My overheating problems.

[blackrose]

I've been onto Bowman who seem to think that increasing coolant circulation through the system will be a benefit! Two different guys there have told me that! I did explain why it wouldn't but they don't understand!

 

With the particular heat exchanger in question, they were talking in terms of flow rates of 32 - 50 litres/minute (on both sides), which seems like a lot. I don't have the specs on my engine's water pump, but I'd be surprised if it does that.

 

I guess that if my engine's water pump can squeeze coolant through the thermostat then it can squeeze it through a heat exchanger, but to be honest, the design of these heat exchangers seems compromised by the tiny ports that restrict flow. It just looks odd to me to reduce the big 1 & 1/4" ID pipes from my skin tank to get into 3/4" ports.

 

By the way, would I plumb the heat exchanger into the pipe from engine to skin tank or the return from skin tank to engine?

Edited June 21, 2012 by blackrose

[Timleech]

I've been onto Bowman who seem to think that increasing coolant circulation through the system will be a benefit! Two different guys there have told me that! I did explain why it wouldn't but they don't understand!

 

With the particular heat exchanger in question, they were talking in terms of flow rates of 32 - 50 litres/minute (on both sides), which seems like a lot. I don't have the specs on my engine's water pump, but I'd be surprised if it does that.

 

I guess that if my engine's water pump can squeeze coolant through the thermostat then it can squeeze it through a heat exchanger, but to be honest, the design of these heat exchangers seems compromised by the tiny ports that restrict flow. It just looks odd to me to reduce the big 1 & 1/4" ID pipes from my skin tank to get into 3/4" ports.

 

By the way, would I plumb the heat exchanger into the pipe from engine to skin tank or the return from skin tank to engine?

 

It's always been my understanding that generally speaking greater flow led to better heat transfer, but others were stating firmly otherwise & I'm not qualified to speak so kept quiet If Bowman don't know the right answer, there won't be many who do.

Your engine integral cooling pump is probably not much more than an assisting paddle, so might be affected by that sort of restriction so you might need to look for a different exchanger.

 

Tim

[Nickhlx]

I too am not qualified as a thermodynamics engineer, but I struggle to see that a slower flow will result in "better" heat transfer - to me that goes completely against logic in a dynamic situation.

 

In the skin tank where there is hot water being supplied, the hotter this water can be kept the greater the heat flow through the skin / steel to the outside world.

 

In the engine, the heat is trying to get from the hot combustion chamber to the cooler liquid and the cooler the liquid is, the greater the heat transfer is going to be.

 

Naturally there will be a law of diminishing returns applying for rate of heat flow against the temperature of the transfer liquid and the rate of flow of the transfer liquid, but one thing that is clear in my understanding is that the faster the flow the better the potential rate of heat transfer.

 

Nick

[bizzard]

I've been onto Bowman who seem to think that increasing coolant circulation through the system will be a benefit! Two different guys there have told me that! I did explain why it wouldn't but they don't understand!

 

With the particular heat exchanger in question, they were talking in terms of flow rates of 32 - 50 litres/minute (on both sides), which seems like a lot. I don't have the specs on my engine's water pump, but I'd be surprised if it does that.

 

I guess that if my engine's water pump can squeeze coolant through the thermostat then it can squeeze it through a heat exchanger, but to be honest, the design of these heat exchangers seems compromised by the tiny ports that restrict flow. It just looks odd to me to reduce the big 1 & 1/4" ID pipes from my skin tank to get into 3/4" ports.

 

By the way, would I plumb the heat exchanger into the pipe from engine to skin tank or the return from skin tank to engine?

Photos can be deceptive but way back hundreds of posts ago, the internal diameter of the end of that rusty elbow that screws into the skin tanks bush doesn't look that it could be much more than 3/4 id.

[Timleech]

Photos can be deceptive but way back hundreds of posts ago, the internal diameter of the end of that rusty elbow that screws into the skin tanks bush doesn't look that it could be much more than 3/4 id.

