Engine overheat - long term damage?

[gtmoore]

Hi all

I have a Betamarine 20hp engine fitted to my boat and was using the calm conditions today to practice some mooring techniques when the engine temperature alarm started to sound. I quickly stuck the boat in the nearest empty pontoon berth and shut the engine down. After opening the engine compartment I was expecting lots of steam or something but all seemed well although I could tell that the engine was hot. First port of call was the strainer - this was completely stuffed full of bright green weed. I cleared this then checked the impeller which appeared to be fine. After leaving the engine for about ten minutes I fired her up and all appeared well as it was after running for a further half an hour.

I'm not sure at what point the engine alarm goes off - my only experience is with car engines that sometimes when 'cooked' are never quite the same again. Does anyone know if I am I likely to have caused some long term damage to the engine or does the temp alarm go off before this happens? I think I may be investing in an exhaust temperature alarm that would have alerted me to the problem probably quite a bit earlier

Thanks


<hr width=100% size=1>Gavin

 

[webcraft]

You are joking, aren't you? The alarm is so that you DONT damage the engine. It worked. You reacted immediately. The cause was obvious. Once fixed it worked perfectly.

Surely there must be something worse to worry about on your boat. If not, then you are very lucky.

Diesels are remarkably tolerant. I seized mine last year when the impellor broke up and I didn't notice.; it just stopped and wouldn't turn over. Took me half an hour to change the impellor, by which time the engine had cooled enough to unseize and restart, apparently none the worse for wear.

- Nick


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[cliff]

Mine did the same twice due to loss of coolant. Alarm goes off - stop the engine and find out why.

The alarm in 20 hp beta goes off at around 115 deg C at which point you still have coolant (50/50 glycol/water) in the engine water jacket and exchanger. This mix will not boil off until around 125 degC so plenty of margin to stop the engine and fix the problem. BTY the sensor in located in the exchanger so you are reading exchanger temp.

All I would do is drain the coolant and replace with fresh 50/50 mix of glycol and water to ensure the proper mix is maintained. The glycol not only acts as a corrosion inhibiter / antifreeze but raises the boiling point of the coolant. DO NOT EXCEED 50/50 - too much glycol will rot the rubber bits.

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[MarkJohnson]

As previous posts, you have saved any significant damage to your engine. I also seized a Bukh through lack of oil many years ago. I booked the mechanic to take it to bits, but he just turned the flywheel backwards and the engine unseized. It lived for several years, though was used a lot oil subsequenlty.

What you might look at, if the water inlet was blocked, is the mixing box where the water cools the exhaust. These are often made of plastic, Without the cooling water the plastic might melt, and break the exhaust system. This might fill the engine compartment with fumes, and it allows water (when you fix the blockage) to fill the engine compartment. (done that as well!)

Give the system a good check out.

Regards

Mark Johnson


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[Althorne]

Although a bit abrupt in his answer webcraft is absolutuly correct in the mechanical part of his reply. The alarm system is designed to prevent any damage and as you's works properly all will be well. Not everyone understands mechanics, nor should they need to and those of us who do can sometimes be a little intolerent of others. I'm sure you have a forte.
Use your engine with confidence and keep up the practising. Might be very useful
one day.

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[gtmoore]

Thanks to everyone for their replys - you've certainly put my mind at rest.

My knowledge of marine engines is limited to servicing and general maintenance as per the manual although I am trying to expand this and did remove the engine this winter with a friends help to replace the engine mounts. I didn't have any information regarding what point the overheat alarm goes off but now I do I'm much happier about what happened.

Regards



<hr width=100% size=1>Gavin

 

[tcm]

Re: vacuum alarm

agree with this.

But as well as a temperature alarm (which measurest hat the coolant is too hot) it would not be a bad idea to have a vacuum alarm - which would show that the pressure of the inlet coolant was too high cos of a blockage or summink - and which would then lead to overheat.

20hp engine is not reallt gonna have a probleem with a bit of overheating. Supertuned hig-revving petrol engine mostly certainly could be busted tho with overheating.





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[AndrewB]

As others say, the engine alarm is there to save the engine. The commonest fault is a blocked inlet, but dumped coolant (specially from a heat exchange system) and a failed pump are also common.

If the engine was running for a while with restricted cooling water it is just possible to do damage to the exhaust hose, even though the engine is fine. Typically this is separation of the inner part of the pipe from the outer, so superficially it looks OK. If there is any loss of power as you open the throttle next time, undo and check the hose particularly where it first leaves the engine.

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[Aja]

When I fitted my new engine a couple of years ago I was advised to fit the type of anti-syphon valve which gives a small discharge from the valve.

I put this on the stern and now just have to glance to see what the water stream is like. I can tell if there is weed in the strainer if the water flow is less than it should be. It is not a replacement for an exhaust temp alarm but a great indication that water is flowing through the engine.

Donald

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[gtmoore]

Donald - I think I have this kind of valve fitted as it is piped into a small tee in the exhaust piping. This is near the exit which is an underwater skin fitting hence I have no idea if water is flowing through the engine.

I guess I could connect this to an above water transom fitting instead to give me an idea that water is indeed flowing.

Thanks

<hr width=100% size=1>Gavin

 

[Aja]

Careful. There are two types - both made by Vetus. One is as you describe which takes water after the inlet pump and goes up over the highest point in the engine (and above the water-line) to an anti-syphon valve then the water goes back down to the exhast manifold where it joins the exhaust proper.

The type I have has this set up as well - in addition there is a small outlet from the anti-syphon valve with a pipe leading to a small skin fitting - in my situation on the transom.

Hope I have described this ok. I dont think you can lead the 1st type to a skin fitting. I could be wrong....

Donald

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