Engine Temperature

[alan_fincher]

Finally got some pictures; What do you think?

It is, as I thought "plumbed" the right way round.

 

Cold water from the skin tank is piped first through the gearbox oil cooler, (the brass thing connected to the gearbox by two smaller flexible pipes), before going in to the engine, (via the "silver" pipe along the top right hand side).

 

The hot water coming out of the engine at the thermostat housing is piped via a 90 degree rubber bend into the header tank, with the "radiator" cap on. The header tank is also the exhaust cooler.

 

The hot water comes out the front bottom of the header tank, and is taken to the top of the skin tank.

 

So please don't try reversing the skin tank connections!

 

It's hard to judge exact skin tank size. I'd say it looks "enough" for normal use, but probably has little cooling capacity in reserve for when the engine is worked really hard. Your problem may be no more than this, I suspect.

 

Have you had a chance to measure skin tank temperatures close to the inlet (top) and outlet (bottom), please ?

 

EDIT:

 

Possibly it was commented on before, I'm not sure.

 

Nothing to do with overheating, but I'm kind of surprised to see the prop-shaft running directly into the gearbox without any kind of even basic flexible coupling in it.

 

I'm not sure what type of stern gear it is - possibly some king of "cutlass" design without greased packing ? Unless it's a type that allows for some movement of engine and gearbox, I feel the arrangement shown could put it under stress.

 

FURTHER EDIT:

 

Wrongly referred to engine oil cooler, when I meant gearbox oil cooler....

Edited June 26, 2008 by alan_fincher

[John Orentas]

I am beginning to agree with Alan now, equally important as the actual temperature try to (literally) get a feel for the heat distribution on the tank, as has been said before hot water can in some circumstances 'short cut' much of the tank and take a direct route from inlet to outlet, indicative of having inadequate baffling, and yes it does now look a bit small generally.

 

Any engineer who could install a drive system, as again Alan pointed out is capable of anything.

 

Sorry WJM to be pulling your boat apart in this way.

[alan_fincher]

.............as has been said before hot water can in some circumstances 'short cut' much of the tank and take a direct route from inlet to outlet, indicative of having inadequate baffling...............

One might reasonably expect LB to get the design, including the baffles reasonably right.

 

But the problem with baffles, is that unless you go for a very expensive method of building the tank, they are generally only welded to one side of the tank, (the hull, usually), but can't be welded to the other side, (the inner skin), which just touches them as much as it can.

 

So I think there is always the possibility of water "short cutting" in the (hopefully small) gap between baffles and inner skin of the tank.

 

I have heard methods described to avoid this, but it involves bigger baffles passing through slots on the inner skin, and then fully welded. Perhaps some of the top of the range builders do this, but I'm pretty confident nobody building for the mass market would.

 

Alan.

[WJM]

Thanks for the feedback all. I promise I dont take any criticisms personally, I just bought the boat, I didnt build it!

 

Re: the transmission; the 'gland' is one of those greaseless non-maintenance types. Because it is a professional (!) build and fit out boat, and in my ownership it has done 700 hours of actual cruising over the last two years, I am inclined to believe it is set up ok.

 

Re: Skin tank temperatures; I will give it a go next time I am out. Insulation does seem to affect the readings from this thermometer. My kettle gave me readings from 95 to 65 degrees while it was boiling, depending on where I read from on the body. That said, a temperature 'map' of the tank should tell a lot.

 

 

If it transpires that the skin tank is inadequate, is there any easy fix, other than to install a bigger one?

 

I am thinking of ideas like; de-black the area outside the tank and paint it silver, enlarge the ventilation slots of the engine hole, improve airflow over the inside of the tank with a fan - anything else?

Edited June 27, 2008 by WJM

[alan_fincher]

Re: Skin tank temperatures; I will give it a go next time I am out. Insulation does seem to affect the readings from this thermometer. My kettle gave me readings from 95 to 65 degrees while it was boiling, depending on where I read from on the body. That said, a temperature 'map' of the tank should tell a lot.

