Yamaha 140Hp Overheating

[Rapson]

I have done a full test of all the circuts and they are all good. I an now convinced that the engine is in fact over heating as it fails the 3 second rule now and both cylinders send off the thermo switches. Had a good run with a mate yesterday and we were not happy with the amount of water comming out of the tell tale when at speed. As this water has not yet passed through the heads I am now leaning towards the water pump, if there was a blockage in the head the tell tale would have heaps of pressure. I have replaced the whole pump, impeller, housing, plates and dispamtled and checked and all looks fine. Recently had the gear shifter bracket break and had to take the power head off to replace it and replaced the gasket at the same time and all looked good from there.

This motor is starting to look like my grandfathers knife, the one with the new handle and the new blade.

[Tucker]

Rapson, It's been mentioned that your pressure relief valve is suspect. Have you changed that?

[Rapson]

Its Easter and ANZAC Day long weekend here so no shops are open but I will be lining up first thing Wednesday morning to get a couple of new ones. This model has 2, one on each head just below the thermostat.

[Tucker]

I'd double check that Rapson usually it's just one. Mine is on the back at the very bottom. There's a hose coming from the housing. There is a redesigned style that looks like a mushroom. Be sure to get a new grommet and gasket. These are usually cheap parts and shouldn't cost a bundle <$20.

[Rapson]

Definately 2. I had to get a new/second hand thermostat cover a while ago (slight crack in the old one) and took a bit of hunting to find one at the wreckers as most covers didnt accomodate the poppit valve. I have taken them both out checked them and they look ok, no damage but for the price of a couple of new ones I will replace them to eliminate them from my problem. Thanks for your input Tucker.

[Tucker]

Rapson, I think we got major confusion here. You have 2-thermostats, and 2-thermo switches but I believe only 1-pressure relief valve. The poppit valve you're refering to is the actual thermostat. The poppit valve senses pressure in the exhaust cover and is located under the CDI. At least that's the way it's on my 2.6L.

[Rapson]

Tucker, my 140 is different and definately has 2 poppit valves. I did see a scematic of it on here somewhere but buggered if I can find it again, all the ones on boats.net are the way you describe. In the attached pic on the head you will see the top hole, thats where the thermostat sits and the hole right underneath is where the grommet, valve and spring for sit for the poppit valve assembly. There is one for each cylinder. The exhaust cover is flat and doesnt even have a sopt you could install a pressure relief valve as you have described.
Dont know why they have done this one differently for OZ, something to do with the roatation of the earth? Our toilets flush to opposite way to those in the Northern Hemisphere!

[drum sticks]

hi rapson,just check 1984 115hp scematic u will see how yours is set up,ie 2 pressure relieve valves,cheers paul.

[Rapson]

Awsome, thats the one, Thanks Paul. I looked up and down a couple of years, obviously didnt go far eneough back.

[rodbolt17]

that design wasnt used long in the US market.
something about a patent infringement with the OMC crossflow V6.
however a few of the 84-85 international market engines were sold in the US.
there again its a diffrence betwee US market stuff and international market stuff.
but yes the hole just below the T-stat hole is for the pressure control grommet.
typically at high speeds the valve doesnt have to be there and it will cool.
the valve is on the discharge side of the water stream coming from the block.

[Rapson]

Quick update to this ongoing saga. I installed 2 brand new poppet valves, the new mushroom type ones, and she is still over heating. When I got up to speed at about 4000rpm a mate had a good look at the motor and saw water spraying out from where the lower case connects to the leg, where it shouldnt be comming from! I am asuming there is a leak somewhere above the water pump, busted seal or even a coroded pipe but atleast I have found a problem!

[Tucker]

When the lower unit was installed, was the feed tube installed correctly in the grommet on top of the pump?

[clivewillgoss]

Quick update to this ongoing saga. I installed 2 brand new poppet valves, the new mushroom type ones, and she is still over heating. When I got up to speed at about 4000rpm a mate had a good look at the motor and saw water spraying out from where the lower case connects to the leg, where it shouldnt be comming from! I am asuming there is a leak somewhere above the water pump, busted seal or even a coroded pipe but atleast I have found a problem!

Hi Rapson!

Any updates on this problem?
I have a 1996 V4 140hp Yam and it does the same thing.
I know it is not overheating, but the alarm goes off if I run at 38knots or more.
We have replaced one sensor, but then found the one goes off, and it does not matter which is which side of the engine.
Best guess so far is than it is a resistance by a bad connection setting it off.
bugger if I can find it though.

Clive

[Rapson]

Hi Clive,
A bit different as I found that mine is actually over heating. I found a product called MACS that is a flushing agent. You hook up a bowl to the butterfly clamp and add it when flushing the outboard. It is supposed to loosen all the salt, corrosion etc and lubricate at the same time. I got some of this stuff on my hands and it is very oil like and a bugger to get off. Flushed my outboard twice with this after a good straight fresh water flush and it loosened up that much muck it blocked up the tell tail!! I took of the thermostat covers and found heaps of much in there as well so I filled up a spray bottle and sprayed it directly in there as well.
Outboard hasnt over heated since. I am asuming it has removed all the muck from the depths of the engine that I couldnt reach.
Good luck with yours!

[captain rednut]

overheating

hi my suggestions are,
1- temp sensor faulty?? Ive had several of these do this and they cant be tested easily if they only fault in operation and when the resistance is rite. disconnect one at a time and see which side triggers and then swap for a re-test??.
2- you may have a hole corroded between your exhaust and water in the exhaust adapter under the power head. again Ive had two of these and they only overheat over 4000rpm approx, one thing i noticed on these was a slight amount of steam which appeared with the smoke from the exhaust.
all had what appeared to be lots of water flow from the telltale and exhaust.
cheers Jim