97 150 2 Stroke Overheating STILL

[BoatMon345]

My S150TXRV 97 Yamaha 150 2 stroke has been overheating at high RPMs.
I can run it no problem under 4200 RPM but as soon as I go higher it begins to overheat (the alarm comes on and power is cut until it cools off). It appears to be the port head that is overheating since it is the port heat sensor which is closing.

I opened up the thermostat housings, cleaned out the gook, removed the thermostats altogether: No change.

I dropped the lower unit and changed the impeller. I also circulated 5% vinegar through midsection water pipe for about an hour: no change.

I tested the 2 head heat sensors with hot water and an ohm meter on the kitchen stove. They closed around 185F or so and opened back up around 145-150F so I believe these are working correctly.

The poppet valve (pressure relief valve) is seized shut, and I am trying to understand whether the poppet valve actually contributes to additional cooling of the motor at high speed, or is its function to simply relieve pressure? It would help if I understood which port the impeller water enters on the underside of the power head - does it enter the exhaust cover cavity first? Or does it enter somewhere else first? I've asked that question in another post but unfortunately have not received an answer, and it is not in the book.

Since the port head is triggering the overheat, as far as coolant flow, are there additional "turns" that the cooling water has to run through before getting to the port head, vs. the starboard head? I ask this short of pulling the heads because I don't know what else to do next.

Thank you.

[BoatMon345]

Not going on anything else but novice instinct, I decided to pull the port head. Here's the head:



The head has some gook but not much I thought to myself.

I cleaned it up real good with a wire brush, and small pointy tools to pick away at the hard crud. I used compressed air also. I finished up by pouring 5% vinegar into the head water jacket cavity and letting it set for a good hour in the sun. Then I shook it up, and rinsed it all off:

[BoatMon345]

I almost purchased a new head gasket for nearly $50, but I decided to take a chance and re-use the existing head gasket since it seemed to be in good shape. I cleaned it up with water, soap and a scrub brush. This gasket I purchased new in 2006 when I rebuilt this engine.

I thinly coated both sides of the gasket, and the head mating surfaces with "Indian Head Gasket Shellac Compound", being careful not to coat the cylinder rings on the gasket. I used carb cleaner spray to clean the accidental coating off of the gasket cylinder rings, and also on the cylinders themselves.








I put it all back together, torqueing the head bolts to the correct spec, and took her for a test run at WOT in the river:
No more overheat! I was surprised that the seemingly small amount of gook in the head caused the overheat condition.

It took me about 4 hours to complete from beginning of disassembly to startup just after assembly, and I took my time with it.

[99yam40]

reusing old gaskets is asking for trouble.
the rings around the cylinder cavities you speak of are what seal the compression in the cylinders and they have already been squeezed down once before.
But every one has their own opinion on what they can get by with, so good luck with your endever.

[TownsendsFJR1300]

How much gook (or was it salt build up?) was around the cylinder water jackets?

Salt usually collects at the bottom of the jackets (and the heads as you noted)

We had a similar issue on my neighbors 200 2 stroke. Salt build up on the lowest 2 cylinder jackets was just about 100% clogged. Like you, we cleaned it all out, issue gone..

BTW, IMO, I would put NEW head gaskets on the engine. They may not be leaking, BUT they should never be re-used. Again IMO, for $50, is it worth potentially having a cylinder inhale water and ruin your engine?? Just my 2cts..

[bajakeith]

OMG !! happy 5th july

Thought I'd get on here for some laugh's and giggle...looks like you using indian head shellac or AV tack..you are WAAAyY over you head messing with your motor..What,,You woke up today and think you can fix your outboard !! are you f-ing crazy or just plain stupid...btw way,,no one,,not even a fool would/will reuse a head gasket !! Sooo many fools on this planet!!

[LEAD PIPE]

I agree with the last last line in the above post but I don't think it pertains to the thread starter. Nice job on the fix, glad it worked out for you.

[bajakeith]

Hmmm

No where did I read that he fixed it..and from looking at his pics,, he is going have major issue's..the head gaskets don't go on the block with chems..common wanna be mistake,,2nd mistake is to touch something that you don't have a clue about....Hey, I have a high speed drill and lots of needle nose..need some cheap dental work ??? I'm from the school that you pay the guy that knows his job, has ethics,,training,,tools and cares...very simple..

[TownsendsFJR1300]

No where did I read that he fixed it..and from looking at his pics,, he is going have major issue's..the head gaskets don't go on the block with chems..common wanna be mistake,,2nd mistake is to touch something that you don't have a clue about....Hey, I have a high speed drill and lots of needle nose..need some cheap dental work ??? I'm from the school that you pay the guy that knows his job, has ethics,,training,,tools and cares...very simple..

