1985 260 overheated

[No Worries]

Okay, ran her for a few hours on Sunday arpund 1200 rpms and about 3200 rpms for about 10 minutes on the way in and the needle never moved. I've been suspecting a bad thermostat. Today I let the wife drive and she says "hey they temp went up some". Yeah it did, it was pegged and the damn plastic cover over the carb smelled like it was burning and there was smoke coming from the carb. Dunno how long or how hot. Also, i have a receipt from the previous owner that shows a impeller install in May of 2016. opinions? I'm hoping heat risers don't just instantaneously fail but I didn't think impeller do either. We keep the boat in a slip and take a canal out to the lake. It's a 1985 250 sundancer with an alpha one.

 

[Scott Danforth]

I would pull the boat and start with the impeller

you could have easily sucked up debris in the impeller and blocked the passage feeding the power steering cooler, or the thermostat housing. with this being a slipped boat, you could have critters living in the system either way, you had a serious overheat.

so due to the overheat
your going to need a new impeller and most likely the complete water pump kit
you will need to back flush the whole cooling system system. this includes the hoses, tubes, oil coolers, etc. basically anything that can hold an obstruction
you will need new exhaust flappers as you burned the ones you had
you will need new exhaust hoses as you burned the ones you had
you most likely scored the cylinder walls and didnt do the bearings any good. motor dont like to be run without coolant

 

[No Worries]

Thats a whole lot of bad news...hoping the cylinders are a worst case scenario.

 

[No Worries]

I would pull the boat and start with the impeller

you could have easily sucked up debris in the impeller and blocked the passage feeding the power steering cooler, or the thermostat housing. with this being a slipped boat, you could have critters living in the system either way, you had a serious overheat.

so due to the overheat
your going to need a new impeller and most likely the complete water pump kit
you will need to back flush the whole cooling system system. this includes the hoses, tubes, oil coolers, etc. basically anything that can hold an obstruction
you will need new exhaust flappers as you burned the ones you had
you will need new exhaust hoses as you burned the ones you had
you most likely scored the cylinder walls and didnt do the bearings any good. motor dont like to be run without coolant

How likely do you think it is the flappers are toast? The engine has to be pulled to get to them.

 

[Scott Danforth]

guaranteed they are toast and most likely the remnants plugging up your exhaust now. no you dont need to pull the motor, you pull the exhaust elbows. they are in the top of the y-pipe

 

[No Worries]

guaranteed they are toast and most likely the remnants plugging up your exhaust now. no you dont need to pull the motor, you pull the exhaust elbows. they are in the top of the y-pipe

Are you sure? It's an '85 260 mercruiser. I thought they were down by the transom in the old ones.

 

[Bondo]

Naw,.... The shutters moved to the top of the y-pipe, well before '85,....

I'd change the impeller, regardless what the Po did,...

 

[Scott Danforth]

here is a link to the drive manual http://boatinfo.no/lib/mercruiser/manuals/mercruiser6.html#/0

here is a link to the motor manual http://boatinfo.no/lib/mercruiser/manuals/mercruiser9.html#/0

 

[No Worries]

here is a link to the drive manual http://boatinfo.no/lib/mercruiser/manuals/mercruiser6.html#/0

here is a link to the motor manual http://boatinfo.no/lib/mercruiser/manuals/mercruiser9.html#/0

I have the manuals. Thank you sir.

 

[No Worries]

Naw,.... The shutters moved to the top of the y-pipe, well before '85,....

I'd change the impeller, regardless what the Po did,...

Pulled the thermostat housing and had a bunch of rust and scale on top of the thermostat. Can the risers just collapse and fail suddenly? I'll be pulling the risers for inspection tomorrow.

 

[No Worries]

overheat update

1985 260 Mercruiser. Risers inspected and in great condition. Replaced thermostat and ran cool all afternoon long at 3200 rpms. On the way in the temp gauge rose to almost the redzone. I dropped the throttle down to idle and the temp began to drop instantly. In a matter of seconds she was back down and running cool! I throttled back up and finished bringing her in to port where I checked temps with an IR gun. The only hot spot was the intake manifold...normal? Anyhow, what's y'alls thoughts on it getting hot and instantly cooling at idle? Thanks all and safe boating. Anchors Aweigh!

 

[jbcurt00]

Bump