Yet more MD11c problems

[Swanrad2]

My engine is overheating, the higher the revs, funnily enough the quicker it goes. I have checked the water filter and inflow- flowing OK, the engine does not seem to make much water from the exhaust however. I have changed the water trap, dodgy hoses, impeller and de-scaled the engine (at least I ran solution through it).

The engine still has the original filter which I guess could be slowing water flow.

This exploration is starting to cost a lot now, anyone got the most likely cause so I can fix that next and not randonly replace expensive bits of decent kit!

Ta

 

[Kurrawong_Kid]

Try looking at the exhaust elbow. A build up of carbon may have restricted the water intake. Try a screwdiver or skewer to dislodge it.

 

[Swanrad2]

Sorry, a bit of a beginner me, is the elbow the bit at the back of the engine that the arnoured hose connects to before going into the waterlock? I also but a bit of a swan-neck into the hose that goes to the exhaust on the stern (basically just bent over the hose into an upward curve)- could this be making things worse?

Again, thanks,

 

[Marsupial]

It sounds like the shaft of the raw water pump is worn out where the oil seal bears against it and/or pump chamber may also be worn, new impellers do not correct this. It means that the water pump sucks air not water and at high revs there is not enough water around to cool the engine, hence the lack of water in the exhaust. Check the pump spindal - (it will cost you nothing to check) - if its worn then a pump overhaul kit will be required.

 

[reeac]

No-one's mentioned the thermostat [I assume that the MD11C has one]. Had overheating on my VP2002 due to a thermostat that was jammed closed.

 

[VicS]

If the overall flow of water from the exhaust is low then check the inlet seacock and strainer (if you have a strainer above the waterline check its cover for air in leaks) all the pipework, including the gearbox cooler for restrictions. Also check the water injection into the exhast as mentioned. Perhaps also check the bypass in the thermostat cover.

Check the water pump, not only the impeller but the body for wear including the cover and the back. If there is any sign that the seal is leaking, indicated by water weeping from the tell tale hole on the body, replace that. (Note that if there is an O ring between the oil seal and the water seal it should be removed.)

Once the total water flow has been restored to normal if the engine is still overheating check the thermostat by slowly heating in water. It should just start to open at 60C and be fully open at 75C.

If that is OK the next thing to suspect are two small channels in the exhaust manifold that carry the incoming cooling water from the connection half way along the underside to the two heads. Take the manifold off and clear these with a stout wire. The one to the rear head in particular may take a bit of persistence to completely clear.

You cannot rely on the temperature gauge as you can have one cylinder running Ok while the other is overheating but get a near normal reading on the gauge so it is then important to check the individual cylinders and heads with a contact thermometer on a digital multimeter.

If you find high temperatures on one or other of the heads or blocks then you are down to a major strip down to clear the water channels in the heads or more likely the blocks. It may be that the only way to really clear these is to have the liners pressed out!

Some chemical cleaning may improve things but you will have to use an acid descaler circulated hot for some appreciable length of time by running the engine, catching the water leaving the exhaust and returning it to the inlet. Personally I would use an acid based based central heating descaler such as Fernox DS 1 or DS 3 but others will use hydrochloric acid. That is much more aggressive, will work more quickly and at a lower temperature but being much stronger could cause other damage.

 

[Kurrawong_Kid]

sorry I did not get straight back to you. The exhaust elbow is the bit just before thr pipe to the waterlock. There is a small pipe from the water pump that injects cooling water to stop the rubber hose catching fire! Carbon often builds up where the hot exhaust gases meet the cold water and this restricts the amount of cooling water flowing out from the jackets around the cylinders. Usually possible to clear!

 

[drawp]

There are drain ports at the bottom of each cylinder block on the starboard side of the engine. Remove the drain plugs [but be careful as they are made of brass and shear easily] and check if there is water coming out of them while the engine is running. If no water then the circulating ports around the cylinder liners are blocked. If water is coming out at least you know that water is circulating around the liners. Best of luck.

 

[Swanrad2]

Thanks all, with my abilities there goes sailing for the next year or so!!

Anyone want to buy a Centaur??