Yamaha Overheating

[BM]

Rapson,

You need to pull the heads off. Its the water galleries on the cylinder side of the heads that normally block up. The whitish/grey powder totally blocks sections of the galleries. Particularly if you have found no real blockages in what you have done so far you cannot have fixed the problem.

You've come this far. To not finish it properly would be a real shame.

Cheers

[ozscott]

I agree to an extent BM, but in my case the small blocked holes where enough to send the alarm off around 4,300 rpm and not under. Once cleared she was sweet again and that was probably 2 years ago now. You can put the covers back on after a good cleaning and you can always go back later and pull the heads right off and leave the cover plates on (ie you wont waste the new gaskets for the cover plates, because they shouldn't have to come off again). The only think you lose is some on water time to test it if you dont go further now.

Cheers

[FNQCairns]

How come you didn't break any bolts? that engine has been apart before??

Seriously once most engines get to cruising speed/rpm the impeller vanes if we could view them by remote camera lay flat, in effect they do very little pumping, water pressure at the leg if there was no internal restriction is now enough PSI to do the job.

here lies a hint IMO although many things can be the cause with higher speed cooling problems very often it is a stuck popet/s, be sure they are clean and in great condition, another point is some engines need restriction, not for controlling swirl and hot spots nor for time water has contact with the head but simply so the block stays full of water, not water cascading down the head unimpeded...this is esp true of the older OMC V4s, before someone highlights they are different engines I know this but still the biology remains more or less the same over all V4s and V6s too.

Your right head has been running hotter for a while already.

if it where mine first thing i did was clean replace thermos and popets then if the result is not much better I would tear into other gasketed regions, this is because I have the luxury of doing it myself, mechanics on hourly rate the ideology is different, no owner want to deliver an engine back to the mechanic for the next basic step in diagnosis.

good luck.

[STUIE63]

if the thermoststs arn't in the I agree put them back in after checking them with boiling water to see if they open

[Rapson]

After much debating I removed both heads this afternoon and I only snapped one bolt! They didnt look to bad, nothing blocked anyway but a bit of sludge, looks like salt, in the bottom of both heads. Anyway gave them both a good clean and will order some new gaskets and see how it goes.

[Dignity]

Rapson,
I have a 1991 150hp merc and I noticed that the temp was going up ever so slightly the other week and looked like it might keep going up as the seas were calm and we were running at speed and as soon as we entered harbour the temp dropped. The problem turned out to be one that has been mentioned a couple of times already, the popets and the other that may have influenced the temp was some wear in the bottom of the impeller even though it was replaced last September. Don't understrand the wear in the impeller but the popets are and can be a different matter.

[BM]

Rapson,

Those pics arent that good but I am a bit suss about how well your head gaskets were sealing. Particularly in the first pic at about 12.30 on the top cylinder it looks like the alloy is eaten away down to the cylinder liner. Is this so? Some higher res pics of the cylinders would be helpful.

Did you have compression numbers prior to pulling down?

Cheers

[RTFM1000]

Looks like water marks in the first image.

[Rapson]

BM I blew up the pic of the Port side top cylinder and I think your right it is just about at the cylinder liner and no I didnt think of doing a compression test.

RTFM what do you mean by water marks?

[BM]

That first picture from before looks as if the number 1 cylinder combustion chamber is partly washed clean (water getting in).

If you have had water getting in, therefore compression getting out, the compression escaping the cylinder would aerate the cooling system water and reduce cooling by creating hotspots and interupt the flow of water around the head.

Shame you didn't comp test it before pulling it down as that would have yielded some handy info.

If that liner is corroded right down to the sleeve then you have some issues. Its unlikely that you would be able to get it welded. You could use a metal mend type product but thy are usually only a short term fix.

Alternately, if there is still a bit of alloy behind the sleeve then you may have enough to seal on.

Were there any traces on the head gaskets of water or compression breaching the gasket?

Cheers

[Rapson]

Update: Garry dropped over this arvo and gave the same verdict as BM, problem with the cylinder wall at 1230 with the wall coroded.

Can anyone recomend someone on the Gold Coast that could weld it up? or BM you mentioned a metal mend type product as a temp fix, any more info on that. I would consider that as I am concerned that if I start welding it could start a snowball effect.

[ozscott]

Mate - sorry to hear about that. I assume that you have not had the motor since new, so you dont know how it was treated (or mistreated) since 1987, but for a motor that is 24 years that is a great run anyway. I would have thought a good tig welder will do it for you. A temp fix with pliable dough is not a good idea. It is likely not to last for you, and if you sell it with the dough in it you will likely face problems from any purchaser - unless you told them and they accepted it of course, but that would severely devalue the sale...

Cheers mate

[Rapson]

Thanks Ozscott, just what I thought although if I ever sell ithis outboard it will be classed as am anchor, not an engine. Was just seeing if anyone had used one of those products with any success. Still looking for a welder.

[Spaniard_King]

Dave,

These are the guys I was telling you about . ask for Scotty

B & H Aluminium Welding



Aluminium--Retail - Southport, QLD

Unit 10/ 15 Pinter Drv, Southport QLD 4215, Australia
(07) 5591 1582

[Rapson]

Update on the overheating issue.
Todate I have replaced the water pump (new housing, impeller, seals the works), new thermostats, taken off water jackets and cleaned, taken off heads and cleaned and replaced with new head gaskets, tested thermo switch (both trigger at 85c) and tested the warning buzzer circut by the book (get engine to over 2500rpm, disconnect thermo switches and connect the wires, buzzer sounds, engine drops to below 2000rpm, disconnect thermo switch wires and buzzer goes off.
After all that I go out the other day, cruising at just over 4000rpm and the buzzer goes off. I pull off the cowling and find that I can comfortably put my hand on the heads for atleast 5 seconds with out being burnt.
Can anyone shed some light on this or do I have a new anchor?