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New skin tank or not


Martin44

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1 minute ago, Martin Trnecka said:

I don't quite follow. What to look for in the hose?

You need to take the hose off and look through it. The inner liner of the hose can collapse casuing a blockage therefore reducing coolant flow and puting more stain on the pump.

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2 hours ago, Martin Trnecka said:

The engine is actually 28hp, but that probably does not have much influence anyway. The beta marine website also has a table what engine size is required for what length of boat. My engine is actually undersized for my boat according to the table. 

Also I rarely run it more than 1500 rpm.

Yes, it is the right way: hot in in upper corner; cold in in lower corner

The point I was making is that the 28bhp is the engine’s max power, that will be a quite high rpm, which you probably do not do for sustained periods of time, so the amount of power that your engine is normally generating will be quite a bit less.

 

Your engine like mine is not sold anymore, but If you look at the Beta 30 as an example, that is 30bhp at 3600rpm.  It you look at the power curve, and you were normally doing 1500rpm, then the engine is only developing 16bhp, so that would say a 4 sq ft skin tank should cool it at that rpm.

https://betamarine.co.uk/wp-content/uploads/downloads/technical_data_sheets/inland_data/B30-KC-DataSheet-REV-01.pdf

again for the Beta 30 example the peak torque is at 2600rpm, so I would say you would not go past that and at that rpm it is generating 24bhp, so a 6 sq ft tank.

 

This needs to be translated for your specific engine.  You probably have the data sheet for your engine with the engine manual in the boats handbook, but you may still be able to fine the data sheet for it online if you don’t.

 

Edited by john6767
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Are the inlet/ outlets on the tank a decent size?

I would remove the lowest hose and drain the system using a wet and dry vac. If the system hasnt had a decent inhibitor in it there is a good chance your bottom tank outlet may be restricted. A good poke and flush would sort that out cheaply too..

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2 hours ago, john6767 said:

The point I was making is that the 28bhp is the engine’s max power, that will be a quite high rpm, which you probably do not do for sustained periods of time, so the amount of power that your engine is normally generating will be quite a bit less.

 

Your engine like mine is not sold anymore, but If you look at the Beta 30 as an example, that is 30bhp at 3600rpm.  It you look at the power curve, and you were normally doing 1500rpm, then the engine is only developing 16bhp, so that would say a 4 sq ft skin tank should cool it at that rpm.

https://betamarine.co.uk/wp-content/uploads/downloads/technical_data_sheets/inland_data/B30-KC-DataSheet-REV-01.pdf

again for the Beta 30 example the peak torque is at 2600rpm, so I would say you would not go past that and at that rpm it is generating 24bhp, so a 6 sq ft tank.

 

This needs to be translated for your specific engine.  You probably have the data sheet for your engine with the engine manual in the boats handbook, but you may still be able to fine the data sheet for it online if you don’t.

 

I would have thought that the size of the skin tank needs to be x ft sq irrespective of how many rpm is the engine making. FWIW when the engine overheats and been running at 1500 rpm, I then slow down to 1000rpm for example, but it still sits at very high temp 90 and more. I had been navigating for few hours without the thermostat and temperature never rose to more than 80C

1 hour ago, PaulJ said:

Are the inlet/ outlets on the tank a decent size?

I would remove the lowest hose and drain the system using a wet and dry vac. If the system hasnt had a decent inhibitor in it there is a good chance your bottom tank outlet may be restricted. A good poke and flush would sort that out cheaply too..

 

1 hour ago, alan_fincher said:

Are you able to post pictures of the skin tank and its connections to the engine?

Here is the only picture on hand in which you can see the outlet hose...

20180617_161255 (1).jpg

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The waste heat created is a factor of the amount of power that the engine is generating, and in turn the amount of power is dependent on the rpm.  Why do you think the amount of waste heat will be independent of rpm?

 

If it is overheating at low rpm, then I would say it is not totally down to skin tank area.  It could be skin tank design or something else.  That outlet hose looks tiny to me.

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1 minute ago, john6767 said:

The waste heat created is a factor of the amount of power that the engine is generating, and in turn the amount of power is dependent on the rpm.  Why do you think the amount of waste heat will be independent of rpm?

 

If it is overheating at low rpm, then I would say it is not totally down to skin tank area.  It could be skin tank design or something else.  That outlet hose looks tiny to me.

It's not overheating at low rpm to start with, only when it's been running at high rpm, going down doesn't lower the temperature. 

To be fair, I don't really fully understand all the intricacies of how the engine works. Just trying to solve by elimination whether new skin tank is needed or not. What is clear to me now though, that I will have to check the coolant and flush the skin tank at the least.

If it's the design, then probably new on outside swim would do the trick.

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10 hours ago, WotEver said:

I think it’s the big fat black one, not the skinny grey one. 

I was looking at the black one, but on a phone.  Looking again I agree it is not so small, so scratch that comment!

