Engine Overheated - Is it Ruined ?

[Bright Eyes]

We have a 1985 Yanmar 3GM30 with 2200 hours on it.

In April 2010, I just changed the oil, transmission oil, oil filter, secondary fuel filter, zinc, and water impellor gasket (not the water impellor).

The engine is raw water cooled.

After all of this maintenance we took the boat out for a trip and used the engine for about 2 hours. There was no problem.

Then this weekend all hell broke out.

When we started the engine up, we saw water coming out of the exhaust so everything seemed fine. We motored out of our marina and up the river. After about 15 minutes an engine alarm went off at the starter panel, I flipped the RPM switch and the alarm turned off but the RPM needle stopped reading also. I figured it just shorted or something. About 5 minutes later the engine turned off.

We wern't sure why it stalled but, it has stalled before so we just started it back up and after a few trys it came on. This only lasted about 1 minute then the engine turned off again. So we said owell and put the sails up and sailed up the river.

A couple minutes later we noticed a light smoke coming from the cabin. Fire extinguisher in hand I opened up the engine compartment and there was alot of smog/smoke coming off the engine. We opened up the cockpit engine access too to let smoke out but there was no fire.

At this point we realized that the engine has overheated.

We sail for another 45 minutes untill we lose wind and without the wind power we accidently run aground. The smoke had all cleared and the engine wasnt as hot so we attempted to use the engine to get us off the ground. The engine came right on and we used it for about 5 minutes before giving up and turning off the engine.

We called Boat US Towing and they pull us off the ground. At this point we should have let them tow us home boat we thought the enigne wasnt so bad since it came on and worked fine after cooling off so we just had him let us go and we sailed to a near by anchorage. When we got the anchorage we turned the engine on for about 2 minutes to get in a good location, at this point we noticed that no water was coming out of the back exhaust. I went below and saw a slight leak at the hose between the water filter and water pump. I tightened that hose as well as all the other hoses related to the cooling system. We tried the engine again and still no water came out the back so we truned it off and left it off for the night.

The next morning we opted not to use the engine and sailed off the anchor and out of the anchorage. But as we were leaving the wind was not strong enough and the current threatened to put us aground again. So as a last ditch effort we turned on the engine to attempt to get us away from the shoal. But instead the engine stalled in forward gear, and would not return to neutral or reverse. We abandon the engine option and manage to dodge the shoal via sail.

On the sail back home, I went down to the backside of the engine compartment to check out why the gear would not leave forward. It was just stuck and only moved slightly back and forth but not enough to enter neutral or reverse.

Also while I was on the back side I noticed that the plastic container between the exhaust manifold/elbow and the exhaust pipe where the exhaust and water meet has partially melted and there was a large hole in the side of it. There was also oil sprayed around this area of the engine compartment.

We had Boat US Towing put us back in our slip and now we have some repairs on our hands.


My plan is to focus on the cooling system and transmission. I will change the water impellor, check/replace all tubing, and ofcourse replace that plastic mixing container. On the transmission side I will consult a Diesel mechanic.

One mechanic friend of mine said that I probably ruined the whole internal engine and will need to have a complete rehual or buy a new engine.

So my question is, do you think this engine is ruined and what advice can you give me on repairs?

Attached is a crude picture.



Thank you in advance to the knowledgable people of CF.

[cantxsailor]

In this order, replace the impellor, replace the melted water muffler, start the engine. My well honed instincts say you lost the impellor and the heat from the engine exhaust without cooling water melted the water muffler and the oily mess is just the exhaust that didn't go out via the exhaust hose to the water. You need to watch for steam coming out the exhaust because you may have warped the head and blown the head gasket. Until you get water to the engine you just won't know. Don't go jumping to conclusions because they very tough engines and will put up with an amazing amount of abuse............m

[S/V_Surya]

I would say you a have an obstruction in your water intake or maybe bad impeller. Your mixing tank I take it is the water lift muffler. I doubt you wrecked your engine. Just because you lost cooling the engine you did shut down engine right away and it did start ok after cooling down. I have melted my plastic muffler before and engine was fine.

[steve_hendry]

I did this with the 3QM30 in my boat. The engine slowed down and stopped as we were motoring back into our home creek. When I tried to restart, woudn't turn over. Sailed into the creek, then as we approached the YC piers, tried the engine. It started, and I idled the boat into the slip.

The engine survived. To the other recommedations here I would add:
1. Change the oil after you replace the impeller and have the engine running agains; the high temps probably did in the oil.
2. Replace the melted/burned plastic muffler (Vetus?) with a fire resistant fiberglass muffler such as Aqualift. Mike Kaufman, who did the prepurchase survey of my boat, put the plastic water strainer and plastic muffler on the boat at the time as priority items to be replace (the water strainer with a metal one).

Hope your engine is OK, the 3GM30 isn't quite as massive a chunk of iron as the old 3QM30.

[roverhi]

I did a similar stupid thing with my 3gm30. Ran the engine and developed a fog below after a short while. Shut it down and continued the sail. Sailed back to the marina and started the engine to get back to the slip without incident. Mine's freshwater cooled with a heat exchanger and noticed the coolant bottle was empty. Filled it up and thought all was well. Took the boat out the next day and powered at moderate revs for about 4 or 5 miles with no untoward indications. On the way back in ran the RPM up to normal cruise and soon developed the coolant fog again. Shut the engine down, refilled the engine and coolant bottle with water and continued to power at reduced throttle. The fog came back after a short while. Reduced the power to slightly more than idle, refilled the coolant bottle and limped back to the slip.

