Yamaha T9.9 Cooling System

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Allezcat
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Yamaha T9.9 Cooling System

Postby Allezcat » Sat Dec 05, 2009 1:55 am

The cooling water flow thru these engines (T9.9 2005 and prior) has always mystified me. This 2004 engine has about 1400 hrs and suddenly showed no flow out the telltale (pee hole). After tearing into it I traced the water flow. From the pump it flows up a tube to the bottom of the crankcase. There a cavity feeds it to the exhaust plate (see photo). It then flows thru the exhaust plate to a cavity which feeds the cylinder walls and cylinder head. From the cylinder head it flows up to the thermostat cavity and out a hose to the exhaust compartment and the telltale. Note that on this engine all three passages are completely plugged. Also plugged are the passages to the upper and lower nipples on the port side of the engine. These passages cool the upper and lower exhaust ports and flow out the nipples to hoses. This water then joins the water from the thermostat. A small portion of this combined water flows thru the fuel pump to cool the fuel and then exits the telltale.
I have added a fitting to the exhaust plate to attach a hose. Hopefully this will help prevent this from repeating the problem.

Chet
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P1010918B.jpg
Plugged Exhaust Plate
P1010918B.jpg (253.48 KiB) Viewed 9716 times

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Re: Yamaha T9.9 Cooling System

Postby eepstein » Sat Dec 05, 2009 12:35 pm

I think your engine had a stroke. :D Until the PDQ36 I had many an outboard look like that after a few years. Flushing a couple times a year helps slow the clogs, but they are inevitable in salt water. Every three to four years I had previous outboards flushed and the water pumps replaced. The ones on the PDQ36 are new, but that'll be their maintenance cycle as well.

The photo is great. Thanks for posting it.
Eric & Bonnie Epstein
s/v Desert Star, PDQ36, Hull 49
Annapolis, MD

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Re: Yamaha T9.9 Cooling System

Postby amytom » Sat Dec 05, 2009 6:36 pm

Chet,

Excellent post!!!

Have you found a way to clean the passages to the nozzles? I have an engine that has the passages completely clogged beyond reach of a paperclip with the nozzles removed. I've put hoses on them and I tried soaking with vinager but haven't had much luck. I'm hoping to avoid drilling out the caps under the valve cover as I don't know how to seal them up again.

Thanks.

Tom

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Re: Yamaha T9.9 Cooling System

Postby Allezcat » Sun Dec 06, 2009 1:00 am

Tom,

I don't suggest drilling out those plugs as you still will be unable to effectively clean out those 1/8" holes on the far end at the crankcase cylinderhead joint. (see photos). Also these holes are fed from a right angle cavity located behind the exhaust plate cover which are also likely plugged. I think your alternatives are A) do nothing! This water just cools the exhaust passages. As long as water is flowing out the thermostat housing you are getting cooling around the cylinder and head. B) Remove the cylinder head and exhaust plate cover so you can clean all the passages. New head gasket and exhaust gaskets about $30.
I removed the entire powerhead to do (B) but I think you can remove the cylinderhead and exhaust plate without removing the cranckase, flywheel, and cam drivebelt. I am going to try this on the second engine. Will post the results next week.

Chet
Attachments
Powerhead Looking Fwd.jpg
Powerhead Looking Fwd.jpg (247.19 KiB) Viewed 9626 times
Cylinderhead 1.jpg
Cylinderhead 1.jpg (212.93 KiB) Viewed 9599 times
Cylinder Head looking aft 1.jpg
Cylinder Head looking aft 1.jpg (186.81 KiB) Viewed 9589 times

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Page 83
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Re: Yamaha T9.9 Cooling System

Postby Page 83 » Sun Dec 06, 2009 10:29 am

AArrgghhhh! I hope Salt-away helps reduce this!
Sandy Daugherty "Page 83" PDQ 36026

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Re: Yamaha T9.9 Cooling System

Postby swithen » Sun Mar 14, 2010 8:28 pm

Hi Chet

I have looked into this issue in some detail. An old article suggested that the white solid is aluminum/magnesium oxide from corrosion of the engine but I have found this is incorrect. The solid is actually calcium carbonate. Sea water is saturated with calcium carbonate and it turns out to have a negative solubility/temperature coefficient which means it precipitates out as it is warmed while cooling the engine.
The only way to dissolve the calcium carbonate is with acid. I have used vinegar (5%acetic acid) successfully. Remove the prop and insert the lower unit into a 40 gal rectangular trash container. Fill with vinegar and run the engine for 15 – 20 mins until the vinegar is warm then replace with fresh water to wash out the vinegar.
A pair of engines which had this treatment carried us just fine to Rio Dulce and back.
Salt-away has no effect on calcium carbonate

Colin
Cadenza 36051

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Re: Yamaha T9.9 Cooling System

Postby Lady of the Lake » Sun Mar 14, 2010 10:24 pm

Colin,
If you run in neutral, why do you have to remove the prop?

