Overheating Merc 5.0 I/O at WOT

[Bono426]

Hello,
This is my first post, and my first boat. I got it 3 weeks ago and love the thing.

21' Wellcraft Eclipse 5.0 I/O 1993

Ran great when I got it, up until the last two times I've put it in. This weekend when I ran it at WOT it over heated and I could smell burning and see smoke. I turned off the engine, and saw that the exhaust was hotter than normal on one side and the salt water cooling system hose that is in there was way hotter than the other side that wasn't smoking.

Then I took a look at my out drive and noticed that there was a huge chunk missing on my cavitation plate on the same side that was over heating... Could this be the culprit? And if so, how to do I go about fixing this? Can a piece be welded on? I'm guessing that the intake on that side with the missing cavitation plate is allowing air to be sucked up instead of water, thus causing the overheating on one side... But I'm just guessing here.

There was no issue when I was going slow on my way back to the boat launch. The temperature was holding at a normal temp and it seemed perfectly fine. No more smoke/no overheating.

I tried searching but couldn't find any correlation between a cracked cavitation plate and over heating issue...

Thanks,
Charlie

 

[hivoltg]

Re: Overheating Merc 5.0 I/O at WOT

The overheating has nothing to do with a cavitation plate.

I recommend two things. Change the water impeller and check your exhaust risers/manifolds for blockage. (impeller kit, new drive fluid, and riser gasket set) Since you don't know the history on this new to you boat...I would recommend those anyways even if it wasn't overheating.

If you can provide us the engine and drive serial numbers some of the great experts here can direct you towards the right parts you need to keep that nice boat cool.

Where was the smoke coming from?

Do you remember what the temp gauge was showing during the overheat?

 

[Bono426]

Re: Overheating Merc 5.0 I/O at WOT

The overheating has nothing to do with a cavitation plate.

I recommend two things. Change the water impeller and check your exhaust risers/manifolds for blockage. (impeller kit, new drive fluid, and riser gasket set)

Where was the smoke coming from?

Thanks for the reply,
It's coming from the left side exhaust. Camera left if looking from the drivers seat at the stern. Smelled like burned plastic.

View attachment 208596

Maybe I'm thinking the Cavitation plate is something else... But the crack I'm talking about looks like the above picture but with a lot more missing.

The boat cools fine when I don't give it to much gas. I can cruise around at a comfortable speed with no overheating issues. Its just when I really open it up, its smoking/over heating.

I don't remember the temp when it happened, but I remember it being much higher than normal. I'll look into changing those things you mentioned.

And I'll get the serial numbers on my lunch break.

 

[Bono426]

Re: Overheating Merc 5.0 I/O at WOT



Here are some pictures of my actual out drive. Any clue how to ID which one I have? I'm guessing Alpha 1 but cant find a sure way of telling

 

[hivoltg]

Re: Overheating Merc 5.0 I/O at WOT

I would recommend you replace the fresh water impeller located in the outdrive. Its easy to replace and the Adults Only sticky section at the top of this forums section has the instructions to get it done by yourself. I did mine using it. The impellers made out of rubber and when they come apart they can clog up stuff and cause overheating also. If you dont know when it was replaced last, I recommend you replace the upper and lower housing it sits in also. I think the complete kit is around $35 so its worth replacing it all.

Usually when you can idle fine and not overheat, but overheat at high speeds its a problem of the motor not being able to get rid of the hot water fast enough or a clog. I would also check the thermostat to make sure its good and its opening. I would also spend the $8 and order riser gaskets. I would file/dremel/screw driver out the manifold and riser water passages the best I could.

Its an alpha 1 Gen 2 stern drive according to your serial number and that section missing doesn't look too bad. I don't think that's the problem at all.

The smoking does concern me. If its smoking hot...thats bad. It can lead to alot bigger problems. Does it smell like oil burning from a leaky valve cover or is the motor steaming? It could be the rubber boots off the exhaust risers if you really are not getting much water through one side of the exhaust.

 

[Fun Times]

Re: Overheating Merc 5.0 I/O at WOT

Serial No: 0D874958 Model No: 50101503S is a 1993 MERCRUISER R.H. ROTATION ALPHA 1.50:1

Serial No: 0F057425 Model No: 6010000FS is a 1993 MERCRUISER ALPHA TRANSOM

Here is your parts catalog for both, http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=818183+91

I can't make out your engine serial number. If you look for a metal tag just above the engine starter you should be able to find the number there as well.

 

[QC]

Re: Overheating Merc 5.0 I/O at WOT

It's coming from the left side exhaust. Camera left if looking from the drivers seat at the stern

FWIW, this is why we use Port and Starboard. You are describing the Starboard side

Edit: BTW, welcome aboard!

 

[Bono426]

Re: Overheating Merc 5.0 I/O at WOT

FWIW, this is why we use Port and Starboard. You are describing the Starboard side

Edit: BTW, welcome aboard!

haha, I actually thought of this after I posted. I remember my father telling me "Left is Port... Both have 4 letters" This has been stuck in my brain whenever I hear port or starboard mentioned.

I was looking at some youtube vids on how to replace the water pump... Seems pretty easy like you mentioned hivoltg

"The smoking does concern me. If its smoking hot...thats bad. It can lead to alot bigger problems. Does it smell like oil burning from a leaky valve cover or is the motor steaming? It could be the rubber boots off the exhaust risers if you really are not getting much water through one side of the exhaust."

It smelled like a mixture of the rubber boots and a leaky valve cover that i saw when I was poking around back there.

 

[hivoltg]

Re: Overheating Merc 5.0 I/O at WOT

Its alittle long but he goes through the whole process of replacing the impeller on a gen2.

 

[Bono426]

Re: Overheating Merc 5.0 I/O at WOT

Its alittle long but he goes through the whole process of replacing the impeller on a gen2.

Thanks!

So I was educating myself on the risers and manifolds and now that I have a better idea on how these things work, it seems that something is clogged in the starboard side riser or a worn out water pump like you mentioned in the first place.

Thanks for your help guys, I'll post back with how this all goes.