Read all I could on the engine and decided it was a clogged coolant elbow, a fairly common problem with long hour 3GM/s. Bought a new elbow, the most expensive piece of cast iron I've ever purchased. Disconnected the exhaust riser from the engine and pulled the elbow off but couldn't undo the pipe fitting plumbing connected to the elbow without a big vice. Called in the cavalry in the form of the local diesel mechanic. He managed to get the pipes off the old coolant elbow with a BIG vice and LONG cheater pipe on a LARGE pipe wrench. Looking at the elbow, he said it wasn't badly clogged but given the Yanmar history with clogged coolant elbows reccomended putting the new elbow on. He reassembled the exhaust system and reinstalled it. Started the engine up but still no coolant flow. He pulled the water pump and found two vanes broken off the impellor which he changed and reinstalled, still no water flow. He disconnected the engine coolant hose from the seacock and there was only a trickle of water. The whole problem had been caused by some mollusk that had made a home in the seacock. He reamed out the seacock with a piece of all thread, reconnected the plumbing and, Voila!!!! engine coolant water flowed like a champ. The engine has run well for at least 20 hours since so no apparent damage. I didn't run the engine till it quit which probably saved me a rebuild. You may be so lucky.

All you can do is find out the cause of your lack of coolant water and fix it, replace your old muffler and anything else that failed because of the excess heat and then restart the engine. Hopefully these are tough old beasts and all will be well. Running an engine till it siezes is usually not a good thing to do, however. Good luck

[Alan Brown]

The same thing happened to me two years ago with my Yanmar 2GM. Fortunately, I noticed the problem in time to prevent any lasting damage.

Here's what happened to me.

There is a flexible hose that carries the exhaust and used coolant water to the stern. As it exits the vessel you can physically see the exhaust and water discharge. In my case, this stopped. I checked the water in-take and pump and all was working fine. When this hose broke, all the hot exhaust filled the engine compartment and the hot coolant water started flowing into the bilge. (Did you notice this?) After awhile, when everything had cooled down, I was able to re-start the engine and return to my marina. Upon docking, the engine compartment was super hot and it was quite likely that I would have fried much of my wiring if I had kept the engine running.

My guess is that this is what happened to you. You may have actually gotten the engine compartment so hot that you melted part of your shifting cable. I was able to replace this rotted-out hose and everything's worked fine ever since.

Before I'd worry about an engine overhaul, I'd locate the source of the original problem, correct it, then cross my fingers and pray for the best.

Good luck!

[Chief Engineer]

After about 15 minutes an engine alarm went off at the starter panel, I flipped the RPM switch and the alarm turned off but the RPM needle stopped reading also. I figured it just shorted or something. About 5 minutes later the engine turned off.


Hmmmmmm, alarm goes off and it is ignored

Change the impeller(get ALL the pieces out), change the oil and see if it runs

[Chief Engineer]

BTW I was just down in Deale....at Shipwright Harbor...what a quaint/boatyard.

Nice folks there.

[Bright Eyes]

Yeah, I really need to learn what the alarm means. It goes off everytime we start the boat when the key is left in the on position. Then I turn the key back and it goes off.


Thanks for all the advice. I took the water pump out last night and found a faulty impellor. Replaced the impellor and got water flowing through the engine again by using a drill to spin the pump. So there was probably the root cause. Now I gotta fix everything that was damaged.

For the stuck gear, we think something might be stuck on the prop. When we hit ground our dinghy tow rope got sucked into the prop. We have a prop gaurd that cut the line (i had to dive in after the dinghy floating away) so I thought the prop was clear. But when we try to manually turn over the engine in gear it is almost impossible. But when we tried to turn it over manually we were able to unstuck the gear. And when in nuetral it turns over just fine.


I will update this thread as I complete work and let you know how it turns out.

So far I changed the impellor.

Next I will replace the muffler, exhaust manifold gaskets, and all hoses and hose clamps. Then change both the primary and transmission oil.

[halberd]

Bright Eyes,

Certainly concur with the other posters here, however if you can go over the side and check your raw water strainer on the hull. It may have excessive growth which will need to be cleaned or it may be that you have picked up a plastic bag and the system has sucked it onto the intake thus cutting off your supply of cooling water; and from there your impeller has run dry and disintegrated. Being alongside, if it was apiece of plastic it may well have floated off, but either way the sea-cock needs to be checked out. Best of luck with it.

[halberd]

The alarm is probably connected to the oil pressure circuitry and when you turn your key on before starting it will sound. Once the engine has started and up to correct oil pressure the circuitry will turn the alarm off.

That's why the alarm sounded when the engine started to shut down due to low oil pressure.

[S/V_Surya]

On my boat the alarm when you start is the oil pressure alarm.

[halberd]

Yes, agreed and that is exactly what Bright Eyes has as well imo.

[DeepFrz]

While you are at it check the exhaust elbow to make sure the water passages aren't plugged up. Taking the heat exchanger apart and cleaning it would also be a good idea. You might be surprised what you find in there. Good luck.

[sigmasailor]

It is quite possible your engine stalled because pistons grow larger when they get hot, more so than the cylinders grow.
When things get hot enough (that does happen when you ignore alarms) the engine simply seizes up, like pistons welding to cylinders. If you are really lucky it will come loose when allowed to cool down.
Make sure the cooling and exhaust are fixed and monitor oil level if it starts; also look at the exhaust. The seize very likely damaged some pistons and rings. If you do not trust it have the engine compression tested before you do more damage. If you are very lucky you can get away with it.

About alarms:
Turn contact on and alarm sounds (low oil pressure), this shows you the alarm system works;
Start engine and alarm goes off (now you have oil pressure, battery is charging and temperature is not too high);
When alarms sounds: engine on idle and investigate quickly, stop if required.
By turning the key while engine is running you stop the alarm but not the reason why it went off.