Beta 25- still some issues!

BigStu

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Joined
23 Apr 2014
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66
Hi all

I've posted before about my Beta 25 in my Cobra 850. I think I have a handle on what is going on now! The engine runs perfectly at 2000 revs, chugging along at about 75 degrees C. However, when I go to 2750 revs (or above), the temp rises sharply and gets to 95 Degrees before I bottle it and go back down to 2000 revs where the temp drops back down. If I run the engine with no load in neutral at 3000 Revs there is no problem and the engine remains at 85 degrees C, which according to Beta is the normal operating temp.

So there is clearly a problem with the engine under load. After it overheated when I first got the boat (which I can only surmise was a temp blockage in the system), I checked or replaced pretty much everything, tested the thermostat, cleared out the tube stack, tested water flow etc and all was fine. One thing I did not replace was the thermostat- but it opened fine about about 77 Degrees.

Any ideas on what I can do here? I still have 1250 revs to play with in theory and the engine should not really be overheating at that speed- but there is a sudden sharp rise in temp.

I have seen that these engines run close to the wire on here- but then I have spoken to, and seen many people who have never had any problems with them, and marine engineers seem to love them and never see many problems.

Any ideas on how to solve the issue or what the issue could be?
 

Tranona

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10 Nov 2007
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40,554
Can you get 3400 at least at full throttle? The reason I ask is because it could be that you are over propped and putting too much load on the engine at the revs you are using.
 

bluerm166

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29 Sep 2009
Messages
982
Replace the thermostat before proceeding.Maybe the opening is insufficient.
If it's a recentish engine can you quiz the previous owners/installer as to the commissioning behaviour.Current commissioning requires tests at no load/1/4 revs/1/2 revs etc to full revs. with speeds achieved so as to winkle out mismatched propping at the start of warranty.Compare props with other Cobra owners ?Is the shaft effectively lubricated ?
 
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ex-Gladys

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29 Aug 2003
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5,188
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Colchester, Essex
I've had Gladys for 10 years and have experienced variable engine temperature throughout. My temp gauge at cruising speed never goes above 70-75. When I run at higher speed I've always backed off, but last week, when I read page by page through the manual discovered thermostat doesn't start to open till 80 and is fully open at 102... I tried it last weekend and ran flat out for a stretch. Sure enough the temp went up and stabilized just below an indicated 100. Quite reassuring.

Not a Beta, but a Lancing Ford XLD...
 

spottydog

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18 Feb 2004
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280
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Norfok
I had exactly those symptoms on my Beta 14. You need to clean the heat exchanger stack tubes.
 

Tranona

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Leighb

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That is a good point. Think it needs a 3/4" intake. Many older installations with smaller engines had 1/2" intakes so important to change as there is not enough flow at higher revs with the smaller intake.

This seems a possibility, if the engineer/owner who did the re-engine did not check on the intake size. When I had a Beta 20 installed the engineer said that he had to replace the 1/2" intake, so would be even more important on the 25 I would think.
 

doug748

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That is a good point. Think it needs a 3/4" intake. Many older installations with smaller engines had 1/2" intakes so important to change as there is not enough flow at higher revs with the smaller intake.

Yes.
Getting that 3/4in, clear, throughout the run on an older boat is sometimes not as simple as it first seems. I doubt I have achieved it.
It is also possible to have a kink in a flexible pipe in some hidden spot.
 

BigStu

Member
Joined
23 Apr 2014
Messages
66
Thanks for all the help- I think I need to look at the intake and maybe a new thermostat.....
 
Joined
13 Jul 2012
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Galicia
Had the same issue on a Beta 20 the guys fitting it had not increased the water intake to the correct size, after going to 3/4 no more problems
 

Birdseye

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9 Mar 2003
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28,083
Location
s e wales
Hi all

I've posted before about my Beta 25 in my Cobra 850. I think I have a handle on what is going on now! The engine runs perfectly at 2000 revs, chugging along at about 75 degrees C. However, when I go to 2750 revs (or above), the temp rises sharply and gets to 95 Degrees before I bottle it and go back down to 2000 revs where the temp drops back down. If I run the engine with no load in neutral at 3000 Revs there is no problem and the engine remains at 85 degrees C, which according to Beta is the normal operating temp.

So there is clearly a problem with the engine under load. After it overheated when I first got the boat (which I can only surmise was a temp blockage in the system), I checked or replaced pretty much everything, tested the thermostat, cleared out the tube stack, tested water flow etc and all was fine. One thing I did not replace was the thermostat- but it opened fine about about 77 Degrees.

Any ideas on what I can do here? I still have 1250 revs to play with in theory and the engine should not really be overheating at that speed- but there is a sudden sharp rise in temp.

I have seen that these engines run close to the wire on here- but then I have spoken to, and seen many people who have never had any problems with them, and marine engineers seem to love them and never see many problems.

Any ideas on how to solve the issue or what the issue could be?

Assuming this is a fresh water cooled engine, the engine temperature should never be varying by 20 degrees and should never be running at 75 degrees. Like my car engine it should settle at somewhere like 90C and not vary very much. So there clearly is a cooling system issue.

Starting off at the beginning, do you have the right sized seacock and is the strainer ( if its the type with a grill on the outside) facing the right way which is astern. Is the seacock opening fully? Is the water pipre from cock to engine collapsing? Is it kinked? Is it the right size? Is there wear in the raw water pump / impellor? Follow on logically through every part of the cooling system taking nothing for granted. make sure that the temperature guage is indicating true.

Dont be worried about the diesel engine side of things. The reason you see the problem under load is because thats when you are putting more fuel through and more fuel = more heat. But if the load were excessive you would see black smoke out of the exhaust. No black smoke - likely the engine is doing its bit but the cooling system isnt. And I am far from convinced that your engine is overheating. As a unit used in small diggers it will be designed to run all day in the 85C 95C region. The bit that would concern me would be the 75C.
 
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