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over heating engine

by betty boop » 20 Jun 2018, 13:33

Here goes on a long story. 4.3mpi alpha Gen 2 - engine was fine in the water at torquay. got it home on the muffs and no water - engine over heat, not going to mention the crack sound 5 mins after I turned her off). manifolds v hot. no water out the back.

Thermostat change - but wasn't the cause, wont be manifolds as the problem was almost instant, she was running on muffs before torquay fine up to temp and another 20 mins no problems.

leg off / impellor is fine no damage. so is back on - engine started and still very little water getting to the engine but only ran it for 15 seconds before shutting down with pulley off the engine pump spines fine no issue as well - so not the problem.

I'm due to finish the rebuild tonight from another broken water part that wasn't related to this problem but just about at the end of logical thinking if nothing is improved tonight when I refill her and start her up.

Luckily weekends have been busy elsewhere so only 1 was lost but any more and I'll get withdrawal symptoms.

cant figure out why she was fine Tuesday AM in Torquay and then on muffs has no water out the exhaust - so any thoughts you wonderful people. - and don't mention the crack I'm ignoring it for now.
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by shibbs » 20 Jun 2018, 13:54

I would start by checking all internal hoses for blockages, starting at the transom and work forward until the manifolds.
Also, the impeller might be ok but have you checked that it is turning..? Might be linked with the crack. If it’s not turning you won’t get any water pumped. Just a thought..?
Good luck. Keep us posted with progress.
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by Ianfs » 20 Jun 2018, 18:48

no water - engine over heat,


engine started and still very little water getting to the engine


On inspection was the key which enables the impeller to turn on the drive shaft in place? :D

Further, now don't get cross , but was there good water flow from the tap? i.e. water spilling out of the bellows before start? I am cowering under the desk at this point! :shock:

A good test for a blockage which may have happened whilst out on the water on the last run in Torquay would be to pour water down each hose, you will here it filling the block, it should run out of the inlet in the leg. If it doesn't then you have a blockage, the hoses will overflow. By filling each hose in turn will tell you roughly where it is.

At a guess if it is a blockage its likely to be where the power steering cooler is in the inlet pipe.

Other test is to fire her up, having disconnected the outlet hose to the water distribution housing to see if thats blocked, then if thats fine, the outlets to the water circulation pump and so on. But as you know only run the engine for a short time on each occasion.

After that, not sure. :?
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by Xboatboyx » 20 Jun 2018, 19:57

I would also say that running it on the muffs could be overheating it. I know our boat has run hotter on the muffs than in the water. I would try running it in a river and see what its like before spending more money.
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by betty boop » 21 Jun 2018, 10:13

So - no laughing but here's what happened. Answers above all checked in advance but thanks anyway always good checking- advise on the Muffs James is spot on, never trust the results on muffs - there is subtle pressure differences between hose pipe and in water that make left and right risers heat up differently - been told this and experienced it too (after I've panicked over it off course)

So new thermostat fitted and all the pumps back on the belts tightened etc. leg in full down position, transform hoses checked etc.

1, hose pipe down the main water feed pipe at the thermostat housing. filling the engine with water and blowing out the thermostat itself.

2, cut the end off the new hose, bought from toolstation with new brass non drip, push fit hose connectors.

3, start engine- with a spare pair of hands holding the hose clear etc.

She works and behaves fine. water pours out of the exhaust like there never was a problem. Engine heats to 1/4 range and no higher for 20 mins at 1000 revs.

SO what was the issue. blockage? I cant be sure but would say I doubt it, the alpha intake is small and torquay marina pretty clean/deep.

The service book doesn't say to back fill the block with water when fully drained but there is a chance (logically thinking) of a air bubble/ minor blockage but I would do that again just in case it happens again.

OK who spotted the new hose and connectors? In February I got a new hose and borrowed an unused hose reel from a local golf course. Toolstation aren't my best friend at the moment for quality as some products are - lets say CHEAP. their brass hose fittings worked fine on the garden but the stop/check value on the spray nozzle concerned me. so as a process of illumination the hose was cut and returned to basic plastic Hozeloc connectors and no drum. Obviously I'm not stupid (no really!) and there was water flowing from it before BUT it could be argued that the check valve disagreed with something, Either way I wont be using it again just in case. For now it is a mystery, what caused it I'll never know and I'm too stressed to want to find out. Onwards and upwards for 2 weekends away - possibly Southampton to Poole Via Lymington or the Norfolk Broads- not sure as I'm yet to be told. ;)
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by mlines » 21 Jun 2018, 11:13

Ah, non-drip/non return hose adaptors.......say no more
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by Ianfs » 21 Jun 2018, 11:36

Further, now don't get cross , but was there good water flow from the tap? i.e. water spilling out of the bellows before start?


Arrrrr not such a bad idea after all eh? He said with his head getting bigger and with a smug tone. :lol: :lol:

Funny thing, last year we changed from gravity fed water in the house (tanks in the loft and all that) to a fully pressurised system. Wow, no shower pumps and water flow over the whole house vastly improved and no tanks in the loft anymore. Except the outside tap flow still didn't represent the available pressure. Plumber said, it might be the tap, I said yeah right pull the other one, he said no really and changed it. My hat got eaten immediately. :lol:

So James's idea of the muffs might mean that the water pressure from the tap is not as it should be. Good call though.

One last thing I ought to add is that Mercruiser say not to turn the tap on fully when on muffs for fear of dislodging muck and creating a blockage. After this topic, I would say a lot depends upon water pressure and if you've been sold a non drip/non return adaptor. :D
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by lewlew100 » 21 Jun 2018, 12:51

I am so glad that you have managed to get it sorted Ian. Enjoy your forthcoming trips. Geoff.
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by Bigplumbs » 22 Jun 2018, 04:27

Well done Ian really glad you have it sorted and a simple fix in the end

Makes perfect sense also now you think about it

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by betty boop » 26 Jun 2018, 08:52

as you'd expect on the river it was fine - changing the thermostat has confused me a little though. where as the temp gauge was at 1/3 all the time now the temp gauge sits at 1/8 of the gauge - if I stare long enough the needle rises and falls but not much but looking and driving is multi tasking and I cant do that. One 2 occasions the gauge went to 1/2 rapidly then fell just as quick - I guess that could be weed as we were in the river Cam - biggish river but very quite so a little over grown etc.

worth worrying about? Repower said the stat was for this engine (4.3 mpi) but wondering if I should put back in the old one and keep the new as a spare.

Only ever changed one before on the last boat (3.0l) the stat went a bit wild until 'settling in' after a few trips no idea if that's normal or me looking for something to go wrong as one does after a problem. Off to the Norfolk broads for 4 days on Thursday so will see how she behaves then.
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