Vapor Lock Vapor Lock

[TCHB]

I remember many years ago my dad had cars that would vapor lock on hot days. Today it is a thing of the past in cars.
A couple boats back our Howard would vapor lock on hot days when the fuel tank would go down below half full. I am not why boat builders do not put a electric fuel pump from the tanks to the engines to feed the high pressure fuel injection pump which would eliminate this problem.
I heard a couple of the tournament boat manufactures are putting in fuel pumps from tanks to feed the high pressure injection system which makes sense to me!

 

[Ziggy]

I remember many years ago my dad had cars that would vapor lock on hot days. Today it is a thing of the past in cars.
A couple boats back our Howard would vapor lock on hot days when the fuel tank would go down below half full. I am not why boat builders do not put a electric fuel pump from the tanks to the engines to feed the high pressure fuel injection pump which would eliminate this problem.
I heard a couple of the tournament boat manufactures are putting in fuel pumps from tanks to feed the high pressure injection system which makes sense to me!

The ethanol in the fuel today is contributing to more vapor lock conditions as well.

 

[kevnmcd]

On the hot days I would have vapor lock issues on one of my motors (HP500EFI) if it sat too long. I tried everything...let idle for long time before shutting off, wet rags on the fuel separator, start it every 15 minutes, leave the hatch open, etc. but it never solved the problem. Anything over 100* and it would vapor lock. Ended up adding a mechanical fuel pump in addition to the electric one off the raw water pump housing and problem solved. Never had a problem again.

 

[TCHB]

Seems strange cars have eliminated this problem but not boats.

 

[460]

I'm pretty positive I've had this happen

 

[Ziggy]

Seems strange cars have eliminated this problem but not boats.

I was having the issue last summer with my 6.2efi. Advised the ethanol in the local fuels were a likely culprit. Suggestion while parked was to open throttle after shutting off engine. Hot restarts were no longer a problem after doing that.

 

[TCHB]

When I started having this problem in our Howard I would make sure to open the engine hatch before I shut it down and I also installed additional vents under the seat that went into the engine compartment. The real fix was the addition of a electric fuel pump to keep a positive pressure on the fuel line going to the engine from the tanks.

 

[Classic Daycruiser]

:thumbup: :eek :thumbup:

 

[TCHB]

It has to be a cost issue for boats of why they do not standardize the fuel delivery system to eliminate Vapor Lock.

 

[FlatNv]

:thumbup: :eek :thumbup:

View attachment 411149

old timers would have just used this

 

[TCHB]

All of the problems that cause vapor lock are easily corrected, even on older cars. Cars can often be retrofitted with the newer technology that reduces the likelihood of the fuel lines overheating. Even on a carbureted engine, for example, a low-pressure electric fuel pump can be installed near the fuel tank, which will keep the fuel moving along the lines even if it starts to heat up in the engine compartment.

 

[racered]

old timers would have just used this

A clothespin alone is a poor heat exchanger,,wrap some tin foil or a tin can lid around the fuel line and clamp it with a clothespin and by that time the fuel has stopped boiling and your good to go

 

[Shortdeck]

All of the problems that cause vapor lock are easily corrected, even on older cars. Cars can often be retrofitted with the newer technology that reduces the likelihood of the fuel lines overheating. Even on a carbureted engine, for example, a low-pressure electric fuel pump can be installed near the fuel tank, which will keep the fuel moving along the lines even if it starts to heat up in the engine compartment.

So your saying a pump similar to this in addition to factory Mercury pump will prevent vapor lock?

 

[ColdSteel]

So your saying a pump similar to this in addition to factory Mercury pump will prevent vapor lock?
View attachment 411250

It can help. Higher pressure fuel pumps with the pressure regulator as close to the carbs as possible is one way to fix it.


Liquid boiling points are a direct relationship of temperature and atmospheric pressure.
You can make water boil at room temperature if you pull a vacuum on it. It's the same principle in which your car does not boil over at 240 with a 15psi radiator cap.

 

[Racey]

Vapor lock today is a symptom of a dead headed fuel rail combined with low boiling point shitty ethanol fuel. OEM builders make their engines this way 1) cheaper than having a flow through and less complicated to install because there is no return line to the main fuel tank, and 2) warming of the fuel by flowing it through the rail adds slightly to it's evap rate, and this is a huge EPA hurdle in the name of emmisions testing.

Most custom builders will run a flow through rail, where fuel is continually being circulated through the fuel rail and back to either a vapor seperation tank, or to the main fuel tank. This completely eliminates vapor lock.

If you have a dead head rail system no amount of fuel pumps/booster pumps will solve the issue, once the fuel has vaporized you can't put enough pressure to it to re-condense it. your only sure bet is to bleed the vapor out of the rail, usually through the schraeder valve on the end of the rail.

On carbs you can use an electric fuel pump to fix vapor lock only because once the float bowls have vaporized the needle and seat opens (or you have supplied enough pressure to overcome the needle and seat) and will bleed themselves when fuel flow is supplied to them, EFI will not do the same thing, the injectors open for such a short amount of time and have such small outlets they will not bleed air very effectively.



