Problem with mariner4 outboard... help!

[matnoo]

It overheats, not a lot of water is coming out of the water outlet, after a minute it boils and steam comes out, which is where i turn it off!!

Its a fairly old beast, has been in storage for 5 years, my dad is very competant with engines, so has given the engine a service, but doesnt know about anything else..

I think it might just be the water filter thats blocked? Where do i get one? how easy is it to replace? how do i replace it!? Or do you think it might be something else!


Mat

 

[alb40]

There is no water filter on them.

I suspect you may simply need to change the impeller, as they become brittle in storage and can break up.

 

[aitchw]

Or blocked water ways. Run in a bin with Fernox descaler.

 

[davidpbo]

I had similar problem with a Tohatsu 3.5.

In my case it was not overheating but there was not much water coming out of the tell tale pipe. That was caused by salt deposits in the tell tale outlet pipe. Most of the cooling water goes down the inside of the outboard leg hence the reason there was no overheating.

It sounds to me as other have said that you either have a damaged impeller or a blockage somewhere. I would check the impeller first which is usually accessed by removing the bottom of the outboard leg. When opening the impeller chamber be careful, the impeller is often located on the shaft by a pin, sliding the impeller up the shaft can leave this free to drop off and get lost.

Because my impeller looked OK I actually took the engine head off the outboard leg and inspected and cleaned the water chambers. It was a waste of time as they were clean but it was not difficult to do. I had to fit a new gasket between the head and leg. Had there been serious deposits blocking the water ways I would have been able to clean them out. I don't know how similar your engine is to mine.

Hope these posts help.

David

 

[MikeBz]

I had the same problem with an elderly Mariner 4. First time it happened the impellor drive pin had worn away so that it no longer drove the impeller. Changed the impellor and drive pin, all was well(ish - it never had issued much water from the telltale since I'd had it, more of a spluttering dribble than a steady stream). About 6 months later it started doing it again - it would run forever at tickover or under a very low load, but put it under load for a few minutes and the telltale would turn to steam. Nothing wrong with the impellor this time, I guess the waterways were corroded/furred up sufficiently for it to only pass enough water to keep it cooled under low loads. No time to investigate properly, needed to get out on the water so I EBayed it and bought another.

 

[m1taylor]

An all too common problem I am afraid. You could be lucky, and its just the impellor. If you are unlucky, you will have to take the head off and clear the water ways. For an old outboard this is a totally uneconomic repair if you want someone else to do it. So choices are selling it as seen, with the problem, or having a go. My inclination would be to do the latter, as success will mean a serviceable outboard for years to come, at minimal outlay (a workshop manual and a new head gasket)

 

[VicS]

I agree with the other suggestions that the first thing to do is to change the water pump impeller.

I have some reservations about Fernox (That's Fernox DS-3 central heating boiler descaler) or an equivalent acid descaler. It is based on sulphamic acid and although safe on all materials you would find in a central heating system it is not recommended for thin or badly corroded aluminium. See here

So use it with caution and stay well within the 10% maximum concentration and the 80 C temperature limit and be sure to flush it out thoroughly afterwards.

If that engine has a thermostat it might be sensible to take that out and check that it opens at the specified temperature, which is probably marked on it.

The best place for advice on outboard engines is without doubt the iBoats forums where you will find separate boards for the different makes of engine. If you try there though be sure to quote the full engine details (Make, hp, year, model and maybe serial number) at least as well as you can.

This site should enable you to identify the year if you do not know it.

 

[sparkie]

Would agree with all the foregoing, check impeller, waterways, thermostat. Strip it all down otherwise you may end up doing the job twice. Quite easy with the workshop manual if necessary, but not needed if you've ever had a motorbike. HOWEVER one note of caution if it is an old engine, and a bit ropey or rattly, I've just done my Yamaha 8hp and the few bits I bought (impeller, exhaust manifold, anode, 4-5 gaskets) cost over 70 squid. May not be worth it.

Safe sailing

Sparkie