Overheating

Overheating and power loss, could just as well be an engine problem, such as injection timing. Use the Vicprop calculator to find out what size prop you should have rather than just guessing that thats what is wrong. Bad fouling of both the prop and the hull can have the same effect, particularly if its coral worm fouling on the prop itself. There could also be problem in the drive train causing overloading.
 
Thanks for that, I take on board what you are saying but the main point of my suspicion about the prop is that the boat is going too fast at low revs. I don't think there is any power loss as the boat is more or less reaching hull speed, and then overheating. My experience of prop fouling is that the boat goes significantly slower.
 
SteveGorst said:
Thanks for that, I take on board what you are saying but the main point of my suspicion about the prop is that the boat is going too fast at low revs. I don't think there is any power loss as the boat is more or less reaching hull speed, and then overheating. My experience of prop fouling is that the boat goes significantly slower.
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You've obviously decided what you think the problem is.
The engine should not be overheating. End of.
For the prop to be your only problem, the pitch would have to be so far out that a couple of inches won't make much difference.
 
Thanks for your help I may indeed have 2 problems and I will deal with them both. I have ordered new heat exchanger parts from beta this morning... O rings anodes and bolts and will service that this weekend.
That may solve the heating problem but I do still think the prop is wrong and needs sorting as well. Its probably a combination. Perhaps I should be scientific and just fix one thing at a time with controls etc.
 
Hi I installed a new Beta 35hp which for best part of two seasons would over heat if run hard for long, I have change d the raw water impeller from a six blade to a ten blade cured the problem completely,
Mike
 
Thanks for that I will check which one I have this weekend. The dealer did put a new one in before I bought it but I don't know which.
 
lw395 said:
You've obviously decided what you think the problem is.
The engine should not be overheating. End of.
For the prop to be your only problem, the pitch would have to be so far out that a couple of inches won't make much difference.
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Suggest you read the original. It is not overheating at lower revs, only when it is overloaded by the oversize prop. A couple of inches of pitch is a lot. Equivalent to between 5-600rpm which is roughly what is happening. The pump is trying to put fuel in for greater rpm than the engine is capable of turning and some of this is being burnt so producing greater heat than the waterflow can dissipate. Hence the overheating - classic of oversized prop. Back off to 2000 and the cooling system copes. May be made worse by poor flow through the HE, but the underlying problem won't go away until the engine is allowed to achieve near maximum revs under load.
 
lw395 said:
According to the Beta datasheet, peak torque is at 2100rpm and 35hp is at 2800rpm. Or is that a different engine?

I still suspect there is more than a pitch problem here.

I would find out what prop you have
try that with the engine data in the various prop calculators
does it stack with reality?
i.e do the models agree on 5.6kt @2000 rpm and 6 @2300?

You can do this manually, by estimating the drag of the boat based on its lwl etc, and a set of prop graphs from a suitable book.
If you look at the numbers, the prop is only slipping a small amount more at the higher rpm. This may not be consistent with too much pitch?
Is there a lot of blade area? Is it a 3 blade?

It would be galling to cut metal and not cure the problem, so doing the maths first would be my approach.
I object when people leap to the conclusion of wrong prop with spares information, as you may have guessed.
(I also believe all sailing boats should have folding or feathering props of course.)
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This is my Nanni 37.5, same base engine as the red engine
Max torque is @ 2200 RPM
I normally cruise @ 2k

 
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Tranona said:
Suggest you read the original. It is not overheating at lower revs, only when it is overloaded by the oversize prop. A couple of inches of pitch is a lot. Equivalent to between 5-600rpm which is roughly what is happening. The pump is trying to put fuel in for greater rpm than the engine is capable of turning and some of this is being burnt so producing greater heat than the waterflow can dissipate. Hence the overheating - classic of oversized prop. Back off to 2000 and the cooling system copes. May be made worse by poor flow through the HE, but the underlying problem won't go away until the engine is allowed to achieve near maximum revs under load.
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agreed
 
Tranona said:
Suggest you read the original. It is not overheating at lower revs, only when it is overloaded by the oversize prop. A couple of inches of pitch is a lot. Equivalent to between 5-600rpm which is roughly what is happening. The pump is trying to put fuel in for greater rpm than the engine is capable of turning and some of this is being burnt so producing greater heat than the waterflow can dissipate. Hence the overheating - classic of oversized prop. Back off to 2000 and the cooling system copes. May be made worse by poor flow through the HE, but the underlying problem won't go away until the engine is allowed to achieve near maximum revs under load.
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I'd expect some black smoke if that were the case.
What actually matters is whether the engine is delivering anything like rated torque or power at the RPM where overheating is happening.
Much better to understand that than to remodel the prop around a potentially sick engine.
 
lw395 said:
I'd expect some black smoke if that were the case.
What actually matters is whether the engine is delivering anything like rated torque or power at the RPM where overheating is happening.
Much better to understand that than to remodel the prop around a potentially sick engine.
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Well, it won't be producing the power because it is not achieving the revs - nor the speed. The prop is wrong and needs sorting as it currently peaks at 1000rpm less than it should. It may well be producing black smoke, but if I remember rightly the exhaust exits under water which will disguise this.

