mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

[toddstockwell]

Newer 3.5 hp Mercury outboard 4 stroke only runs for 15 min max then bogs down and quits. If I wait 10 min it will start again and run for a while. I don't know if it overheats or if it is a fuel problem. Any ideas? Thanks Todd

 

[Bosunsmate]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

Is it pumping water ok?
Put your hand on the head when it bogs down, it shouldnt be scolding hot. Sounds overheating to me if it is running alright for the first ten or so minutes

 

[joed]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

Fuel tank air vent open?

 

[toddstockwell]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

Is it pumping water ok?
Put your hand on the head when it bogs down, it shouldnt be scolding hot. Sounds overheating to me if it is running alright for the first ten or so minutes

thanks for your reply. Yes it does squirt water. I'm not sure if it's enough. It does feel like the head is hot. Do these things have a thermostat, Or do you think it could be that the impellar needs to be replaced?

 

[toddstockwell]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

Fuel tank air vent open?

Yes the vent is open. Thanks Todd

 

[Bosunsmate]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

thanks for your reply. Yes it does squirt water. I'm not sure if it's enough. It does feel like the head is hot. Do these things have a thermostat, Or do you think it could be that the impellar needs to be replaced?

Yep it does have a thermostat, i just checked.
It could also be a restriction between the fueltank and the carb bowl so you may want to pull off the fuel line and check that it is flowing out ok at the end where it joins onto the carb.
If you cant put your hand on the top of the head when it cuts out, it is in my opinion scolding hot and would be overheating with possible preignition or worse.
That could mean its the impellor or something else like the thermostat. If its is coming out with a squirt the impellor is normally ok but not always... if its a dribble then thats definitely not ok.
You could remove the thermostat and heat it up in a saucepan to check it opens and make sure its not clogged up.
The thermostat housing is by the sparkplug. just undo the two bolts and try and be careful to not rip the old gasket there but you will be able to tell if its leaking on reinstall pretty easily there.

 

[quicktach]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

Are you using a good octane straight gas ? Pulled a plug to check for oil / carbon ? Water intake clean ?

 

[toddstockwell]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

I'll try both things. Are you from Bay of Islands? I was there once. Beautiful. Our fishing guide took us by Zane Gray's house. I was amazed he had a house there . I am from So. California. He has a house here also on Catalina Island. I guess he got around OK back in the day. Thanks for the tips, Todd

 

[toddstockwell]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

I'll Pull it, Thanks

 

[Bosunsmate]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

I'll try both things. Are you from Bay of Islands? I was there once. Beautiful. Our fishing guide took us by Zane Gray's house. I was amazed he had a house there . I am from So. California. He has a house here also on Catalina Island. I guess he got around OK back in the day. Thanks for the tips, Todd

Yep, i live in the bay of islands, the opposite side of the bay from Zanes place. Thankfully it doesnt take me with my merc 500 the 26 days to get there it use to take him to get out from CA to those deepwater fishing grounds. The big snapper are in the shallow waters lately as they warm up so you can fish quite well close in to home at the moment. Hopefully your charter got you a marlin, a lot of world records go to the local waters around here.
This is heading back from Cape Brett in my friends boat last week, a few nautical miles out past Zanes, constant work ups out there by king fish, kahawai and killer whales

 

[toddstockwell]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

Bosunsmate: my issues just got worse it won't even idle . I start it with choke, it runs for 7 seconds, then reves up to high rpm and dies. I just replaced the fuel filter. I can't find the thermostat. Did you say you knew where it was? Todd

 

[erie_guy]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

It does sound like a fuel issue. Fuel starvation causes a rev to high rpm just before it dies. Check for fuel line problems or carb issues. If possible try a different fuel line and tank.

erie_guy

 

[Bosunsmate]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

I agree with erie, it wont be just a thermostat if it wont idle.
It may of had some dirty fuel stuff/fuel gum block the float valve or something in the passages.
Take the sparkplug out after it has being pulled a few times and see what it looks like? Brown,wet/dry etc

 

[toddstockwell]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

I changed the fuel filter. Do they have different flow rates? It doesn't look like the original

 

[Bosunsmate]

Re: mercury 3.5HP outboard quits after 15 min , then can restart after 10min rest.

I didnt know it had a fuel filter.
If it got worse when you changed it, run it without one and see how that goes for a few minutes.
All my small outboards have never had a filter but my ride on lawnmower does probably due to all the dust/grass in the air.
check the new filter isnt gunk covered first too