1979 Mercruiser 260 MR-1 impeller melted down AGAIN

[zentodd]

Hello,
This is my first post but I've certainly benefited from all the knowledge gathered here on the forum. Thank you!

I have a 1979 Mercruiser 260
Chevy 350 with a MR1 outdrive.
Raw water cooling. No heat exchanger.
The boat is new to me.
It starts and runs strong but I've been chasing my tail for a while with an over heating issue.

-It immediately started to over heat.
-I checked the impeller in the outdrive and it was melted down.
-I replaced it with a new impeller, top and bottom housing and cleaned all debris from the outdrive.
-It over heated again.
-I checked the thermostat and it was rusted - replaced with a new marine thermostat.
-It over heated again. This time the starboard manifold cracked. :grumpy:
-I pulled off all the cooling hoses, manifold and riser. I checked for blockage - nothing substantial.
-I drilled out the cracks and jb welded the manifold and bolted it back up (a temporary fix) to continue testing the system.
-It over heated again so I finally decided to check incoming water flow - I know i'm a little slow.
-No water flow into the boat.:facepalm:
-Pulled the outdrive and the impeller was melted down again.

Any thoughts on what could be causing this problem? Like i said i replaced the entire housing, impeller and gaskets the first time. The key was properly inserted and fully engaged on the shaft.

I did notice that the new impeller was very tight. I had to put a wrench on the shaft to turn it once it was in the housing. Also, I torqued the impeller housing bolts to spec and the gaskets didn't seat so i torqued it beyond specs to get contact and then backed it off to specs. It seemed to be seated and sealed but i'm wondering if that indicates that I did something wrong or maybe got the wrong impeller?

Any help or suggestions will be very appreciated. Thanks before hand.

 

[duckman4548]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

Pull the tube down between the w/p housing and the upper housing, there is a plastic tube that links the 2 together. Start there

 

[zentodd]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

Thank you for your reply.

I think i did that already. the tube your talking about is in the upper part of the outdrive and the plastic tube that goes into the water pump fits around this tube?

I pulled that tube out and looked for obstructions. I also back flushed from inside the engine compartment thru the outdrive and no obstructions were noticed.

 

[Bt Doctur]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

have you examined the gears in the upper housing. no flow would mean your not pumping because the shaft is not turning.another cause would be a stripped coupler not turning the input shaft.

 

[zentodd]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

I'm pretty sure the shaft is turning - the impeller was melted in a clockwise direction.

 

[ktbarrentine]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

I dont see any mention of how much water is flowing to the muffs from the water hose, or what flow is observed coming out of the idle relief ports when the engine is running.

Also, what was the setup for backflushing from the engine compartment through the outdrive. With a properly installed impeller, you wont get any flow past the impeller during a backflush.

 

[dingdongs]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

exhaust flappers stuck in cow horns down the bottom .maybe able to see when drive removed and look up the exhaust bellows. A restriction here is no good too. Check flow to the engine b4 running up too hot and the water should be pumping out the side vents when running as well as centre of prop. Rubber pieces of impellor may be collected in various places in engine but remove all pipes from around thermostat area ,inspect and clean out stat too.a small tube between the bell housing and transom of about an inch maybe split kinked or blocked and this will prevent water reaching higher up stream towards the thermostat housing.
You could try removing drive and run a hose directly up this hole and the tube to see if you have flow whilst engine running too.

 

[zentodd]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

I dont see any mention of how much water is flowing to the muffs from the water hose, or what flow is observed coming out of the idle relief ports when the engine is running.

Also, what was the setup for backflushing from the engine compartment through the outdrive. With a properly installed impeller, you wont get any flow past the impeller during a backflush.

Thks u. Yes plenty of water flow. Not sure what an idle relief port is ... But the hole on the starboard side was plugged. I cleared it out and no water came out with the engine running, muffs on and water flowing.

I back flushed with the bottom of the Outdrive off and it flowed water easily.

 

[zentodd]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

exhaust flappers stuck in cow horns down the bottom .maybe able to see when drive removed and look up the exhaust bellows. A restriction here is no good too. Check flow to the engine b4 running up too hot and the water should be pumping out the side vents when running as well as centre of prop. Rubber pieces of impellor may be collected in various places in engine but remove all pipes from around thermostat area ,inspect and clean out stat too.a small tube between the bell housing and transom of about an inch maybe split kinked or blocked and this will prevent water reaching higher up stream towards the thermostat housing.
You could try removing drive and run a hose directly up this hole and the tube to see if you have flow whilst engine running too.

I thought about the flappers but I would expect the engine to be low on power with an exhaust restriction. What do u thk?

I cleared all hoses and thermostat. Even with both impellers melted and broken up I didn't find many pieces through out the cooling system.

 

[Grub54891]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

Did you look at the oil cooler? Them pcs have to be someplace.

