502 MPI w/cool fuel return line fuel flow
07-16-2014, 11:58 AM
#11
Registered
You won't hold pressure in the rail if you run the return back to the tank. But, that's OK. As soon as you turn on the key and the pump primes, it will fill the rail and pressure it up. It's not a problem not having pressure in the rail when the engine is not running.
If you are referring to when it's running, the return line is after the regulator, so all of the fuel being returned is excess fuel.
Eddie
07-16-2014, 12:54 PM
#13
Gold Member
Do you notice the vapor lock more prevalent in the port motor than right? Or are they the same?
Mine seems to always happen on the port motor, and I came to the conclusion that it may be because that water separator is on the right side of that motor which puts it in the center of the boat and close to (2) manifolds rather than just one. Therefore, I relocated my port side water separator to the port side stringer in front of the cool fuel pump assembly. Gonna try this and see if it cures the problem.
Good luck! Btw, where did you source the fill tube adapter for the new return line?
Mine seems to always happen on the port motor, and I came to the conclusion that it may be because that water separator is on the right side of that motor which puts it in the center of the boat and close to (2) manifolds rather than just one. Therefore, I relocated my port side water separator to the port side stringer in front of the cool fuel pump assembly. Gonna try this and see if it cures the problem.
Good luck! Btw, where did you source the fill tube adapter for the new return line?
Currently doing the return line from fuel/water separator housing to gas tank modification on my stock '99 502's to rid the huge vapor lock issue.
I'm going to tee the return lines together so that I may run a single hose up to my gas fill hose and tee into it, vs running 2 separate hoses up. (No provisions at tank, nor sending unit return port option possible, gotta go to the fill hose)
I have no idea on how much fuel flows thru the return lines. Plan is to use 3/8" ID hoses. Will a single 3/8" hose handle the return flow of both motors for the 13' of hose? Don't want too small to where too much restriction effects the fuel regulators, nor any larger hose than needed.
Thanks
I'm going to tee the return lines together so that I may run a single hose up to my gas fill hose and tee into it, vs running 2 separate hoses up. (No provisions at tank, nor sending unit return port option possible, gotta go to the fill hose)
I have no idea on how much fuel flows thru the return lines. Plan is to use 3/8" ID hoses. Will a single 3/8" hose handle the return flow of both motors for the 13' of hose? Don't want too small to where too much restriction effects the fuel regulators, nor any larger hose than needed.
Thanks
07-16-2014, 01:08 PM
#14
Registered
The fuel pressure regulator persay regulates the fuel to the injectors that is needed any excess fuel the regulator bypasses it thru then thru the return line back to the fuel filter head.
I will say this the boats that have the electric fuel pump mounted inside the gas tank never have problems with vapor lock. One the fuel is cooler thru the system, the electric fuel pump is better pushing fuel rather than pulling it - so this alone helps with fuel cavitation hence really helps with vapor lock.
Also the electric fuel pump stays a whole lot cooler being mounted inside the gas tank especially after engine shut down. It does not heat soak being mounted inside the gas tank.
Mercruiser or Volvo has never mounted a electric fuel pump inside the gas tank. I believe Ilmor is or wants to. OEM engine manu's and boat builders have to work with the coast guard on the design of it. Mastercraft, Indmar does this on a lot of their boat installs.
I will say this the boats that have the electric fuel pump mounted inside the gas tank never have problems with vapor lock. One the fuel is cooler thru the system, the electric fuel pump is better pushing fuel rather than pulling it - so this alone helps with fuel cavitation hence really helps with vapor lock.
Also the electric fuel pump stays a whole lot cooler being mounted inside the gas tank especially after engine shut down. It does not heat soak being mounted inside the gas tank.
Mercruiser or Volvo has never mounted a electric fuel pump inside the gas tank. I believe Ilmor is or wants to. OEM engine manu's and boat builders have to work with the coast guard on the design of it. Mastercraft, Indmar does this on a lot of their boat installs.
07-16-2014, 02:29 PM
#15
Banned
iTrader: (9)
it is a better set up that way plus never see vapor lock. In Texas especially the one year we set record high temps for 3.5 months straight - and the warmest high temps for the water in the lakes - vapor lock was so very common.
Even for some boats that ran the line back to the tank. Granted we do not see that many boats having the return line set up back to the gas tank compared to the stock set up. To add to this the boats that had the electric fuel pumps in the gas tank never had vapor lock issues that same year. IMO I rather have that set up and never have a boat with the VST set up. The VST is a problem child itself even without vapor lock.
Even for some boats that ran the line back to the tank. Granted we do not see that many boats having the return line set up back to the gas tank compared to the stock set up. To add to this the boats that had the electric fuel pumps in the gas tank never had vapor lock issues that same year. IMO I rather have that set up and never have a boat with the VST set up. The VST is a problem child itself even without vapor lock.
Last edited by BUP; 07-16-2014 at 02:35 PM.
07-16-2014, 02:40 PM
#16
Banned
iTrader: (9)
Most rec boats in the past 15 years that have MPI or TBI engines have all the air ducts and hull air vents in the rear of the hull just under the engine hatch cover. In that case it does matter which side the water sep fuel filter is located on the front of the motor. Just saying.
07-16-2014, 03:09 PM
#17
Registered
I have a 1st Gen vst pos so if anyone knows of an in tank pump I would do that and be done with it. It's been over a 100 here for the he last couple weeks so it's going to be problem time again
07-16-2014, 05:11 PM
#19
Registered
iTrader: (1)
Too bad someone couldn't make a system like Aeromotive's Phantom: http://aeromotiveinc.com/phantom/
to install in most marine tank's sender location. That would be cool. Someone get on it. Snap. Snap. Lol.
http://www.youtube.com/watch?v=aFd-zQN_aoA&feature=player_embedded
to install in most marine tank's sender location. That would be cool. Someone get on it. Snap. Snap. Lol.
http://www.youtube.com/watch?v=aFd-zQN_aoA&feature=player_embedded
07-16-2014, 05:42 PM
#20
Registered
Do you notice the vapor lock more prevalent in the port motor than right? Or are they the same?
Mine seems to always happen on the port motor, and I came to the conclusion that it may be because that water separator is on the right side of that motor which puts it in the center of the boat and close to (2) manifolds rather than just one. Therefore, I relocated my port side water separator to the port side stringer in front of the cool fuel pump assembly. Gonna try this and see if it cures the problem.
Good luck! Btw, where did you source the fill tube adapter for the new return line?
Mine seems to always happen on the port motor, and I came to the conclusion that it may be because that water separator is on the right side of that motor which puts it in the center of the boat and close to (2) manifolds rather than just one. Therefore, I relocated my port side water separator to the port side stringer in front of the cool fuel pump assembly. Gonna try this and see if it cures the problem.
Good luck! Btw, where did you source the fill tube adapter for the new return line?
In some boats it just doesn't matter and they both vapor lock. It all depends on the ventilation it has. Moving your filter head may be enough to stop it from doing it.
If not, return the fuel to the tank and it will certainly stop for good.
Eddie