 

It looked to me like a bog standard M&F elbow.

 

Tim

[bizzard]

It looked to me like a bog standard M&F elbow.

 

Tim

Yes it was an M/F. The internal bore size is usually stamped on them.

[blackrose]

Yes it was an M/F. The internal bore size is usually stamped on them.

 

Ok, I'll have a look at that. It goes inside 1 & 1/4" ID hose so I think it's probably 1" ID.

[blackrose]

I too am not qualified as a thermodynamics engineer, but I struggle to see that a slower flow will result in "better" heat transfer - to me that goes completely against logic in a dynamic situation.

 

In the skin tank where there is hot water being supplied, the hotter this water can be kept the greater the heat flow through the skin / steel to the outside world.

 

In the engine, the heat is trying to get from the hot combustion chamber to the cooler liquid and the cooler the liquid is, the greater the heat transfer is going to be.

 

Naturally there will be a law of diminishing returns applying for rate of heat flow against the temperature of the transfer liquid and the rate of flow of the transfer liquid, but one thing that is clear in my understanding is that the faster the flow the better the potential rate of heat transfer.

 

Nick

 

I think you have to differentiate between the rates of flow on either side of a heat exchanger. In the case of a skin tank an increased flow rate of river water over the outside of the hull will certainly improve heat transfer, but increased coolant flow beyond a certain rate will not provide sufficient opportunity for heat transfer to the cooler medium (the river water) to occur.

 

In the case of a tubular heat exchanger the same principal applies. So moving the raw water faster through one side of the heat exchanger will improve cooling, but moving the coolant faster will not. In both cases it's the increased flow rate of the cooler medium that will provide improved heat transfer.

 

I'm not a thermodynamics engineer either - these are just my thoughts, but if it were true that increasing the flow rate of hot engine coolant improved heat transfer then why would the engine manufacturers install such inefficient water pumps (or "assisting paddles" as Tim put it) into their engines? It is because they know what Bowman seem not to: namely that some movement of the hot coolant is required, but too much flow will not assist and may reduce heat transfer.

Edited June 21, 2012 by blackrose

[Timleech]

Yes it was an M/F. The internal bore size is usually stamped on them.

 

Yes, my point was that it looked to be equal rather than reducing, so the size will be determined by the thread in the skin tank socket and the presence of the elbow really makes little difference.

 

Tim

 

I think you have to differentiate between the rates of flow on either side of a heat exchanger. In the case of a skin tank an increased rate flow of river water over the outside of the hull will certainly improve heat transfer, but increased coolant flow beyond a certain rate will not provide sufficient opportunity for heat transfer to the cooler medium (the river water) to occur.

 

In the case of a tubular heat exchanger the same principal applies. So moving the raw water through one side of the heat exchanger will improve cooling, but moving the coolant faster will not. In both cases it's the increased flow rate of the cooler medium that will provide improved heat transfer.

 

I'm not a thermodynamics engineer either - these are just my thoughts, but if it were true that increasing the flow rate of hot engine coolant improved heat transfer then why would the engine manufacturers install such inefficient pumps (or "assisting paddles" as Tim put it) into their engines? It is because they know what Bowman seem not to: namely that some movement of the hot coolant is required, but too much flow will not assist and may reduce heat transfer.

 

Because that's all that is needed (in the usual context for that engine)?

 

Tim

[blackrose]

Because that's all that is needed (in the usual context for that engine)?

 

Tim

 

Exactly! All the engine manufacturers know is that whatever type of cooling system is installed, the coolant doesn't have to move very fast.

Edited June 21, 2012 by blackrose

[Timleech]

Exactly! All the engine manufacturers know is that whatever type of cooling system is installed, the coolant doesn't have to move very fast.

 

That's not what I meant.

The resistance that has to be overcome is usually low, so a powerful pump is not required. You might be surprised at how quickly the coolant can move with a fully open thermostat.

