1988 Yamaha 150's high temp alarm

[Z-man228]

I have a pair of 1988 150's in which I am getting an overheat alarm at 4000+ RPM that I can't solve. Here is what I have done to the motors:
1) replaced impeller, base plate, cap and all gaskets in March and everything had been running fine until May. Went to the Keys and got the boat up to 4200 RPM on two occasions and it went into limp mode both times.
2) I changed all 4 thermostats and gaskets ( one was hung wide open, the rest work as they should) while I had them out I left the thermostats out of the right head and started the motors to check waterflow. Both motors had water pouring out of the thermostat hole.
3) I changed poppet valve spring and grommet, new poppet won't be in until Wednesday( one was hung in grommet pretty tight, Had to use pliers to pull it loose but grommet and spring are now new)
4) removed and cleaned all 4 temp sensors, Placed in hot water on multi meter for continuity and all 4 passed, reinstalled into motors

Ran boat today same condition presented itself. I unplugged all 4 temp sensors and boat ran flawlessly. Plugged in starboard motor temp sensors and alarm went off when over 4000 rpm. I verified it was the right head by unplugging both while alarm was going off. I then switched temp sensors and ran up to speed again. Right head temp sensor went off again
5) port motor alarm went off but as soon as I put motors in Neutral it stopped which it hasn't done before so I am wondering if the motors are somehow linked thru the key switches causing the port motor alarm to go off when there may not be a problem. I was not able to check head temp sensor on port motor since alarm would quit as soon as I pulled throttles back into neutral.

Here is the real rub. when this condition presents itself I have a stream of water peeing from the outlet and it is warm as it should be. I can touch all 4 heads when the condition happens and leave my hands on the heads and thermostat covers without burning myself. I am at a loss. Any ideas on anything I may have missed or is it time to pull the heads and head covers???

Any help will be much more than appreciated.

[boscoe99]

First thing to recognize is that the tell tale water has nothing to do with the cooling or not cooling of the motor. Water from the tell tale only indicates that the water pump is doing its job. Water from the tell tale in a Yamaha has not gone through the block or done any engine cooling. As in your case you can have great water flow from the tell tale and still have a lack of cooling issue.

How are you differentiating the port motor warning from the starboard motor warning? Are you actually seeing a light on the port motor tachometer illuminate versus a light on the starboard motor tachometer?

[Z-man228]

my gauges are only tachs with the low oil light on them. I am getting two distinct sounding alarms from behind the key switch. when I turn the key switch to off for each motor one of the alarms go away. That is how I know it is both motors. when it has happened I have shut one motor down two make sure they are both doing it. I pulled the red wire from the temp sensor connection to determine which sensor in which head was causing the alarm.

[TownsendsFJR1300]

IDK if the engines are linked for the alarm, but the rest of your symptoms sounds like the head/cylinder is blocked up with salt (from salt water use).

My neighbors V6 200, 2 stroke, did the exact same thing.

We did most of what you did as well.

Ended up pullling the heads, the lower coolant passages around the cylinders (where the sensor is), was approx 95% clogged with salt. Very little if any water was getting thru there. He wasn't much on flushing..

Once everything was cleaned out (about 4" deep salt) the engine ran great.

[Z-man228]

that's what I am leaning toward too. I have tried flushing with saltaway with no Luck. I am considering using rydlyme to see if it might clean it out. I really don't want to pull the heads on 26 year old motors if I don't have to. Scared to death of breaking off a bolt. I read a thread for the Rydlyme and it gets great reviews from outboard and inboard owners. Worth a try???

[Z-man228]

BTW I am a fanatic about flushing I live in Central Florida so when I get back from the Coast the boat goes in the lake, washdown, livewell, and bilge pumps get a go wash out with fresh water too

[TownsendsFJR1300]

I thought I had the thread saved (I don't) where a member had Rydlyme set up, pumping (with a tank under the engine), thru the powerhead, back into the bucket, etc. (as I recall he had the lower unit off). It kept circulating for quite awhile (12 volt bilge type pump). The pic's posted afterwards looked pretty good after the treatment.

Unfortunatly, if your not not getting ANY WATER flow thru there, how successful it would be would be questionable. Can't hurt to try.

I can say that picking out that salt was difficult as it was very, very hard, lots of nooks and crannies..

The local shop down here charges about $800 to do the job. We did it for the cost of gaskets, etc, a bunch of labor, NO broken bolts, for a little over $100.00.

There are some tricks for loosening bolts up of that age but you won't know until / if you do it... The previous owner of my neighbors boat aparently wasn't real big on flushing, cleaning under the cowl either and it showed..

[TownsendsFJR1300]

BTW I am a fanatic about flushing I live in Central Florida so when I get back from the Coast the boat goes in the lake, washdown, livewell, and bilge pumps get a go wash out with fresh water too

Thats good but the salt water and salt, as soon as you pull from the salt water, drains and the salt likes to crystalize, especially inside a hot engine.

Maybe overkill, but if you have a built in fresh water tank, I'd (with the engine off), using the powerhead hose attachement, flush some fresh water thru the block as soon as it comes out of the salt water.

I live off the Intercoastal waterway (brackish, salt water). As soon as I get the boat on the lift, the hose is hooked up to the powerhead hose attachment for at least 15-20 minutes. Then it gets run on the muffs for another 10 minutes

[Z-man228]

unfortunately no hose hook up on a motor that old. Only way to flush is thru the muffs or running. Most of the ramps I visit don't have freshwater to use. I think Ft Desoto may be the only one. sounds to me like the heads need to come off Gaskets Are about $200 for head and head cover. I appreciate you giving me your expertise on this I think I knew what needed to be done prior to posting but was hoping somebody might have a different idea

[TownsendsFJR1300]

I'm sure others will chime in and give different opinions / recommendations as there are some professional marine mechanics here and some not so..

The above was my hands experiance..

Good luck..

[Z-man228]

Flushed both motors with Rydlyme. I am absolutely amazed at what came out of them. I literally picked up a handful of stuff that looked like mud out of the bottom of the bin. I don't know whether to be happy all that stuff came out or scared to death that all that crap was in there. Waiting for rain to clear so I can reassemble and see if I am fixed or not.

[TownsendsFJR1300]

Flushed both motors with Rydlyme. I am absolutely amazed at what came out of them. I literally picked up a handful of stuff that looked like mud out of the bottom of the bin. I don't know whether to be happy all that stuff came out or scared to death that all that crap was in there. Waiting for rain to clear so I can reassemble and see if I am fixed or not.

Well it certainly won't be any worse...

Did you pull the lower unit or just use a bucket and keep re-circulating it thru, ?? Just curious..

And good luck on the test run

[midgiegualla]

Can recommend Rydlyme treatment. My alarm would come on over 3500 rpm. 115hp 1989 . Flushed with Rydlyme and has been running without fault for over a year.

[midgiegualla]

oh here is the link for the flushing procedure that i used;

http://www.yamahaoutboardparts.com/f...g-th19434.html

regards

[Z-man228]

I Pulled the lowers and ran a small fountain pump to circulate. I followed central texas's thread from start to finish before I did mine trying to install lowers this morning and run tonight after work. Will post results later.