flushing the engine - a short story.

[EASLOOP]

I have a raw water cooled BUKH DV10ME, circa 1975ish. I have abused this poor engine but like a faithful dog it sticks by me through thick and thin. This year I decided to give it a treat and flush out the engine with fresh water and anti-freeze and mabye later when I get some redylyme some of that as a second 'treat' as well. Anyway, with the boat ashore I drained the engine. I filled a bucket with fresh water and placed this on the cabin sole up next to the flywheel. I disconnected the water inlet hose from the stopcock in the hull and put the end of the hose into the bucket of water. I then started the engine. I expected that once the running temperature had been reached the engine would start sucking up the water into the water jacket. I planned to keep the bucket topped up with fresh water as the coolant was squirted out of the exhaust thus using up the fresh water in the bucket. However, after a while all i got from the exhaust was steam at frighteneing levels. I stopped the engine in a panic before it could seize. Thinking conventionally (per car engine) I decided that the thermostat must be knackered. I took that apart and looked down the hole. All I could see was bone dry metal - no sign of water? The impeller was whizzing around nicely but not sucking up water and the thermostat was working well. In the end I put the bits back to gether, held up the water inlet hose so the open end was at or above the waterline and poured fresh water down the hose via a funnel. The engine soon filled with water and it sqirted nicely out of the exhaust when it got back up to temp again. I then filled it with antifreeze using the same method, closed up the water inlet hose and stopped the engine. It is now full of a strong solution of antifreeze that I hope will slowly clean the water channels.
After anguishing over this I began to realize that when afloat and the cooling water inlet stopcock open the water level in the engine would rise instantly to near the top of the engine, at the waterline. The impeller would push this water around the engine obeying the requirements of the thermostat.
In conclusion I seems to me that the impeller cannot create the sort of vacuum necessary to suck water up out of the bucket in this setting - the cooling system requires there to be water already available for the impellor to work. There is no 'water pump' per se, only the impeller.
Is my conclusion right or is there a water pump somewhere I am missing that has the capability to 'suck up' the water from below the waterline? I have heard others say they use a bucket of fresh wtare and flush it through the engine. Or am I being a bit 'tup'.
Looking forward,as always, to your esteemed views.

 

[Rivers & creeks]

I had the same engine on a Macwester and the impellor had no trouble doing this - I would flush either using a bcket on the cabin sole or a bucket under the keels with a bit of hose jammed into the inlet (3 foot of lift required). I can't think what's wrong - is the impellor new? Is the spindle worn? Or maybe the hose has a tiny hole or crack so that air is sucked when the water level is much lower (i.e. when using the bucket). If I were you I'd investigate as it maybe a sign that something is near to failing.

 

[davidbains]

Many pumps will not suck unless primed with water first. Apparently a new or smoothed cover plate over the impellor can improve the seal.

 

[Krusty]

It sounds as though your raw-water pump might have needed a new impeller: now it almost certainly does!
Possibly a replacement cover-plate too.
Running these pumps dry is very damaging unless the impellers are first lubricated with a smear of grease, olive oil, etc. and the the dry-run time kept short; i.e. measured in seconds, not minutes.
I found out the hard way!

 

[awol]

I once spent a nauseous half hour replacing an impellor on a Bukh in a windless swell. It was on the third attempt, after I had liberally coated the cover plate with grease, that it finally began to suck water again. Once it was wet, though, it never had problems again.

 

[EASLOOP]

It seems either my pump is knackered or there is an air leak somewhere. Guess it is going to take some investigation to find out what is happening - ugh!

Thanks everyone for your help.

 

[fireball]

Our Yanmar had the same problem when we flushed through - replacing the impellor was enough to resolve the problem - the old one couldn't create enough suction ... but the new one could .. simple and cheap to resolve! Hope yours is the same!

 

[smeaks]

The impellor is a pump. As already stated it is not a self priming pump. Imagine a positive displacement pump, like a big piston with a couple of simple valves. That is a self priming pump and as it works would create a vacuum and air pressure would then force the fluid up the delivery pipe into the inlet and the pump would merrily shift the fluid along. These pumps rely on the fluid being present and it is the movement of the fluid through the pump that both primes and helps seal and lubricate the pump.

Best thing is you sussed out an alternative method and i bet if your engine had a tail it would be wagging... all this attention!

 

[nightjar]

In addition to checking the cover plate on your pump for wear, have a close look at the cam plate inside the pump. The cam can be removed by undowing the screw that holds it to the pump housing. Inspect the cam which should look the same colour over its width. Any dull areas indicate the impellor is not making contact due to uneven cam wear so poor or no suction. New cam will cure the problem I think.

 

[PeterGibbs]

With the engine turning, put your thumb over the pipe you've attached to the raw water pump. Is is sucking? If not, change the impeller, and be sure to seal the face plate well (Vaseline and paper seal) to give the thing a chance. Also check the back of the face plate - if heavily scored by the impeller, rub flatter with fine emery. Eventually, if the plate has taken a lot of wear over the years it may require replacing. Also check the "wedge" is firmly in place inside the pump - this is the piece that displaces the rubber impeller blades as they rotate and creates the suction.

Of course, if there's any distortion, or cracking in any of the impeller blades, it's time for a new one. Likewise, if the tips of the blades are other than rounded and "full bodied"

PWG

 

[PeterGibbs]

A final thought about flushing: on my Volvo the perceived wisdom is flush and leave filled over winter with quality antifreeze - 50;50 mix.

When I had a Bukh I bought some Volvo winter inhibitor fluid -and ran that through until the engine was warm and the thermostat opened. Some make their own flushing fluid with an oil and water mix, run it through on a continuous loop from the bucket, and finish off with the antifreeze.

PWG

 

[seascape]

on the subect of flushing/descaling bukh engines(dv20) whats best stuff to clean out any built up gunge?
also:
once heard of a trick to drill a small hole in the thermostat(which bit of it?) to release a build up of pressure.can anyone enlighten me?
sorry to interupt!

 

[Avocet]

That's odd. Mine is out of the water at present and I periodically fire up the engine to give it a bit of a run, get the oil round it and use it as a bilge pump to empty the rainwater out of the bilges! As the boat is long-keeled, the lowest part of the bilge is nearly 4 feet below the water pump and it always self-primes pretty much instantly. In fact, there's one hell of a suck on it! All I can think of is that there may have been a tiny air leak on the suction side - possibly if you'd joined two hoses?

 

[Taffy]

Hi,

I do this every year when the boat is lifted out. I expect the basic problem was that I always have to prime the hose that is connected to the pump. If the hose is just connected when empty, the impeller is not able to suck water up and fill the hose but will still be able to empty the water that is already in the engine so before long everything is dry.
The impeller could then be damaged but it depends on the quality and age.
So I immerse the hose in the bucket to get all the air out before connectin it to the pump. Keep your thumb over the end to prevent the water running out as you lift it.
I would certainly change the impeller after running dry just to be safe.