2000 454 MAG MPI, no water with exhaust

[Gallf1]

Totally stumped....was time to replace manifolds, risers and exhaust elbows as preventative maintenance on a totally running fine port motor. I also installed new seawater impeller and flushed and visually inspected the heat exchanger.

I saw some signs of water reversion inside the riser (didnt get to the exhaust valves that I can see), so to be safe I added the plastic resonators in the exhaust hoses as per mercury spec (even though I have the newer water lift muffler, they are still recommended) and due to known cold manifold warm riser condensation issue I added the stainless steel turbulator plates between the manifold and riser:

https://www.perfprotech.com/plate-turbulator-864838/product/188398

Installation was straight forward, no issues, torqued everything down to spec. Engine started right up, no issues and good water flow out the exhaust discharge. Outboard exhaust hose and elbow got warm as normal but inner exhaust hose and elbow eventually got too hot so I shut it down.

When I pulled the hot hose, it was obvious that the cooling water was not coming out thru the elbow as the hose was dry inside? I disconnected the seawater cooling hose at the bottom of the new manifold and started the motor for a minute and observed water out the hose/heat exchanger side that leads to the bottom of the manifold (which told me that seawater was indeed being pumped thru the cooling passages to the manifold).

I then put a garden hose on the elbow on the bottom of the manifold and after it filled all the passages, water came out of the end of the exhaust elbow as it should to cool the exhaust gas.

I did the exact same maintenance to the stbd side motor with zero issues....

Am I missing something?

 

[scoflaw]

Sum it up with fewer words, are you saying the engine is pumping water to the manifold but not making it out?

 

[Gallf1]

yup....the only thing I can think of but I havent checked yet if I accidentally reversed the hoses on the back of the seawater pump when I installed the new impeller.

If I did, would that cause a loss of volume significant enough to not "push" the water all the way thru the inboard manifold?

 

[scoflaw]

This can happen if it's on a flusher. Is the boat in the water?

 

[Gallf1]

Yes, boat is in the water but seacocks closed and using flushing system.

3 years ago (when I bought the boat), I installed a 3/4"manual valve and tee fitting between the seacock and strainer. A short section of 3/4" reinforced hose connects to the valve and the other end goes inside a 5 gal bucket that has fresh water in it from a garden hose.

I wait until the bucket is full to crank the motor and with the garden hose running, the bucket never empties. I add Salt Away to the bucket and turn off the garden hose and when the bucket is empty, I shut down the engine.

I am upgrading my flushing system to full-flow 1-1/4" Tee, Valves and hose as I always thought the 3/4" system was too restrictive for the seawater pump.

Do you think the 3/4" system isnt allowing enough volume to flow thru? I guess an easy test would be to NOT use the flushing system and open the seacock and see if it corrects the issue. Then I know the 1-1/4" flushing system should cure it?

Thx

 

[scoflaw]

Yes try that, my engine acts the same when on a hose, no problem in the water.

 

[Gallf1]

Yes try that, my engine acts the same when on a hose, no problem in the water.

yup....ended up being not enough water coming thru my original flushing valve setup (garden hose system). I never used it with the pressurized water just let the 3/4" hose draw fresh water out of a bucket.
Running with seacock open to the sea, plenty of water and cool.

I then replaced my 3/4" flushing valve setup with 1-1/4" full flow valves, tees and hose into a full 13 gallon bucket and it ran/cooled just as well. I add about 5-6oz of Salt Away in the bucket, run it up to 2,000rpm to clear the exhaust and then slowly bring back to idle before shut down.

I now also have the added benefit of having a strainer on the end of the 1-1/4" pickup hose and being able to use it as an emergency bilge pump.

It is amazing how much water that little seawater pump impeller moves

 

[Gallf1]

Yes try that, my engine acts the same when on a hose, no problem in the water.

yup....ended up being not enough water coming thru my original flushing valve setup (garden hose system). I never used it with the pressurized water just let the 3/4" hose draw fresh water out of a bucket.
Running with seacock open to the sea, plenty of water and cool.

I then replaced my 3/4" flushing valve setup with 1-1/4" full flow valves, tees and hose into a full 13 gallon bucket and it ran/cooled just as well. I add about 5-6oz of Salt Away in the bucket, run it up to 2,000rpm to clear the exhaust and then slowly bring back to idle before shut down.

I now also have the added benefit of having a strainer on the end of the 1-1/4" pickup hose and being able to use it as an emergency bilge pump.

It is amazing how much water that little seawater pump impeller moves