Yanmar 1 GM 10 Again!!

Appledore

Appledore

Well-Known Member
Joined
13 Nov 2011
Messages
810
Location
Bodmin Moor, Cornwall
Visit site
Hi all,

I know that the Yanmar 1 GM has been done to death in these Forums. However...

Never had any water temperature problems before, including 300 + miles cruising last year in Channel Islands. Now, on my mooring the temperature alarm starts to scream after running the engine about half revs (on mooring), after about 10 minutes.

I've bought a new thermostat and temperature alarm switch, and went down today to try to sort things out (off for a week tomorrow!). Started the engine as usual, and let it run fairly fast, and the alarm sounded after about 10 minutes. Shut down, and removed the thermostat, which was still in the open position, but closing down, so that appears to be ok. Checked all the hoses, and replaced the impeller in the water pump. (One of the 3 little screws snapped off when I was undoing the cover plate!!). Replaced thermostat cover without thermostat. Oh, and as far as I can see, the water ways appear to be reasonably clear.

Started engine and it pumped water as before. Water is only luke warm, not hot and steamy. Ran for about 15 minutes with no sign (or sound) of alarm.

So, what to do next? Do I replace the thermostat with the new one (£31!!!), or can I leave it out and see what happens? I know there are mixed views on leaving thermostats out, so your views will be most welcome.

If I put the thermostat back, and the alarm sounds I guess it's a faulty temperature alarm, and as I said, I have a new one of those.

Many thanks for your input.
 
Had exactly the same on mine. Almost certainly a poor electrical connection, probably in the multipin connector in the wiring loom. Might be worth checking the inlet into the block to make sure the water is actually going in, although the thermostat working suggests it is circulating. BTW good investment to fit a Speedseal for the water pump. Saves breaking or losing those silly little screws!
 
I dealt with a similar problem on a mate's boat. We cleaned the strainer first, then the inlet for the salt water to no avail. Then a new impelor and a new thermostat. Eventually it was traced to salt encrustation in the wee pipe into the exhaust manifold. I believe it is unusual for these to last long enough for this to be a problem. My engine is fitted with the bronze high level bend. I've never had that particular problem with it.

BTW my thermostat has a small by-pass hole in it that gets clogged occasionally, but it doesn't set off the temperature alarm. I only notice it when servicing the engine.
 
Thanks for the replies so far. I've read about the Speedseal units, but I actually removed the complete pump (very simple to do) and had a complete spare pump so used a screw from that one.

My thermostat also has the little by-pass hole, which was clear, and, as I mentioned, the 'stat had obviously been working.

The hose into the exhaust manifold is clear, and the exhaust itself was checked only last winter.
So, the next thing will be to remove the alternator to get to the Temperature alarm switch.
 
Is the engine actually overheating or is it just an alarm problem? Does it feel hot to touch?
No reason why removing the thermostat should make it run cooler.
When The thermostat opens at around 42 degrees c it closes off the bypass circuit and forces water through the engine block. Removing the thermostat means water will flow around the engine and the by bass circuit so this shouldn't make the engine cooler as most of the water will take the path of least resistance which is straight out through the exhaust elbow and not around the engine. Removing the thermostat would mean longer to reach operating temp and a risk of overheating.
I think the small bypass hole in the thermostat place ensures some water will still get to the exhaust in the case of a blockage in either circuit.
I don't think a problem in the wiring loom would give you these symptoms, it's a simple circuit that is activated when the temp sensor switch closes and applies an earth to the wire connected to it.
The temp sensor switch is very close to the thermostat housing so removing the thermostat may mean a good flow of water near the switch is keeping it cool enough not to operate the alarm. This goes back to my original question....is the engine actually getting hot?
 
Hy Spyro,

Yes, the engine is getting hot, but not too hot so that you can't touch it. Having said that, I would have (probably) expected the exhausted water to be warmer than it is. However, the boat was on its mooring so no engine load.

I will put the new thermostat in place in the morning, and if the alarm still sounds I'll have to replace the temperature alarm switch. Of course, it could be this switch that is the actual fault!
 
Appledore said:
Hy Spyro,

Yes, the engine is getting hot, but not too hot so that you can't touch it. Having said that, I would have (probably) expected the exhausted water to be warmer than it is. However, the boat was on its mooring so no engine load.

I will put the new thermostat in place in the morning, and if the alarm still sounds I'll have to replace the temperature alarm switch. Of course, it could be this switch that is the actual fault!
Click to expand...
I assumed when you said you had bought a sender unit that you had fitted it. The new one will almost certainly solve your problem.
 
No, I started from the Kingston cock upwards;)

The sender unit will be fitted in the morning, but that's a bit more difficult as the alternator has to be removed. Still only a 20 minute job. Hopefully that will fix things. If not, then I really wouldn't have a clue what to do next:confused:
 
Might be worth changing the anode while you have the alternator dropped as well. Don't think (from memory) you have to take it off, just swing it down.
 
