[sanukc]

Hi guys!
We finally had our maiden voyage on our Davanti today and it was a day of mixed emotions I suppose. The day was beautiful and the boat was amazing on the water. I had not initially thought of taking my kids out on the water the first trip but since the water and wind was calm I decided to. The boat responded well. She planed quickly and I could get good speeds on her. WOT I was at 35mph on the guage at 4200 RPMs.
BUT there was a huge problem: Around close to an hour of boating at various speeds, we saw very heavy smoke coming through the engine compartment. After shutting the boat and taking a few moments to collect our thoughts, after opening the engine bay, we found that the smoke was just steam from the freshwater cooling system. The engine had run up to a temp of 225 (the max on the temp guage), although I did not hear any audible beep. I would have thought there would have been some kind if audilble tone. If you look at the attached pic IMG_0115.jpg, the yellow tube that connects to the top near the cap of the freshwater cooling tank, was not connected any more and steam (with spray of antifreeze) was all over the place. After it cooled down, I could not see any coolant in the tank and we had a lot of it in the bilge.
What could cause the engine to heat up so quickly to such a high temp? I even waited for the engine to cool down to around 175, but within 30 seconds of starting it again, the temp was back up to 200+.
Luckily I had Vessel Assist from BoatUS and the towboat came and brought us back to the dock in a couple of hours.
All in all a very adventurous first voyage on our Mariah. Now to figure our what could have caused the overheat and why the tube got released like it did. Any advise you guys have would be greatly appreciated.

[harrisdm]

Most common that I have seen is the raw water(water pulled from the outdrive to cool the heat exchanger) pump impeller. The impeller can be damaged by running with no water going through it. It also fails with age. Other potential problems include a dirty or plugged heat exchanger, bad heat exchanger cap, leaking or burst hose on the freshwater side of the cooling loop, plugged raw water inlet port on the outdrive, broken hose from the outdrive to the transom mount, very low coolant levels in the fresh water system, and the thermostat.
Bummer on the maiden voyage.

[Zackattack]

Sorry to hear about the overheat. I agree completely with harrisdm, and as was his first response would be the thing to check first. Very simple to check with garden hose attached in driveway, and startup. The tube is just a discharge line for fluid and it probably popped off under the extreme heat and pressure.

You have to find out why the heat exchange wasn't getting cool from the water delivered from the outdrive. Did you happen to check the outdrive for debris? Maybe a piece of Kelp or gunk? where the water intake is?

And I would replace that overheat sensor, or at least test that puppy and see why it didn't alarm. Maybe someone can identify the exact temp it should alarm at, I think it is 200+-. Do you have an alarm? If you put the key in the run position and do not start the engine, will the alarm activate after 30 seconds or so? This is the same alarm wired in to the low oil pressure, outdrive and overheat I believe. Easy way to test the alarm from low oil sensor.

Well, hopefully you will learn more today. Do you know when the seawater impeller was replaced last?

[sanukc]

There was no debris on the outdrive. I ran the engine in the driveway before we launched it and it was running fine. I was not sure if it was because I was running it through it's paces going WOT for a few secs and all. The boat was a dream to ride on.
I don't know when the impeller was last changed. I hope that is all the problem with it. That is not an expensive repair is it? The weird part was I was worried about something like this and that is why I ran it for around for 30 minutes in the driveway and the temp did not go beyond 175.
Sanu

[harrisdm]

Sanu,
Running the boat in your driveway won't tell much about an overheat problem. First there isn't much heat since the engine isn't under a load, and secondly the water pressure from your house pushes past the pump and provides all the cooling the heat exchanger needs. The only way I know to determine if it is the pump impeller is to remove the pump. The impeller, wear plate, and
O-ring seal is relatively cheap( about $22 impeller, $15 wear plate and $3 for the seal). If the pump body is damaged you can buy a complete kit to replace all the worn parts for $80. If you fix it yourself the repair is relatively cheap. Not sure what it cost to have it done. If the pump is accessible it is a relatively easy repair. Not sure where it is on your boat. If you do fix it yourself and you find segments of the impeller missing you will need to remove them from the cooling circuit. The segments could be lodged anywhere between the pump out let and the oil cooler inlet hose. The tubes in the cooler keep the pieces from going past the cooler.
Don

[sanukc]

So it looks like I need a new impeller and a new water pump. Initially they thought that it was just the impeller because the original one was in pretty bad shape. But after they replaced it, they found that the water pump was not circulating anything either.
Sanu

[mikeyt]

Originally Posted by sanukc

So it looks like I need a new impeller and a new water pump. Initially they thought that it was just the impeller because the original one was in pretty bad shape. But after they replaced it, they found that the water pump was not circulating anything either.
Sanu

Chunks of the impeller may be in the waterpump causing the problem but it may be a good time to replace it for peace of mind.

[Zackattack]

Originally Posted by mikeyt

Chunks of the impeller may be in the waterpump causing the problem but it may be a good time to replace it for peace of mind.

These are separate systems in the closed cooling of Sanu's boat, so definitely need both since they are not related with the same flow. Will be a nice peace of mind though having them both new and under your scrutiny of replacement.

What is the cost estimate?