 

Tim

[blackrose]

That's not what I meant.

The resistance that has to be overcome is usually low, so a powerful pump is not required. You might be surprised at how quickly the coolant can move with a fully open thermostat.

 

Tim

 

I know it's not what you meant, but I was using what you said to support my point.

 

What the engine manufacturers don't want is for hot coolant to return to the engine uncooled. A powerful pump, or a faster flow rate could do exactly that which is why they only use "assisting paddles".

Edited June 21, 2012 by blackrose

[Nickhlx]

I know it's not what you meant, but I was using what you said to support my point.

 

What the engine manufacturers don't want is for hot coolant to return to the engine uncooled. A powerful pump, or a faster flow rate could do exactly that which is why they only use "assisting paddles".

 

Surely it all comes down to the rate of heat transfer is proportional to the difference in temperature of the two sides of the interface and the thermal conductivity of that interface ?

 

A faster flow rate of the hotter (or cooler) liquids on each side will try to maintain that greater difference, so the rate of heat transfer will increase with increasing flow rates on either side. ?

 

Nick

[blackrose]

Edit: I've just found this document and while I've only skimmed through it, it seems that you and Tim are right while me, Alan and others are wrong.

 

http://www.aip.org/tip/INPHFA/vol-2/iss-4/p18.pdf

 

They talk about increasing the flow because it increases turbulent rather than laminar flow which increases heat transfer. So there were other factors which none of us had taken into account.

 

So, if we accept that increasing the flow rate of the coolant will increase heat transfer and cool the engine more efficiently, perhaps I should just add a decent pump to my system and forget the expensive heat exchanger, raw water cooling etc?

Edited June 22, 2012 by blackrose

[RobinJ]

They talk about increasing the flow because it increases turbulent rather than laminar flow which increases heat transfer. So there were other factors which none of us had taken into account.

 

So, if we accept that increasing the flow rate of the coolant will increase heat transfer and cool the engine more efficiently, perhaps I should just add a decent pump to my system and forget the expensive heat exchanger, raw water cooling etc?

The problem is that it is a dynamic system and quite complicated!

The specific heat of the fluid tells you how much heat can be absorbed by a particular mass of fluid with a particular temperature difference, so in theory the more flow, the more mass, the more heat transferred. Heat transfer is not instantaneous and the transfer rate will tell you how much heat can be transffered in a given time over what area, so if you have a high flow rate and a small area, there will be less transfer than a smaller flow or a larger area. The answer is in balancing these factors to find the optimum, made harder by the fact that across the engine speed range, both flow rate and amount of heat are changing.

Engine designers generally over engineer with higher flow rates than required and larger pipes than necessary, so there may be a little leeway, however it is a bad idea to reduce flow, doing so will create a temperature increase, more expansion, but better heat transfer (provided you can stop it boiling)!

[blackrose]

If I buy the pump that I pasted a link to earlier (32 litres/min) and install it in my system to test the theory, should it be installed in the skin tank loop or can I install it in the calorifier loop which would be easier? I figure that if it doesn't work then I'll need the pump anyway when I buy the heat exchanger, etc, for raw water cooling.

[RobinJ]

If I buy the pump that I pasted a link to earlier (32 litres/min) and install it in my system to test the theory, should it be installed in the skin tank loop or can I install it in the calorifier loop which would be easier? I figure that if it doesn't work then I'll need the pump anyway when I buy the heat exchanger, etc, for raw water cooling.

And see if you get hotter water quicker?

[blackrose]

And see if you get hotter water quicker?

 

But if the calorifier loop is part of the same circulation system, then as soon as the thermostat opens I thought the new pump would circulate coolant through the skin tank? Since that's exactly how the engine's water pump works, then why would it be any different if I fit a more powerful auxillary pump?

 

What have I missed?