If it was just a cooling problem one would expect it to occur at the 2000 rpm the OP uses as the engine is well loaded at that point. It is not the overheating that is preventing it from achieving revs, but the prop.
 
SteveGorst said:
yes it is a three bladed propeller. I dont think it is slipping as such just working too hard at low revs. It looks like it is reaching its peak torque but not managing to get past that. I thought I had read somewhere that it was supposed to reach 3600rpm as my old beta but it appears the 38 is 3600 and the 35 is 2800 so it may not be as bad as I first thought prop wise.

I definitely will check all the water supply possibilities. I have cleaned debris from the heat exchanger inlet but not actually taken the heat exchanger out to check the tubes. I'll put that on the list for this weekend. Also the propeller may be covered in Barnacles so I may dry her out against the wall and see.
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Check the inside of the water pump, the cam that the impellor lobes bend against to pump actually wears. If it is worn then this can cause overheating. Was reading an article the other week about it, cant remember where though!
Stu
 
Another test that may be worth doing, bollard pull.
What will it rev to with the boat tied to the dock?
If you can measure the pull as well, that would give something to feed into a prop model.
 
Ok further developments. When I bought the boat I sent the following email

On the trip up the Lough and back she did overheat on the way back at 2000 revs. 5.5 knots which is cruising speed really.

Could you change/inspect the impeller and clean out the heat exchanger cylinder and fit a new anode.

and received the following bill

Attend boat at Gallanach. Inspect for leaks at fuel system. Leak at fuel bleed nut on top of secondary filter. Replace fuel filter. Bleed system and tighten nut. Remove tube stack.
Clean tube stack and end caps. Replace anode.
Re-fit with new O rings. Re-fill coolant. Run up
and check over. OK.

So when the engine continued to overheat although at slightly higher revs I was puzzled.....

This weekend I took the tube stack out and found it 80% blocked. Cleaned it out with brick acid and its nice and shiny now but I am a bit p****sed off.

On the bollard pull I only got 1800 revs, No overheating though.
 
SteveGorst said:
Ok further developments. When I bought the boat I sent the following email

On the trip up the Lough and back she did overheat on the way back at 2000 revs. 5.5 knots which is cruising speed really.

Could you change/inspect the impeller and clean out the heat exchanger cylinder and fit a new anode.

and received the following bill

Attend boat at Gallanach. Inspect for leaks at fuel system. Leak at fuel bleed nut on top of secondary filter. Replace fuel filter. Bleed system and tighten nut. Remove tube stack.
Clean tube stack and end caps. Replace anode.
Re-fit with new O rings. Re-fill coolant. Run up
and check over. OK.

So when the engine continued to overheat although at slightly higher revs I was puzzled.....

This weekend I took the tube stack out and found it 80% blocked. Cleaned it out with brick acid and its nice and shiny now but I am a bit p****sed off.

On the bollard pull I only got 1800 revs, No overheating though.
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Did you pay for that work and do you still have proof of that?If so I think you may have a significant claim against whomever failed to carry out the work.There is a safety factor here as well given that the engine may have failed at a time when you most needed it-----?
Might be worth showing this thread to relevant party.
 
SteveGorst said:
Ok further developments. When I bought the boat I sent the following email

On the trip up the Lough and back she did overheat on the way back at 2000 revs. 5.5 knots which is cruising speed really.

Could you change/inspect the impeller and clean out the heat exchanger cylinder and fit a new anode.

and received the following bill

Attend boat at Gallanach. Inspect for leaks at fuel system. Leak at fuel bleed nut on top of secondary filter. Replace fuel filter. Bleed system and tighten nut. Remove tube stack.
Clean tube stack and end caps. Replace anode.
Re-fit with new O rings. Re-fill coolant. Run up
and check over. OK.

So when the engine continued to overheat although at slightly higher revs I was puzzled.....

This weekend I took the tube stack out and found it 80% blocked. Cleaned it out with brick acid and its nice and shiny now but I am a bit p****sed off.

On the bollard pull I only got 1800 revs, No overheating though.
Click to expand...

When you did the bollard pull, was there any black smoke? or black bits in the water coming out of the exhaust?
I assume this was after cleaning the heat exchanger?
As the heat exchanger was so bad, I would suggest that the exhaust mixing elbow might be in need of a clean too?

I am still inclined to suspect the engine may be down on power due to a fuel starvation issue or similar.
Although a heavily fouled prop and hull or the wrong prop are still possibilities?
Possibly the deposits in the heat exchanger show your area is rich in calcium, ideal for growing barnacles on the prop.?
 
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