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.

Glad to hear that was your issue. I have the same setup in my 2006 Rinker 226 and my problem was the fuel booster pump. There was a service bulletin on this through merc. Since I had the fuel booster pump installed I have had no issues.

Hmm, I've been having similar issues with my VP 5.0 GXI. Sit in a cover for an hour on a warm day and it will not immediately start unless I advance the throttle, and/or it will start right up and spit, sputter, and pop trying to get on plane. Let it idle a bit then it will run fine. Seems to happen only on warm days with less than a 1/2 tank of fuel. Sometimes I can hear the fuel pump whine when it's having issues. So either I have a pump dying or a vapor lock issue.

On Saturday, it cranked a while to get started, as we were idling out of the cove it was having a hard time staying running, I advanced the throttle, then it was popping and bogging down, I put in neutral and it started idling at 2500rpm, slowly went back down to normal idle, then ran fine.

Sunday, I filled the tank and it was a much cooler day. After sitting in the cove for an hour, she fired right up and ran fine.

Jeez, I'm getting flashbacks to the 60's when vapor lock and other hard-start issues (or warm-start) were fairly common.

We would never accept that as normal maintenance nowadays on cars, why is it apparently so common on boats?

Well, some boats still use carburetors, for one thing. I realize RX's doesn't have one, though. But the environment for a car engine is about as different as possible. On a boat, the heat has nowhere to go. On a car it's got the whole underside to get out of of. And a lot of air passes over a car engine, but not a boat engine. Then there is the added possibility of water in a boat. It all leads to needing to maintain a boat a lot more carefully than your car.

Now there are just some things that break (like fuel pickup hoses) that shouldn't. But remember, there are far fewer boats built every year than cars, so the parts makers may not have made as many parts in 10 years as a car maker makes in 1. So problems may not show up as fast, or be as quickly corrected.

Yet we get the privledge of paying lots more for boats and parts.

Hey, you gotta pay to play!

Topeka, I'm having a hard time understanding how a cracked pick-up is causing your trouble. It seems to me if the fuel system is sucking air from the crack, which it would do all the time--hot or cold, the boat should be giving you problems from the first start of the morning--not just after it gets hot.
For your sake I hope they did find your culprit, but things aren't adding up in my simple mind...

Just a thought, and it is only a thought. Fuel pick up always introduces small air bubles into the line. Not enough to cause loss of prime on the pump or impact running of the motor based on boating style.

After running for a while, motor shuts off and air bubbles expand due to heat and now it loses prime on the pump and can't get running.

Again, I could be totally off base.

IMO boat engines don't get hot enough to cause vapor lock (gas vaporizing in the fuel line). What sometimes passes for vapor lock is gas boiling in the carb, which can cause the same symptoms.

The reason the cracked pickup would cause the trouble is because the fuel in the line can drain back into the tank. This results in air in the fuel line, which is a mirror image of vapor lock. And I've read what many folks here have said about air in the fuel filter/separator...

I just find it strange that I only have the starting problems after the engine has been off 30+ minutes on a hot day. If it's over 85 out it almost always happens, under that it never does.

My VP 5.0GXI runs 175 degrees. That's quite a bit of heat.

I might have the dealer do some diagnostic work in the fall. The problem has been getting worse, so maybe something is wrong with the fuel system.

JMO...Since it is fuel injected, I would be looking at the ISC motor real close. Heat build up after shut down causing it to bind up and not allow for proper movement of the spool valve causing a hard start and or ruff idle. After replacing mine I now relize that it was going bad for a while but I didn't pay close enough attention to the signs. I would be idleing down a nowake zone and every miniute or so it would surge. Not alot but just enough to hear. Soot on the transum tunnel every now and then. Thought it was from pulling tubes and the stop and go. The $90 part is real easy to change. I'm not sure a scanner would pick anything up until it fails.

RX, I take it your engine is fuel injected? If so, you can do a little diagnostic checking yourself. You'll need a medium sized phillips screwdriver, and a sacrificial rag. You'll need to locate the schrader valve on the fuel rail, and remove the cap...

Next time you've sat for 1/2 hour on a hot day, remove the valve cap, bunch up your rag in one hand (wearing gloves wouldn't hurt), hold the rag above the valve, then press in the valve QUICKLY with the screwdriver...

You SHOULD get a good spray of gas out of the valve. If you get a small dribble, or nothing, then your fuel line has lost pressure (which it shouldn't do for hours). This could indicate a similar problem as tumbleweed's, or a bad fuel pressure regulator, or possibly a bad check valve in your fuel pump. It could also indicate an injector that's leaking down, which would be indicated by lots of black smoke when it finally starts.

All I can think of for a reason why it only happens on a hot day is pressure buildup in the fuel system from residual heat, which could be the difference between a sketchy check valve or regulator holding pressure, or not...