Yanmar 2GM20 - Overheating Help!

[Hornet_UK]

Hi all I need some help and advice on an over heating problem with my Yanmar 2GM20.

Whilst out sailing ant the weekend I started up the donk and after few minutes the overheating alarm went off. I took the water pump off checked it was able to turn and all seemed ok there. I then left the inlet hose disconnected but pointing into the bilge and turn the seasick back on and water was running through it so no blockage there. After leaving the engine cover off for around 45mins we got near the marina and I started the engine again and all seemed to be ok. However when I got back to the marina and went to stop the engine I discovered that the ignition had accidentally been turned off so the Overheating Alarm was off also. Then when I turned the ignition key back to on with the engine running the alarm sounded straight away, the engine must have been running like that for about 20mins! I did check if there was water coming out of the exhaust but it was obvious it wasn't once I was in my berth

What damage would I have done to the engine running it hot like that?

Also what would be the next likely place to look for a blockage In the raw water cooling system?

I read some where that exhaust elbow can get coked up, never checked it TBH, could this be a cause of the problem?

 

[Salty John]

Next thing after the seacock will be the raw water filter - check it isn't blocked. Then check the pump impeller still has all it vanes.
If it's a 2GM20F you'll need to check the heat exchanger tubes aren't blocked. Next check the exhaust mixing elbow which may be blocked up.
I assume you've checked the pump drive belt is tight. Check for collapsed water hoses - sometimes they can look ok when the engine is off and then suck themselves closed when the engine starts.
Hopefully you'll find the blockage somewhere in the forgoing and won't need to worry about head gaskets and clogged coolong water channels in the block.

 

[earlybird]

I think you would be unlucky to have damaged the engine itself, but cylinder head gaskets can be vulnerable to over-heating, keep a check on sump oil etc. for a bit.
More likely, you could have damaged the exhaust system, esp. the rubber hose near the elbow, and any plastic component such as a water lock. Give them a visual at least.
Can't really see a blocked elbow causing complete water flow loss, but worth taking off and checking, this will enable you to examine the rubber hose better.
Did you actually look at the pump impeller?
Is your engine fresh or raw water cooled?

 

[prv]

Check for collapsed water hoses - sometimes they can look ok when the engine is off and then suck themselves closed when the engine starts.

This is definitely a possibility, though I'm not saying it's any more likely in this case than any of the others. The first time out after I reinstalled our engine, we had an overheat. It turned out the hose from the strainer to the pump had gone on with a twist (due to the way the pump is mounted "backwards" on this engine. When the hose was cold, it was stiff enough to hold its shape, but as the engine box warmed up the hose softened and allowed the torque to twist it shut.

Pete

 

[misterg]

Also, IF it is 2GM20F, check the coolant level in the fresh water side.

 

[pete]

I found that the Johnson pump on my 2GM20F would occasionally not prime, or after a fast sail had lost its prime.
I checked all the usual things,fitted a new impeller, checked the seacock and seawater strainer were clear, made sure that the strainer top was making a good seal, flatted the pump end plate, checked the heat exchanger and exhaust bend were clear (no problems found) I suspect the pump is worn after 1000 hours and that the inner surface of the pump may be worn out of flat.
Once I manage to get it primed it will be OK for a week or two then loose its prime again.
Rather than buy a new pump I lowered the water strainer down to the static water line from it's original position of above the engine so hopefully it will be easier for the pump to prime. I will be launching in a couple of weeks so I will find out if this has been successful.
I had a similar problem on a 1GM10 but that had an easier inlet route and was easier to prime by loosening the hose clip above the pump.
I think this is a common fault on these pumps.
Pete

 

[Hornet_UK]

Thanks for all the relays so far, Just clarify my engine is Raw Water cooled.

 

[Tranona]

Thanks for all the relays so far, Just clarify my engine is Raw Water cooled.

If there is no water coming out of the exhaust then air has got in or there is a massive blockage somewhere. The usual culprits are loose hose clamps, poorly sealed water strainer (if you have one) or worn pump, either impeller or face plate.

