Yamaha 8hp 2 Stroke Not Cooling

landlockedpirate

landlockedpirate

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Looking for some suggestions. I bought a 'Refurbished' 2001 Yamaha from a dealer last year. Thanks to the rubbish summer we didnt have, I haven't had chance to use it till this weekend.

Just to check everything was fine, I ran it up in the test tank to find very little cooling water coming out, just drips really.

Have done all the usual, new impeller, cleaned through all the water passages with wire, run a batch of Rydlyme through it. But very little improvement. Starting to delve a little deeper, took the back plate of the Thermostat to find no thermostat !

Its obvious to me I have been sold a dud with pre existing problems, but the dealer went into administration and no longer exists. I have a couple of questions, will the actual act of removing the thermostat effect the water flow from the pee hole ?

The only other thing I can think of is to replace the waterpump ? It looks in decent nick, but I'm running out of things that it could be.

Thanks
 
The back pressure from the closed thermostat MAY assist in diverting more water to the tell tale, but just because you get a good jet from it then it doesn't confirm that you have good cooling, only that the impeller is working. The reverse can also be true, that is you can have a trickle but cooling is OK. Is it overheating? if not then put in a thermostat and see how you go. There may be a bit of an airlock in the tell tale circuit even.
 
I take it you have checked that the telltale is not obstructed?

You have the water level correct in your test tank ( see the diagram in the manual)

Lack of thermostat may well be the cause.

The important question is, is it overheating?

You should be able to touch and briefly maintain light finger contact with any part of the cylinder and cylinder head, except perhaps for the head around the spark plugs.
If you cannot, or if steam issues from the telltale or the exhaust relief ports, or if a splash of water sizzles and boils it is overheating and you need to look again at the pump, delivery tube and cooling system.
 
VicS said:
I take it you have checked that the telltale is not obstructed?

You have the water level correct in your test tank ( see the diagram in the manual)

Lack of thermostat may well be the cause.

The important question is, is it overheating?

You should be able to touch and briefly maintain light finger contact with any part of the cylinder and cylinder head, except perhaps for the head around the spark plugs.
If you cannot, or if steam issues from the telltale or the exhaust relief ports, or if a splash of water sizzles and boils it is overheating and you need to look again at the pump, delivery tube and cooling system.
Click to expand...

With the engine running poke a bit of wire into the telltale. They do block easily.
 
Thanks for the suggestions. Yes, I have run a piece of strimmer wire around 100cm back through the tell tale, no obstructions.

Just put it back in the tank at the right level and tried to get it hot. I think it is starting to overheat. I have also tried it muffs, no improvement in tell tale, but good volume of water coming through the prop. Not sure if this is because of hose pressure or working impeller/waterpump :confused:

So, new thermostat and new waterpump ?
 
Having had a Yamaha 8 2 st for many years, I can confirm that the Pee hole is not very active and I would guess your engine is fine, however you can tell if its getting too hot as the metal plates next to spark plug or elsewhere on the engine cylinder head will get too hot to touch and you may see steam coming out of the pee hole. Spit on it first to see if its too hot and touch with the back of your finger if your worried.

Edit Check the water pump first , you'll need to drop the bottom of the leg to get at it , the bolts to undo are fairly obvious, but first you'll need to loosen the gear rod clamp which is accessed from the front high up on the drive shaft, which is a bit of a fiddle.

When mine got to this state ( years of not flushing on a drying mooring) it wasn't hard to fix, take off the plates on the back and side and scrape all the salt crystals out with a small screw driver and a bit of wire, also check the thermostat near the top of the engine. There is a tricky hole to find accessed from the side plate at the bottom of the chamber IIRC. You may need to put a fresh set of gaskets on the plates as they often come apart when you take the plates off and go gently getting the bolts undone, replace with added grease.
 
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I have had this a couple of times on my Tohatsu. I pull the hose off the telltale spigot and connect to a hose connected to a tap to backflush the system. Sometimes something can get in and block the channels where you can't get at it. Has worked so far.
 
neilf39 said:
I have had this a couple of times on my Tohatsu. I pull the hose off the telltale spigot and connect to a hose connected to a tap to backflush the system. Sometimes something can get in and block the channels where you can't get at it. Has worked so far.
Click to expand...


I don't think that can be done on the Yamaha as I believe the tell-tale comes directly from the engine block not via a hose.
 
landlockedpirate said:
Thanks for the suggestions. Yes, I have run a piece of strimmer wire around 100cm back through the tell tale, no obstructions.

Just put it back in the tank at the right level and tried to get it hot. I think it is starting to overheat. I have also tried it muffs, no improvement in tell tale, but good volume of water coming through the prop. Not sure if this is because of hose pressure or working impeller/waterpump :confused:

So, new thermostat and new waterpump ?
Click to expand...

First reaction is to say that if you get good flow out of the prop when running on muffs then all is well except for the lack of thermostat

But

Confirm that the flow is due to the pump pumping water through , not just due to water pressure from the water supply to the muffs. Little or no flow when engine not running?
Also be sure that it is not due to water leaking from the pump or water tube.
 
On my Yamaha 4 (which was overheating last week) and which I believe has an almost identical cooling system, I found the hole from the pick up holes in the leg up to the pump was blocked. Lots of fiddling about with small screw drivers, hot water and drill bits of various sizes cleared the hole and it now has coolant coming out of the tell-tale from the block better than I have ever seen it before.

To complete the story, I treated it to a new impeller and changed the gear oil in the leg and its like a new o/b compared to what it was. (I am going to have to keep an eye on the gear oil as it was slightly emulsified and I had to flush it through several times and blow it through with an airline to clean it out properly.)
 
I also have a 2 stroke 8hp 8cmh 6N0S with the same issue. Where is the thermostat on mine? And does anyone have a parts list? This is my first outboard.
Thanks in advance
 
Not Technical advise but had very little water coming out of my Johnson 8hp seahorse outboard whilst testing before launching but after 15 minutes into the launch the water started coming out how it should. Guess it just needed a load. Doesnt like cold starts tho and seems to like a squirt of easystart each day.
 
If the engine hasn't been regularly flushed and this is a saltwater motor I can almost guarantee that the waterworks will need a good scraping out. This is not difficult at all and I'll see if I can find a helpful guide in the morning. You may need a new thermostat (£50) and then everything should be as good as new :D
 
Thanks for the help and support.
I wasn't aware that resurrecting an old thread was a forum faux past. We were all noobs at some point.
I borrowed an air compressor and gave it a couple of bursts of air and it's now peeing like a champ.
I'd still like to know where the t-stat is though, so if it's not too much trouble Dom, I'll still accept the info with pleasure.

Thanks again!
 
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