Edited June 26, 2012 by blackrose

[nicknorman]

But if the calorifier loop is part of the same circulation system, then as soon as the thermostat opens I thought the new pump would circulate coolant through the skin tank? Since that's exactly how the engine's water pump works, then why would it be any different if I fit a more powerful auxillary pump?

 

What have I missed?

Surely the pump will pump water around the path of least resitance, which is mostly around the calorifier loop and back to the engine, not through the skin tank loop. The engine's water pump is located in a different place, before the loops split into 2 (calorifier and skin tank loops). In fact if you drew a diagram I think you would see that the pump installed in the calorifier loop might pull water away from the skin tank loop and actually reduce the flow to the skin tank!

 

Just a thought, if you add an electric pump in the skin tank loop (which is the only place where it is going to make any difference), you are adding a layer of potential engine failure - if the electric pump stops working (no electricity, pump damaged etc) it will block the flow to the skin tank and the engine will overheat big time in a very short time. (I am assuming the pump is a vane type, not a centrifugal type from the picture).

 

Whilst I think it is true that increasing the flow might improve cooling slightly (as you have said, turbulent flow plus more of the skin tank area at the max temperature, hence maximising the heat loss), since you have said that the skin tank is fairly hot at the bottom I don't think it is going to make a great deal of difference. No harm in experimenting of course, but don't be too disappointed if it makes a barely detectable difference.

Edited June 26, 2012 by nicknorman

[homer2911]

I've now ruled out the thermostat being the cause of my engine overheating problems and I got in touch with the owners of a 60ft x 12ft LB widebeam (3ft longer than mine) with the same engine and same size skin tank who haven't managed to get their engine over 85C despite two trips at max revs (2000rpm) for an hour on the Severn estuary. So does that rule out the skin tank?

 

Tony Brooks mentioned that I might have a small head gasket leak, but the engine's been the same since it was new and it's only done about 600 hours. All engine services have been carried out as per the owner's manual.

 

I'm really running out of ideas how to solve this problem now - any help appreciated.

 

Mike

 

My apologies for lacking the patience to read every page oft his thread, but the following has been my experience of overheating.

 

We bought our boat 12 years ago, and the first time we ventured up the Llangollen the engine overheated when navigating the ChirkTunnel, and wasn't very happy on the Froncysyllte aqueduct either, the problem being a combination of excessive water resistance and lack of cooling capacity

 

I asked Oxley Marine, near Wolverhampton, to give me a quote for adding a second skin tank, but was persuaded instead to let them fit asimple steel pipe in series with the engine cooling system. The pipe travels out of the hull, along the swim towards the rear, in the corner formed between it and the counter, then turns and returns the other way down the swim before re-entering the hull and connecting again with the circulating system.

 

This simple pipe, no more than about 2 inches diameter, cured my overheating problem overnight. It seems that a great many boats are built with a totally inadequate skin tank!

Edited June 26, 2012 by homer2911

[Albion]

My apologies for lacking the patience to read every page oft his thread, but the following has been my experience of overheating.

 

We bought our boat 12 years ago, and the first time we ventured up the Llangollen the engine overheated when navigating the ChirkTunnel, and wasn't very happy on the Froncysyllte aqueduct either, the problem being a combination of excessive water resistance and lack of cooling capacity

 

I asked Oxley Marine, near Wolverhampton, to give me a quote for adding a second skin tank, but was persuaded instead to let them fit asimple steel pipe in series with the engine cooling system. The pipe travels out of the hull, along the swim towards the rear, in the corner formed between it and the counter, then turns and returns the other way down the swim before re-entering the hull and connecting again with the circulating system.

 

This simple pipe, no more than about 2 inches diameter, cured my overheating problem overnight. It seems that a great many boats are built with a totally inadequate skin tank!

 

You're quite right. In this case the diagnosis was made and a course of action to rectify it decided but now solution drift has set in again.

Roger

I used to be undecided but now I'm not so sure.

