Mariner 75 2st Warning beep

Phil M · 19 June 2013, 11:51

I'm hoping somone can offer a sugestion on an intermittent problem I have on my 1988ish Mariner 75 clamshell. The engine seems in good condition and starts, runs, idles very well however the first time I took it out we got a continuous warning tone after short run. It came and went but the teltale was weak so we limped back to harbour and I ook it home and replaced the impeller and flushed out the cooling pipework as there was a blockage at the teltale exit point where we had picked up some silt. The next run out was fine, no warnings, teltale flowing like a pressure washer. Last weekend we went out again and again the teltale was fine, but whilst idling in the harbour lock the beep came back for a short while before fizzling out again. As the oil level was good, teltale very strong and beep had gone, we carried on with the trip with no further warning beeps. It ran at idle for a while afterwards on the muffs with again no warnings.

So, my question is (finally) what coudl be causing this? Genuine overheat due to internal blockage? Faulty temp or oil sender? Is there anything else that these engines warn of or is this a common "quirk" of these engines?

Any suggestions appreciated!

Phil M

solent spence · 19 June 2013, 11:57

Could be a problem with thermostat, have you replaced that yet?

Phil M · 19 June 2013, 14:23

Not yet. I'll see what I can get hold of and give it a go.

Phil M

solent spence · 19 June 2013, 15:14

Sounds very similar to a buzzer alarm I had on a 175 merc, which had same symptoms and ended up being down to the 2 thermostats on that engine.

Phil M · 22 July 2013, 17:18

I finally got round to looking at this again and have had the thermostat out and done the hot water dunk test. The inner spool lifted by about 6mm and completely compressed the spring in just boiled water, so it seems to be functioning. The waterways look a bit scaled up but largely clear of debris. I did notice the popper valve seems quite firmly in its hole. As a test I pulled it out then placed it over the hole (just inside) then put the cover, spring etc back on. The spring doesn't have enough strength to push the valve back in so i'm guessing it is too damp tight and won't push out under water pressure. Could this be the problem? Recent trips out saw the alarm on on tick over and on higher revs but quiet in mid throttle.

Phil M

Nos4r2 · 22 July 2013, 18:01

Could well be-is the grommet swollen?

Phil M · 22 July 2013, 21:00

it looks ok with no damage but I don't know what the inner diameter should be. it could well have swollen slightly making it a bit of a tug to remove the poppet. I assume the poppet should slide quite easily. I will try to pull it out tomorrow and take a better look then see if I can get a new set of parts.

thanks,

Phil M

Nos4r2 · 22 July 2013, 21:04

Mine on the 225 touches-but easy to get in and out. I'd replace the spring, gaskets and grommet.Just did mine, and it's not expensive.

Phil M · 26 August 2013, 09:36

Ok, I've replaced the thermostat, gaskets, poppet, spring, grommet and engine block liner (which took a beating to fit!). Ran it out yesterday and the problem is still the same. I know that the poppet is working because I put a thin piece of wire through the cover breather as an indicator and I can feel it open under higher revs, although it seems to bounce around a bit. The thermostat opens in hot water and I know it pumps well up to the thermostat. The problem starts with a beep at tickover, which is initially cured by revving the engine, presumably opening the poppet. After a while though the beep is constant regardless of engine speed. My next port of call is the sensor. Trouble is, I cant get it out. I've removed the plastic retainer and given it a pull but the only thing to hold on to is the cable and I'm concerned about ripping it out of the back of the sensor and ending up with a broken sensor stuck in there.

Anybody know how to get these out? Also, does anybody know what temperature the sensor is supposed to go open circuit? I'd like to check it before I shell out for a new one.

Thanks,

Phil

uncle al · 26 August 2013, 12:45

Just a note on testing thermostats, if you look on the btm of the wax (the bit in the middle) you should see a number usually 60 if its not there look else where on the thermostat, that is the temprature that it should open.If you put the thermostat in near or boiling water , you have either buggered it or damn near buggered it. If you have a thermometer in the water and the thermostat opens on or near the correct temprature did it open smoothly , and when removed from the water close smoothly if it did its a good un, if it didnt throw it away.

Phil M · 26 August 2013, 14:55

I had the old to hand and it has 143 stamped on it. I have tested it in a bowl of cold water and added hot until it opened, using a multimeter with thermocouple and it just started to crack open at 62 deg C, which is pretty much 143 deg F. I am now happy that the thermostat opening is not the problem but will pull out the new later and do the same test and check the numbers on it. I think the key now is to figure out how to get the temp sender out and see what that activates at.

One other thing i did notice yesterday was that, whilst the temp alarm was on, the engine block around it, poppet/thermostat cover etc. were all pretty cool to the touch.

Phil M

uncle al · 27 August 2013, 07:43

the over heat sender you gently prise the rubber bung out, then pull out the temp sender,has it got paint flecks salt doposits on it, if it has that could be the problem.Make sure the sender and the hole it slids into are clean I used to put them back with silicon grease. I should have mentioned that some thermostates the temprature numbers are in farenheight not centigrade.

9D280 · 27 August 2013, 08:26

And if all that doesnlt work, get a bulb / buzzer & disconnect each sensor one at a time & see if you can get the Independent buzzer / lamp to squeak / light.

Then at least you'll know what it thinks the problem is.

jezza2011 · 27 August 2013, 09:35

Mine also does this although the engine is running normaly.

I spent hours tracing it down to the ignition switch and remote.

the symptons were it would beep as it should when you turn the key
start and run normaly.
but slowly the annoying beep would come on.
and go from a quiet screechy intermittent beep to a full on very loud constant beep.

it was not the senders as could disconnect all of them and it still did it. I even replaced the alarm unit and it still did and does it.

but I can turn the ignition switch back a little and it stops. so flakey ignition switch in may case.

Phil M · 27 August 2013, 13:37

Thanks all for the tips. It'll be a few days till I can get a look at it again. I am pretty sure it is the temp alarm and not the ignition as I've tried disconnecting the sender and that shut it up. I'll take a look at the controls and ignition anyway, just to make sure.

Thanks,

Phil M

Phil M · 16 September 2013, 17:27

Ok, update time. I've checked the temp switch and it goes to ground at about 110 degrees C, so I'm guessing I have an overheat issue. Any thoughts what could cause this? I wonder if I have a blockage or salt build up in the cooling channels. Is there any easyish way to inspect these without buggering up any alignments or adjustments?

Thanks,

Phil M

Phil M · 10 December 2013, 11:31

I finally got round to opening up the engine and inspecting the water channels. They are all pretty clear so I'm satisfied there is no problem with blockages or anything wrong with the water supply. I have, however, found a burnt deposit on the middle piston side wall, the section that is exposed through the exhaust port when the cylinder is at TDC. It doesn't apear to be a blow by problem, as the piston rings are clean in good condition and there is no fouling on the cylinder side or between the rings. I have also checked the compression and it is pretty much 100psi on all cylinders. At a guess I'd say the temperature in the exhause manifold was getting too high and burning the oil film on the middle cylinder, but that could be rubbish. Does anybody have any ideas? Unfortunately I'm quite a way from any outboard repair places and would like to try to diagnose the issue at least before I take the boat anywhere.

Thanks,

Phil M

indaba1991 · 10 December 2013, 18:16

Quote:

Originally Posted by Phil M

Does anybody have any ideas? Unfortunately I'm quite a way from any outboard repair places and would like to try to diagnose the issue at least before I take the boat anywhere.

Thanks,

Phil M

Hi Phil - is this a two stroke engine? If so I had one - exactly the same problem - it was a faulty sensor on the oil reservoir.

Rgds
J