2004 Yamaha F115 TLRC no start when hot

Majek RFL

Recruit
Joined
Jan 18, 2023
Messages
5
I bought this boat and 700 hour engine a few months ago- I rewired the entire boat. Then, I was out fishing one night and it quite running at idle. Had to get towed in. I found a couple of issues with the fuel system then-the pickup tube in the tank was only 15 inches in an 18 inch tank, and I had a about 4 inches of fuel at the time. Also, the engine fuel filter plastic housing was cracked.
While troubleshooting this, since it was an old engine, I wanted to make it as reliable as possible so I replaced the following parts.
All new fuel hoses
New pickup tube in tank
New squeeze bulb
New high pressure fuel pump
Cleaned VST and filter
New low pressure fuel pump
New fuel filters all around
New fuel pressure regulator
New thermostat
New spark plugs
Oil change

I continue to have a problem with the engine not starting when hot. Today I ran it on a long run slowed down and idled a few minutes and shut it down, but it will crank but not start. I pumped the bulb which only took a couple of squeezes to get tight. Depressing the schrader valve on the fuel rail yields air and fuel, almost an atomized mist. I wasn't able to start it until I had someone crank it while purging the air from the shrader valve. I've also had an issue where I was able to pump the bulb and keep it running, but it seems to correct itself after a minute of this.
The engine runs great when it runs, I ran it for hours today with no issues until I stop and try to restart it.
I am at wits end trying to fix this myself. I also just had to replace the lower unit because the gear carrier nut threads stripped out when we removed it to repair some corrosion on the drive shaft due to bad seals. I have the winky blinky yamaha tool I am going to hook up to it, and I am going to buy a fuel pressure tester to check it. I suspect there is a temperature sensor acting up, but the air in the fuel rail is throwing me off. I am wondering if anyone has any ideas or tips to help.. Thank you-this is driving me nuts!
 
Last edited:

Majek RFL

Recruit
Joined
Jan 18, 2023
Messages
5
possibly the VST is getting hot enough to vaporize the fuel
I was thinking about this last night.
Fuel flows from high pressure pump, through the fuel cooler to the fuel rail.
Water flows through the fuel cooler just before exiting through the tell tale pee hole.
So if there is no water flowing out the tell tale, there is no or insufficient fuel cooling.
One thing I left off was I was getting an overheat alarm at various times yesterday, which I left off because I have had this problem in the past without overheating issues. Yesterday it was combined with the overheating issues. I think the thermostat was sticking closed at times. I ran it for 20 minutes at 4000rpm, then idled into the dock and there was a nice stream of water from tell tale. 10 seconds after I docked, the overheat alarm came on, so I shut the engine off, after 3-4 minutes, I started it and it took it 30 seconds or so to stream from the tell tale. It had done this before but not started, and that's when I got the vapor/air out of the fuel rail.. I'm thinking that the thermostat was stuck closed, causing the water to not flow through the fuel cooler, which didn't cool the fuel to liquid, causing the fuel issues.
This morning I ran the engine in a barrel. I removed the thermostat and ran it with no issues in the barrel. Bought a fuel pressure test kit and fuel rail pressure is 42 lbs. I ordered a new OEM thermostat, and gutted this old one and reinstalled it while I wait on the new OEM thermostat.
I had read a ton of posts, but I have seen no posts referring to the fuel cooler not getting sufficient water to cool the fuel.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,891
I do not remember which motors, but some had Yamaha make kits for overheating VSTs
just something to look into
 
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