Help to eliminate vapor lock

[Puddy905]

I have a 98 Maxum 1750NB with a 3.0 Merc. Two winters ago, I decided to gut the boat and install and brand new interior. It turned out looking great. I decided to bring the look up to date by removing the center engine cover and building a full sunpad and bench seat. Over last summer, I had several occasions when the boat wouldn't start. This would only happen on warm days, when the boat had been running for a while, or on long cruises, where the motor had been runnning for over an hour. After process of elimination, I attributed the problem to vapor lock.
So, to avoid the problem this year, I need to figure out how to eliminate the problem. I believe bc the new style sun pad completely encapsulates the motor, a lack of ventilation is causing the majority of the problem.
To resolve this, I figured I could add two new ATTwood Turbo 4000 blowers, on either side of the motor...one to bring in cool air and blow it into the bottom area of the motor, and then one on the other side drawing hot air off of the top of the motor and out of the boat.
Next I was going to wrap the exhaust with "race-car" style exhaust wrap, to try and keep the heat in the pipe.
Lastly, as a final measure, I can remove the old fuel line, and make a new one which travels from the pump, away from the motor, then back to the carb, to try and keep the fuel which sits in the line cooler.

I haven't rebuilt the carb in a while, but it starts fine when it's cold, and idles/runs perfectly.

I would like to know if I can put the two Attwood blowers on the same existing blower switch.
Also, any other suggestions on how to overcome this issue would be great.

Thanks

 

[spdracr39]

Re: Help to eliminate vapor lock

I did the same thing and it kicks the 5 amp breakers. I checked the wire size and switch specs and found mine would handle two 10 amp breakers. I have two three inch bilge blowers stock at 3.5 amps each and added two 4 in blowers circulating cool air across the top that draw 4.5 amps each. They are split on two breakers and one switch. It hasn't been hot enough to know if this works for sure but so far it has solved the issue. Both of my add ons are blowing air in from one side and letting it vent on its own on the other. Hopefully pressurizing the engine compartment with cooler air. I also left my bilge blowers sucking the gas fumes from down low and sending them straight out the back as the factory installed them.

 

[Puddy905]

Re: Help to eliminate vapor lock

Thanks for the reply. I will try that and post the result.

 

[Don S]

Re: Help to eliminate vapor lock

You do need more ventilation to get the heat out, since heat is what causes vapor lock. But I sure wouldn't wrap the exhaust. You want the heat away from the engine and carb, and wrapping up the exhaust keeps the heat in the exhaust AND INTAKE which also heats up the carb.
Insulation and plugging up all the areas around the engine may help keep the noise down, but it also prevents the hot air from getting out.

Each blower needs it's own switch and own fuse. Then if one fails, you still have the other working and you won't be overloading the 16ga wire that most manufacturers use for a single blower.

 

[rallyart]

Re: Help to eliminate vapor lock

I had the interior redone on my 18' I/O and the installer had covered some of the paths to allow air into my engine compartment with material. I had a very frustrating time with vapor lock for a month until I spent a couple hours rearranging things and making sure the ventilation was very good. No problems since.

 

[NYBo]

Re: Help to eliminate vapor lock

Do NOT use a blower to draw air in! If the other blower fails or moves less air, you will pressurize the engine compartment. This will force the air, potentially with gas fumes, out through any and all openings in the engine compartment. This would not be a good thing.

Insulating the fuel line might help.

 

[Utahboatnut]

Re: Help to eliminate vapor lock

Have you tried just leaving the blower thats already there running all of the time? I sometimes forget to shut mine off and dont even realize its running until i shut down.

 

[LippCJ7]

Re: Help to eliminate vapor lock

I would like to see some pics of the boat, I think you are focusing too much on getting heat out and could use more getting cool air in, there are vents that you can install on the sides of your boat and then duct the air to your engine compartment that would help a bunch, if your boat has the two seats on either side of the motor could you redo the setup to be more like a bench seat in front of the motor and allow for more space in the engine compartment?

some other options would be an electric fuel pump with a return fuel line or just upgrade to fuel injection completely which does this anyway, increasing the size of your fuel lines may help somewhat.

