Shredded impeller peril? Mariner 30

[HughN]

Hi,

My father has a Selva 350 with an oldish Mariner 30 on the back (I believe it is a re-badged Yamaha engine). It is a good combination that has been a lotof fun over the years.

The boat /engine hasn't been used too much recently (it needs tides, weather and the right people to all be right and I had some heart surgery which meant no boating). Discovering problems and then troubleshooting them is somewhat a drawn-out process.

A while ago the engine shredded an impeller. Only the hub and a couple of blades were retrievable from the lower unit - the rest had vanished. A new impeller didn't pump well so the engine went off for repair. The powerhead, middle-section and lower leg were separated and the powerhead stripped down and rebuilt. Because of one thing and another it didn't get used at all last year (I know, I know... ).

The engine starts well and pumps from the tell-tale. However, after being loaded for a minute or so the buzzer sounds, the warning light comes on and the revs drop (which I believe are all to do with an overheat being detected). The oil level (that can also trigger the warnings) is fine and the level sensor tests OK.

My theory is that somewhere there is a bit of impeller stuck in a cooling channel where it wasn't visible during the rebuild. Under load the water flow isn't sufficient to cool the engine properly. Is this a valid theory and if so, what (if anything) could be done about it? Suffice to say the work is out of warranty and the boat / engine are in a very awkward location (on a beach with no trailer access, etc.,).

Thanks
Hugh

[uncle al]

If I was doing the job the first thing I would do iis recheck the impeller, then try and look up the water pipe to the p/h looking inside as far as poss and the outside to see if there are any holes in the tube, if they look ok , then I would take of any covers that give acces to the water jacket on the p/h, otherwise it would be a major strip down and start again,Have you started it up out of water?

[HughN]

Thanks Al,

Yes, it runs fine on flushing-muffs - although it has mains water pressure behind it then which might help overcome any blockage.

I will get my spanners out...

[9D280]

I reckon your theory is pretty close.

Places to look first are where there are relatively small passageways and easily accessible openings - AKA the thermostat and /or Poppet valve (if fitted) They will be very easy to check by removing the housings.

Most engines have a permanent feed to the outer jacket of the exhaust -it needs to be kept cool whether it's idling or running flat out. Telltale usually taken from that subsystem as it;s always "open". Thermostat in essense deals wioth the rest of the powerhead, and the poppet valve (if you have one) Supplies "extra" cooling when the pump is spinning at high RPM - i.e at WOT (likely open about 1/3 throttle or so)


Another thought is if you have had helath issues, try talking to the place that fixed it. It's a long shot, but they may "bend the rules" with regard to warranty in these circumstances? If you donlt ask....

[HughN]

Thanks - I can feel a 'cunning plan' coming together.

Looking like I might die on the premises within the next five minutes should do the trick w.r.t warranties (and lots of other things). Perhaps I should also mention that "the Voices" told me to take the engine back to them!

[HughN]

Sorted (I hope).

I took the thermostat out and poured water in both directions - it went through the head and through the inlet with equal ease.

It still "overheated" after a few minutes.

I thought I cracked it when I found the wire from the temp sensor rubbing on the starter ring, but it still "overheated" after a few minutes.

Pulling wires off one at a time and restarting the engine on the water, it turned out to be the low oil sensor that appeared to be triggering it. There was loads of oil. A change of oil seems to have fixed it - the oil was being used and causing the float to drop and set the switch off. The filter was nice and clean but the oil might have been a bit on the old side and appeared not to be going into the cylindrical filter quickly enough to keep the float floating.

A good run at WOT went fine, so hopefully this is sorted.

The obvious is sometimes wrong!