From post #8;

"No more overheat! I was surprised that the seemingly small amount of gook in the head caused the overheat condition." So it was apparently repaired...

I have to disagree about cleaning the head/cooling passages on a two stroke. With some basic mechanical knowledge, a shop manual and torque wrench, I don't need a degree on the wall to do something that's more time consuming than anything..

Agreed 100% about the head gasket, (and any other gaskets), just don't cut corners there..

The shop wanted over $800 to clean the passages of my neighbors V200 Yam 2 stroke. (Same issue, overheat and RPM /alarm reduction once over 4200 RPMs.) With gaskets, etc, about $125.00. He did most of the cleaning, he helped me with the tear down re-assembly. No broken bolts, text book head(s) R&R. The lower cylinder passages were about 90% clogged with caked up salt..The head, not much better.

BTW, IME, I've had some (not all) VERY bad experiences with both Marine and motorcycle "professional mechanics". (Honda, Kawasaki and Yamaha motorcycle mechanics). Parts not installed correctly, parts missing (time = $), etc.. Had to threaten a law suit with Honda after I got the bike back after a warranty repair. It leaked more oil than a Harley. Brought it back to the shop for that repair, put an engine mount nut back on(lost/not installed, etc). Brought the bike 2.5 hours away to another shop(I trusted) and told them to fix it, I'd pay for it out of my pocket and sue EVERYONE including Honda. Oil leak was a badly nicked clutch cover and several new o-rings not installed correctly and were leaking. (very easy to not screw up but someone didn't give a shit). Honda did eventually pick up the cost of the "do over". I won't buy ANY Honda product after that, NEVER...

Once you find a good mechanic, stick with him..

[BoatMon345]

It is funny how when I asked for help, I didn't get a single response. But as soon as I posted what I had done to fix the problem I got much more advice.
Thanks folks

reusing old gaskets is asking for trouble.
the rings around the cylinder cavities you speak of are what seal the compression in the cylinders and they have already been squeezed down once before.
But every one has their own opinion on what they can get by with, so good luck with your endever.

Thank you. It ran strong all weekend. I was confident enough after careful testing and observation that I even went 4 miles offshore.

How much gook (or was it salt build up?) was around the cylinder water jackets?
Salt usually collects at the bottom of the jackets (and the heads as you noted)

There was very little buildup around the water jackets of the cylinders themselves. I have a before picture of the cylinders if you'd like to see.
The head had two noticiable deposits on either side of the middle cylinder, and I am guessing that is where a "full blockage" ocurred causing the overheat.
It is interesting how the gasket blocks water between the head and water jackets except for a few passages.

Thought I'd get on here for some laugh's and giggle...looks like you using indian head shellac or AV tack..you are WAAAyY over you head messing with your motor..What,,You woke up today and think you can fix your outboard !! are you f-ing crazy or just plain stupid...btw way,,no one,,not even a fool would/will reuse a head gasket !! Sooo many fools on this planet!!

Yes, I did wake up that day thinking I could fix my motor, thank you very much. I am not way over my head - as I stated, I personally rebuilt my (simplistic) 2-stroke engine in 2006, and it has been running strong since.
You clearly resemble someone such as those professionals in the AC industry - Publicly bashing a DYIer (and withholding information) in effort to convince the weekend DIYer to let the professional mechanic handle it.
So many know-it-all morons on this planet. Who the hell do you think you are - Get off my thead d!ckhead.

No where did I read that he fixed it..and from looking at his pics,, he is going have major issue's..the head gaskets don't go on the block with chems..common wanna be mistake,,2nd mistake is to touch something that you don't have a clue about....Hey, I have a high speed drill and lots of needle nose..need some cheap dental work ??? I'm from the school that you pay the guy that knows his job, has ethics,,training,,tools and cares...very simple..

Nobody cares. Is my thread causing you to lose business to the DIYer who is on the fence about considering to tackle this themselves? So sorry ****. You are tremendously transparent. I've seen your responses to other threads where you attempt to intimidate people. There are plenty of guys out there who won't attempt to touch their motor like I have. Market yourself to them, if you are intelligent enough (questionable).
You would have been more effective saying "I am an X year marine mechanic, and doing X Y & Z is really a bad idea, and you should take it apart and do it this way instead." Instead, you decided to be an ass. Don't talk to me bud.

From post #8;

"No more overheat! I was surprised that the seemingly small amount of gook in the head caused the overheat condition." So it was apparently repaired...

I have to disagree about cleaning the head/cooling passages on a two stroke. With some basic mechanical knowledge, a shop manual and torque wrench, I don't need a degree on the wall to do something that's more time consuming than anything..

Agreed 100% about the head gasket, (and any other gaskets), just don't cut corners there..