Ultimately like I said earlier I think you need to focus on getting more cool air in, taking it in from the sides naturally (with scoops) as your boat runs would be best and get a lot of airflow into your engine area, but another idea would be to install vents on the top of the engine cover and then more vents on the rear transom up high, give the heat a place to go and then give it some flow to help it get there.

 

[NHGuy]

Re: Help to eliminate vapor lock

My boat has a full sunpad and rear bench seat. It cools fine with nature and the blower. But I think the manufacturer left some air gaps on purpose to assist with air flow.
Example, behind the rear bench there is a bulkhead with a 4' wide opening that goes from the floor up about 10 inches. Also along and just below the gunwales the air can pass through into the engine compartment. So sure a blower might help but I'd also try something passive like the venting in mine.
The blower is a great thing, I run mine after shutdown and before restart on hot days just to remove some of the heat soak that happens in there. You can also play smart by running the motor at 12 or 1600 rpms for a time before shutdown to remove some of the engine heat through the cooling system. When it's running without load it does not make much heat, running above idle can help.

 

[oldjeep]

Re: Help to eliminate vapor lock

With a 3.0L, the secret usually is to just make sure to let it idle for a bit so that it cools down before turning it off. If you shut them down after a full throttle run then they tend to get cranky about starting back up.

 

[Oshkosh1]

Re: Help to eliminate vapor lock

Buy a ?" Phenolic spacer to put between the carb and intake manifold...I had the same symptoms and after I did that they went away. It keeps the carb from acting as a heat sink. I can't remember the numbers (temps) I saw with my IR gun on it, but do know that the temp of the carb dropped significantly.

 

[Puddy905]

Re: Help to eliminate vapor lock

Thanks for all the good ideas. I do have vents on each side of the boat. One has the blower attached and the other just a hose for natural air. I think I may try repositioning the hoses first and possibly opening up more area for air to circulate around the motor. If this doesn't work I will go to a bigger blower. I do leave the blower on the entire time I run the boat and let it idle for a minute or two before shutting down. I will post pics early in the week

 

[LippCJ7]

Re: Help to eliminate vapor lock

Thanks for all the good ideas. I do have vents on each side of the boat. One has the blower attached and the other just a hose for natural air. I think I may try repositioning the hoses first and possibly opening up more area for air to circulate around the motor. If this doesn't work I will go to a bigger blower. I do leave the blower on the entire time I run the boat and let it idle for a minute or two before shutting down. I will post pics early in the week

ok if you have side vents then I would add vents on the transom, I would then put your blower on one of the transom vents, if your side vents are mounted in a good free flowing area its likely that your blower will only impede free air flow while underway sort of like a radiator fan, at some point the fan blocks more air then it pulls so most radiator fans have a clutch which eliminates this problem, also by installing rear (rear facing)vents you are allowing the air a place to go, allowing a more natural flow through the engine compartment.

 

[frantically relaxing]

Re: Help to eliminate vapor lock

Only vehicles I've ever had vapor lock were motorhomes with underhood temps in the BBQ range, and even then only when climbing hills while towing something with the engine on the verge of overheating. A boat motor that runs water cooled exhaust and a 150? thermostat should never get warm enough to cause a vapor lock. And even if it did, it would happen while running, not while parked. The only way vapor lock would prevent a warm start is if the all the gas in the carb boiled away from the heat. Not gonna happen. It is possible the gas may boil in the carb from residual heat, but not for long, and certainly not long enough to evaporate it all. If it did, you'd have an explosion hazard under the engine cover.

I'm going to bet a buck your problem is just the opposite; your engine is hard to start not because it's starving for fuel, but because it's flooded...

A warmed up engine needs very little fuel to restart. While sitting still, it doesn't take long for your choke plate to start closing. If your choke is set up on the rich side, then it may be nearly closed within a short time, adding way more fuel than needed when trying a warm re-start. Another possibility is your float level may be a snick high, and when shutting down some fuel percolates out of the venturi's and/or the bowl vents into the carb throat. This fuel will leak past the throttle plate and sit inside the intake manifold. If it's much fuel, it can cause a hard start.