 

[zentodd]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

Did you look at the oil cooler? Them pcs have to be someplace.

Yes - it's clear. A bunch of pieces were in the lower portion of the Outdrive. Surprisingly, several came out were the water goes in.

 

[Rick Stephens]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

Yes - it's clear. A bunch of pieces were in the lower portion of the Outdrive. Surprisingly, several came out were the water goes in.

You're sure that the suction side isn't plugged? Sounds like you have the upside fairly scoped. Maybe the pump isn't getting water.

Rick

 

[zentodd]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

You're sure that the suction side isn't plugged? Sounds like you have the upside fairly scoped. Maybe the pump isn't getting water.

Rick

Hmm....
I opened up the fins were the water goes in to make sure it was clear. I'll take another look.
Thkds

 

[tazrig]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

Zentodd,

When was the last time you replaced the exaust elbows and or manifolds? If they are caked up with rust exhaust will flow out fine but they may be blocking the water from exiting the drive. Pull one of the elbows off and check for excessive rust in the outer jacket of the elbow. If it's clogged you have to replace both elbows together. On your vintage engine (if you're using it in salt water) they should be replaced every 5 years or so. If the elbows are bad your manifold may also be suspect and in need of replacing.

 

[BigDog98]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

Welcome to iboats OP. Hope you enjoy your stay. :joyous:
Hmm..... This is very odd. There are many reasons why it can cause it but you have checked almost everything and now you narrowed down the possibilities. Im thinking you placed the gaskets on the wrong way/side. Also as i recall the MR1 out-drives should have a plastic impeller housing and maybe when you torqued it beyond spec you may have cracked it without even noticing. Also make sure your thermostat sender is not stuck and fully opening and closing when should. Make sure that your thermostat sender is rated from 145-160F as it would say in your manual. Check the risers for any restriction in them. When was the last time you replaced your manifold and risers? They are rated for 4-5 years MAX. Also what you can do it disconnect the intake side of the thermostat and connect your water hose to that hose and check it the engine is cooling down now ( make sure to take the drive off if doing so). Also check the engines impeller it should be a brass but they go bad over a long period of time. And also make sure your belt is on tight! This can also cause no water pickup!! Good luck

 

[Fastatv]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

Welcome to iboats OP. Hope you enjoy your stay. :joyous:
Hmm..... This is very odd. There are many reasons why it can cause it but you have checked almost everything and now you narrowed down the possibilities. Im thinking you placed the gaskets on the wrong way/side. Also as i recall the MR1 out-drives should have a plastic impeller housing any may be when you torqued it beyond spec you may have cracked it without even noticing. Also make sure your thermostat sender is not stuck and fully opening and closing when should. Make sure that your thermostat sender is rated from 145-160F as it would say in your manual. Check the risers for any restriction in them. When was the last time you replaces your manifold and risers? They are rated for 4-5 years MAX. Also what you can do it disconnect the intake side of the thermostat and connect your water hose the that hose and check it the engine is cooling down now ( make sure to take the drive off it doing so). Also check the engines impeller it should be a brass but they go bad over a long period of time. And also make sure you belt it on tight! This can also cause no water pickup!! Good luck

I was thinking the the raw water impeller would bring the water up to the engine's water pump regardless of whether there was a belt on the engine water pump or not. Isn't the engine mounted pump for circulation only?

 

[84EdH]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

yes.

 

[BigDog98]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

I was thinking the the raw water impeller would bring the water up to the engine's water pump regardless of whether there was a belt on the engine water pump or not. Isn't the engine mounted pump for circulation only?

Actually i thought that too at one point and i did all the same tests as OP before and then realized that the belt was loose and was not spinning the pulley to which the pump was attached too and then i did not have that problem anymore. A mechanic told me that the impeller pump actually pumps the water through the engine. It comes up from the drive and enters the pump which has a suction in it and brings the water through all the hoses. This was what i was told.

 

[Bob_VT]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

Look at this diagram and you will see the water flow. As mentioned above check the risers.

Read this post too http://forums.iboats.com/mercruiser-...on-329915.html

 

[zentodd]

Re: 1979 Mercruiser 260 MR-1 impeller melted down AGAIN

Zentodd,

When was the last time you replaced the exaust elbows and or manifolds? If they are caked up with rust exhaust will flow out fine but they may be blocking the water from exiting the drive. Pull one of the elbows off and check for excessive rust in the outer jacket of the elbow. If it's clogged you have to replace both elbows together. On your vintage engine (if you're using it in salt water) they should be replaced every 5 years or so. If the elbows are bad your manifold may also be suspect and in need of replacing.

'Thank you Tazrig - boat is new to me. I'm all about replacing things when needed but after removing the riser (elbow) and manifold I was surprised to find so little corrosion. No doubt that they are old - probably original but I doubt they are blocking enough water to cause the impeller to melt down.