

I believe we established earlier in this thread that 1" thick is ideal, and that thicker tanks are less efficient (despite them being common - mine is also about 2" thick).

 

Tony

I suppose thinner still would be even better if the area was increased disproportionately, but where do you stop!! There are so many variables I suppose the op question is oversimplistic to answer accurately and any set up will be a compromise if the operating conditions vary dramatically. Another point is that if its only 1 inch thick and about 9.5 sq feet in area this wouldnt cool anything above tickover on calm water.

[WotEver]

Take a look at this pdf: http://www.betamarine.co.uk/newsite/downlo...inland/Keel.pdf

 

It's from Beta Marine and they discuss the optimum sizing and positioning of skin tanks. Assuming the tank is around 30mm thick the area of the tank in ft² should be at least one quarter of the engine bhp. So a 50hp engine should have a minimum of 12.5 ft².

 

Tony

 

Edit to add this quote from the above document:

This area assumes that the engine is developing its maximum continuous power at full engine rpm and is therefore what we recommend. In practice much smaller areas have been used without overheating and this is possible due to a number of factors which affect the engine. These are:-

 

a The power used by most boaters when cruising on the canal is considerably less than maximum.

 

b Many canal boat engines are over propped and are incapable of reaching their maximum rpm and therefore power even on a river

 

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

Edited July 1, 2010 by WotEver

[nb Innisfree]

I thought over-propping reduced available engine revs? My engine only revs to 2000rpm in gear (2700 in neutral).

 

I would guess your prop is contributing to overheating. We have a 40 bhp @ 3000rpm Lister Petter running from a 6.5 sq ft x 1.5" thick skintank, max revs available with our prop are 2750 so slightly over propped. Engine shares coolant with CH and 2 calorifiers (engine runs unpressurized) We have had no issue with overheating, engine runs at 82C whether it's hammered up the river or tootling along the cut, I can't be sure but this may be down to always having the calorifiers + one bathroom rad in circuit. If we did have probs we can open all the rad valves and dump some heat, though it could be a bit warm in the boat in hot weather it would only be on a rare occasion and we would be outside on the deck anyway.

[alan_fincher]

Another point is that if its only 1 inch thick and about 9.5 sq feet in area this wouldnt cool anything above tickover on calm water.

 

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.

[WotEver]

I would guess your prop is contributing to overheating.

I'd always believed that to be correct but it's not right according to Beta Marine.

 

Tony

[ChrisPy]

I suppose thinner still would be even better if the area was increased disproportionately, but where do you stop!! There are so many variables I suppose the op question is oversimplistic to answer accurately and any set up will be a compromise if the operating conditions vary dramatically. Another point is that if its only 1 inch thick and about 9.5 sq feet in area this wouldnt cool anything above tickover on calm water.

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

[Timleech]

I suppose thinner still would be even better if the area was increased disproportionately, but where do you stop!! There are so many variables I suppose the op question is oversimplistic to answer accurately and any set up will be a compromise if the operating conditions vary dramatically. Another point is that if its only 1 inch thick and about 9.5 sq feet in area this wouldnt cool anything above tickover on calm water.

 

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

Edited July 1, 2010 by Timleech

[nb Innisfree]

Take a look at this pdf: http://www.betamarine.co.uk/newsite/downlo...inland/Keel.pdf

 

It's from Beta Marine and they discuss the optimum sizing and positioning of skin tanks. Assuming the tank is around 30mm thick the area of the tank in ft² should be at least one quarter of the engine bhp. So a 50hp engine should have a minimum of 12.5 ft².

 

This area assumes that the engine is developing its maximum continuous power at full engine rpm and is therefore what we recommend. In practice much smaller areas have been used without overheating and this is possible due to a number of factors which affect the engine. These are:-

 

a The power used by most boaters when cruising on the canal is considerably less than maximum.

 

b Many canal boat engines are over propped and are incapable of reaching their maximum rpm and therefore power even on a river

 

Tony

 

Edit to add this quote from the above document:

 

 

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

 

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