Yamaha 115 2-stroke cooling problems

[MikeCC]

Having had a starting problem a couple of weeks ago, I wanted to run up the engine in a tub just to make sure I didn't have another wasted trip.

First of all, no tell-tale, so I pushed a hose up agains the hole to wash some water back through.

After starting the engine OK, the tell-tale jet appeared OK. Ran lukeewarm as expected, with a reasonable flow coming through. Engine was just running on tickover. So I was a bit surprised when the temperature warning alarm came on (at least I know it works now).

Switched the engine off pronto and went to take a look. The heads were quite warm but the odd thing was that one pair seemed hotter than the other. You wouldn't want to keep for fingers on them for more than a couple seconds.

Thought I would take a look at the thermostat arrangement only to find that they were actually missing! I looked at a Yamaha parts website which showed the assembly together with the pressure control valve. Apart from the obvious reply, what does that do within the cooling system?

Would the absence of thermostats have any real effect? I had thought that water would just circulate freely without them there.

Is it possible that there is some obstruction that would restrict flow one side and not the other?

If there is a blockage in the water galleries, is there an effective way of clearing muck out (eg squirting water in somewhere else)? Or is it a more radical investigation?

I have spoken to a dealer about the replacement thermostats and asked about the age of the engine etc but they haven't got back to me yet.

It is a 115 AET serial 6E5 302858 if that helps with any answers.

I haven't gone as far as inspecting the impeller yet but I have read elsewhere that even with a tell-tale jet the impeller might not being doing enough.

Sorry about all the details, but didn't want to leave any info out.

Thanks

Mike

[Richard B]

Mike, unless it's definitely been changed very recently, I would replace your impeller first otherwise you could be assuming that this problem is much more complex than it really is! I assume that you've found my thread on this: Yamaha Impeller Change

[MikeCC]

Originally Posted by Richard B

I assume that you've found my thread on this: Yamaha Impeller Change

Thanks for reply Richard - yes I found that while I was searching for info. In fact I was quite relieved when I read it as the job looks much less painful than I had expected. Will probably do that anyway - as you observed, once you've taken a look you may as well change it. (Bit like clutches really - why don't people/garages replace the thrust bearing automatically with the clutch?)

My only concern after that is the uneven heat on the heads themselves which might suggest some other blockage.

Mike

[MikeCC]

No time like the present I thought to take a look at the impeller . . .

Undid the 7 bolts as per Richard's fine pictures - nothing.

The two parts are still firmly stuck together.

I've used a block of wood and a few tentative knocks with a lump hammer, but to no avail.

Any ideas please?

Mike

PS I gave up this sort of stuff on my car years ago - haven't a clue why I thought this was a good idea! Something about 2-strokes being simpler?

[Richard B]

Did you find the bolt (No.8) that's uncovered once you have removed the trim anode?

[MikeCC]

That'll be the problem (I did say tentative knocks!). Thanks again Richard. Sorry - didn't read your previous stuff properly. I had thought the anode bolt WAS the extra one.

Just had enough light to slacken it off and see the two parts separate. Bit dark now to do any more and I suspect domestic duties will beckon tomorrow. Might get away with an inspection on early doors.

Anyone got ideas on the uneven head temperatures please?

Mike

[Rogue Wave]

There is a guy in Southampton who knows your engine ( he serfviced it for the previuos owner) and he is a fine Outboard Mechanic, Dean @ Hedge End Outboards, If you want I will happily forward you his number

[Hightower]

After checking and replacing your impellor I would turn my attention to why the themostat/s are missing. Usually peeps take em out if things need cooling down and so might lie your problem.
I would ask the guy Stuart has said serviced the outboard to find out more Info. Ask if the outboard had regular flushing and was it on a mooring where access to services would be a problem.

A friend earlier this year had cooling problems with his 4 Stroke Yammy and ended up a few quid lighter because of salt blockage though lack of flushing.

Andy

[MikeCC]

Andy - Impeller coming out v. shortly. I suspect there is some sort of blockage as well. How did they clean out your mate's engine?

As the engine is quite old, anything could have happened really.

