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502 Mag MPI Gen VI Hot start issue

Old 03-07-2021, 08:14 AM
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Originally Posted by carnutsx2 View Post
Is it against coast guard regulations to return the warm fuel back to the tank?
Nothing in the regs, and diesels have always done its. That said, Ilmor started doing it years ago

https://www.uscgboating.org/assets/1...YC.1002.01.pdf
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Old 03-07-2021, 10:34 PM
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Originally Posted by Griff View Post
If you have the cool fuel plastic covers around your fuel filters, take them off.
I wouldn't waste your time wrapping the fuel rails or lines. That silicone jacket will hold heat in as well as keep it out.
Heck, just opening the hatch and dumping a bottle of cold water on the fuel filter and lines when you dock will probably cure it.
I have never had to open my schrader valve when I've had an issue. Just cycle the key about 5 times to the run position and on every 5th time try and start it. Repeat a few times if needed.
Good info. Did a test run to recreate the Vapor lock and we succeeded but this time we were at our dock. Schrader valve fix worked like a charm so thats my ace in the hole. Ill try the key on off method next time. Do you know about the Mercury check valve fix? It goes between the TStat and the cool fuel to prevent hot water from draining back into the cool fuel system after shut down.
https://nuwavemarine.com/oem-mercury...t-21-862271a1/
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Old 03-08-2021, 01:06 AM
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Originally Posted by lear60man View Post
Good info. Did a test run to recreate the Vapor lock and we succeeded but this time we were at our dock. Schrader valve fix worked like a charm so thats my ace in the hole. Ill try the key on off method next time. Do you know about the Mercury check valve fix? It goes between the TStat and the cool fuel to prevent hot water from draining back into the cool fuel system after shut down.
https://nuwavemarine.com/oem-mercury...t-21-862271a1/
Never heard of that as a fix for vapor lock.
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Old 03-08-2021, 01:09 AM
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Originally Posted by Griff View Post
Never heard of that as a fix for vapor lock.

Im going to make a call or two to investigate the check valve in the AM. Im also looking into a wireless remote for the engine latch. Problem with my boat is you cant really get on or off with the hatch/bench up. A remote would solve that issue from the dock.
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Old 03-08-2021, 08:15 AM
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Originally Posted by lear60man View Post
Good info. Did a test run to recreate the Vapor lock and we succeeded but this time we were at our dock. Schrader valve fix worked like a charm so thats my ace in the hole. Ill try the key on off method next time. Do you know about the Mercury check valve fix? It goes between the TStat and the cool fuel to prevent hot water from draining back into the cool fuel system after shut down.
https://nuwavemarine.com/oem-mercury...t-21-862271a1/
Same here have not heard that as a fix for VL
Merc did start putting in check valves in the pump feed, but at the same time the pump was moved to the starboard side and it became a box with high priced filters. It may help keep the fuel cooler in the box, but don't see how that will keep the heat away from the rail
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Old 03-08-2021, 09:49 AM
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Originally Posted by AllDodge View Post
Same here have not heard that as a fix for VL
Merc did start putting in check valves in the pump feed, but at the same time the pump was moved to the starboard side and it became a box with high priced filters. It may help keep the fuel cooler in the box, but don't see how that will keep the heat away from the rail

I never hear of it before investigating this issue and reading through the Mercury Service Bulletin. They talk about it in section 6.c of the below document...........
"EFI and MPI engines with the ‘Cool Fuel’ system should have the fuel cooler temperature measured after the engine is shut off. The coolant hose going to the ‘fuelcooler’ should not get much hotter to the touch after the engine is shut off for 10-20minutes than what it is with the engine running. If it gets hot after the engine is shutoff, hot water from the cylinder block might be siphoning back. Installing the CheckValve Kit will stop this backward water flow."

https://stu-in-flag.net/blog/wp-cont.../vaporlock.pdf

Ill hit this hose with a infared thermomoter after an engine flush today to see if and how much a rise I get. If I get a significant rise, I might look further into this check valve. Adding Stabil is another cheap/easy recommendation in the Service Bulletin but my local fuel source said their fuel does not contain Ethanol.

Hell, Im leaps and bounds ahead of where I was a few days ago chasing down this hard start issue thanks to you guys.
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Old 03-08-2021, 11:07 AM
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Good to know, thanks
Was put out in 99 and looks like this is Merc first try's in trying to solve the problem. Some of the later model small blocks used the check valve on some open and closed cooling models but later was only used on closed. Then when box pump/filter was used on 3 point drain and not on 7 point.

The new 8.2 use closed and no check valve
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Old 03-08-2021, 03:10 PM
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So after much thought and wading through various solutions, I came up with a game plan. Put rubber washers under the bilge blower (MUCH quieter) and start using it after shutdown, a Bottle of Sta-Bil every fill up, removed the Cool Fuel covers as per Griffs suggestion, and adding a wireless controller to the engine hatch actuator. I found an industrial wireless controller for the lifting actuator, made in the USA for $150. Its designed for dump trucks, heavy lift gates etc and has internal relays. The receiver also has UP/Down buttons and will be mounted in an easy to get to location for when I loose the remote. 4 wires, 2 to the ram, Pos and Neg. Easy peasy.

If that doesnt work, Ill look into adding pre pumps or reroute the vent lines back to tank or? So yea, dock, turn on blower, hop off boat, raise hatch, come back to a boat that will start. Sounds good according to the bar napkin last night. Ill post a link to the wireless controller once I get it hooked up and working.
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Old 03-08-2021, 03:43 PM
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If you want the problem gone for good, just run the return back to the tank. It is an easy fix and it doesn't require any sort of check valve. Just unscrew the return line from the filter head and plug the hole in the filter head. Hook a hose to the return line and hook it to a barb on top of your fuel tank. This works 100% of the time in my experience. No need to reinvent the wheel for an easy fix
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Old 03-08-2021, 03:48 PM
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^^ Agree
and keep the Sta-Bil on the shelf for winterization
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