Silly Question - Thermostat?

A_Sails_Pace

A_Sails_Pace

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I’m finishing off winterising my Bukh DV20 and was about to check the thermostat, fill with antifreeze through the thermostat compartment before giving the engine a bit of a clean up.

Am I entirely wrong to think there should be an actual thermostat in this compartment? It’s my first winter owning a boat and so this is my first time accessing this area.

Any advice welcome.

Thanks
 

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The thermostat on the Bukh is double acting, simultaneously opening the flow to the engine and closing the bypass. Running without a thermostat can have the opposite effect of what may be intended, it causes the engine to run hotter, not cooler, as most of the flow from the pump goes through the bypass.
 
Thanks, gents. That’s what I thought. I was wondering why the previous owner may have run it without one and in the last half hour I’ve seen a few varying opinions online (interesting regarding the opposite effect it can have).

I too was running it for the last few months as well without knowing.
 
Wish I had a quid every time I heard someone in the old days say they'd thrown the thermostat over the side.

Drift: my bro in law was once told by his dad, correctly, that you could help an over hot engine by turning the heater up. Riding with him I noticed the engine is running cool, thermo failed, obs. But he thinks that a cool engine is good, and every time we stopped at a junction he's frantically fiddling with the heater, 'managing' the engine temp. Doubt it ever runs correctly.
 
A_Sails_Pace said:
Thanks, gents. That’s what I thought. I was wondering why the previous owner may have run it without one and in the last half hour I’ve seen a few varying opinions online (interesting regarding the opposite effect it can have).

I too was running it for the last few months as well without knowing.
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The thermostat was probably removed by the previous owner because the engine was overheating. The wrong thing to do as explained above.
You may find that descaling the cooling system is a task that lies ahead.
 
shortjohnsilver said:
When I had my previous boat - moody 29 - she had a Bukh 20 - great engine and never let me down, I used to buy my thermostats from Halfords matched a Ford escort apparently. Much reduced cost and worked a treat.
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That is useful to know. Provided, of course, that they operate at the same temperature.

Do they?

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shortjohnsilver said:
When I had my previous boat - moody 29 - she had a Bukh 20 - great engine and never let me down, I used to buy my thermostats from Halfords matched a Ford escort apparently. Much reduced cost and worked a treat.
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That is very surprising because a directly seawater cooled engine should be run at a much lower temperature than a fresh water cooled engine to avoid excessive scaling and corrosion

I would advise A Sails Pace to ensure that the thermostat is not only of the correct design but also opens at the correct temperature for a seawater cooled engine.
 
I would suggest you stick to the proper Bukh part, make sure is for the raw water cooled version. It is robust unit and has the correct shape at the top go restrict flows as Tranona has said. What you show on the picture is the bottom of the thermostat housing, the ,long bolt clamp the top housing and bottom housing to the cylinder head. I would suggest you take off the bottom housing and give it a good clean, Also have a look at inside of the head and clear any carbonate build up.
I don't know if I have been lucky but my thermostat has lasted at least 25 years.
I would steer clear of any car part that seems to fit as it was not designed for the needs of the Bukh engine.

David MH
 
davidmh said:
I would suggest you stick to the proper Bukh part, make sure is for the raw water cooled version. It is robust unit and has the correct shape at the top go restrict flows as Tranona has said. What you show on the picture is the bottom of the thermostat housing, the ,long bolt clamp the top housing and bottom housing to the cylinder head. I would suggest you take off the bottom housing and give it a good clean, Also have a look at inside of the head and clear any carbonate build up.
I don't know if I have been lucky but my thermostat has lasted at least 25 years.
I would steer clear of any car part that seems to fit as it was not designed for the needs of the Bukh engine.

David MH
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Tranona?
 
I'd be surprised if BUKH had thermostats specially made for its engines. It would have made much more sense to have designed the thermostat tower to fit an off-the-shelf one.
 
My bukh 24 was overheating. Always hovering in the fresh water scale red . Checked the stat , found it was embossed 60c , so correct raw water . Popped it in a pan and discovered it only open at 70 + . Was ready to order a replacement though decided to Heath Robinson it an compressed the lower section with a pair of grips .Re tested and its opening around 62c . I will get a new one before relaunch. I have also swapped out the intake from 1/2 " to 3/4" and new strainer.
 
Very insightful thread. Thanks again for the advice above.

I too have found some Bukh thermostats, but none cheaper than £100 unfortunately. Oh well, hopefully it'll just be a case of purchasing and fitting it, and fingers crossed there isn't any other issue for the previous owner binning the one he may have had prior.

Though one thing that has been niggling at me, and I don't know if it's linked or not. When I drained the raw water a few days ago, very little seemed to drain out. Or at least very little in comparison to how much antifreeze I have put in. Once I had filled the system with about 2.5 litres of antifreeze, I then opened the drain plug again to see if there was a difference after my clean-up/fill. This time it flowed perfectly and seemed to be pure antifreeze. This has left me wondering why there wasn't a larger quantity of raw water draining initially and whether or not this may be linked to the reason there was no thermostat in there. I feel better now that the draining flow is good, and it's been cleaned etc ( Previous Drain Plug Query )

Again, really insightful comments/advice above. Much appreciated.
 
A_Sails_Pace said:
Very insightful thread. Thanks again for the advice above.

I too have found some Bukh thermostats, but none cheaper than £100 unfortunately. Oh well, hopefully it'll just be a case of purchasing and fitting it, and fingers crossed there isn't any other issue for the previous owner binning the one he may have had prior.

Though one thing that has been niggling at me, and I don't know if it's linked or not. When I drained the raw water a few days ago, very little seemed to drain out. Or at least very little in comparison to how much antifreeze I have put in. Once I had filled the system with about 2.5 litres of antifreeze, I then opened the drain plug again to see if there was a difference after my clean-up/fill. This time it flowed perfectly and seemed to be pure antifreeze. This has left me wondering why there wasn't a larger quantity of raw water draining initially and whether or not this may be linked to the reason there was no thermostat in there. I feel better now that the draining flow is good, and it's been cleaned etc ( Previous Drain Plug Query )

Again, really insightful comments/advice above. Much appreciated.
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Had you taken the pump cover off first . You would drain a bit this way also.
 
VicS said:
The thermostat was probably removed by the previous owner because the engine was overheating. The wrong thing to do as explained above.
You may find that descaling the cooling system is a task that lies ahead.
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Engine was overheating due to the thermostat not working correctly or a bigger problem?
 
When you have installed a thermostat: remove the metal pipe that splits the incoming flow between the engine block and the bypass circuit. Its a bit of a fiddle to undo the bolts but you can do it with the flywheel in place. Make sure it has no blockages of either flow path, use an old coathanger wire or similar to ensure the bend is clear, Precipitates here have caused me oveheating issues in the past on a DV24.
 
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