Stuart - yes please, Dean's number would be great.

Thanks

Mike
Update -Impeller looks fine - no real wear amd no splits, nicks etc. The casing looks OK too with just very light surface marks.

[MikeCC]

After taking the leg off and flushing through the water intake with a hosepipe for a few hours (Not running!), everything seems to be OK. Thanks to everyone that responded.

Haven't put thermostats back in - will see how engine runs without them.

Richard - next time you do your impeller there's an easy way (courtesy Clymer manual). Slide the impeller onto the shaft first and get it located on to the key. Drop the housing down over it and line up. Now turn the shaft clockwise as you gently push the housing down. This might be a bit easier with 2 people - one on the shaft and one on the housing. This method has the added benefit that you can't then point the impeller blades in the wrong direction (as long as you turn the shaft the right way!).

Anyway, looks like we'll finally get out tomorrow (Mon) assuming the weather doesn't turn.

[Rene]

MikeCC

Regarding the age of you engine.

On the plate with the serial number, there are more letters. One of these reference the legth off the leg, the other the age of the engine.

You will have the find this letter and ask around, maybe someone here can guide you to the right age off you engine, when we have the letter.

Hope I make sense

Rene

[commtrd]

I have also experienced cooling problems with my C115. I changed the water pump amd the thermostats. The problem got worse! I looked at the lower unit while running over 3500 rpm (not for long!) and there was a huge amount of water coming out of the top of the lower unit at the front. I had never seen it do that before. I thought I screwed something up installing the new parts. So I dropped the lower unit again and didn't find anything wrong. I removed the thermostats and ran it on the water hose and it ran fine but that is not the same as running over 4000 rpm while out fishing.

I suspect that maybe it is the pressure control valve that is hung partially open? I really would rather have the thermostats in as designed but I am in S. TX so running in real cold water (most of the time) is not a problem. I have not taken the boat out to test it without the thermostats in. I found another web site that shows the prv to be at the lower part of the center between the cylinder banks with a larger hose clamped to the housing going I presume down to the lower unit. I think the prv opens up to avoid overpressuring the cooling system when the thermostats are not open yet (engine cold on start-up). The thermostats are rated at 50 degrees C which is 122 degrees F. If I run without the thermostats in the engine would likely be running too cold all the time...what will this do to the engine if anything?

I am going to get the parts to replace the prv and try that. Of course I could just leave the thermostats out and I will if that is the only way it will run without the overheat sensor(s) kicking in and cutting out the ignition. There were salt deposits mainly in the port side thermostat housing and galleys but the stbd side was real clean.

How could I apply a solution to cut salt deposits in the cooling system? Any insights into this would be greatly appreciated.

[jyasaki]

Thermostat is supposed to allow the engine to get warm before water being cooling.

One effect of thermostats stuck open is "making oil". usually occurs with boats that run at low rpm for extended periods (i.e. trolling), but has been known to happen in other cases.

Making oil is when unburned gases pass the rings and end up in the crankcase, where it mixes with the lubricating oil. Eventually, enough builds up to where it dilutes the oil, increasing wear. Usually signalled by a rise in oil level and a milky or foamy appearance to teh crankcase oil.

jky

p.s. You do realize you're posting to a 3 year old thread, right?

[Nos4r2]

Originally Posted by jyasaki

Thermostat is supposed to allow the engine to get warm before water being cooling.

One effect of thermostats stuck open is "making oil". usually occurs with boats that run at low rpm for extended periods (i.e. trolling), but has been known to happen in other cases.

Making oil is when unburned gases pass the rings and end up in the crankcase, where it mixes with the lubricating oil. Eventually, enough builds up to where it dilutes the oil, increasing wear. Usually signalled by a rise in oil level and a milky or foamy appearance to teh crankcase oil.

jky

p.s. You do realize you're posting to a 3 year old thread, right?

And that 2 strokes dont' 'make oil' either?

[jyasaki]

Hmmm. Could have sworn I saw "F115" in there somewhere...

I know I'm old enough to not see things that are there; maybe I'm old enough to be seeing things that aren't, too...


jky