But my money's on the choke needing adjusting. And the extra heat you may have created with the remodel would make a rich condition worse...

FWIW, I keep the chokes on the engines of our SkipperLiner to where the choke opening is at least 1/4" at around 45? air temp. Both engines start instantly when cold with one throttle push 'n back, even after sitting for weeks. But when warmed up the starters run about 2 seconds before firing, with NO throttle push. If I DO throttle push when warmed, it takes even longer to start...

Just my opinions...

 

[spdracr39]

Re: Help to eliminate vapor lock

Vapor lock does exist on boats and it occurs because of heat soak after the engine is shut off. My boat is fuel injected and it does it. The fuel boils in the fuel line and won't pump. A primer pump will help but is very expensive. Lowering engine compartment temps is the solution but it hard to manage without whacking new holes in the boat which I think we all try to avoid.

 

[H20Rat]

Re: Help to eliminate vapor lock

Each blower needs it's own switch and own fuse. Then if one fails, you still have the other working and you won't be overloading the 16ga wire that most manufacturers use for a single blower.

No need for multiple switches, that just clutters things up. Wire the existing switch to a dedicated relay and fuse, one per blower. The factory switch kicks on all the relays, and the relays turn on the blowers.

 

[spdracr39]

Re: Help to eliminate vapor lock

You do need more ventilation to get the heat out, since heat is what causes vapor lock. But I sure wouldn't wrap the exhaust. You want the heat away from the engine and carb, and wrapping up the exhaust keeps the heat in the exhaust AND INTAKE which also heats up the carb.
Insulation and plugging up all the areas around the engine may help keep the noise down, but it also prevents the hot air from getting out.

Each blower needs it's own switch and own fuse. Then if one fails, you still have the other working and you won't be overloading the 16ga wire that most manufacturers use for a single blower.

Mine has a twenty amp rated single switch but the circuit breakers run one bilge and one vent blower each. The 16 gauge wire is rated at 10 amps at twenty feet and I am only drawing 8. Just be sure to check the ratings of all your components.

Do NOT use a blower to draw air in! If the other blower fails or moves less air, you will pressurize the engine compartment. This will force the air, potentially with gas fumes, out through any and all openings in the engine compartment. This would not be a good thing.

Insulating the fuel line might help.

My engine compartment only vents to outside air. I have no sparkable compartments or cuddy so this isn't a problem for me but is something to consider.

Have you tried just leaving the blower thats already there running all of the time? I sometimes forget to shut mine off and dont even realize its running until i shut down.

In my situation that was not enough because the factory blowers remove air from the bottom of the bilge which is cool already. All the heat builds up at the top and just sits there.

With a 3.0L, the secret usually is to just make sure to let it idle for a bit so that it cools down before turning it off. If you shut them down after a full throttle run then they tend to get cranky about starting back up.

I did this too and no dice.

No need for multiple switches, that just clutters things up. Wire the existing switch to a dedicated relay and fuse, one per blower. The factory switch kicks on all the relays, and the relays turn on the blowers.

More complicated to wire up but definately the best scenario. You could go one step further and wire in a temp sensor and have them kick on and off automatically. If your existing wiring won't handle the extra load I would go this route for sure.

My original fix was to just open the engine cover and leave it open while we swim. The biggest problem with this was the sail effect (we dont always drop anchor). Also, so many friendly boaters would stop to make sure we weren't having trouble that I felt compelled to do something different.

 

[Puddy905]

Re: Help to eliminate vapor lock

I did think choke right off the bat. I actually adjusted it all the way off, but still had the same problem. Vapor lock does exist bc new boats have an option of a fuel cooler. I don't have room between my flame arrestor and sundeck to add a spacer to the carb. I am
Going to do a compete rebuild on the carb, and I may replace the diaphragm on the fuel pump at the same time, just to rule that stuff out. The vents on the sides of my boat aren't the greatest. They have covers over them that don't let much natural air in. I considered adding a vent at the back, but I'm worried about water penetration when it rains. Anyways, lots of work to do this week. Hopefully with all these great tips the issue will go away!