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13 hours ago, Martin Trnecka said:

I would have thought that the size of the skin tank needs to be x ft sq irrespective of how many rpm is the engine making. FWIW when the engine overheats and been running at 1500 rpm, I then slow down to 1000rpm for example, but it still sits at very high temp 90 and more.

 

This suggest that even when you reduce revs & the engine still stays at high temperature then there is insufficient cooling (obvious).

 

The options are :

 

Water is not circulating

Insufficient water is circulating

The water in the skin tank is not being cooled sufficiently (due to either size, design, or insulation by layers of blacking)

 

The temperatures you mention are ENGINE TEMPERATURE, not the temperature of the cooling water - what temperature is the skin tank (& contents) ? Do you have an infrequently read thermometer ?

 

Is your engine thermostat opening fully ?

Are your engine cooling pipes 'furred' up (restricting flow) ?

Has one of your cooling pipes delaminated internally causing a partial obstruction ?

 

"I had been navigating for few hours without the thermostat and temperature never rose to more than 80C" 

 

The part of your post I've highlighted in Red could be the cause and solution to the problem.

 

I would suggest there are a number of investigations to take before going for an 'engineering', costly (may not solve the problem) solution - spend £1000's on a new, additional. skin tank and then find it was actually a £5 thermostat and you have a "Doh" moment.

 

 

 

NB - I had a Reeves 1998 45 footer with a Lister LPWS4 engine. Regularly used on the tidal Trent, and the river in flood - never had the temp gauge go above about 85c, I doubt Reeves would produce an undersize cooling tank.

Edited by Alan de Enfield
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Also worth checking that your prop is properly matched to engine and drive chain. I think that engine should be topping out at about 3000 rpm under load but the manual will tell you. About 10 - 15% less than no-load max. It made a lot of difference to my engine when I replaced the over-large prop.

 

Martin/

Edited by Onewheeler
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18 minutes ago, Alan de Enfield said:

 

 

Is your engine thermostat opening fully ?

"I had been navigating for few hours without the thermostat and temperature never rose to more than 80C" 

 

 

He did say that he had replaced the thermostat, I make a point of testing before fitting using a bowl of hot water and lowing the thermostat into the water it should just pop open. If not you have a dud.

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2 minutes ago, nbfiresprite said:

He did say that he had replaced the thermostat, I make a point of testing before fitting using a bowl of hot water and lowing the thermostat into the water it should just pop open. If not you have a dud.

Agreed, but his post saying that it doesn't overheat if he runs with the thermostat removed postdates the one saying he has replaced the thermostat.

 

I do the same test (put into a pan of water and bring to the boil) to ensure the thermostat opens at the correct temperature, and, opens fully.

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13 hours ago, john6767 said:

The waste heat created is a factor of the amount of power that the engine is generating, and in turn the amount of power is dependent on the rpm.  Why do you think the amount of waste heat will be independent of rpm?

 

If it is overheating at low frpm, then I would say it is not totally down to skin tank area.  It could be skin tank design or something else.  That outlet hose looks tiny to me.

 

No, no, no.

 

The amount of power the engine is producing depends upon load not the RPM although the two may be closely linked but not necessarily. Revving the engine in neutral will get you high RPM with minimal power developed but in gear it will take more power to reach the same RPM. If you then fitted an oversized prop or got the prop fouled you may well need even more power to reach the same RPM.

 

Looking at it another way the governor in the injection pump  supplies just sufficient fuel for the engine to reach the RPM the governor spring is set to by the throttle. If the load goes up the speed goes down so the governor supplies more fuel to speed the engine back up. Burning more fuel produces more heat.

 

I basically agree with the sentence about overheating at low speed BUT all those other things people have mentioned also need addressing like prop size, hose size, overplaying, build up of blacking and so on.

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1 hour ago, Tony Brooks said:

 

No, no, no.

 

The amount of power the engine is producing depends upon load not the RPM although the two may be closely linked but not necessarily. Revving the engine in neutral will get you high RPM with minimal power developed but in gear it will take more power to reach the same RPM. If you then fitted an oversized prop or got the prop fouled you may well need even more power to reach the same RPM.

 

Looking at it another way the governor in the injection pump  supplies just sufficient fuel for the engine to reach the RPM the governor spring is set to by the throttle. If the load goes up the speed goes down so the governor supplies more fuel to speed the engine back up. Burning more fuel produces more heat.

 

I basically agree with the sentence about overheating at low speed BUT all those other things people have mentioned also need addressing like prop size, hose size, overplaying, build up of blacking and so on.

Yes I agree it’s a simplification, but you have to start somewhere with parameters that you can measure, and all other things being equal I thin’ it gives a good start point.  I was assuming the engine under load, clearly in neutral not under load it is different.  If the prop was fundamentallay wrong, so over loaded, that would have the opposite effect.

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