I have a 2000 38 fountain with 500 efi that I have owned for 5 years. Starting last year every time we took the boat out it would vapor lock always the port motor and sometimes the starboard. We only took it out 5-6 times last year and every time we had stopped for a while and it got heat soaked. Read to fox the issue is to add the mechanical pumps and we did that this year with new plugs wires cap rotor and fuel filter. All mercury parts. Took the boat out Memorial Day port engine would not start after sitting but starboard was fine. Had my mechanic look at it and he brought a computer check fuel pressure etc could not get the boat to duplicate the problem. Took boat out this Saturday and ran it about 3 hours without shutting it off stopped to talk to someone for 5 minutes while boat was idling and went to take off and port dies. Finally get it started and it is popping and back firing finally clears out get back to the trailer where the wife tells me the port dies before we put it on the trailer: my mechanic is a mercury master tech and tells me that when he was running the computer on the engines he noticed that the port may have a hotter thermostat in it 170 vs 150 in starboard and also is recommending having the injectors cleaned and tested. He is saying this is not the root of the problem but could be contributing to it. I was wondering if any of you have had the same issues and what the fix was. I trust my mechanic but don’t want to jeep throwing money at parts if someone has had a similar situation and could steer me in the right direction. Thanks

Had exact same problem with my formula 382 and 500 EFI. I installed the mercury electric booster pump kits on both sides and never had another vapor lock. Im not sure what you meant by 'mechanical pumps' but if you already installed the merc recommended booster pumps (they mount near the fuel filter and are powered by an electrical pigtail from original electric fuel pumps) then im not sure what could be causing. Just sharing in case you put something other than the electric booster pump kits in.

The stock merc t-stats are 140*f in 500efi’s.
https://www.mercruiserparts.com/bam/...31341/7595/160

When it’s the port engine having most issues, it is typically a heat causing vapor lock issue. The port engine’s are more likely to vapor lock since fuel line from tanks and fuel filter/water separator on port engines are in between the two motors.

The mechanical pumps I added ride along with the impellers.

I know the port motor gets most of the heat but I was wondering if someone maybe had a weak fuel pump wiring issue or something like that. Not sure if it is common for the boat to just die due to vapor lock when it was never shut off .

I have the same year 32 with the same motors and they will do this. I am going to do the electric pumps, but what I do to prevent it is to always have the blower motors on at idle, lots of time open the hatch a little. You have split hatches so even easier. Years ago I did have to replace port high pressure pump and eliminated the stupid little screen.

Every chance I get I try and get cool air into the engine room.

I have those kind of regulators in front of an electric pump before the separator. I also have a second electric pump underneath the front of the engine. Never had an issue. Are you set up like that too?

No mine is not set up like that

I would have that issue with my Cigarette with 500efi motors when i stop i would just open the hatch, never had a problem again

Jeff32 - that the electric antisiphon valve merc suggested as an update at one time and lots of sea rays seemingly come with ?

Isn't that just a solenoid, not a regulator?