If you have a 525EFI, 502 Mag EFI, or similar motor with a single dead head rail you can take a rag, and small screw driver and just bump the tip of the schrader valve on the end of the rail and all the vapor will burst out. Do it while someone cycles the key, but not cranking the engine. And remember fire saftey, have an extinguisher etc ready because you will be allowing fuel to escape doing this, you do not want a fire.

 

[JDKRXW]

It has to be a cost issue for boats of why they do not standardize the fuel delivery system to eliminate Vapor Lock.

Nope.
This is the reason;
http://www.uscgboating.org/regulations/boatbuilders-handbook.php

Each manufacturer has to comply with electrical/ventilation/fuel system regulations and to meet all the standards, all of them do it a little differently.

 

[TCHB]

A lot more information on the problem!! With all this data hopefully it can help people with this problem.
http://www.offshoreonly.com/forums/...ion-lawsuit-mercruiser-vapor-lock-issues.html

 

[Shortdeck]

It can help. Higher pressure fuel pumps with the pressure regulator as close to the carbs as possible is one way to fix it.


Liquid boiling points are a direct relationship of temperature and atmospheric pressure.
You can make water boil at room temperature if you pull a vacuum on it. It's the same principle in which your car does not boil over at 240 with a 15psi radiator cap.

Thanks. I asked because I have a 8.2 Mag with a small similar booster pump and I was going to remove it. There a small fuel filter before it that's been clogging because ethanol are through silicone on the fuel tank sender gasket.

Looks like the fix is a better badder filter and keep the booster pump.

 

[TCHB]

A small fuel pump will add pounds of pressure on the line from the tank to the engine which is a lot better that no pressure. It is all about pressure and temperature. As some one said earlier just like a radiator with a pressure cap. Without it the water turns to vapor at the same temperature.

Again in my Howard I added more engine vent cooling and the fuel pump. Problem went away.

 

[rvrrun]

Ditto on ethanol being a major culprit. All we do at work is points and carbs so we see tons of this. On my t-bird, getting rid of the crappy t-pot carb and using a holley with an electric pusher just after the tank helped tremendously. On my '32, which is driven nearly daily, I use a stock mechanical pump but added 1" phenolic spacers under each of the carbs. If I stop for a few minutes and then re-start it cranks a bit longer, but I attribute that to the tri-power more than heat soak.

 

[Havasu Surfer]

When I started having this problem in our Howard I would make sure to open the engine hatch before I shut it down and I also installed additional vents under the seat that went into the engine compartment. The real fix was the addition of a electric fuel pump to keep a positive pressure on the fuel line going to the engine from the tanks.

Which Howard model?

 

[relaxalot]

Try cycling the key several times without firing the motor. Builds head pressure.

I was having this problem with the 600 sci. Change to a larger diameter fuel line coming into motor. Problem stopped.

 

[Cook'n]

Try cycling the key several times without firing the motor. Builds head pressure.

I was having this problem with the 600 sci. Change to a larger diameter fuel line coming into motor. Problem stopped.

Hi Relaxalot,
I believe this vapor lock thing is happening to me. Won't start after it sits on the beach for a while. I have a 2020 600 sci. How would I go about changing the fuel line to a larger diameter?

 

[farmo83]

I converted to EFI. Was talking to Alexi and put a fuel cooler on my system and returns it to the regulator. In discussions he advised to run ethanol free fuel as A it wouldn't eat up the fuel lines, Ethanol doubles your chances of Vapor Lock.

 

[Shlbyntro]

Solution for nearly all mercruiser engines that are experiencing vapor lock issues:

This is a low pressure, high flow fuel pump kit that mounts on the bulkhead or stringer of the boat next to the fuel tank and feeds positive fuel to the engine rather than making the engine suck it through a straw. The kit comes with everything you need and will actually work with most brands of inboards with only minor wiring required but is plug and play on a mercruiser

862264A7

PS: never pump through a mechanical diaphragm pump

 

[Cook'n]

Just to be clear... this kit would apply to the Merc Racing 600 sci and help solve vapor lock?

 

[Shlbyntro]

It is designed to be used on any engine with a gen2 cool fuel system but i have successfully used them on many engines including 700SCIs.

If you have a diaphragm style low pressure pump on your 600 engine, you will have to remove it and use a fuel pump block off plate. And then bypass it.

 

[Icky]

I was having the issue last summer with my 6.2efi. Advised the ethanol in the local fuels were a likely culprit. Suggestion while parked was to open throttle after shutting off engine. Hot restarts were no longer a problem after doing that.

This is was was suggested to me as well here on my 7.4, just gotta remember to pull it back before you start or it sounds funny

 

[relaxalot]

I had absolute marine install larger diameter fuel lines and the problem stopped.. in the mean time try cycling the key two or three times to let the pump build more pressure before actually starting it.