Yamaha Overheating

[Rapson]

I have hit a brick wall.

My 1987 Yamaha 140Hp 2 stroke is overheating. I can cruise at 3800rpm with no worries, go over 4000 and after about a minute the alarm starts screaming its head off.

I just put a whole new water pump kit in the leg, new impeller, housing seals etc. Put the boat in a Fingle and headed out to the 36's with out the alarm going off. I though you beauty its fixed until it went off comming in and now its back to just how it was.

I have taken off one of the plates around the head and it looks ok, going to take the other off today to see if there is any obstruction in there.

The lower leg that was on this outboard had a leak in the gearbox and had a dodgy weld repair and Garry amd I couldnt get the prop off with sledge hammers so I got a second hand leg and new prop. The only other thing that is different is the spark plugs are not an exact match to the old ones but I got them from the Yamaha dealer.

Has anyone had anything similar to this problem? It has got me buggered!

[timddo]

What about the theromstat.

[Rapson]

Hey Timddo,
Took both thermostats out when it started, and they were brand new.

[timddo]

Hey Timddo,
Took both thermostats out when it started, and they were brand new.

You will need to test if they actually open. Take them out and pour some warm to hot water on them. Do you have a steady stream coming from the telltail??

[Rapson]

I have left the thermostats out at the moment so it should be cooling to the max. There is a steady stream from the tell tail to.
I have just got the starboard side cover off and it has a bit more muck in it than the port side but there is nothing blocked. I will post up some pics.

[Noelm]

pretty common with Yamahas, the over heat over 4,000RPM, the water passages are very small and can get partially blocked very easily, also be sure when you changed the water pump that all the impellor was still intect as small bits can break off and get stuck, if you remove the heads you will see the water jackets are partially clogged and need cleaning.

[Rapson]

Pics of the starboard plate off

[Noelm]

the head needs to come off too, to fully investigate, trust me it is a very common problem, of course you need to be sure it is indeed over heating and not a false alarm.

[ozscott]

Looks ok mate - just run a drill bit with you finders inside those small return holes, check popoff valve, and if that failes take off heads, not just covers and also exhaust covers and check for blockages. My 93 115 had exactly the same symptoms after new therms, impeller, pop off etc and mine was just those small holes blocked with sand.

Cheers

[ozscott]

1987 hey..still not corroded out at 24 years. That entirely consistent with my small experience of these supposed non-salt-water series motors, but good to hear.

Cheers

[Rapson]

Thanks Nole, I have tested the alarm sensors and they look fine. I have taken off the gasket and found a bit of muck behind but nothing blocked, will give it a good clean and see how it goes. If its still overheating might have to get Garry to help me take the heads off as you say, not game to tackle that one on my own.
Cheers

[BM]

Rapson,

In that second pic you still haven't removed the gasket to clean the lower section. I presume you have done that since?

Also, as mentioned, you will need to remove both heads. On the inside face of the heads they salt up with a hard, white crusty salt corrosion that will restrict water flow (and create overheat issues).

This is a classic Yamaha problem. Pump lots of water and run fine below about 4000rpm. Get above that (when the engine produces maxium heat) and the cooling issue will present itself.

So to reiterate, water jackets off and cleaned out (above and below the gasket in pic 2) and heads off so you can clean the water galleries in the inner face of the heads and also the galleries around the cylinder walls.

Gives you a good look at the condition of the pistons and bores at the same time.

Bottom head bolts will be a bit of a challenge (not so much removing them but getting a torque wrench onto them at reassembly) if you don't remove the powerhead. Wouldn't hurt to lift the powerhead off and clean out the sandwich plate area too as I have seen Yammies seriously restrict the water tube with corrosion.

The problem you have doesn't just affect 1 area. At that age it gets right through the engine. Not a problem though. Pull it apart, clean it out and she's good for the next 20 yrs.

Don't forget new head gaskets (and powerhead base gasket if doing the whole job) and check the thermos for correct operation (pour boiling water on them and see if they open). Head torque from memory is about 20ftlb.

Cheers

[Noelm]

yep, what BM said!!

[Rapson]

Thanks for that BM.
I have taken the water jackets off and the gaskets and given them a good clean. The exhaust plate had a couple of small holes in the centre that were blocked.
I took the powerhead off a couple of months ago to replace the gear shift bracket and replaced the base gasket then.
I will give this a run and see how she goes but I think I will be taking the heads off some time anyway to give them a good clean to.
Thanks for your input guys.

[ozscott]

Yes in that photo on the left those little holes were the ones blocked on mine.