 

[Spyro]

Re' worn pump .The face plates on these pumps can usually be turned round if they are worn.

 

[pete]

Re' worn pump .The face plates on these pumps can usually be turned round if they are worn.

Agreed but if the face plate wears the surface at the opposite side of the impeller in the pump body must also wear and I think
this is maybe where the suction is lost.
Pete

 

[cid]

I have a 2gm20f and I had an issue with the impeller. It looked ok but the center bush had parted from the rubber,Thus at low revs it appeared ok but failed on high revs

 

[Talbot]

The impellor bush problem is well worth checking, But there are other possibilities

1. Thru-hull blocked by bag/sealife
2. if you have a water strainer fitted above the waterline between the thru-hull and the seawater pump, and the boat has dried out, you may need to prime the system by filling the strainer.
3. It is a Yanmar 2GM, and these are known at about 1000 hrs to block at the exhaust elbow. This is the most likely problem. it is also amongst the easiest to check as access to this is normally pretty easy. This elbow wears out and can cause leaks, or even back pressure sufficient to get seawater to the valves.

 

[LenT]

I had a number of overheating issues on my raw water cooled 2GM20 and after a lot of research and testing it came down to the pump not priming properly. I followed all the advice on all of the threads on the subject and was still having problems, but then found that my problem was due to wear on the pump cam (specifically caused by the fixing screw hole). The pump was clearly worn and as replacements are prohibitably expensive, I was able to flatten mine by removing it and then using some wet and dry paper wrapped around a large socket.

First check the pumps performance. Remove the top hose from the exhaust elbow and replace it with a 2m length of transparent pipe and suspend the end of this as high as possible. Remove the pump V belt and get a battery or electric drill with a socket to run the pump. (this can be achieved with a rope around the pump pulley, but it takes much longer.) Run the pump. The water should climb up the transparent pipe. If it does not, the pump is either not priming or there is a blockage (which I think is unlikely given the thermostat bypass system used and the test you have already described).

If the water climbs up the transparent pipe but then falls quickly, this means that the water is falling back through the pump due to a bad seal between the impeller and pump body (cover, shaft, seal, body or cam). It would be good to see the water stay up in the transparent pipe, I think that is unrealistic, but after working on my pump, the water fell back down slowly.

If the pump is off the boat, it is easy to set up a test rig for this test.

When I was content that I had improved the performance of the pump, I did some water throughput tests by setting the engine at given revs for 1 minute and then collecting the water in a bucket out of the exhaust. I got: 1000revs = 5ltrs which gives approx. 300ltrs per hour; 1500revs = 8ltrs which gives approx. 480ltrs per hour. Although this sounds relatively low, if you look at the size of the waterway in the thermostat housing, you will see the restriction.

All this is about the cause of the problem, given the size of the lump, I suspect and hope that you have not done any damage to the engine by overheating.

 

[Hornet_UK]

Ok time for a bit of a confession!

What seems to have happened is when I started the engine something got sucked over the water inlet on the hull causing the overheating problem. Stoping and restarting 10mins or later didn't help with the over heating as the engine must have still been hot so alarm goes off again. On the sail back I removed the water pump, turned the raw water seacock on and water flowed into the bilge so blockage was gone. Checked the pump by filling inlet with water and washing up liquid and turning the pulley water seemed to be pumping through ok. Reattatched the pump left the engine cover off for about an hour to cool the engine down restarted the engine and alarm had not gone off, this was caused by accidently knocking the ignition off. I then discovered the ignition was off when I was back in my berth!!!!!!

Anyhow towards the end of last week I had a bit of an epiphany where I couldn't remember if I had Turned the Raw Water Seacock back on! I checked the boat at the weekend and found I left it shut!!!

I ran the engine for about 45 mins at different revs and all seems to be ok, the only problem I did find was the exhaust hose had worked loose from the plasic box (no idea what its called) it was connected to.