Not a Yamaha question but hope for some help from Viacom or one of you guys

[dray0151]

Boscoe or any of you I don’t have a lot of info yet but a relative has an old 2 stroke mariner that over heats after running a bit. Has good pee stream until it heats up then that begins to stop. He has been told this engine has no thermostat and a mercury guy looked at the lower unit and said the impeller looked good. I was Told there’d is a plug between two cylinders that can be taken out and see in the water jackets and it looks clear. 1986 45 horse mariner called a classic 50. Ideas?

[dray0151]

Sorry I was typing this on my phoneWas asking Boscoe or one of the other guys Townsend or fairdeal I’d they were familiar with this engine and had any ideas

[boscoe99]

Need the engine ID from the engine data plate.

[99yam40]

I will jump out there and guess a blown headgasket

[dray0151]

Serial number OC103135. Thanks Boscoe

[dray0151]

Thanks Yam he was going to do a compression test next week, if that doesn’t show much I’ve told him the leak down test would tell more. Will let you know as I find out things, I will only be here this week so hopefully he can find out some things soon.

[boscoe99]

I found the motor at the Mercury Marine Parts Express website. There does appear to be two plugs between cylinder one and two and between three and four.

Does not look like anything made by Yamaha.

[boscoe99]

[TownsendsFJR1300]

Do you have a link for that site Boscoe? I found what I believe to be it ( https://www.boatengine.com/mercury-parts-express/ ) but no Mariner parts come up...


Dray, you mention the engine has no thermostat... Is that because someone removed it? If so, it should be replaced. Water may very well NOT be staying in the powerhead long enough to cool the engine, thus the over heat.

I would pull off the thermostat cover, run it in a bucket of water and check for water flow up to the power head.

If a borescope is available, and it fits in the access hole, might be interesting to peek. Looking for corrosion, old WP impeller vanes, etc.

I would also personally check the WP, WP HOUSING for wear, and any other parts possibly corroded or missing. That parts link would be nice to have to compare to..

Inspecting the spark plugs would be worthwhile too.


As noted, a compression test and leak down test should give you an idea of the general health of the engine

[dray0151]

Thanks Boscoe he was not aware of the second bolt we will see if that is open also. He was planning on doing a compression test and I reminded him of the leak down test maybe showing more so we will see. I will be gone after this week so I’ll try to follow up later but it may be a while

[TownsendsFJR1300]

Boscoe, I found what I believe to be the website you found (and posted it here but my ENTIRE POST GOT DELETED). Maybe PM it to me and Dray? Or try posting(probably will get denied)



Dray,

You mentioned there’s no thermostat. I gather it’s been removed however it should be replaced.
Water not staying in the power-head not long enough can cause issues.

With the thermostat housing off, I would run the engine in a bucket of water and check the water flow in the power-head. It also gives you a peek internally.

I would also inspect the WP itself and the housing.

Depending on where those access holes are, you may not be seeing the head for corrosion build up or the lower cylinder jackets also for salt build up. I suspect if nothing unusual is found, the head will likely have to come off..

[boscoe99]

Like the Yamaha parts catalog they won't link directly to the specific catalog. Have to work your way in.

http://www.mercurymarine.com/en/us/p.../parts-catalog

https://public-mercurymarine.sysonli...=englangDB=eng

[boscoe99]

[dray0151]

Thanks guys but I am being told it has no thermostat. I will try to look at the parts diagram and see if one shows.

[boscoe99]

I looked and could not find one. My Mercury 25 HP did not have one. It was a bare bones motor.