Merc gen 4 454 Mag no water exiting
 

After many problems last season with run-ability/ troubleshooting I discovered that I had a burnt valve possibly a couple, decided to pull the heads have them rebuilt. Decided to go with EMI thunder manifolds/risers. After many headaches with fitment and waiting on parts that were built wrong from Eddie marine, finally got it put back together and fired up, also did a new sea water impeller and Hardin thermostat housing since the emi only requires a 4 hose thermostat housing versus the original 6 hose with the ball/spring contraption. Got it started and after about 1-2 minutes still no water exiting, HELP PLEASE!

Verify the water hoses on the raw water pump aren't crossed?

On my Gen 4 454 mag, the lower nipple is for water coming IN, upper nipple is water OUT.

Are you using the stiff water inlet (wire wound type) hose on the water inlet hose? A softer hose can collapse.

Pull a hose off or engine block drain and see if there is water in the system. Might have just not waited long enough.
If no water then you could have your sea pump hoses reversed. Chances are you burned up the impeller if there is no water in the engine.

I’m almost positive this may be the case, have only had the raw water pump off one other time and couldn’t remember which way the hoses went so put them on the same as my dads Gen 6. Thank you

Thanks Griff, yeah I suspected I had burned it up but let luckily I used the merc grease on it so it didn’t get smoked 😅

I have an older Formula that I maintain and the pumps are different from one engine to the other. one has the suction on the top and the other on the bottom. it was that way from the first time I saw it so dont know if someone did it for a reason but I mark which is which when I pull the pumps.

On my mk IV 454 mag (330hp) input for the pump is top and output to cooler is bottom

Those pumps are bidirectional depending on rotation the suck and blow ports can change, its marked on the back of the housing

Not positive on this but I’m pretty sure if you have twins, you have one left hand rotation engine and one right hand? That would explain why the pickup hose is on a different nipple of the impeller housing right? Maybe I’m way off but that’s how the impeller housing is marked.

UPDATE: swapped the hoses after reinstalling the impeller housing and bam! About a minute after running, full flow exiting the exhaust! 😅 Motor is running good so far after lots of headaches over the last few months and basically missing the entire season, hopefully can squeeze in a few days before summer actually is over. The only thing that gets through the winter in WA is the thought of being out in my boat all summer so this was quite the emotional rollercoaster for me,
🤞🏻🤞🏻🙏🏻here’s to a good lake test tomorrow!