Yamaha 150hp runs very hot

[Ketchitdave]

My 150hp yamie has just started running very hot, not enough to set off the heat alaram. It is a 2000 model with only 220 hours on the hour metre. The spark plugs are also showing signs of getting hot. Any suggestions on possible causes or is it normal for this motor.

Dave

[FNQCairns]

Dave I assume this is V6 and 2st? depending on that duty the engine is doing when it gets hot either the popets or the thermostat will most likely be at fault on a middle aged engine. I assume the water pump is ok because that is a basic maintenance item.
Of coarse the block and associated water gallerys could be choked with salt or goo but it's best and most cost effective to assume popet/thermos first because they can never in an over serviceable condition. Typically if a mechanic wants to jump straight in tear down and clean the galleries before trying to bring these parts up to spec it's best to move on to the next one as you will never know what the problem was because these parts will either be replaced or in the case of popets sometimes cleaned up within the operation -of coarse the cleanout will be the stated reason for the lack of overheat after repair but the bill might have near trippled!!

Does your hand also say it is getting hot? if so which bank? or both?

Thermos failure is not uncommon they can open late. open too little, stick open or not open at all. Poppets can get sticky and not open on time or at all causing higer speed overheats.

cheersfnq

[Jru29]

2 Stroke or 4 stroke?

Okay I'm not a mechanic but these are things I've seen blocked/need attention on my early 90's yammie 150 2 st....not sure about the 2000 model but I'd check the thermostats are not clogged up (4 bolts at the top of each cylinder set), they are relatively cheap to replace. Easy to test too, just drop them in some hot water and you should see them open up, the temp they open at is usually stamped on them I think (if they are genuine).

Another thing you could look at is (again not sure of the 2000 motor) a hose on the lower part of the exhaust manifold, which is the flat plate between the cylinders. If you take the mount (2 bolts I think from memory) that attaches to the hose off there is a simple poppet type valve inside, mine was caked with salt one time and severely blocked, I think some people refer to it as the blow off valve, I don't know if thats its correct name...

You could also check your water pump...

And also my mech told me thats it's normal for one cylinder side to feel hotter than the other as when you look from the side you'll notice that one cylinder head clearly higher than the other - heat travels upwards...

Hope that helps a bit...good luck.
:)

Jru

ps failing those simple sorts of things you may be heading down a path you don't want to know about...possibly gassing or blocked cooling system.

[ozscott]

My 93 115 Yammy V4 s stroke with about 500 hours got an overheat at high revs, brought revs back down and no problems - ie keep it under about 4k and it ran fine. It had only just had a full service with new thermostats, impellor and water pump seals etc...turned out to be the poppet valve was all gummed up with salt and crud...dealer I trust removed, cleaned and re-assembled. Before he found that he dropped the leg again and made sure the water pump hadnt done anything funny - all up an hours labour and well worth it, running like a bought one...try what people have recommended above.

Cheers

PS - The Yammys 2 strokes are a very good motor that has stood the test of time, so you should suss it pretty readily.

[freddofrog]

Check your thermostat as suggested.

If it's only heating up at WOT then it's probably your high speed release valve sticking (this should be sitting right next to your thermostat after you pull of the thermostat housing) - this may be what others are calling a poppet valve/blow off valve but I'm sure what a these are.

Basically the valve (what ever it's called) is the one that "blows" and allows water to bypass the thermostat at high rpm. On my 2 st yammie it is nothing more than a seal held in place by a large spring. The faster you go more water pressure builds up to push the spring back and alow the water to continue without having to go through the thermostat. At WOT your motor should actually be running cooler because of this.

cya
ff

[uripper]

If nth bris is an option for you, then suggest talk /take to Jeffers Motorsport 3204-7443 Graham Jeffers & Keith Falkenhagen - Hard to find ANYONE who knows more about YAMs ... (& other boating stuff too)

Mal ;)

[Ketchitdave]

Thanks everyone for such informative responses. Thermostats and popets...will take the advice given and get the spanners out and check it out......

Hope you all have a great fishing Queens birthday long weekend.

Good fishing, regards Dave.:)