Overheating Bukh 20

Conachair

Conachair

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I have a Bukh 20 onboard, raw water cooled. I've had a lot of overheating problems. First time i thought it was the thermostat so I just took it out. Seemed to do the trick but then it overheated again (alarm goes off - about 94 deg I think). Temp guage not working so I keep an eye on the temp using a multimeter measuring ohms across the temp sensor, alarm sensor goes back to panel as normal. I put the sensor in a pan of water and slowly brought it to the boil with a digital thermometer making a note of the temp and ohms along the way. Seems to read slightly differently with engine on but I think it's pretty accurate. Now I have the pipe going from the Y split to the thermostat housing blocked so that all the water from the impellor goes through the engine which seems to work, runs about 50 deg C. Impellor seems fine. Before blocking that pipe the problem was intermittent, some days would be fine, very stable, anotherday it ran cool for a while, shot up to about 70 then back down again after, say, 20 mins. Engine was built in 1983. I attached mains water to the water input into the engine and ran it for a while with the output into a bucket to catch and crude, some what looked like sand came out with other bits of debris.
Any ideas? Problems occured between north of spain and portugal so sea temp pretty constant. (about 16/17 deg C if ST40 readout is to be believed.)

TIA

Padz - Conachair
 
Hi
I am not familiar with that engine but a common cause of overheating in raw water cooled engines of that age is salted up waterways. Particularly between the block and the head. The deposit is very hard - like the stuff they put on roads - and has to be dug or scraped out. You can still get lots of water thro' the exhaust bend but that does not mean much is going thro' the engine itself. Have you ever had the head off?
 
Don't be concerned about taking the head off -it really isn't that difficult. It provides an opportunity to clean the waterways and replace the cylinder head gasket, Bukh sell a kit of all the parts you need - and someoine has produced a little booklet with step by step guide. It makes a nice winter project !
 
Hi Andrew
As you say it is not that hard a job. I wish someone had done it to my now dead Volvo years ago before I bought this boat. The guys who replaced my engine said that long term overheating was one of the commonest causes of engine mortality.
/forums/images/graemlins/frown.gif
 
Re: Little Booklet

Hi Andrew

Where can one obtain a copy of the little booklet with step by step guide.

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Howard
 
Re: Little Booklet

Yes sorry my post wasn't very helpful telling you about something but not where to gte it from. I still have acopy but I'm afraid it is on the boat quite along way away, I will try and get it when I am next there. From recollection it was advertised at one stage through the Westerly Owners assoc. - you could try their Yahoo users group which is very active.

Regards
 
Why bother liftinn the head - the kit is expensive. Do a forum search on fernox and you will find several threads on chemically cleaning the waterways out - no need to dismantle.

Several forumite have followed the method I used with great success - give it a go - you know it makes sense...... /forums/images/graemlins/wink.gif
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Head never off to my knowledge. I is on my list, I need to take the engine out anyway to get at corrosion underneath so was going to lift it out, descale repaint etc.
From replys sounds like a problem with the waterways. I was wondering if the intermitent nature of the overheating might be caused by some debris getting dislodged and then getting stuck in somewhere else down the line.
But how does it know to overheat just as you go past a headland or come into a marina? Small squid whick likes it hot in there?

Thinks for the info guys.

Padz - Conachair
 
If it is the same as my DV10, then this is how I fixed similar symptoms.

The 'Y' piece which directs water to the thermostat or diverts it through the block gets clogged with salt water calcium deposits in the the form of a white sludge.

Take the pipe off and rod it through with a wire coat hanger for example and wash it in a vinegar solution of hot water.

Stage 2, inspect the block opening which has been revealed by removing the flange fastening the 'Y' piece pipe to the block - this is a larger rectangular hole giving access to the water galleries and most likely, as I did, you will discover a quite impressive build up of salt sludge which you can poke free and fish out then wash through with vinegar and water again-you may have to resort to something like the limescale remover recommended for dishwashers and washing machines if it is really thick , but most likely it will just be the orifice that's blocked.

Reassemble and that should be that
 
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