Accepted that the IR thermometer may be affected by the colour / texture of what it's measuring.

 

But as your skin tank has the same surface all over, you should get good comparative results, even if not 100% absolutely correct.

 

As John says, you can learn a lot by placing your hand on, and feeling for hot and cold spots, but go cautiously, 95 centigrade is nearly boiling, so don't injure yourself.

 

If it transpires that the skin tank is inadequate, is there any easy fix, other than to install a bigger one?

I'm not sure how effective any of the alternative measures you have mentioned might be. Perhaps others can comment. (Personally I'd have thought cooling by air on the inside of the skin tank is relatively insignificant in the overall picture, compared to cooling by water on the outside).

 

It's notoriously difficult to increase skin tank size within the confines of an existing engine compartment, although it's often possible to add a second one on the other swim. (They are usually then plumbed "in series", so that the water goes from the engine through one skin tank, then into another for further cooling, before returning to the engine).

 

We found it easier to abandon the original tank, and to have a new slender one welded on the outside of the swim. Very much easier to do, as you don't need to work round existing fixtures and fittings. It doesn't seem to have had any untoward effect on how the boat swims or handles. But not cheap, so you need to be confident it's necessary first.

 

Alan

[larkshall]

To increase cooling area or thermal efficiency:-

 

Remove paint from front surface of cooling tank.

 

Obtain some aluminium heatsink material, similar to that used to cool computer chips/power supplies (its finned or honeycombed to increase surface area.

 

Obtain some heatsink bonding compound (white messy stuff in tubes).

 

Coat all but the outside 1/2 inch of the heatsink. The remaining 1/2 inch should be coated with fasting setting heatproof epoxy cement. The attach heatsink to cooling tank.

 

Alternatively Obtain Kenlowe slimline cooling fan Mount in front of cooling tank and connect to starter battery. Kenlowe fans often come with a temp sensor to cut the fan in/out at predetermined temps. This should be connected via epoxy putty to the tank.

 

You could of course use heatsink, AND fan.

[WJM]

Thanks Alan - I am not sure I like the idea of the tank on the outside. I tend to be very hard on boats and I am sure I would eventually find some opportunity to crush an external tank.

[alan_fincher]

Thanks Alan - I am not sure I like the idea of the tank on the outside. I tend to be very hard on boats and I am sure I would eventually find some opportunity to crush an external tank.

It's quite hard to hit the outside of the swim very firmly with anything, even with my boating skills.

 

Anyway the new outside of the tank is in 6mm steel, so is the same thickness as the swim it's mounted on.

 

With the honeycomb of internal baffles, cushioned with a water filling, the box like structure is probably the strongest bit of the boat.

 

It only sits proud of the swim by about an inch.

 

There's at least one other forum member who has a boat where the same thing has been done. In his case I don't think it was because the existing tank was inefficient. IIRC, it had sprung a leak at a very inaccessible point, and it was cheaper to slap a new one on the outside, than to attempt to seal the existing one.

[alan_fincher]

Whilst looking for something else, I found this document on skin tank design and sizing....

 

http://www.betamarine.co.uk/newsite/downlo...inland/Keel.pdf

 

OK, it's Beta rather than Isuzu, but that shouldn't affect the logic.

 

In a nutshell, Beta suggest sizing at HP divided by 4 (giving a result in sq ft). So for a 38 HP engine, Beta would only suggest 9.5 sq ft. This is massively less than the 34 square feet suggested by Russell Newbery, and which I feel would be impossible to achieve in most 'normal' narrowboats.

 

Rounding up to 10 sq ft, gives a tank 5 feet long, by 2 feet deep - easily achieved on just one side of the swim.

 

I don't think I'm misreading Beta's paper, but I am surprised they don't cover themselves by suggesting a larger size.

[NB Teila]

Could it be a duff thermostat? Not opening fully when temp rises under load?

 

Just a thought.

[alan_fincher]

Could it be a duff thermostat? Not opening fully when temp rises under load?

 

Just a thought.

