Engine overhead - guardian kicking in

[jiriki 13]

I just got back from the lake. At low speeds, the engine overheats. Basically wakesurfing speeds. If I take the engine up past 20 mph, it works just fine. It holds 175 degrees perfectly

 

So I replaced the impeller a few weeks ago. It was shattered. I unhooked the hose leading to the transmission cooler and turned on the engine. Water gushes out. So I think the sea water pump is working fine.

I checked the grate and there's no obstruction.

 

I'm wondering:

 

1) The serpentine belt isn't tight enough. I think it is. But going out higher speeds, the water seems to work better.

2) The water temp sensor is shot. What's the correct part number?

3) I installed the wrong impeller. If the impeller is too small, I can see it's not pushing enough water pressure. At higher speeds, the water pressure is much higher. What's the part number?

 

I have a 2006 Black Scorpion Mercruiser.

 

Thoughts?

 

PS. Title is supposed to say Engine overheating.

Edited May 14, 2014 by jiriki

[duramat 462]

First thing I'd check is your Tranny cooler filter again. Pop off that electrical plug and get that hose fitting and check again.

 

Can you push more than a 1/2" play in your belt? (Can't remember if its 1/2 or 3/4")

Where did you get your impeller? Have a part # that you used?

 

I'm not by any means the the expert on this, only that my overheating issues have been at that spot LOL

[jiriki 13]

This is the impeller I replaced: 47-862232A2

[jiriki 13]

First thing I'd check is your Tranny cooler filter again. Pop off that electrical plug and get that hose fitting and check again.

 

Can you push more than a 1/2" play in your belt? (Can't remember if its 1/2 or 3/4")

Where did you get your impeller? Have a part # that you used?

 

I'm not by any means the the expert on this, only that my overheating issues have been at that spot LOL

 

Pop off the electrical plug?

[crew chief 4]

That's the right impeller. I would back flush all your coolers

[RhuntIII 555]

Good Call crew chief. If you now have a working water pump it could be pushing broken pieces into the coolers. I'm have the Merc350 not the black scorpion, my belt play 1/4 inch.

[duramat 462]

On my Black Scorpion in order to get access to my tranny cooler filter I have to pop off a plug or two to undo my hose clamp.

 

Failure to put back on will result in a high tension moment at the ramp followed by muttering and swearing. Recognition of those plugs will result in even more muttering and swearing at ones self.

 

Good call Chief!

[jiriki 13]

That's the right impeller. I would back flush all your coolers

I thought about that too. How do you do that?

[jiriki 13]

On my Black Scorpion in order to get access to my tranny cooler filter I have to pop off a plug or two to undo my hose clamp.

 

Failure to put back on will result in a high tension moment at the ramp followed by muttering and swearing. Recognition of those plugs will result in even more muttering and swearing at ones self.

 

Good call Chief!

 

I can remove my hose without removing the electrical plug. The clamp is positioned such that I can reach it underneath the plug.

[Tommywalton1974 175]

Somebody will chime in on how to back flush it. Did your old impeller have pieces missing? I know you said shattered. Were some entire fins missing?

[jiriki 13]

Somebody will chime in on how to back flush it. Did your old impeller have pieces missing? I know you said shattered. Were some entire fins missing?

Yep. Missing most of the fins. I found most of the pieces near the pump itself. Found the rest at the grate at the transmission cooler.

[Tommywalton1974 175]

I'm trying to figure out if there is a screen designed to trap them, and you got all of them out? Not much more that can be going on. It could be either more have found their way to that screen or the new one is doing it. Or some other obstruction.

[Tommywalton1974 175]

Also maybe it has a fault code now that needs to be cleared.

[jiriki 13]

When I replaced the impeller, I noticed the grooves on the brass housing.

 

 

The grooves look fairly small but I'm wondering at lower speeds, there's just not enough water pressure. Thinking back, when I had the hose off the transmission, water did come out but I didn't leave it on very long to see how well it does.

 

If it wasn't going to rain today, I'd take the boat back out again. I never had a problem with it when using a garden hose but I wonder if the house water pressure is assisting the water pump.

[duramat 462]

H has said in the past that those grooves can cause issues with overheating. My local dealer says its no biggie. If ya got cash to burn (order a new cap and prove it one way or another I'm interested to know what the outcome would be

[Tommywalton1974 175]

H has said in the past that those grooves can cause issues with overheating. My local dealer says its no biggie. If ya got cash to burn (order a new cap and prove it one way or another I'm interested to know what the outcome would be

I posted that little impeller replacement in the articles section. I remember you asking me about the grooves in mine dura. I never had an issue but I don't think mine was that scored.

 

I will say my buddies boat has a merc inboard/outboard and his impeller was junk, causing a low water pressure issue putting it in a limp mode. Could only idle the engine.

[Bigcatpt 408]

Some have had problems with grooved faceplate on the water pump. If I remember correctly, someone sanded it smooth and fixed the problem???

[duramat 462]

Those grooves do look a little more deep than mine. There could be actually some truth to it being an issue.

[jiriki 13]

If the rain holds out long enough tonight, I'll attempt to video the water output for review.

 

I may have a way of temporarily fixing the grooves tonight. I have to think about it a lot more.

[bcollins 18]

So you never had overheating issues with the old impeller, that was basically finless and torn to shreds and now that you've replaced it you're having overheating issues. Sounds like my boat.

 

Thermostat? Didn't notice that above. Also, make sure with all your tinkering you didn't just knock something loose. I did last year when I pulled the pump and it gave me similiar symptoms. It was a tiny hose under the serpantine belt that came loose and was dumping water into my bildge. At speed it ran a bit warm but at idle it ran hot as a result. Different engine but just something to look for.