Port engine overheating at inboard exhaust elbow

Southern Cross

Southern Cross

Member
Jul 29, 2013
65
Alexandria, VA
Boat Info
2005 320DA
Engines
Twin 350 MPI, V Drives
Hello everyone,

One of our engines is overheating and I'm at a loss. Boat is a 2005 320 with 350 V drives, closed cooling, 350hrs of fresh water use. It has an older smart craft but I don't think there are water pressure sensors or gauges.

Quick background, last weekend I ran into shallow water on the Potomac (2-3ft of silt bottom). Both engines and the generator overheated soon afterwards. I cleaned the sea strainers of some mud, oyster shell fragments, and some weeds. Engines remained hot (just under 175deg) but were pumping water with steam in the exhaust. I limped back to the dock on one engine at idle and did the following:

1. Drained the strainers and cleaned them again. Used Sea Flush kit and a shop vac to flush from the strainer to the thru hull.
2. Flushed the water hoses from the strainer to the water pumps
3. Replaced the raw water pump impellers on both engines as well as the generator. (all looked fine, no cracks or missing vanes but replaced with new anyway)
4. Removed all raw rater hoses and the end caps on the heat exchanger and flushed with a hose. No major debris came out.
5. Flushed both engines with the dock hose and the engine's fresh water flush system.

The generator and starboard engine now run great. The starboard engine exhaust expels water strongly with increasing force as I increase throttle. Both manifold elbows are warm but not hot and the temp gauge reads normal.

The problem remains with the port engine. The water coming out of the exhaust is does not come out forcefully like the starboard side and the inboard elbow is much hotter than the outboard one or the ones on the starboard engine

I rechecked all hoses by disconnecting them...it looks like water is pumping strong through the hoses and heat exchanger.

A few possibilities I've considered:
1. Is it possible for a raw water pump with a good impeller and proper belt tension to not pump enough water? I've only ever had them fail completely.
2. Could the elbow or riser be clogged? I'm at a loss for how something could make it all the way though the strainer, transmission cooler, and heater exchanger and then clog a riser.
3. Thermostat? The problem seems to be with the raw water side of things--do the two systems interact in any way that this could be the problem?

I stopped short of pulling the elbow off tonight because it was hot and I have never done that before--frankly I don't even know what I would be looking for and was concerned about needing a gasket if I took it off.

Curious if anyone else has experienced something similar or can think of something I am missing. Thanks in advance, I am looking forward to the discussion.
 
I would check the riser elbow and see if has a restriction. Did you also flush out the heat exchanger with both ends off? You must still have some type of clog somewhere how about the raw water? Pulling the elbow is pretty easy make sure you have some new gaskets to put back afterwards. Also you may have to replace the whole raw water pump housing not just the impeller could of warped the housing and it is pumping some air.
 
Loyd Dinneen said:
I would check the riser elbow and see if has a restriction. Did you also flush out the heat exchanger with both ends off? You must still have some type of clog somewhere how about the raw water? Pulling the elbow is pretty easy make sure you have some new gaskets to put back afterwards. Also you may have to replace the whole raw water pump housing not just the impeller could of warped the housing and it is pumping some air.
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Hi I've seen where the oil or transmission cooler retained a lot of crap and caused the same condition.
IF you can, disconnect both hoses from transmission cooler and back flush real good with a water hose.

Good Luck
 
Thanks for the replies. I’ll take a crack at the riser and elbow tonight. The raw water intake seems fine—I flushed it with the sea flush kit and shop vac and it seemed clear.

The water pumps are the brass ones, can they still warp?

I’ll also flush the oil cooler and heat exchanger again.
 
Southern Cross said:
Thanks for the replies. I’ll take a crack at the riser and elbow tonight. The raw water intake seems fine—I flushed it with the sea flush kit and shop vac and it seemed clear.

The water pumps are the brass ones, can they still warp?

I’ll also flush the oil cooler and heat exchanger again.
Click to expand...

do you know when your Elbows were last replaced ?
 
If you have Smartcraft what does the raw water pressure port show vs starboard in the same RPM ranges?

Also, check your belt tension (a loose belt will allow the pump to slip) and check the belt path (improper path could allow belt to slip also). I had to deal with each of these issues in the past. A bad belt this year and a long time ago when I did a water pump impeller and mis-routed the belt (everything work except the water pump above idle).

-Kevin
 
KevinC said:
If you have Smartcraft what does the raw water pressure port show vs starboard in the same RPM ranges?

Also, check your belt tension (a loose belt will allow the pump to slip) and check the belt path (improper path could allow belt to slip also). I had to deal with each of these issues in the past. A bad belt this year and a long time ago when I did a water pump impeller and mis-routed the belt (everything work except the water pump above idle).

-Kevin
Click to expand...
Thanks, Kevin. The smart craft is older and I don’t think it measures water pressure. If it does I can’t find the “page” on the display.

I’ll check the belt routing. Pretty sure I mirrored the starboard engine but maybe not.

