97 Vmax 150 - mechanic replaced the thermostats and water pump, still overheating!!

[aphextwin]

Hi all,

So just bought a used boat, and noticed that the tell tale is not coming out as it drips when using the water hose. Took it into my local mechanic and recommended water pump and thermostat replacement. He's done those things now and says engine is still overheating. He has called me back to say that water is not getting into the engine and suspects that he will have to take apart the engine which is to the tune of potentially about $1500 to $3500 to take apart and put together or I could just call it a day and post it with the issues. He said engine itself is fine, compression etc all checked out minus overheating.

Is there anything I'm missing here that I should be trying before just dumping the boat? I was thinking of checking the poppet valve myself too...but don't want to go on a fools errand either.

Thanks everyone for any advice.

[robert graham]

Maybe a previous water pump impeller deteriorated to the point that the rubber blades came off and circulated up into the motor plugging the passages???.....

[99yam40]

you did not mention it was overheating just TT was not working well.
are you sure it does overheat?
what did the mechanic find when he opened up the water pump and stat?
how well do you know and trust this mechanic?
old motor so what did the pump and passages look like/
you may need to open them up yourself to see if he did anything and what things look like.

[Jason2tpa]

Not trying to pile on here but it appears you've already committed to being the fool for buying a motor without water testing. I know that's harsh and you're here looking for help...but always good to acknowledge the reality of the situation, ya know. The cooling system might be just the 1st of many issues.

If you're paying someone else to handle quite simple maintenance installations as the water pump and stats then be prepared to continue dumping money into service labor costs. Maybe cut your losses and sell for parts. Otherwise, get yourself a model/year specific service manual and dig in.

[ausnoelm]

There's a couple of things at play here, does it only over heat above about 4,000RPM? was a genuine water pump kit used, not just a cheap after market impeller?

[aphextwin]

Thanks everyone. So I got it home. I read what mechanic wrote on the notes. Old impeller in bad condition, gear case installed run on hose - water coming from tell tale but still overheat after 10 minutes. Removed thermostats and re-run, overheat still present. Run engine briefly with t-stat covers off to view water flow - no water flow to top of cylinder heads. Suspect blockage in cooling lines somewhere. Basically the next job was quote was to remove cyclinder heads and cooling ports if not that then remove engine. He thinks it's a pinched tube and that would require engine removal......

So took it home, as this is an amazing DIY forum, I took off the T-Stat covers myself, ran water house through the t-state covers on both sides for 5 minutes each. Unplugged the tube to the engine, blew through it, didn't seem plugged at all. Ran the engine with the t-stats covers off myself for 10 minutes...water actually came out of the t-stat the whole time. Temp was 86 F on left side and 110 on right side on idle.
I put back the t-stat covers and ran for 10 minutes, now both showing 110 on each side the whole time. I ran it again at half throttle for a few minutes and still at 110F. Is that an acceptable temp at idle? I am not sure what I need to do next now...if it is acceptable, do I take it on the lake? or use a rain barrel to simulate the lake since hose has water pressure?

If 110 is bad, my next step would be trying to remove the head gaskets but water is flowing through the t-stat.

What is considered overheat temp?

Thanks everyone!!!

[ausnoelm]

Running with no load is a completely different kettle of fish to running under load.

[aphextwin]

How do I run it on load at home or closest to it? So I get a rain barrel and have it completely submerged then run it at 4K rpm to see if it overheats? How does the shop do it? Thank you

[99yam40]

that does not sound like it overheats.
shop may have a test prop to run the motor, but not sure if yours has that.
back the trailer/boat into the water and run it on the trailer.
just make sure it is tied on to the trailer well so it does not jump off.

talk to the mechanic, ask how he was testing .
what kind of water hose connector did he use?
what abut you?
maybe different muffs ,hose, water pressure made a difference

trying to run in gear in a tub will just blow the water out of the tub

[ausnoelm]

Just run it in the water, launch the boat and go for a run, but stay close to the ramp, it's not that hard.

[aphextwin]

Thanks everyone I will give that a go then. Will give update. Appreciate all the advice here. You guys are awesome

[aphextwin]

I used a garden hose with single side ear muffs. I will call on Monday as he doesn’t work weekends. Thanks

that does not sound like it overheats.
shop may have a test prop to run the motor, but not sure if yours has that.
back the trailer/boat into the water and run it on the trailer.
just make sure it is tied on to the trailer well so it does not jump off.

talk to the mechanic, ask how he was testing .
what kind of water hose connector did he use?
what abut you?
maybe different muffs ,hose, water pressure made a difference

trying to run in gear in a tub will just blow the water out of the tub

[99yam40]

there are some chemical flushes out there to help remove scale from the cooling passages you could try
before ripping the heads and covers off to do a manual scrape
Rydlyme marine descaler is one I have read about in the past
do a web search on it

[aphextwin]

Thank you I will look into that.

there are some chemical flushes out there to help remove scale from the cooling passages you could try
before ripping the heads and covers off to do a manual scrape
Rydlyme marine descaler is one I have read about in the past
do a web search on it

[aphextwin]

Well, I tried to simulate the lake before I went out. I put ear muffs on and submerged the propeller exhaust. Exposed the thermostat covers and it went up to 130 F on both sides......no water coming out of the covers at all except smoke and no tell tale either. The back pressure on exhaust is causing it not to push water out? BTW I did re-read the notes and he had run the boat on hose with ear muffs. So at this point I am baffled....
1. Mechanic runs it with hose - water tell tale but no water to t-stat covers
2. I run it with hose - water tell tale but water flow to the t-stat covers no overheat steady at 110F
3. I run it with mufflers and submerged prop - no tell tale and heats to 130F

The next step is try the redlyme and if that doesn't work then take apart cooling jacket?

I am no mechanic by any means but this is telling that there is not enough water pressure going up to the engine and maybe mechanic is right? the bottle neck is the tubing? What do you guys think?

The next step is try the redlyme? Taking apart the cooling jacket won't matter since water isn't even getting there right? Should I check the Poppitt Valve and expose it to see if water is getting there?

Another thing I read is maybe I take the leg aprt again.

"After dropping the lower unit again, I got the motor in a position where i could look thru the water tube to the head of the motor - AHA, there it was, pushed up the water tube a few inches was a rubber grommet." I could check to see if there is any debris blocking it? Should I go try that?

I was also thinking the Poppitt valve but from my understanding, a bad valve is when you are gearing up and it overheats. In this case I am idling and it's overheating.