Sam
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Re: Yamaha T9.9 Cooling System

Postby Page 83 » Mon Mar 15, 2010 8:00 pm

Where do you get, and what do you do with afterward, 40 gals of vinegar?
Sandy Daugherty "Page 83" PDQ 36026

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I think he meant to say Lime-Away....

Postby thinwater » Mon Mar 15, 2010 9:50 pm

swithen wrote:Hi Chet

I have looked into this issue in some detail. An old article suggested that the white solid is aluminum/magnesium oxide from corrosion of the engine but I have found this is incorrect. The solid is actually calcium carbonate. Sea water is saturated with calcium carbonate and it turns out to have a negative solubility/temperature coefficient which means it precipitates out as it is warmed while cooling the engine.
The only way to dissolve the calcium carbonate is with acid. I have used vinegar (5%acetic acid) successfully. Remove the prop and insert the lower unit into a 40 gal rectangular trash container. Fill with vinegar and run the engine for 15 – 20 mins until the vinegar is warm then replace with fresh water to wash out the vinegar.
A pair of engines which had this treatment carried us just fine to Rio Dulce and back.
Salt-away has no effect on calcium carbonate

Colin
Cadenza 36051

... which is what Sandy once told me. It is mostly phosphoric acid and is effective, as are many other lime removal products.
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Re: Yamaha T9.9 Cooling System

Postby amytom » Mon Mar 15, 2010 10:14 pm

Page 83 wrote:Where do you get, and what do you do with afterward, 40 gals of vinegar?



Where else? Costco right next to the five gallon buckets of ketchup. :lol:

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Re: Yamaha T9.9 Cooling System

Postby Page 83 » Tue Mar 16, 2010 9:10 am

"nope, I got it wrong" he said, pleading diminished capacity.

My new engines have a full season on them, and all I've done for them is an occasional rinse with salt-away. I want to make them last a long time, so I will follow Colin's advice. I'm worried about just dumping the acid afterwards, because everything but the the residential sewage ends up in the Bay here. In fact, the storm drain at my driveway runs less than 600 yds into Glebe Bay on the South River. Am I overly concerned?
Sandy Daugherty "Page 83" PDQ 36026

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Re: Yamaha T9.9 Cooling System

Postby next exit » Sat Apr 10, 2010 5:52 pm

Pass the vinegar on to a neighbouring PDQ
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Re: Yamaha T9.9 Cooling System

Postby Lady of the Lake » Sun May 22, 2016 6:16 pm

Chet,
It looks like the images that you posted back in 2009 have been corrupted. Could I ask you to re-upload the photos if you have them close at hand?

Thanks,
Sam
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Re: Yamaha T9.9 Cooling System

Postby SecondWind » Mon May 23, 2016 6:36 am

Vinegar is not Phosphoric Acid, It is Acetic acid. I would suggest the following, which I now use to clean my heat exchangers. Rig a small bilge pump with a hose to the flush fitting, suspending the engine over a bucket with the bilge pump in it, such that the engine can drain back into the bucket. Fill the bucket with a gallon of CLR (or enough to allow it to fill the engine cooling system with enough to cover the pump) and allow it to circulate for at least an hour (use a battery charger to power the bilge pump). CLR will discolor most metals, but won't cause damage to them. If you don't trust the CLR you can use acetic acid the same way. If you can find acetic acid it can be diluted to the same strength as vinegar and the 40 gallon method applied, but I would use it in a concentrated form as above. You do not need to run the engine
Terry Green
s/v Second Wind
36040

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Re: Yamaha T9.9 Cooling System

Postby catalacmarc » Wed Aug 31, 2016 9:30 am

Just purchased Honu, a 36. Neither old engine was pumping water out the telltale. Talked with a mechanic who told me that they normally used compressed air to blow out the clogs. Thanks to the local Goodwill Store, a Room of Requirement if there ever was one, I obtained a working old Bostich compressor. Removed the tubing and thermostat and blew out the nipples. Also discoverd some odd things. One engine had a longer than normal tube leading to the fuel pump which putting the cover on would kink and stop water flow. The multiple nipple plastic fittings that bring tubes together have small bores and are another site of water stoppage. Finally found the only nipple with a spring retainer, it is directly under the power head and nery difficult to reach. It is a water return to the leg. Don't know if the compressed air took it off or it had been off for a while. It took a mirror, flash light and persistance to get it back on. Water seems to be running fine now.


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