'99 Yamaha VMax 150 Overheat Alarm at 3k rpm

KDMatt

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Aug 8, 2009
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Hey guys, I'll try to keep it brief.

'99 Carbed Yamaha Vmax 150hp outboard. It was just rebuilt late last summer. I was out today to finish up the break-in (I've got about 5/6 hours on it so far, just putting around at 1500 rpm and below) -- spooled it up to plane the boat out, then backed off to 3000ish rpm's (as per rebuilder's instructions). Oh, and it's also double-oiled for the break-in (in fuel + direct injection)

... and after about 30 seconds or so at 3000ish RPM, the overheat alarm came on. Could definitely see some steam coming from the back of the motor as I slowed it down -- alarm stayed on for quite a while. So I doubt it's a sensor/instrumentation.

I'm perplexed because:

1 - good water stream coming from the "pee'er"

2 - Oil tank topped off.

I wasn't hoping I'd have to spend my fourth of July putzing around with a motor, but I guess it can't be helped this time.

It's on the lake right now, so suggestions for things I can try while it's in water would be helpful.
 
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KDMatt

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Aug 8, 2009
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Update: No start is my own stupidity. Left the lever in gear.

That said, I got it running but encountered the same problem. Revved to 3k, cruised around for a minute, then got the overheat warning... Thermostats??
 

KDMatt

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Aug 8, 2009
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Update: Got the boat out of the lake -- was able to putt around at low RPM and idle for a substantial period of time with no warnings from the motor buzzer.

I'm on the hunt for parts now ... Found the thermostats with no problem... but I can't find much for the pressure control valve for this year... '99 P150TLRX ... any ideas? Are they all pretty much the same?
 

99yam40

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Sep 7, 2008
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but I can't find much for the pressure control valve for this year... '99 P150TLRX ... any ideas? Are they all pretty much the same?

are they the same as what?

Why not do as most would when over heat happens and check(look at) the stats and PRV and replace the water pump with a kit not just the impeller to make sure water flow is what it should be.
Stats and the temp switches can be tested in a pot of water as you heat it up monitoring temperature the stats and switches change state.
If PRV sticks open it can dump too much water at lower RPM and cause overheat at low RPM, but seems your problem is at higher RPMs so I would be looking at water pump
 

KDMatt

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Aug 8, 2009
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Thanks for the reply!

I was referring to the PRV. I saw in another thread somewhere that the older design had been superceded by a newer one, and I was wondering if that was the reason I couldn't find the specific one for the P150TLRX ... i.e. a later design/part-number is what's called for.

The water pump was allegedly replaced last year, but I suppose I could crack it open to see what's what. Any pitfalls or tricks I should be aware of as I do this?

Thanks again.
 
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