Steven
 
Here's my guess, the silt made it to the manifold. The manifold was already near its end of life via scaling inside. The silt filled in the remaing water flow gaps enough to seal up and harden via the high temp as the water flow was severely restricted. Now its concrete and wont flush out. Most likely on the stern end corner of the manifold.
 
LG111 said:
Here's my guess, the silt made it to the manifold. The manifold was already near its end of life via scaling inside. The silt filled in the remaing water flow gaps enough to seal up and harden via the high temp as the water flow was severely restricted. Now its concrete and wont flush out. Most likely on the stern end corner of the manifold.
Click to expand...
I'm thinking the manifolds should be fresh water, Most likely the elbows !
 
The non ferrous sea pumps used on the Merc freshwater cooling are very prone to wear when they ingest shells ,sand and mud etc, check the replaceable wear plate and the pump interior when doing impeller changes . They can get beaten up enough and grooved to where suction is greatly reduced . Mercruiser started offering wear plate replacements that actually have stainless steel inserts to off set grooving on the covers . The pump interior unfortunately is another story because it can groove and when this happens it needs replacement. What does your smart craft H2O read on that engine at idle? My thoughts are that raw water only enters the exhaust elbows ,heat exchanger and cooler. Also there are some quirky cool fuel tubes which house a very diabolical little check ball that can get stuck check that as well.
 
Thanks everyone for your input. Still not fixed but narrowing it down to the water pump. I took off the elbow tonight and its passages are clear. Water seems to flow through all the places it is supposed to just not with enough strength. I also noticed that the single point drain system will not "purge" on the lines that go to the water pump in question.

Photo below is of the pump sans impeller. Are those circular grooves normal or is that the "scoring" I have read about? Of note, there was no plate in-between the halves of the pump, just the gasket.
IMG_4533.jpg
 
new cover plate is disposable with a stainless steel wear surface and yes those groves are how a pump interior and cover plate wear out to the point the suction loss can happen. What I see here is an original cover plate with some substantial grooving and a scored pump housing . It doesn't seem like much but the surface area affected is pretty large and that is where the sides of an impeller press along to create suction. I replace my wear plates during my yearly impeller changes and my pump housings when needed ,they ( the housings )aren't cheap but the wear plates are relatively cheap and generally the item that takes the most wear .
 
Thanks White Glove Boat and to all who replied with ideas. That water pump was an older model and did not have the wear plates. Replaced with a new one -- not an inexpensive or easy endeavor.

The new water pump didn't improve things much not did a back flush with a sea flush kit. Water was moving just not enough. Over the side I went and found what can only be described as a Brillo pad of sea grass clogging the intake. Removed it, flushed from the strainer to the intake again and fired it up. Drew the another chunk of sea grass through the sea cock which thankfully got caught at the basket (photo below)

Starboard engine runs well and pumps strong, but there is still a blockage at the seacock or intake. Starboard water pressure PSI is higher than port above idle. Also, when I remove the sea strainer lid with the seacock open, the strainer basket does not fill up much less overflow like the port side.

Any ideas on how to clear the seacock or intake with the boat in the water? I may just haul it anyway to have the bottom cleaned.
IMG_4537.jpg
 
Southern Cross said:
Thanks White Glove Boat and to all who replied with ideas. That water pump was an older model and did not have the wear plates. Replaced with a new one -- not an inexpensive or easy endeavor.

The new water pump didn't improve things much not did a back flush with a sea flush kit. Water was moving just not enough. Over the side I went and found what can only be described as a Brillo pad of sea grass clogging the intake. Removed it, flushed from the strainer to the intake again and fired it up. Drew the another chunk of sea grass through the sea cock which thankfully got caught at the basket (photo below)

Starboard engine runs well and pumps strong, but there is still a blockage at the seacock or intake. Starboard water pressure PSI is higher than port above idle. Also, when I remove the sea strainer lid with the seacock open, the strainer basket does not fill up much less overflow like the port side.

Any ideas on how to clear the seacock or intake with the boat in the water? I may just haul it anyway to have the bottom cleaned.
View attachment 60699
Click to expand...

I have something you can try, And you will get results ! It's worked for three different people i know. Take the intake hose off the seacock and drop it into a 5 gal pail (you may have to extend the hose) fill the bucket half way with water, Then add a quart of muriatic acid to the bucket start the motor when the bucket is empty shut down wait five minuets hook the hose back to the seacock , Restart let it flush out
good But be carful with the acid. It will clear the blockage
 
Southern Cross said:
Any ideas on how to clear the seacock or intake with the boat in the water? I may just haul it anyway to have the bottom cleaned.
View attachment 60699
Click to expand...

I've been fighting similar issues this summer. You mentioned that you have a SeaFlush. One procedure that I was able to do was to use the output of my shop-vac and blow air into the sea strainer while my sea-cock was open. Blew plenty of air out the bottom of the boat and I'm confident the intake was clear.
I also did the Barnacle Buster flush that Express390 mentioned. It helped me run a few degrees cooler, but I'm still not confident that I'm getting enough water flow.
I'm now 90% certain that my problem is related to scoring inside the pump, so I just took delivery of those stainless steel plates.
 
sorry i just saw twins how much trouble would it be to cross feed the intakes?
 
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