The shop wanted over $800 to clean the passages of my neighbors V200 Yam 2 stroke. (Same issue, overheat and RPM /alarm reduction once over 4200 RPMs.) With gaskets, etc, about $125.00. He did most of the cleaning, he helped me with the tear down re-assembly. No broken bolts, text book head(s) R&R. The lower cylinder passages were about 90% clogged with caked up salt..The head, not much better.

If I have to take it apart and replace the head gasket with a new one, I will. I wouldn't coat the new gasket with shellac, and I will also think to myself "lesson learned". It was a calculated risk I decided to take, based mainly on the excellent condition of the existing head gasket. I didn't expect to re-use it before disassembly, until I cleaned it up and noticed how well it looked.



For the casual DIYer reading this, it isn't that hard to take care of this problem. It just takes time, patience, attention to detail, and the right tools. Take it from me - I spent a lot of time researching and asking questions.

Here are initial steps you can take if your 6 cylinder 2-stroke overheats and your impeller is confirmed working properly:
1. Shut the motor off.
2. Turn the key back on so you hear the alarm.
3. Pull the cowling off quick.
4. Locate the two head temperature sensors (top of the heads and have 2 wires coming from them)
5. Disconnect one at a time.

If the alarm stops sounding when you've disconnected one of the temp sensors, you've just identified the head which is overheating.

I hope I have helped someone save substantial money.

(Now waiting for a rebuttle from the famous flamer who has too little business, and conversely, too much time on his hands )

[TownsendsFJR1300]

I agree, a fair amount of the mechanics, if you have some experience, especially an easily fixed issue< (a hard part, simply needing cleaning/replacement) is VERY do-able, (just as I did my neighbors 200HP).

I never had a Yamaha head off before. I did replace an Evinrude head once. I've pulled apart and repaired MUCH more complicated motorcycle engines with integrated 6 speed gear boxes, clutches, water pumps, balancer's, dual over head cams, etc..

An engine is an engine...

I don't need a certificate on the wall to know whats inside an engine block. Yamaha does like to put different parts/systems on them which can complicate finding the issue.

I don't agree with re-using the head gasket. There's too much to loose if it fails and IMO, just isn't worth it..

BTW, re your first thread, IDK the answer to your question re the water flow..I won't post as it doesn't help anyone.

There are some very knowledgeable folks here, sometimes it does get out of hand or if something is mis-worded, yep, it can get ugly, but I guess that's part of the net...

Glad you got it running.

IE. some pic's of a Kawasaki MC engine(250cc, single, 4 stroke, dual over head cams, 4 valves, dual balancers, water cooled). I had to replace the stretched cam chain on it. Easily 5x harder to do than a belt change on a yamaha OB engine...Both side cases have to come off, clutch, water pump, valve cover, side covers, one cam, generator, two balancers(chain driven, etc).. And no, no diploma's for that either, just a shop manual and a bunch of time..

[rodbolt17]

obiviously you have not had the joys of removing the heads or changing the belt on the F350.

on reusing the head gasket, typically the fire ring will only PROPERLY crush 1 time.

its why they have a torque spec for head fastners.

scale build up is rather common, affects all makes.

[TownsendsFJR1300]

obiviously you have not had the joys of removing the heads or changing the belt on the F350.

.

Nope and probably never will.. I don't do it for a living, as you do.

There's nothing better than hands on experience... If its something I'm NOT comfortable with, yes, it'll go to the Master tech, (that I trust) W/O hesitation..

I enjoy learning here as time marches on, for the tips. How something specific works, what to look for, etc.. Especially the fuel system and electronic's..

I enjoy wrenching and the sometimes challenge of finding what the issue is.

[rodbolt17]

but typically doing a set of heads on an old 2 stroke is straight fwd.
although I typically check the head and block surfaces for warpage and ALWAYS use new gaskets.
if a fire ring fails water gets in the cyl.

in the last two weeks I have replaced the block and head assy's on 2 F350. got 4 more to go with valve jobs. keeping Jeff down at flagship marine busy.
then I have a locked up F250 to figure out what inside the block locked up.

[TownsendsFJR1300]

but typically doing a set of heads on an old 2 stroke is straight fwd.

I think that was the point of the op.

Baja sounded to the OP(I may be wrong), that you pretty much needed to be a marine mechanic to handle a simple task as such. And it ISN't..

99Yam40 I don't believe is a certified marine mechanic. However he was able to rebuild his engine (crankshaft, with some help here).

Some folks are naturally able to mostly figure out how things work. Not just engines, about anything. I built my house in 1985. Short of just replacing the entire MAIN electrical panel and central A/C unit, I've done all my own repairs, plumbing, electrical, etc. I've added electrical breakers, outlets, put in 220 outlets for the welder, etc.. Learn as you go. And with the net, searching and reading is a big help. Obviously there's a lot of crap out there but its usually easily figured out...