Blockage/Restriction???

[LetsRock]

My marina is notorious for barnacle growth. Last year my boat would start to over heat whenever I would go over 2500 RPM's so after pulling the boat I saw the intake filled with barnacles. After scrapping them and and cleaning out the intake the boat ran cool the rest of the season.

This past weekend the same thing happend. Right above 2500 RPM's the temp started to rise. This time when I pulled the boat there was a thick slimy substance caked in the intake as well as the area around the drive. I throughly cleaned the intake and put everything back together again. This time no luck, when I took it out the temp started to rise again above 2500 RPM's.

Is there some type of screen or filter that might be clogged with this slimy stuff that I need to get at and clean?

I have a Mercruiser 5.7L I/O

 

[techmitch]

I will assume that you have an alpha drive, so when is the last time the impeller in the drive was replaced?

 

[LetsRock]

I will assume that you have an alpha drive, so when is the last time the impeller in the drive was replaced?

Yes Alpha One...

I am sorry but I failed to mention that I had a new impellor put in this spring and all new manifolds, risers and thermostat last spring.

Also the boat runs pefectly cool at idle and form 0-2500 RPM's so it seems like some sort of partial blockage.

 

[techmitch]

Have you been in any low depth situations where you may have sucked up some sand or even some mud? it doesn't take much to trash a new impeller. You can check for water flow/volume from the pump in the outdrive by taking the hose off at the engine and starting the engine. Not sure of the spec. IE: XX=gallons per hour but should fill a bucket quite fast.

 

[LetsRock]

Have you been in any low depth situations where you may have sucked up some sand or even some mud? it doesn't take much to trash a new impeller. You can check for water flow/volume from the pump in the outdrive by taking the hose off at the engine and starting the engine. Not sure of the spec. IE: XX=gallons per hour but should fill a bucket quite fast.

My marina is actuallt situated on Mud Creek...the water is a mess. So you think it could be the impeller? I will try your test and see what happens

 

[LetsRock]

Have you been in any low depth situations where you may have sucked up some sand or even some mud? it doesn't take much to trash a new impeller. You can check for water flow/volume from the pump in the outdrive by taking the hose off at the engine and starting the engine. Not sure of the spec. IE: XX=gallons per hour but should fill a bucket quite fast.

So I suppose there isnt any type of screen or filter that might be clogged up or any other type of restriction that might have formed?

 

[Jim M]

You must wet slip your 220. Sounds like you need to employee "bottom scrappers". Once a month they will clean the bottom of your boat.

 

[LetsRock]

You must wet slip your 220. Sounds like you need to employee "bottom scrappers". Once a month they will clean the bottom of your boat.

The bottom is perfectly clean since it is bottom painted. I also painted the outdrive and trim tabs, it just seems that this crap gets into the intake.

 

[jitts3]

On my 78 merc there is a single hose that runs to the engine. Wonder if a person couldn't "T" it off to a ball valve to flow test the raw water impeller. Just a random quick thought.

 

[techmitch]

Not a bad idea Jitts, that would be good for periodic testing. Just remember that creates 2 more connections and 1 more part for potential leaks

 

[techmitch]

So I suppose there isnt any type of screen or filter that might be clogged up or any other type of restriction that might have formed?

No screen, but there is the fitting that goes through the transom that the intake hoses attach to on both the inside and the outside that could possibly clog. So far, if it only happens at higher rpm's my bet is on the water pump impeller.

 

[LetsRock]

Spoke to my mechanic and he said there is a screen (I forgot what he called it) that is most likely clogged. He siad its about the courseness of a cheese grater and would easily restrict water flow.

 

[LetsRock]

I am now almost at wits end!!!

After changing the thermostat, changing the intake hose (which BTW has a large kink in it and the mechanic was positive this was causing my problem), pulling the risers to inspect them which they were clean, cleaning the gunk out of the intake I am down to pulling the impeller which was replaced in the spring and of course our last resort. Lets just assume it is working fine....WHAT THE HELL ELSE COULD IT BE?????

Ok, I am better now.....

 

[techmitch]

I am now almost at wits end!!!

After changing the thermostat, changing the intake hose (which BTW has a large kink in it and the mechanic was positive this was causing my problem), pulling the risers to inspect them which they were clean, cleaning the gunk out of the intake I am down to pulling the impeller which was replaced in the spring and of course our last resort. Lets just assume it is working fine....WHAT THE HELL ELSE COULD IT BE?????

Ok, I am better now.....

When you replaced the intake that (HAD?) a kink in it did you check the fitting that goes through the transom for blockage when you had the hose off? Also remember the exact length of this replacement hose is critical. This all still goes back to the flow/volume test i spoke of in post #4.

 

[LetsRock]

When you replaced the intake that (HAD?) a kink in it did you check the fitting that goes through the transom for blockage when you had the hose off? Also remember the exact length of this replacement hose is critical. This all still goes back to the flow/volume test i spoke of in post #4.

I will ask my mechanic about the fitting. He did pull the a hose right at the thermostat and started the boat to show a good water flow. He did not measure it with any type of device so Im not certain how he knows its sufficient.