2007 496MAG stalls when idling for 10 min.

[Atomboy]

This happens with it without refueling. When this happens I let it sit for 20 minutes and I can start the engine just fine. I also tried to start the engine with the transmission disengaged so I can start the engine at a higher RPM but I had the same result. I thought he was related to vapor lock however I don’t see how this is related to idling.
Other than this problem I have had no problem at all with this engine. Any help would be much appreciated in advance.

 

[alldodge]

Need serial number
Does it do it with the motor cold and hot or just hot?

After idling for 10 minutes, it has to sit for 20 before it will restart and run another 10 minutes?
Or something else, need more info

 

[Atomboy]

Only when hot. I typically tie up and wait 10-20 mins with the engine off when this happens. No aceesss to serial # at this moment. The engine temperature is within the normal range. Thank you.

 

[Atomboy]

DTS with 200 hours. Only unleaded fuel. Cool fuel filter looks clean.

 

[alldodge]

I would think its vapor lock, but it normally takes more then 10 to 20 minutes to get heat soak going. What happens to most is the engine is stopped and folks go eat lunch or float around for an hour or so. When restarted it seems fine but then starts to die out, and then cannot restart. Has to sit long enough to cool down or air needs to be purged from fuel rail

If you bring a rag with you, remove cap on fuel rail covering shrader valve. Place rag over valve and use small tool to press in on the valve. Might need to cycle the fuel pump. If you get air and fuel, then need to get air out then it should fire up

 

[Atomboy]

So when idling cool fuel filter is not cooling the fuel line at all? That’s what got me confused. I wonder if running blows would help. Thought?

 

[alldodge]

The term "cool fuel" is just what Merc calls it. Yes there is some cooling water that comes from the seawater pump that is used to cool the fuel. The issue is the fuel that gets heat soaked is on top the motor in the rail. The best fix for vapor lock is to return the unused fuel back to the tank, but Merc returns it to the fuel filter.

Yes it does help to run the blowers, also to let the motor idle for several minutes after running on plane for a bit. The idling helps cool the motor down a bit more, and blowers with the air.

You can have the return line routed back, and many have don it, I also have mine going back to tank

 

[Atomboy]

The term "cool fuel" is just what Merc calls it. Yes there is some cooling water that comes from the seawater pump that is used to cool the fuel. The issue is the fuel that gets heat soaked is on top the motor in the rail. The best fix for vapor lock is to return the unused fuel back to the tank, but Merc returns it to the fuel filter.

Yes it does help to run the blowers, also to let the motor idle for several minutes after running on plane for a bit. The idling helps cool the motor down a bit more, and blowers with the air.

You can have the return line routed back, and many have don it, I also have mine going back to tank

Thanks. I've reread your response and am still trying to figure out why idling or running it very slow , say 2-3 mph for 10-20min can cause the vapor lock. I can see if I turn off after running it hot, heat soaking period can cause the vapor lock. However, if I idle or run very slowly, do you think there will be still unused fuel that returns back to the fuel filter? In other words, if I idle long enough do you think it can still cause the vapor lock? it only happened when I was waiting a the locks by either idling or barely moving just trying to hold the position. Thanks in advance.

 

[alldodge]

If it is doing it, then its the first motor I've heard of doing it. The pump is supplying more fuel then the motor can use, so it keeps circulating fuel back to the filter. If this is enough to make it happen, I don't know, this is why I mention using the rag. If you see bubbles then there is vapor lock happening or there is something else.

Might have something to do with fuel pressure regulator or other. If you place a fuel pressure gauge on the rail we can get this info. Most high pressure gauges also have a clear bleed tube and push button valve. So when this happens, the pressure can be read, then the button can be pushed to see if air is found.