[blackrose]

Surely the pump will pump water around the path of least resitance, which is mostly around the calorifier loop and back to the engine, not through the skin tank loop. The engine's water pump is located in a different place, before the loops split into 2 (calorifier and skin tank loops). In fact if you drew a diagram I think you would see that the pump installed in the calorifier loop might pull water away from the skin tank loop and actually reduce the flow to the skin tank!

 

Just a thought, if you add an electric pump in the skin tank loop (which is the only place where it is going to make any difference), you are adding a layer of potential engine failure - if the electric pump stops working (no electricity, pump damaged etc) it will block the flow to the skin tank and the engine will overheat big time in a very short time. (I am assuming the pump is a vane type, not a centrifugal type from the picture).

 

Whilst I think it is true that increasing the flow might improve cooling slightly (as you have said, turbulent flow plus more of the skin tank area at the max temperature, hence maximising the heat loss), since you have said that the skin tank is fairly hot at the bottom I don't think it is going to make a great deal of difference. No harm in experimenting of course, but don't be too disappointed if it makes a barely detectable difference.

 

Thanks. I've decided that the hybrid raw water cooling option is too expensive and have told the fabricator to carry on making the skin tank. He told me he'll make it for 60 - 70 quid. I don't know if he wants to weld it in as well (with the boat in the water), or if a welder from work will do it, but if the welds crack then I won't connect it and just wait until the boat comes out the water to get it welded in properly.

 

I'll report back on the outcome.

 

My apologies for lacking the patience to read every page oft his thread, but the following has been my experience of overheating.

 

We bought our boat 12 years ago, and the first time we ventured up the Llangollen the engine overheated when navigating the ChirkTunnel, and wasn't very happy on the Froncysyllte aqueduct either, the problem being a combination of excessive water resistance and lack of cooling capacity

 

I asked Oxley Marine, near Wolverhampton, to give me a quote for adding a second skin tank, but was persuaded instead to let them fit asimple steel pipe in series with the engine cooling system. The pipe travels out of the hull, along the swim towards the rear, in the corner formed between it and the counter, then turns and returns the other way down the swim before re-entering the hull and connecting again with the circulating system.

 

This simple pipe, no more than about 2 inches diameter, cured my overheating problem overnight. It seems that a great many boats are built with a totally inadequate skin tank!

 

That's one solution, if you want to take the boat out the water and don't mind some underwater hull penetrations. I had considered it, but it's not my preferred solution.

 

You're quite right. In this case the diagnosis was made and a course of action to rectify it decided but now solution drift has set in again.

Roger

I used to be undecided but now I'm not so sure.

 

A course of action was decided and solution drift came about due to new information which I had been previously unaware (an ignorance I shared with the vast majority of contributors to this thread).

 

Delving deeper it seems that the new solution also has some potential problems and is also working out quite expensive, so I have decided to go back to the original plan but not necessarily expect it to work until the boat comes out of the water.

 

Personally I view flexibility in one's plans and taking onboard the advice of others as something positive. If I didn't then I wouldn't bother to ask for advice on this forum (even though I don't necessarily implement all the advice offered). I was just trying to find the right solution without wasting a lot of money.

 

Mike

Edited June 27, 2012 by blackrose

[bowten]

347 replies to your problem with a lot of members pitching in with good advice.I think it is praiseworthy to the forum as a whole.I am sure you will get the problem sorted with a little imagination and for not much money.The answer lies in one of the posts.Good luck with your problem and keep us all informed of the outcome.

[blackrose]

347 replies to your problem with a lot of members pitching in with good advice.I think it is praiseworthy to the forum as a whole.I am sure you will get the problem sorted with a little imagination and for not much money.The answer lies in one of the posts.Good luck with your problem and keep us all informed of the outcome.

 

Yes, I could never get anything like this many ideas and this much much advice from any other source. Brilliant.

 

I will let you know how it goes.

 

Thanks to everyone.

 

Mike