Another overheat question.

[nickmo]

Mercruiser 5.0 carb. Alpha 1 Gen 2 drive.

A few weeks ago I was running the boat and trimmed the drive up too high (switch stuck) and smoked the impeller. I changed the impeller (no pieces missing) and all was ok except that the motor was running hotter than it should (about 180) but was the same as before the impeller problem. I decided to replace the manifolds and risers as they were 7 years old (RWC). I replaced the flappers while everything was apart also. They were not damaged or broken. After replacing I started the motor to look for any leaks. All ok and motor idled for about 1/2 hour at 170. I took the boat out through no wake zones temp 170 for the whole time. Got on plane (3000 rpm) and temp slowly rises (180-200) and continues to rise until you go back to idle when it quickly drops to 170. I removed the thermostat and the same result except instead of idling at 170, it idles at 120 or lower, still overheats on acceleration. Any ideas?

 

[DeepBlue2010]

You confused me when you said "but was the same as before the impeller problem". Are all the symptoms you described existed before the impeller issue or just it was running consistently at 180?

If it the latter, you have a restriction issue in our water passages. Are you sure you got all the pieces out. Are there any other pieces that got hot or melted?

Your trim limit should not have allowed you to get the outdrive that high unless you used the trailer button. You might want to check the limit switch also.

 

[thumpar]

If the impeller had all it pieces how was it smoked? Try backflushing from the thermostat housing to the gimbal with the drive off or remove the power steering cooling and look for debris.

 

[nickmo]

You confused me when you said "but was the same as before the impeller problem". Are all the symptoms you described existed before the impeller issue or just it was running consistently at 180?

If it the latter, you have a restriction issue in our water passages. Are you sure you got all the pieces out. Are there any other pieces that got hot or melted?

Your trim limit should not have allowed you to get the outdrive that high unless you used the trailer button. You might want to check the limit switch also.

Before the drive coming out of the water, the motor ran around 180. I didn't backflush when I replaced the impeller. It was intact, but the ends were worn. Nothing melted.

Limit switch was an issue that's now ok. (adjusted)

 

[nickmo]

If the impeller had all it pieces how was it smoked? Try backflushing from the thermostat housing to the gimbal with the drive off or remove the power steering cooling and look for debris.

The impeller was worn but all pieces intact.
When you say with the drive off, do you mean the entire drive or the lower half? Where's the power steering cooling? Thanks

 

[nickmo]

I followed the hose from the stat housing and found the power steering cooler. I will remove the hose and check for debris. With the hose removed can you start the motor for a minute or so to flush out the raw water line? The boat is in the water and I don't own a trailer. I want to do all possible before having it hauled.

 

[nickmo]

Removed hoses from both sides of the power steering cooler. No debris or restriction. I flushed it out anyway with a garden hose. I started the motor for a few seconds. Water was gushing from the raw water hose into the bilge. I didn't see any debris. Does the good flow of water indicate the impeller is good?

 

[nickmo]

Bump

 

[nateo]

Been working on a similar issue with my new boat. Im not sure what year you're workng on but my 2006 manual has the numbers for doing a flow capture test into a bucket. Before doing anything else pickup a ir temp gun and am at different aresa of block. Sometimes temp sending unit or gauge goes bad and just misreports. If you get different readings on certain areas this can help pinpoint issues. Theres also a clear tube test to check for bubbles. I pieced all this together from numerous threads

 

[nateo]

Also make sure you dont have any kinked hoses

 

[Raypex]

nickmo,
I am not a mechanic but isn't there a water pump on the engine? Forgive me if i'm wrong but this could be involved.

 

[nickmo]

I thought of that and did a bit of research. Most experts agree that the engine water pump rarely fails, but it's on the list of things to inspect/replace.
It only overheats at 3000 rpm or more. An automotive mechanic said that if it was the circulating pump, it would overheat more at idle. Thanks for the response.

 

[crazy charlie]

ssagewaysDid you use dry gaskets on the manifold to riser or did u use gasket sealer ?? Using gasket sealer can cause the sealer to enter and restrict the passageways between the riser and manifold after tightening it down.Charlie

 

[nickmo]

I didn't use any sealer. They are dry joint manifolds and risers so the gasket was the metal with rubber type. Besides it overheated before the manifold/riser replacement. They needed replacement, but weren't completely restricted. The motor does run cooler with the new manifolds and risers until it overheats. If that makes sense.

 

[nickmo]

UPDATE
I pulled the boat and rechecked the impeller. I bought a new kit with the housing. I replaced everything including the housing which did have some grooving. The new bottom plate came with the rubber gaskets already attached which is really an improvement over the old style. Ran the boat WOT and no overheat. I don't know if it was the housing or the new style gasket/bottom plate.