This is why we really could do with an accurate update on skin tank temperatures, and temperature gradient across it.

 

What you are suggesting could well be the case if temperature is indeed 95 degrees at the stat, but the water immediately beyind the stat is at nothing like that temperature.

 

Best wishes,

 

Alan

[WJM]

I will take some readings next time I have the boat out.

[Mike Poole]

I seem to have found a way to increase cooling but I'm sure there must be a side-effect or two somewhere.

 

After all my fiddling with finrads and fans (although they are useful just for warmth) I thought I'd experiment in a different more crude direction. I was cleaning out the engine room bilge which is split into three sections by the engine bearers and I had an 11-watt energy saving lightbulb moment. The larger central area under the engine has the drip tray and bilge pump. To the one side is a dry smaller section where I keep oil and stuff and on the other side is a similar small section in which sits the impossibly small skin tank and the copper skin tank return pipe. I just poked the hose pipe down and filled up that bilge section until the water covered the bottom 8 inches of the skin tank and copper pipe. I took it for a thrape along the test track that is the Shelmore embankment and blow me down it ran perfectly sweetly while hovering around the thermostat temp unlike previously where it hovered precariously under boilng point even with all the fans blowing. I presume that there is some heat transference taking place between the skin tank, loose water and then an additional area of side and base plate but it seems amazing that the difference is so noticeable.

 

Can anything go wrong? Will the shell split like a pea pod? Will the ducks clamour for a sauna in the engine bay? I suppose it would need a bit of antifreeze in Winter although the added water is well below surface level.

[blackrose]

While doing an engine service today I was interested to see that the Izusu engine manual cautions against over cooling (below 75 deg C) which it said can lead to premature engine wear. I guess the oil is not up to its operating temp.

 

Sorry if this has already been posted - I didn't read the whole thread.

 

My Izusu 55 is plumbed in the same as yours WJM. I think you should change the coolant as specified in the Isuzu manual: With a cold engine and the radiator cap off you can drain the coolant via the water drain plug at the rear of the alternator on the left hand side of the engine (facing forward on the boat) - at least that's the set up on my 55. Also as someone else said, make sure your fanbelt tension is properly adjusted: With your start battery isolator off take the middle of the start alternator fanbelt between your thumb & forefinger and twist it lateally through 90 degrees. If you can twist it more than this it's too loose and may be slipping on the water pump pulley so that your cooling is impaired. The other way to check it is just to depress the belt in the same place - it' shouldn't move more than about 10mm.

Edited July 14, 2008 by blackrose

[andywatson]

Whilst looking for something else, I found this document on skin tank design and sizing....

 

http://www.betamarine.co.uk/newsite/downlo...inland/Keel.pdf

 

OK, it's Beta rather than Isuzu, but that shouldn't affect the logic.

 

In a nutshell, Beta suggest sizing at HP divided by 4 (giving a result in sq ft). So for a 38 HP engine, Beta would only suggest 9.5 sq ft. This is massively less than the 34 square feet suggested by Russell Newbery, and which I feel would be impossible to achieve in most 'normal' narrowboats.

 

Rounding up to 10 sq ft, gives a tank 5 feet long, by 2 feet deep - easily achieved on just one side of the swim.

 

I don't think I'm misreading Beta's paper, but I am surprised they don't cover themselves by suggesting a larger size.

 

According to the RN paperwork I have, a DM2 is 22HP and RN recommend 1 sq yard per cyl which would be 18 sq ft for a DM2.

[alan_fincher]

While doing an engine service today I was interested to see that the Izusu engine manual cautions against over cooling (below 75 deg C) which it said can lead to premature engine wear. I guess the oil is not up to its operating temp.

If the thermostat is doing it's job, over-cooling isn't possible, even if you couple up to a skin tank massively larger than the engine actually requires.

 

Until the thermostat opening temperature is reached, no water flows to the skin tank anyway, and, when it does, if the temperature starts to drop, the stat will close to keep it up.

 

People who have 2 skin tanks, and only bring the second into use for river work are over-complicating things. They might as well have both in circuit all the time, IMO.

