Hit a snag today... Mercruiser 470 problem... not sure what

[davemoore]

1983 Marlin 18 ft. runabout w/Mercruiser 470 - "Alpha One" outdrive

So, after doing a full tune up last week, and putting in a can of SeaFoam today, the boat was performing outstanding! The increase in torque and WOT was impressive.

Today we were out on the delta, and after we had taken a break, we started up again and I noticed something wasn't right... didn't "feel" right...

I started to watch the gauges and noticed the temp climbing - it NEVER goes over 165 degrees... when it got to about 190 or so, I knew something was wrong and shut her down.

After a bit of investigation, I noticed that the exhaust - which normally comes out the prop - was NOT coming out there, but out the sides of the outdrive instead. And there was a nasty burning smell coming from the outdrive.

Fortunately a very nice couple came along and gave us a tow back to the marina.

Any ideas? One person suggested water pump, another said impeller.

What exactly does the impeller do? Why would the exhaust not be coming out the prop?

Thanks for any help,

Dave

 

[HT32BSX115]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Howdy,


It sounds like you have a failed Sea Water Impeller.

Part numbers #22-40 in the crummy picture below. (the actual impeller is #34) ......They're usually replaced every 3 years or so +/-

If you did not run it long enough to severely overheat your engine that's good but it does sound like you may have overheated some of the exhaust components. That would be the burning rubber smell.

The drive "lower" must be removed to replace the pump impeller and if it hasn't been replaced in a long time you may have to replace the whole assy. Also, you may have had impeller fragments go downstream to the oil cooler or cooling heat exchanger so you need to recover them so they do not plug the oil cooler or heat exchanger.


Regards,

Rick

 

[davemoore]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Hey thanks for the response.

So, if it is the impeller, how would that affect the exhaust? Why would the exhaust not be coming out the center of the prop like it usually does?

That's the part that confuses me.

 

[windsors03cobra]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Lack of water in the exhaust stream caused the in rubber exhaust pipe flapper door to meltdown and plug the prop exhaust port ?
The rubber flapper door prevents water from backing up into the motor, whether or not the doors are needed is a area of great debate. :redface:
Probably melted the water pocket cover too, I heard the screws that hold the water pocket cover on are impossible to remove.

Atleast you did not over heat the engine.

 

[davemoore]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Well, everyone was right. It was the impeller. See photo below. Does it seem like something got in there, or is that normal for an aged impeller? I'm sure it was quite old...

I got it out and will be ordering a new one tonight... and the tube/sleeve in the photo just to the left of the impeller was quite melted from heat...

I also backflushed the sea water system and then forward flushed it. I saw the little rubber chunks come out on the backflush, so I think I'm ok.

If not, I will open up the heat exchanger and clean it out (and I measured it too - it's a 4" diameter version so that's good).

I also discovered that the gear oil was VERY black and not filled to capacity per the manual (have only owned this boat for about 3-4 weeks).

Fortunately, I did shut down before the engine had a chance to get really hot but I guess it was hot enough to mess up that exhaust thing...

Thanks for the help... now I just have to figure out the exhaust.

Dave

 

[HT32BSX115]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

It would be a good idea for you to replace everything in your picture. You can buy a "kit" that includes everything there.

Also, you should try to locate all the pieces of the old impeller. (and pieces of the previous impeller failure too)

They'll last 2-3 years (or more) ........ the problem is, that if you wait for them to fail, then you have the problem that you're having now but it's out in the water far from shore.......

It's always better to replace them as a preventive measure.

I also discovered that the gear oil was VERY black and not filled to capacity per the manual (have only owned this boat for about 3-4 weeks).

You're VERY LUCKY you're not replacing the drive too.....

 

[davemoore]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Yes yes - I was planning to do the kit and replace EVERYTHING in the pic.

I know what you mean about the drive/gears/oil... I have a feeling that the previous owner(s) just put her in the water, cracked some beers, and put the fishing line in... Not many signs of regular maintenance... However, there were NO metal shavings or flakes in the gear oil, so that's good...

 

[davemoore]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Ok, I found the exhaust shutter here on iboats parts, and also a diagram of where it's located. This makes total sense now...

I think it may have been messed up for a while, at least partially, because even before this event today, some of the exhaust was going out the port side water outlet...

Thanks for the help...

Dave

 

[45Auto]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

You have 3 bellows on your boat: Big U-joint bellows in the middle, smaller exhaust bellows in the middle right below the u-joint bellows, and a shift cable bellows low on the starboard side of the outdrive.

The exhaust bellows is what sends the exhaust through your propellor. When your engine quits getting water it usually takes out the exhaust bellows as well as the water shutter. Check your exhaust bellows.

If the impellor hasn't been maintained the u-joint bellows probably wasn't either. A leaking u-joint bellows will trash your u-joints, gimbal bearing, outdrive input shaft, and whole outdrive when the rusted input shaft takes out the upper seal. You should pull the whole outdrive (not just the lower), takes about 5 minutes, and at least grease the u-joints and check the u-joint bellows for leaks.

