Confirmation on water pump leaking affecting cool fuel

[ryan04]

Hey gents, I have a 2006 tahoe with a 5.0 mpi mercruiser engine with a bravo drive. In this boat it's got the raw water pump on the engine.

I was out yesterday cruising along at 3000rpm, my regular low cruise speed, when suddenly the boat started to slow down and run rough. I backed off the throttle for a second then pinned it to see what would happen and the boat slowed even quicker while choking and running rough. I looked at the temp and it rose faster then i've ever seen up to around 185 vs it's usual 165. The oil pressure also went up from 40 to around 50 psi.
One the boat was put in neutral and was just floating along, it kept idle beautifully and the temp came down almost immediately. The oil pressure stayed at around 50 psi at idle.

I turned around and was able to drive the boat back to the doc at around 2000rpm. Just before plane. The temp didn't go up and the oil pressure came down to around 45 and it acted great the whole way back as i "limped" it in.

After inspection my raw water pump is leaking water out of the seal on the face of the pump. It was spitting water on the inside of the engine. Not a lot just like if you dipped your fingers in water and flicked it.

Here's my question:

IS it possible that for whatever reason the water pump gave up and started a small leak that the temp rose and in turn didn't cool the fuel properly which led to the boat choking to a slow down? I've had the temp rise before from too much trolling. It got close to 200 once and I sped up and it cooled down instantly. I say that because even at hotter temperatures the fuel system still did it's job. Hence why I need your brains.

Thoughts?

Thanks!

 

[alldodge]

IS it possible that for whatever reason the water pump gave up and started a small leak that the temp rose and in turn didn't cool the fuel properly which led to the boat choking to a slow down?

No
Cool fuel is a bad attempt to cool the fuel down to reduce vapor lock. A small leak would not be an issue with fuel temp increase. About 99+% of the water going thru the pump is to cool the motor and exhaust.

With motor temps rising and also oil pressure rise, I would look at electrical connections. If te,ps rise oil thins more. With oil thinning this would mean oil pressure would drop a bit, with your raising maybe the voltage was dropping

 

[ryan04]

The battery I was using was suspect. I had thrown it in right before we went out. I just figured as long as the boat can start, which it did but laggy, the alternator would keep up the voltage to a constant. With that said, if the alternators job is to charge the battery wouldn’t the alternator be able to keep up with the electronics to keep it running smoothly? Basically make up for what the battery is lacking.
Or the battery is only putting out 11 volts or something lower and the alternator is charging it but the output of the battery remains low despite being charged so the electronics start acting funny.
ya? No?

 

[alldodge]

If the battery has a shorted cell (seeing 11V) then the ALT is unable to keep things working correctly. When running you should see close to 14.5V

 

[ryan04]

UPDATE: PROBLEM SOLVED

Hey guys, just wanted to offer an update for anyone whose experienced anything similar. I feel foolish with the fix as it was very simple and very obvious.

I took the boat out again after I swapped a new battery in. I pinned it and for the first 15 minutes it ran perfect. I did notice a louder than normal "sucking air" sound. I kept slowing down and gunning it to see if I could it do choke out. I kept on a eye on the temp and it fluctuated between 160-180. Oil pressure was around 40 at idle and when I was flying along it was around 50psi. Close to the doc I gunned it one more time as it was fine at this point for about 20 minutes. Then it happened!! It choked out and couldn't get up on plane. It would sit around 2500-2800rpm and just choke along plowing water. So I figured I'd like to get a better ear on the situation so I opened the rear hatch and gunned it. The boat took off like a champ?! So at this point I figured it was an air flow issue. I closed the hatch and sure enough after a couple tries it started choking again. One last time I opened the hatch and it took off no problem.

I got back to my garage and popped off the flame arrester and it was pretty dirty looking. I blasted it out with carb cleaner and lots of black drained out. I then blew it out with air. Secondly, just for good measure I replaced the thermostat. I've never done it and i've owned the boat for 5 years. (I know...) The old thermostat was pretty messed up looking. The middle "pin" was off centered and there was a build up of gunk around the tip.

Long update short: My thermostat was intermittently sticking and my flame arrester was clogged.

I'm glad it wasn't anything more serious then that. Anyway. Thanks for the support and Ideas fellas. Maybe this will help someone else in the future.

 

[ryan04]

UPDATE: PROBLEM SOLVED

Hey guys, just wanted to offer an update for anyone whose experienced anything similar. I feel foolish with the fix as it was very simple and very obvious.

I took the boat out again after I swapped a new battery in. I pinned it and for the first 15 minutes it ran perfect. I did notice a louder than normal "sucking air" sound. I kept slowing down and gunning it to see if I could it do choke out. I kept on a eye on the temp and it fluctuated between 160-180. Oil pressure was around 40 at idle and when I was flying along it was around 50psi. Close to the doc I gunned it one more time as it was fine at this point for about 20 minutes. Then it happened!! It choked out and couldn't get up on plane. It would sit around 2500-2800rpm and just choke along plowing water. So I figured I'd like to get a better ear on the situation so I opened the rear hatch and gunned it. The boat took off like a champ?! So at this point I figured it was an air flow issue. I closed the hatch and sure enough after a couple tries it started choking again. One last time I opened the hatch and it took off no problem.

I got back to my garage and popped off the flame arrester and it was pretty dirty looking. I blasted it out with carb cleaner and lots of black drained out. I then blew it out with air. Secondly, just for good measure I replaced the thermostat. I've never done it and i've owned the boat for 5 years. (I know...) The old thermostat was pretty messed up looking. The middle "pin" was off centered and there was a build up of gunk around the tip.

Long update short: My thermostat was intermittently sticking and my flame arrester was clogged.

I'm glad it wasn't anything more serious then that. Anyway. Thanks for the support and Ideas fellas. Maybe this will help someone else in the future.

Forgot to mention the IAC muffler was super dirty as well. That was the main sucking air sound.

 

[ryan04]

The plot thickens. I took the boat out again and it was great the first trip. The second trip it bogged down. I ended up hiring a mobile mechanic to come by and scan my engine. We found the ACTUAL problem. My water pressure sensor went bad so the guardian system kicked in and limited my power to 20%. IT doesn't help that the previous owner had snipped the warning buzzer. Once we scanned the engine a horn warning came up that pointed us toward it showing it was cut. Swapped the sensor and hooked up the horn and so far so good.