 

Typical thermostats in a keel cooled arrangement are in the 80-90 degree range, but can be lower. My BMC is 74 degrees, which is what it was actually designed to run at in an automotive environment. I'm thinking of moving up to an 82 degree one, but, like many boat jobs, I've yet to move it up the priority stack.

Edited July 14, 2008 by alan_fincher

[blackrose]

If the thermostat is doing it's job, over-cooling isn't possible, even if you couple up to a skin tank massively larger than the engine actually requires.

 

Until the thermostat opening temperature is reached, no water flows to the skin tank anyway, and, when it does, if the temperature starts to drop, the stat will close to keep it up.

 

People who have 2 skin tanks, and only bring the second into use for river work are over-complicating things. They might as well have both in circuit all the time, IMO.

 

Typical thermostats in a keel cooled arrangement are in the 80-90 degree range, but can be lower. My BMC is 74 degrees, which is what it was actually designed to run at in an automotive environment. I'm thinking of moving up to an 82 degree one, but, like many boat jobs, I've yet to move it up the priority stack.

 

I didn't know that. I just thought coolant flowed around the whole system at any temperature, but what you say makes sense. So I wonder why Isuzu have the warning in the engine manual?

 

Also Alan, if what you say is correct then why don't builders just always over specify skin tanks? (i.e. make them over-sized?) If the engine cannot ever run too cool then why not make give skin tanks a big margin of error on the + size, like 25% too big? It just sounds like most are made exactly the right size which may end up right on the edge so the engine runs a bit too hot.

Edited July 14, 2008 by blackrose

[alan_fincher]

Also Alan, if what you say is correct then why don't builders just always over specify skin tanks?

Some are, I suspect, just cutting costs.

 

In other cases it may well be that the shell builder, who is expert neither on engines or heat transfer, just does what they think will suffice.

 

Our boat is "Evans & Son", which I gather effectively means Mike Heywood, a firm which built huge numbers of boats, (and I believe still does, under the guise of his sons). Despite his large slice of the marketplace, it didn't stop him fabricating skin tanks only 2 feet square, about four times too thick, and with no internal baffles.

 

Whethe he was being lazy, ignorant, or both, I'm not sure, but it didn't work very well!

[blackrose]

I had a thought about WJM's problem yesterday which may also be an issue on my boat (apologies if this has already been covered)

 

If your engine is connected to a calorifier and the top of the coil in the calorifier is higher than the coolant cap on the engine, then the system could develop a air block in the coil that you will be unable to bleed. This could lead to higher than normal engine temperatures. The solution would be to blank off the coolant cap on the engine and run a pipe from the overflow just below the coolant cap to a header tank positioned higher than the calorifier.

 

The top of my calorifier is certainly higher than the coolant cap on the engine but I've no way of knowing how high the coil rises inside the tank.

[bottle]

I believe the top of the coil will be on a level with the top entry for the coil.

 

A bleed valve could be connected to the highest point of the coil pipe run.

Edited July 16, 2008 by bottle

[blackrose]

I believe the top of the coil will be on a level with the top entry for the coil.

 

You mean the coils just go in horizontally (on a vertically mounted calorifier)? That makes sense, for some reason I thought they went up.

 

In that case the coolant cap is higher on mine so there's no problem there.

Edited July 16, 2008 by blackrose

[bottle]

You mean the coils just go in horizontally (on a vertically mounted calorifier)?

 

I believe so, not cut one about to find out for definite.

 

To get the most amount of hot water the coil has to be as low as possible inside the calorifier.

 

All to do with convection currents.

[blackrose]

I just found this on the net. It may be relevant: http://www.betamarine.co.uk/newsite/downlo...inland/Keel.pdf

[alan_fincher]

I just found this on the net. It may be relevant: http://www.betamarine.co.uk/newsite/downlo...inland/Keel.pdf

Already posted at post 84.

[blackrose]

Already posted at post 84.

 

I was just reminding you

Edited July 17, 2008 by blackrose