Outboard cooling water problem - help please!

[KAL]

Outboard cooling water problem - now solved!

My 1999 Yam 8hp 4 stroke developed an intermittent problem towards the end of last season, where the cooling water flow seemed to be restricted. It was still cooling the engine, but flowing much more slowly than usual. I put this down to a combination of, possibly, a bit of mud in the circuit and the need for a new impeller.

When I got it home and winterised it, the flow was re-established strongly, so I congratulated myself on shifting the mud/grit/cr4p that might have been causing the problem and resolved to change the impeller before launch.

Today, I serviced the engine and changed the impeller but, to my dismay, the cooling water flow, after being strong at first, then became feeble and stopped.

I have checked that all the channels are free, but there's almost nothing coming up from the lower unit.

The water pump looked fine when I changed the impeller.

Does anyone have any idea where to turn next? I plan to get the lower unit off again tomorrow morning and check that the channels down there are all clear, but I can't think what else to do apart from replacing the water pump unit, but that's expensive and I'm not sure that's the problem or how to diagnose it if it is.

Any ideas folks?

 

[PetiteFleur]

Does the impellor have a metal centre - on some makes they have been known to part company from the rubber - looks fine initially but slip when trying to pump water. Worth checking.

 

[Rigger Mortice]

It doesn't have a thermostat that's playing up?

 

[Tam Lin]

I have that trouble with my flow - must be my age!

 

[KAL]

Does the impellor have a metal centre - on some makes they have been known to part company from the rubber - looks fine initially but slip when trying to pump water. Worth checking.

Not as far as I can see. It's a genuine Yamaha impeller, so maybe someone knows. Thanks for the idea anyway.

It doesn't have a thermostat that's playing up?

It might, but I'm not sure where to find it. I have a service manual so will check it out. Thanks!

I have that trouble with my flow - must be my age!

Try some Saw Palmetto standardised extract in tablet form (Holland & Barrett)

 

[VicS]

Before you tear anything apart again check the actual telltale, its hose and the connection on the engine are not blocked.

I am sure it will have a thermostat
I did not find a diagram of a 1999 4stroke but is #6 in this diagram of a slightly later model **http://www.boats.net/parts/search/Yamaha/Outboard/2001/F8MLHZ/CYLINDER CRANKCASE 1/parts.html
However the telltale may come off before the thermostat anyway


Other wise check that the water pump is correctly assembled and fitted. Check the drive key for the impeller is in place.

Check no blockage in the water tube and that it is correctly fitted. Stick a hose on it to confirm that you can get water up to the power head and out of the telltale


**With the full model ID you should be able to find the correct diagrams at http://yamahamc.partsandwarranty.com/SyndicateNav.cfm

 

[KAL]

Before you tear anything apart again check the actual telltale, its hose and the connection on the engine are not blocked.

I am sure it will have a thermostat
I did not find a diagram of a 1999 4stroke but is #6 in this diagram of a slightly later model **http://www.boats.net/parts/search/Yamaha/Outboard/2001/F8MLHZ/CYLINDER%20CRANKCASE%201/parts.html
However the telltale may come off before the thermostat anyway


Other wise check that the water pump is correctly assembled and fitted. Check the drive key for the impeller is in place.

Check no blockage in the water tube and that it is correctly fitted. Stick a hose on it to confirm that you can get water up to the power head and out of the telltale


**With the full model ID you should be able to find the correct diagrams at http://yamahamc.partsandwarranty.com/SyndicateNav.cfm

Thanks Vic. Wise advice as always.

The hoses are all clear.

I've found the location of the thermostat - will check it tomorrow. It might well be gummed up.

I cleaned the water pump housing before reassembling, after installing the new impeller. I can't get the 'wash' plug to undo, so can't force water up the leg. I will use some penetrating lube tomorrow to see if I can shift it, otherwise I'm stuck with a tub of water.

If it's any use, I can email you a copy of the service manual for a Yam8/9.9. Let me know by pm if so.

Thanks!

 

[Rigger Mortice]

I've found the location of the thermostat - will check it tomorrow. It might well be gummed up.

Take the thermostat out, refit the housing and run the engine sans thermostat. (It won't matter for a short time)

If your cooling is then working properly, you've probably found the answer.
Replace thermostat.

 

[William_H]

Can't be sure about Yam but many o/bs use the thermostat as a kind of bypass to allow the engine to warm up. So tell tale will be the same with bad thermostat.
Second Vic's suggestion of garden hose on the tube up to the engine. Do this to get a benchmark f for checking blockages in the head. (in future) A good easy flow including tell tale indicates all is OK up top so bad pump.
As said boss of impeller may be slipping in rubber vanes. Also this kind of pump relies on good seal between the side plates of the pump and the impeller. good luck olewill

 

[rogerthebodger]

I have a similar problem with my suzuki DT16.

With the power head removed and the drive shaft powered by an electric drill there is water flow up the feed pipe. If I put my finger over the feed pipe end there seems to be very little pressure.

With the power head fitted (plugs removed) and the motor driven by an electric drill water comes out the pee hole.

With the outboard powered up exhaust gasses only comes put of the pee hold.

Looking at the water flow and all cooling jackets all clear. New and correctly fitted impeller , pump body fitted correctly and all specified gaskets sealed

Following all these tests the only thing I can think of is that the pump body has warn so the fit at the tips and/or the sides are allowing water to escape thus reducing the available pump pressure to a point that it cannot over come the exhaust back pressure.

Am awaiting a new pump body to arrive so as to confirm.

The OP could have a similar problem or I could have the wrong end of the stick in my case

Any one like to comment pls.

