Engine cooling

[RayJones]

Has anyone come across this problem?
Yanmar 8hp diesel, cooling water from exhaust pipe stops flowing after 5 mins idling and shorter time at any more throttle. On restarting after a few mins engine runs perfectly and there is good flow from the raw water pump and from each hose in turn as they are removed with the engine running.And then the problem repeats. My theory..exhaust back pressure at the water injection point becomes stronger than the water pump pressure ergo no flow. The owner tells me the pump has been reconditioned but it still my main suspect. I will fit a spare new one for a test but would be interested in any feedback from readers. thanks in advance. I will keep you informed of further developments.

 

[ParaHandy]

Might be the water injection elbow? Thats where a lot of crud builds up. Yanmar recommend these be replaced every so many years. You could also try Yanmar engine forum at:
http://forums.sailboatspecialists.com/eThreads/view/Yanmar
You can do a search. Most often, somebody else has had the same problem.

Good luck.

 

[drawp]

I don't know what type of pump there is on a Yanmar, but when I had an intermittent failure of the flow of water through my Volvo MD11C engine, I eventually found that the cover of the water pump had become slightly concave. This must have allowed the pump to cavitate from time to time. All I did was file the outside of the cover flat, reverse the cover and the pump has run another 3 years and is still going. It might be worth looking at.

Best of luck.

 

[dah]

Peter, Could you do me a favour and look at a message I posted on 3 september 2001 re MD11c problems. You seem to have had a similar problem. The main difference being that my problems seemed to start when I changed my old pump cover to a Speedseal (coincidental??). The engine runs ok without a thermostat but probs start with one in place.

Thanks in Anticipation
Dave Hanna (DAH)

 

[drawp]

Dave. I think I have your answer as I also encountered your problem but at a different time! (Bloody engines!!!). Your problem is not related to the water pump but to blocked circ ports either in the exhaust manifold or in the engine block. What you have to do is to clear all the ports. Remove the manifold and soak it in an oxalic acid solution to clear the scale. Boots the chemists will sell you oxalic acid powder on special order. Don't ask me what strength to mix the solution - I just threw some into a plastic bucket of water and soaked the manifold till it was clean. On the engine block, remove the drain plugs and clean thru the circ ports with a length of wire while flushing with a water hose. Put it back together including the thermostat and the engine should run at the correct temp. I was advised to do this by Mike Pilkington of Pilkington Marine in Newton Abbott who certainly knows his stuff. Have fun.

 

[Trevor_swfyc]

Guess you have checked the intake side of the pump is not restricted. Both the filter and external hull inlet grid. If pump was faulty then you would probably not get it to pick up very well if at all. If you want to decalcify then dilute formic acid is very effective and can be obtained at a store such B&Q or Homebase. Works on the kettle a treat! (wear eye protection) and wash acid free with plenty of water.

Hope this helps,
Trevor

 

[scottie]

check that the exhaust hose has not been run without water and imploded causing restrictions

 

[dah]

Peter,
Sincere thanks, will give it a go and see if owt improves,
DAve H

 

[Guest]

Assuming this is a direct sea water cooled engine...
Maybe there is a blockage in the engine block water cooling channels perhaps behind the thermostat -my MD2 had this problem. When the thermostat is cool the water bypasses the engine block as goes straight to the exhaust, thus water flows. As the engine warms to running temperature the thermostat diverts water through to the engine block. If there is a blockage here the water flow will slow and perhaps stop. It may be worth checking behind the thermostat for a build up of black gunge.

 

[Guest]

probably not the problem, but do check the pressed steel pulley on the water pump. if this becomes at all loose, it quickly wears away the flat and the result is a pulley that only intermittently turns the impellor.

a worn pump results in the reverse of what you describe ie water flows when the engine runs fast but not at idle. i cannot imagine how waterways could be blocked to stop flow when warm but not when cold, unless they are blocked enough to reduce flow to the point where cooling water boils and comes out as steam when the engine warms up. does it?

suggest you remove the exhaust manifold and check the injection point. i had corrosion in this area which quickly caused corrosion between head and oilways with oil in the exhaust and no water, just steam.