Water flow problems

[SteveGorst]

I've got a really strange problem with the engine at the moment. When pushing the tide at full revs after a few minutes the overheating alarm goes off. Our manual suggests that we should check our impellor and thermostat so first we did the impellor and as the problem persisted we then did the thermostat. Once i'd got over the price of a volvo thermostat we tried her again and it is still over heating. We were booked to go on a cruise this weekend so I got an engineer to look her over and we ran her till the alarm went off but apart from the sound of the alarm there was no real sign of overheating or distress in the engine so we decided to just take it easy and check out the sensor when we got back.

Thats the background and when we did the cruise we found a level of throttle that allowed us to make good progress without the alarm sounding. However after a period of sailing with the engine switched off we started the engine and the exhaust had the dry throaty sound and the alarm went off more or less straight away. Hardly any water was circulating. We switched off the engine and sailed up the estuary back to our mooring and just used the engine for mooring up. Again the dry throaty overheating.

Now the confusing bit. After leaving the boat on the mooring for half an hour I started the engine again and the water came through just fine. I tried it again this morning and the water was coming through fine again. I have dried the boat out recently so am sure nothing is obstructing the water intake.

Can anyone think of anything that may cause these symptoms?

The engine is a volvo 1982 MD5C with a saildrive leg.

 

[[2068]]

Check the pump face isn't worn or there isn't a loose hose on the inlet side of the pump - this can cause it to suck air instead of water at high rpms or after stopping for a bit.

 

[VicS]

Hose(s) deteriorating internally, collapsing and obstructing the water flow while appearing Ok externally?

 

[PembrokeshirePromise]

Friend had a boat where one of the cooling hoses was replaced with substandard rubber - all was fine when cool but collapsed when it got hot restricting flow.

I appreciate it doesn't quite explain why you had a problem after extended sail - but maybe hose could stay collapsed ?

Difficult to trace - as involves looking at engine at point you have the problem (e.g. after 30 minutes motoring or so)

Just a suggestion ...

 

[SteveGorst]

The water hose collapses when it gets's hot... Now that could be something as when we run it on the pontoon the flow always looks fine and increases with the revs, the trouble is when it does overheat we're at sea and can't see the outlet as it discharges beneath the overhanging stern. I have looked into the engine compartment and felt the pipes and sniffed the engine and if it is really overheating it is ceratinly not by much. The pipes look fine externally so maybe it could be a partially collapsing internal lamination of the inlet pipe. Perhaps as we are sailing there is some negative pressure put on the inlet pipe due to the flow of water past the hull, causing it to collapse. It's worth a try anyway and I'll check for air leaks at the pump as well while I'm at it. The inlet pipe is only a push fit into the pump so I may put some sealant around it to be sure.

 

[2Tizwoz]

Is your saildrive leg water entry obstructed ?

I have had problems with growth inside the leg on ocasion. Cleared it with a mains hose connected to the valve on the saildrive while still afloat. its rather difficult to antifoul the inside of a saildrive leg. Maybe someone has found a cure ?

 

[SteveGorst]

we haven't got a hose on the pontoon so i tried connecting a dinghy pump and backflushing it. We did lift her out this winter though and give the inside a good clean, it was full of mussels. The overheating problem started so early in the season I wouldn't have thought there would be any fresh growth but when I'm near a hose i'll give it a go if the new inlet pipe doesn't solve the problem.

 

[sailingrbg]

Re your problem with growth on your sail drive, I seem to be having a similar problem to that described above. Can you advise where the water inlet on the sail drive is. I had my boat lifted out a fortnight ago to get work done on a faulty sea cock an notices some small musscels shells on the side of the sail drive (there are three flared indentaions on either either side) is this the sea water inlet on the sail drive or is there another through hull fitting. I have only had the boat for a few months so am still finding my feet any help or assistance would be greatly appreciated

Regards

Ross

E-mail rossbagordon@yahoo.co.uk