A few things that I've encountered with my 1GM10 that cause overheating:

1. check the impeller; I've had several where the bond between the brass shank and the rubber failed. It looks OK, but you can rotate the shaft and rubber separately .. I clean those up, re-attach them with epoxy and throw them in the tool box for emergencies.

2. impeller vanes that are weak/cracked/broken .. presumably you'd have found those

3. riser from the water pump calcified (or chloride equivalent) restricting flow; remove the rubber hoses and poke accordingly (yes, I read that you've done that)

4. motoring while rolling in a swell picks up air; the impeller presumably cavitates leading to no water and the alarm going off. Not likely on a mooring :)

5. running the engine without opening the sea cock .. obvious, and not something you tend to repeat :)


so, I'd go for 1.

I doubt the sender's the problem, it sounds as though it's working as it should.
 
Assuming you find nothing today, including salt encrustation in the anode cavity, one thing that caused me problems was a blocked exhaust. If the exhaust hose partially delaminates it can constrict the flow, this is not unknown. This caused real overheating (engine hot to touch) but also a very distinctive change in exhaust note. In my case it was the muffler baffle coming detatched and blocking the outlet rather than the hose itself, so I also learned that it's worth positively diagnosing the fault before investing in expensive new parts. :mad:

The other thing I find is that salt does build up around the anode and in the flexible hose, and also can form a sort of cap over the water pump outlet spigot, but from what you've said so far I think you'd have spotted that.
 
Previous posts have covered all the obvious options. My yanmar sits on a drying berth, recent over heating problem was traced to a very small flat stone being sucked into the skin fitting and jamming before reaching the seacock. It pivoted in the pipe so flow caused it to partially close the inlet but rodding back down the pipe just passed the stone. A long shot I know but worth actually looking down the fitting to check. Next winters job is to fit a 25mm skin fitting to replace the ridiculous 12mm one.

Good luck in sorting it all out.
 
Good Morning Gents,

Well, we didn't leave for pastures new yesterday. By the time I'd spent another 4 hours with my head in the engine compartment, and the rain still, err, rained, son and I felt it was not prudent to challenge the Channel feeling worn out.

However, removed alternator to access the anode and temp sensor. The anode was all but gone, so replaced that. The temp alarm switch was very tightly fitted, and I slipped with the adjustable spanner, ripping off the end of the sensor! When it was out, it was totally salt encrusted, but I have no idea if that could have been part of the problem. New sensor fitted. There' a boatyard a mile up river (Weir Quay) and I 'phoned their engineer before leaving home, and he just happened to be doing a sea trial yesterday midday, so he came alongside to take a look. (Thanks Spence!). He thought part of the problem may have been salt encrustment in the t-piece from the pump to the water jacket and thermostat, so lots of rodding here! I put everything back, including the thermostat, and we ran the engine in gear on the mooring for a short while, then gunned it up the river and back to the mooring. No sound from the alarm!

Spence suggested flushing the engine, so he sent his workmate down river with some flushing agent (it must be some sort of acid as it burns a bit if you get it on your hands! We did have some problem pouring this in as it had to go in through the top hose by the thermostat (which of course would be closed). And it frothed like a badly pulled pint of beer!! I guess this was the reaction with any salt in the hoses. Anyway, I removed the thermostat again, and we managed to get the best part of a litre of the stuff in the engine. So, another reason for not leaving yesterday. That will be flushed out this morning.

Hopefully that will be that. No actual ' ah, so that's the cause', but maybe a combination of things.

I'll report back in a week and hopefully not before.

Thanks for all your help and hopefully this will help others.

Geoff
 
If it's any consolation, you're not the first person to break a temperature sensor in that way. :) Sounds like a sensible decision.

Also sounds like you may have fixed it, I have a theory that when left for any length of time, the anode continues to fizz away producing insoluble salts. Running the engine regularly flushes them out, but otherwise they settle and cause all the problems you (and in the past I) have experienced.

In the winter I flush the engine through with fresh water and antifreeze, then leave it, which seems to help a little.
 
Hi Gents,

Back from France this morning, and the engine has been fine.

We flushed it through last Thursday and re-fitted the thermostat, and had no further alarms - except one - the oil pressure alarm this morning!! This alarm is intermittent on my engine and usually works if I clean the screw which secures the wire to the sensor. Didn't do anything this time, but I had changed oil and filter and had spare with me, so I wasn't worried. All the stops and starts en route and still no alarm, then when finally back on my mooring this morning, turned the engine off and the alarm sounded! Oh well. I did shred the drive belt, but had a spare with me. We motored for much of the outward journey, and almost all of the return, probably 35 hours or so.

Thanks again for all your input.

Geoff.
 
You must log in or register to reply here.

Other threads that may be of interest

B
How does a tacho get RPM and engine-hours data, and how to fix faulty readings?
Replies
16
Views
439
Babylon
B

Share this page

Top