 

[davemoore]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Picked up the new water pump kit today (genuine Mercruiser parts), along with a couple quarts of gear oil (and a pump for it) and the exhaust shutter.

As I was putting the water pump/lower unit back together tonight, I discovered that whoever put the last one in put things together incorrectly and reused the old housing. Instead of putting the oil seal inside the housing at the top (between the metal and plastic), they left the old rotten one in there, and had just slipped the new one over the shaft and set it on top of the housing, which was probably allowing water to escape the pump housing, thus lowering the water flow into the heat exchanger... probably not much though.

So, the lower unit is all back together with new gear oil in it. Tomorrow night I will tackle the exhaust shutter.

Dave

 

[davemoore]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Well, tonight was not a good night...

I dove into the exhaust pipe to get out the old shutter parts and put in the new shutter, and hit a brick wall real fast.

I started by removing the hose clamps off the stepped hose below the exhaust elbow. Then I went after the three 12-point-head bolts in the exhaust riser pipe flange (which is almost impossible to get to). The first one came out - with MUCH force, the second one came out a few turns and then sheared off, and the third one (which IS IMPOSSIBLE to reach) had the head round off... sucks...

So, I found a product online called Loctite Freeze & Release that looks like it might be promising. Between that and an "EZ Out" I think I might be able to get the two remaining seized bolts out... after I remove the heat exchanger and fuel tank...

Anyone ever had a situation like this, and if so, what did you do?

Anyone have any experience with the Loctite Freeze and Release?

The rust/heat may have won this round, but I WILL win the war... I HOPE!!!

 

[davemoore]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Wow! What a day - 12 hours straight, wrenching on the Mercruiser.

Learned a lot though.

Pulled the fuel tank, the heat exchanger, and the exhaust elbow. Found the rest of the rubber from the impeller when I drained the exchanger.

FINALLY got the exhaust apart and found the toasted - no make that burnt to a crisp - exhaust shutter - all that was left was the metal piece and frame. I think it's been this way for quite some time. Ended up having to cut off the two seized bolts and drill/tap the holes.

Ran the exhaust path between the riser pipe and outdrive, then within the outdrive, tested it all with suction and compressed air - no leaks, no obstructions.

Tomorrow, we'll put it all back together (with the new shutter in place) and start her up... can't wait to get back on the water.

This was good in more ways than one... lessons learned, and further purging of the "jury rigging" that has plagued this poor boat for years.

Happy Boating!

DM

 

[o-jay]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Wow! Great attitude Dave -

My boat would have been a smoking pile if I had to go through everything you've described!

 

[danond]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Wow! Great attitude Dave -

My boat would have been a smoking pile if I had to go through everything you've described!

Everybody goes through it at some point. If your drive hasn't been off for regular maintenance, your shutters are probably fried, impeller is probably weak, etc.

Time to break out the wrenches and beer.

 

[Rocky_Road]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Wow! What a day - 12 hours straight, wrenching on the Mercruiser.

Learned a lot though.

Pulled the fuel tank, the heat exchanger, and the exhaust elbow. Found the rest of the rubber from the impeller when I drained the exchanger.

FINALLY got the exhaust apart and found the toasted - no make that burnt to a crisp - exhaust shutter - all that was left was the metal piece and frame. I think it's been this way for quite some time. Ended up having to cut off the two seized bolts and drill/tap the holes.

Ran the exhaust path between the riser pipe and outdrive, then within the outdrive, tested it all with suction and compressed air - no leaks, no obstructions.

Tomorrow, we'll put it all back together (with the new shutter in place) and start her up... can't wait to get back on the water.

This was good in more ways than one... lessons learned, and further purging of the "jury rigging" that has plagued this poor boat for years.

Happy Boating!

DM

Did you use the Loctite Freeze product?

I have seen a video on this product...and it looked pretty interesting!

Please let us know....

Nice work...and happy boating!

 

[davemoore]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Did you use the Loctite Freeze product?

I did not use it... I elected to cut off the seized bolts and drill them out and tap the holes.

I did try some stuff called "PB Blaster" that is supposed to be the best product for loosening seized/rusted bolts, but even after several applications over two days, it did nothing for them. I think these bolts became part of the flange...

 

[dubs283]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

quick question:

did you replace the water pump base and gasket?

 

[stonyloam]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Nice work! One last thing that you might want to do is a compression check on the engine to make sure that you did not damage the head gasket when it got hot. Those engines are particularity sensitive to overheating, and head gasket leaks (even when not overheated). Good luck!

 

[davemoore]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

quick question:

did you replace the water pump base and gasket?

I did replace the gasket, but not the base. The base was in really good shape (and the Mercruiser dealer was out of stock).

When I do the impeller next time (probably 1 year), I will replace the base too...

 

[davemoore]

Re: Hit a snag today... Mercruiser 470 problem... not sure what

Nice work! One last thing that you might want to do is a compression check on the engine to make sure that you did not damage the head gasket when it got hot. Those engines are particularity sensitive to overheating, and head gasket leaks (even when not overheated). Good luck!

Thanks for the tip. I will check it.

DM