1987 165 hp Alpha 1 Gen 1 Overheat

[jshoe]

Took 1987 wellcraft out for first time this year (sad). Drove through no wake 10 min and as got near to open water heard a pop, crack like plastic breaking from rear of boat. About a minute later started to steam and smoke. Shut it down and the antifreeze boiled away. Took lower unit off today and found the impeller just fine, but there was something in the lower unit that looked like a badly burnt marshmallow. Not really sure where to look next. Have ordered a new impeller and housing. Help, please.

 

[ThomW]

What do you mean anti-freeze boiled away? From winterization? After 10 minutes that should have all been out of the motor.

Where in the lower unit was this "marshmallow"? Any pictures of it? Was the housing for impeller burnt up? was the impeller key still there?

 

[jshoe]

The engine was so hot that the fresh water section (antifreeze and water) boiled and overflowed until gone, The housing for the impeller was not burnt up and the impeller was still flexible. The impeller was still properly connected to the key. The "marshmallow" was in the section where the gear that connects to the shifter? is located.That section that is on the front of the lower unit. Don't have pics and don't know how to post.

 

[kenny nunez]

Where the drive mounts to the bell housing put a garden hose in the hole and just let water run through the system to see if there is any thing restricting the flow. There should be no resistance and water should be running out the exhaust . If you cannot hold the hose in the passage then start looking for the blockage. The part that is melted may be one of the exhaust shutters.

 

[stonyloam]

That is the water pocket. Melted due to exhaust heat. #2 here http://www.mercruiserparts.com/bam/s.../30870/2203/80 He has a antifreeze cooled 470 type engine. For some reason you were not getting cooling water through the heat exchanger. Did you lose propulsion when it popped? Failed coupler or broken vertical driveshaft could do it. Are the splines intact on the shaft in the lower?

 

[stonyloam]

There is a good chance you blew the head gasket when you overheated. When you get it running again, do a compression check ASAP.

 

[jshoe]

Did not lose propulsion at any time. The splines on the top of the of the shaft on the lower unit are intact.

 

[jshoe]

With the lower unit off, I can see the water pocket cover assembly. Do I need to take that out to see if something inside that melted? Just looking inside the upper part of the out drive I see the water pocket assembly and nothing seems to be out of order.

 

[jshoe]

Obsessing on trying to figure this out. Where the water tube from the impeller assembly(lower unit) joins the tube from the water pocket, does one tube just slide inside the other with no o-ring or seal of any kind?

 

[Rake722]

There should be a rubber seal there.

 

[QBhoy]

Is it not likely it's the well known engine driven water pump seal/shaft issue that has caused the overheating ?

 

[Bondo]

Where the water tube from the impeller assembly(lower unit) joins the tube from the water pocket, does one tube just slide inside the other with no o-ring or seal of any kind?

Ayuh,.... Welcome Aboard,..... In the water pocket piece is sorta a big black o-ring that snugs 'round the copper tube,...
At the water pump housin' is another sorta big black o-ring that snugs 'round the copper tube,....
The plastic tube there is just to help guide the copper tube home,... No o-rings there, not needed,....

Unfortunately, the odds are quite high that yer motor didn't survive the over-heat,..... 470s rarely do,....
Expect a full-on rebuild, or replacement motor,....

 

[jshoe]

Have out drive off and found more overheated rubber remains.. Is there a rubber spacer that sits on top of the intermediate shifter? That part has a lot of up and down movement. All of the water pocket seems to be fine. Any way to check if motor is trash without reassembling?

 

[Bondo]

Any way to check if motor is trash without reassembling?

Ayuh,.... Pull the spark plugs, 'n do a compression test,....

Stuff a hose into the hose comin' from the outdrive, to the heat exchanger, 'n start it up,...

The antifreeze went Somewhere,.... Findin' where should lead to lotsa clues,....
Is the oil level high,..??
Water in the cylinders,..??
Drain the antifreeze side, 'n pressure test it,..??

 

[stonyloam]

OK that black burnt thing was probably your exhaust shutter was part of it metal? The pop may have been it letting loose. For some reason you lost cooling water to the exchanger. When was the last time the impeller was changed?

 

[QBhoy]

Stonyloam has likely nailed it here.
Still think the overheat was likely caused by the FW cooling system failure at the engine driven pump.

 

[QBhoy]

After which, it's a series of horrible events which usually involve the disssimilar metals from head to block expanding at an uneven rate causing cylinder head failure or it gets that hot, the heat from exhaust and assembly near FW header tank gasket fail....or both...

 

[stonyloam]

If the water pump seals fail it will either leak antifreeze out of the water pump weep hole or if that is plugged will leak into the crankcase. If the oil is clean the seals are not a problem. The engine water pump itself will never fail because the impeller is bolted to the end of the cam, so it is not the cause of the overheat. If the shutters were burnt that says there was no raw water exiting the heat exchanger. That water is dumped into the exhaust elbow and cools the exhaust gasses. I can only think of two things that could cause a raw water failure. Either the impeller in the outdrive failed or the exchanger tubes were plugged. Try pulling the forward tube off of the exchanger and insert a hose and see if water flows freely through the exchanger and out the outdrive. You can remove the end caps to clean the exchanger.

 

[jshoe]

Impeller changed 4 years ago.No part of the burnt rubber was metal. Whatever that burnt part was I will need to replace it, thus my question about whether the intermediate shift shaft has a rubber spacer? on it.

 

[stonyloam]

It does not. There is a metal "C" clip.