I'll try to be brief. The boys and I went out last weekend and enjoyed a morning of tubing. We came back in and picked up the wife for lunch on the lake. After an hour of eating and swimming, we tried to get back to the marina. The boat turns over but wouldn't fire. A kind gentleman and his family towed us back to the marina. The shop came out and could not find any problems as it fired up and started for them. So, the boys and I go out again today and spend an hour of tubing with multiple starts and stops. We find a cove and decide to swim for about 30 minutes. You guessed it, when we try to head in the boat won't start and we get towed back to the marina. This time it is a gentleman on the shore who has to go down to his slip and come out and get us. The boat turns over, but won't fire.

Any thougts as to why it will start with short stops while switching tube riders but won't start after sitting for 30 minutes on extended breaks.

Vapor lock. Try leaving the engine hatch open while you swim and see if that is enough to cool things down. You can also try laying some wet towels on the intake to help cool it down.

And probably the biggest thing you can do is to let the boat idle for three or four minutes before you shut down. this lets it pump cool water through and take out some of the heat buildup from hard running.

Not only is this a classic vapor lock symptom, you might want to see why it is getting and staying so hot that it keeps happening. Is your engine compartment getting good ventilation and is the fan working? Has a fuel line gotten too close to the exhaust manifold?

Deepv brought up a good point that I forgot to mention, keep the bilge blower running when the engine is on. And if your boat is still under warranty you might have the dealer take a look the next time you have it in.

TT - My boat has done the same thing several times the past few summers. In my situation, ambient air temp was over 110 degrees (and it was desert air - very dry). After lots of investigating, I have not been able to pinpoint the exact cause. However, it does seems to happen when the fuel tank was 1/2 or less full. The last time it happened, I loosened the gas cap, let the vapors escape, put it back on and it fired up.

Food for thought....

That's never happened to me but reading this topic it makes me think of a normal procedure I do when boating. I just randomly turn on the blower about once an hour for 5-10 minutes. I don't know if it helps but it's something my Dad used to do with his boat when I was a kid and I guess it stuck.

I like the idea about venting the gas tank by opening the cap too. Sure makes sense.

Which engine do you have? If you have a fuel-injected one, I doubt that the problem is vapor lock. If you have a 5.0 carbed power-plant, maybe.

First things first, verify whether you have spark or not when the no-start situation happens. An old spark plug and a jumper wire to ground it with is all you need....be sure to run the blower for a while first.

Vapor lock and bad ignition modules seem to be what cause this the most, but you've gotta isolate the the problem to fuel delivery or ignition before you can go about getting it fixed.

Intermittant problems are always the most aggravating to repair, and in this case you're gonna have to diagnose things while the issue is happening.

Thanks for the ideas. To answer some of your questions, I have a 2006 210ssi Chaparral with 52 hours. It has the Mercruiser 350 Alpha Drive. My tank was 1/2 full and stabilized through the winter, and I topped off the tank a couple of weeks ago. Our temperatures have been in the mid-80's recently, so we're not experiencing anything "extreme". I run the blower at all times except for extended stops such as swimming or meals, and this is when our problems start.

I thought of another "symptom" that I've had while trying to start the boat. It does not truly backfire, but we can hear a "burp" of gas coming out of the exhaust.

Again thanks for your input.

TT

There are many other things this could be such as a faulty oil pressure sender or fuel pressure sender. Many engines must detect signals from these senders before they will start.

Vapor lock is the most common cause of these symptoms though. And usually the boat will start and run fine after sitting for an additional 30 minutes or so.

I would find out who the Merc factory rep for your area is and let him and your dealer know that you are experiencing intermittent problems. There may be a service bulletin concerning this that pertains to your particular model. The dealer should know of any bulletins but sometimes one slips through the cracks.

I got my $5 bet on an ignition problem that is heat sensitive.

+1 on the ignition module -- seen it too many times before.

Same here. Sounds like thats exactly what its doing.

Yeah, could be he module or the coil but the boat is pretty new for that.

Anything added to the engine compartment over the winter that might be affecting it?

Well, it has been a bad summer for us on the boat, but I'm finally following up on our issue. We did go out again in June, but had to be towed back in another time (I guess I'm a slow learner).

I had a local mechanic go out to the slip to look it over, and he felt it was the ignition module. However, he wasn't a "certified" mercruiser rep and there was another month on the warranty. So we pulled the boat and towed it to our dealer who I haven't been real satisfied with their customer service.

Our dealer indicated that there was a crack in the fuel pickup within the gas tank and that was why we were getting the air in the fuel line. They held the boat for over 2 weeks while we waited for the part to arrive. The admiral finally got involved (don't anger the misses) and gave a good tongue lashing to the dealer, as a result they did an "in-house" repair to get us back on the water. We weren't excited about getting the boat out with "in-house" repairs, but yesterday we finally found the time and gave it a whirl.

It ran great and gave us no problems.