Overheating Issues (1GM10)

[asdf38]

I've been trying to pull away from my winter marina to my summer mooring but have twice overheated and found myself drifting in the exact same spot 1000ft from the marina.

Prior to the first time, I ran the engine about 30 minutes before pulling away (idling, full rev, and in gear). I check the water flow out the exhaust routinely. After pulling away from the dock at about 2800 RPM's I got an alarm after about 2 minutes. I anchored and took apart the impellar but it looked perfect. After replacing it anyway and starting the engine again I saw no water flow and shut things down.

I called up a pro and he diagnosed it as an intake hose that was too long (it was long, it came form the PO that way, but gave me no problems last season). He confirmed that there was no flow at first.

So I tried again, checked the engine at the dock again, and pulled away. I ran at 2800 RPM's for a minute, I checked for water flow (at this point I was mostly just checking for water or no water, not evaluating how much) and got an alarm at the exact same spot. This time I waited it out while drifting slowly until the engine had cooled and ran it again. There is flow, I can run at low RPM's, but I'm suspecting it's not as much as it should be.

Another fact is that an impellar failed in the middle of last season and I never recovered 2 or 3 of the blades.

So any thoughts? I'm thinking the cooling system has an obstruction (possibly an impellar blade) that is restricting flow and intermittently stopping it. Is that reasonable? Other ideas? On the 1GM10 where is there likely to be an obstruction in the system (note I have no strainer)? Ideally I'd do this myself but given that I'm tight on time I'm debating whether to call the pro (again) or take a day off work to look at this myself.

[JimsCAL]

Does sound like you have restricted flow - probably from the impeller blades. Is this a raw water cooled engine? Backflushing the engine may be the best way to clear the blockage. Note also that raw water cooled engines can develop scale on the inside of the engine cooling passages which can also result in the same issue.

[Faster]

Impeller bits, as suggested, or whatever else may have been picked up at some point since you have no strainer. In addition to Jim's good advice the mixing elbow itself or it's injection line may be clogged.

Or there's some weird distortion in the 'Force' near the location of your repeated failures...

True story: Friends had a Honda outboard, low hours, seized under way just off Long Harbour, Saltspring Is one season. After warranty wrangling with Honda, received a replacement. The new engine seized after similar service within 100 meters of the first occurrence... FWIW....

[dabnis]

Possible air bubble (lock) somewhere? Suggest you bleed
the coolant system if fresh water cooled with a heat exchanger.

Dabnis

[asdf38]

JimsCAL, how does the backflush process work exactly? Remove the hose at the mixing elbow, use a funnel to fill it up? Blow into it? Probably remove the impeller first. Would that work or would a pump or something else be needed?

Faster, which is the injecting line? Yeah, also ironic was that 30 seconds after the alarm, while I was standing there adrift and trying to decide what to do, the marina owner called to ask if I had fixed my problem and left yet (he had been nice enough to let me borrow the dock but wanted me off). I had to tell him that yes I left but I was coming right back.

It's raw water cooled.

Thanks for the suggestions so far.

[casey1999]

I have the 3gm raw water cooled- basically your engine + 2 cylinders. I am guessing your thermostat is clogged. Replace and clean any deposits prior to installing new. I'll bet the pump impeller parts are here too. The way the cooling system works is that the raw water pump sends water to the thermostat, but if the thermostat is closed (cold engine) or clogged (probably your case) the water goes to the bypass hose and out the exhaust. You have water going out exhaust but it is not flowing through the engine and cooling it so it overheats. Let us know what you find. By the way, the thermostat is extremely small and it does not take much to block it. I surprised they do not clog more often, probably good idea to inspect whenever pump impeller is inspected/replaced. I would replace the thermo every two years- cheap insurance.

I see you have no strainer- I would install as without one that thermostat is sure to clog. Just a teaspoon of sea weed would do it.

Also, my raw water pump suction hose is long and it pass through the transmission cooler. It was this way from PO. The pump still pumps a lot of water so I think you are ok with your suction hose. Plus if you see a lot of water going out exhaust, this shows the pump is pump ok. When you get a chance, I would replace the hoses and clamps, again cheap insurance.
Good luck

[asdf38]

Originally Posted by casey1999

I have the 3gm raw water cooled- basically your engine + 2 cylinders. I am guessing your thermostat is clogged. Replace and clean any deposits prior to installing new. I'll bet the pump impeller parts are here too. The way the cooling system works is that the raw water pump sends water to the thermostat, but if the thermostat is closed (cold engine) or clogged (probably your case) the water goes to the bypass hose and out the exhaust. You have water going out exhaust but it is not flowing through the engine and cooling it so it overheats. Let us know what you find. By the way, the thermostat is extremely small and it does not take much to block it. I surprised they do not clog more often, probably good idea to inspect whenever pump impeller is inspected/replaced. I would replace the thermo every two years- cheap insurance.
Good luck

Ok that makes sense that there could be an obstruction there. Seems like a good first place to look. But I don't think the thermo can be the problem because the engine can run indefinitely at low loads (at the moment. Previously it seemed to be blocked altogether). And I believe, although it's subjective, that I'm not seeing enough flow out the exhaust.

[casey1999]

Originally Posted by asdf38

Ok that makes sense that there could be an obstruction there. Seems like a good first place to look. But I don't think the thermo can be the problem because the engine can run indefinitely at low loads (at the moment. Previously it seemed to be blocked altogether). And I believe, although it's subjective, that I'm not seeing enough flow out the exhaust.

The pump impeller parts would probably not make it past the thermostat, and if they did they would probably pass through engine and out exhaust. Check the discharge hose of the pump which leads to the thermostat housing. The parts are probably stuck in the hose or jammed against the thermostat. What may be happening is at low rpm you get enough water past thermostat to cool engine, but not at high rpm. The thermostat may not be opening fully which would cause the same thing. The thermostat are cheap, I would just get a new one and install, replace any questionable hoses and clamps. When I bought my boat a year ago it had over heat problems, I did above and have no issues now.

[JimsCAL]

Originally Posted by asdf38

JimsCAL, how does the backflush process work exactly? Remove the hose at the mixing elbow, use a funnel to fill it up? Blow into it? Probably remove the impeller first. Would that work or would a pump or something else be needed?

You need pressure - either from a pump or a garden hose. Basically you connect the water to the normal engine output and then connect a hose to the normal supply and run it overboard or to a sink or a large bucket. Idea is you force water through the engine passages in the opposite direction and hopefully dislodge whatever is blocking the cooling water flow. I had put a washdown pump on my previous boat with a raw water Universal 5411 for this purpose and also to make winterization easy.

[Tempest]

I agree with Casey's thermostat diagnosis...look for the impeller pieces there too.