 

[theoldsalt]

KAL,

You don't explain what makes you think your water flow is restricted. The tell-tale is just that it does not really give any real indication of the flow of cooling water through the cooling jacket.

I have an intermittant problem with tell-tale flow on my Yamaha 8hp. I just push a bit of wire up the tell-tale and the flow is returned. It is just an accumulation of salt.

The main flow of cooling water exits via the exhaust. This cannot be seen easily with the engine in the water. To check the flow out of the exhaust the engine needs to be out of the water and cooling water supplied to the engine either via the intake using a devise that looks like head phones clamped on the leg intakes or via a hose adapter that screws into the leg above the gearbox.

If the engine is not overheating then main cooling flow is probably OK and only the tell-tale needs claring.

 

[KAL]

KAL,

You don't explain what makes you think your water flow is restricted. The tell-tale is just that it does not really give any real indication of the flow of cooling water through the cooling jacket.

I have an intermittant problem with tell-tale flow on my Yamaha 8hp. I just push a bit of wire up the tell-tale and the flow is returned. It is just an accumulation of salt.

The main flow of cooling water exits via the exhaust. This cannot be seen easily with the engine in the water. To check the flow out of the exhaust the engine needs to be out of the water and cooling water supplied to the engine either via the intake using a devise that looks like head phones clamped on the leg intakes or via a hose adapter that screws into the leg above the gearbox.

If the engine is not overheating then main cooling flow is probably OK and only the tell-tale needs claring.

The water flow is usually very strong emerging from the telltale. Suddenly started to be very weak at end of season. The difference is what raised my anxiety.

Problem now solved. The thermostat was fine, so replaced.

Had the lower unit off again and inserted a water hose up its jaxi. Nothing.

Then used a sink unblocker (flexible wire with pigtail at end), both from the bottom and the top. Then water pipe inserted again. Hallelujah! Water from tell tale.

Reassembled lower unit and started engine. Just beautiful. Telltale just as it should be. Load of sand and shell fragments in the bucket.

Thanks to all for your help. I have that Yam 8.&.9.9 workshop manual if anyone needs it.

 

[theoldsalt]

KAL,

That's good news. I'm glad you've got it sorted.

 

[KAL]

I have a similar problem with my suzuki DT16.

With the power head removed and the drive shaft powered by an electric drill there is water flow up the feed pipe. If I put my finger over the feed pipe end there seems to be very little pressure.

With the power head fitted (plugs removed) and the motor driven by an electric drill water comes out the pee hole.

With the outboard powered up exhaust gasses only comes put of the pee hold.

Looking at the water flow and all cooling jackets all clear. New and correctly fitted impeller , pump body fitted correctly and all specified gaskets sealed

Following all these tests the only thing I can think of is that the pump body has warn so the fit at the tips and/or the sides are allowing water to escape thus reducing the available pump pressure to a point that it cannot over come the exhaust back pressure.

Am awaiting a new pump body to arrive so as to confirm.

The OP could have a similar problem or I could have the wrong end of the stick in my case

Any one like to comment pls.

I found that the cooling channel around one of the heads was pretty much blocked. I removed the hose and got a bit of plastic tubing but could neither blow or suck sit through the lower channel. I got a bit of water in there and attached a high capacity bicycle stirrup pum, then blew it through. Bingo.

Once everything was reassembled, I ran the engine in fresh water for quite a while to make sure that everything was well flushe

I suggest checking your cooling circuits are all running free.

 

[duncan99210]

A couple of summers back, our Yamaha Malta overheated and stopped. I stripped the leg, replaced the impeller, checked the condition of the water pump and then stripped the power head exposing all the water channels surrounding the bottom of the power head. The channels were all well blocked with salt and bits of stuff. Also removed the thermostat and checked that it worked (placed in a pan, heat pan up and if thermostat opens, it works(ish)) and reassembled. Since then the tell tale has been digging holes in the sea and the outboard has been running fine.

Moral of the story? A cooling problem on a small outboard is most likely to be a worn out impeller and blocked water channels. Cleaning them on a small motor will take a day or so work and repay your love and attention by further years of service.....

 

[KAL]

A couple of summers back, our Yamaha Malta overheated and stopped. I stripped the leg, replaced the impeller, checked the condition of the water pump and then stripped the power head exposing all the water channels surrounding the bottom of the power head. The channels were all well blocked with salt and bits of stuff. Also removed the thermostat and checked that it worked (placed in a pan, heat pan up and if thermostat opens, it works(ish)) and reassembled. Since then the tell tale has been digging holes in the sea and the outboard has been running fine.

Moral of the story? A cooling problem on a small outboard is most likely to be a worn out impeller and blocked water channels. Cleaning them on a small motor will take a day or so work and repay your love and attention by further years of service.....

Useful to know.

When you strip down the cover to the cylinder head cooling channel, do you need a whole pile of new gaskets?

 

[duncan99210]

Useful to know.

When you strip down the cover to the cylinder head cooling channel, do you need a whole pile of new gaskets?

Didn't remove the cylinder head, just removed the drive head from the leg. On the Malta, that exposes most of the channels for you to clean. I used a dental pick to clean as much as I could out of the channels as they disappeared round the cylinder etc. There is a gasket between the powerhead and the leg but I was careful not to damage that as I removed the leg. I did have tube of silicone instant gasket stuff available in my tool box if the gasket had been damaged enough to require replacement. Worked OK, as it seemed that most of the cr4p was in this areas rather than round the cylinder itself. All of this done at anchor in Nidri; SWMBO clearly stated that it was too far to row ashore so I'd better do something or else we'd need to buy a new engine....