91 115 alarm sounding

[Fast Eddie]

I recently purchased a boat w/1991 115TLRP. Boat sat up for 3 years. Had boat in shop to rebuild carbs and they said that it was giving a false overheating alarm. They replaced the thermo sensors and sent me on my way. I can run the boat all day long under 3500RPM. Once at 3500 the alarm sounds and the motor reduces RPM. Once this happens, I can idle for about 30-60sec and the alarm quits and I can go again, but not over 3500. The "pee" stream never quits, nor does it get hotter than luke warm. Is this an overheating situation of could it be something else? I can't really afford to go back to the shop again. Any help would be appreciated.

[jb123]

how bout an impeller change ???

[Fast Eddie]

The impeller is going be changed this weekend. My concern is that the pee stream never stops or looses pressure when the alarm sounds. Is the alarm only for overheating or is it also for the oil injection system?

[jb123]

sure theres oil sensors but most likely water related as it cools for a few mins and runs again, no rpm reduction... right??

[Ken]

Eddie,
There are several reasons why your 115 may be overheating above 3500 rpm:
1)low water pressure due to weak water pump. If the impeller is at least three years old (I assume it is), then it needs to be replaced, even though it has set up for that time.

2)stuck or faulty thermostats - remove the stats and test them in a pan of heated water and thermometer. They should be fully open at 140 degrees f. - 0.120 inches.
Also, debris can collect around the stats - clean.

3)stuck open pressure relief valve - remove and inspect/clean. The prv is designed to open above 20 psi. They can get clogged with debris and not close completely and allow cooling water to dump out the relief holes of the upper casing.

4)water pump intake restricted - inspect and clean

5)clogged head water jackets from mineral deposits - have to remove the heads and clean out jackets - also, replace sacrificial anodes at the same time.

The water pump pilot hole discharge, aka pee-stream, tell-tail, will not feel hot - it is water from the pump that has not gone thru the cooling jackets. It is just an indication the pump is working, but does not tell you how much pressure the pump is putting out - you need a water pressure gauge for that.
Good luck [img]smile.gif[/img] ,
Ken K

[Fast Eddie]

Ken,

Thanks for the advice. I checked everything and had to replace both t-stats & the water pump.
Now for the fun part --

Before these changes the tell-tail would never get above luke warm (even when the alarm went off). Since I replaced these parts, I ran the motor in a test tank (your Walmart tub from another post -- works great). Now the tell-tail is very hot after 2-3 minutes of idleing and the engine itself it very hot to the touch. This did not happen before. One of the old thermostats was stuck partially open, and I'm thinking that this was causing the engine not to properly warm up at idle. I also noticed some smoke (exhaust ??) coming from the 2 holes just beneath the cowling on the rear of the motor. I have not put the engine in the water and run it under load yet, because I'm worried about the hot water from the tell-tail at idle. Is this normal or have I uncovered another serious problem? Also, there appears to be no leaks. I'm about ready to turn this "gift" from a family member into an artifical reef. Any suggestions?

[Hamfisted]

Eddie a V4 will warm a tub of water up pretty quickly, and that warming water is all there is to cool the motor. So it's a snowball affect, except with heat instead of snow. The "Tell-Tale" stream should always be cool water. This is the water coming up from the water pump, and if it's already hot to the touch its not going to do very well to cool the powerhead.
The motor typically needs a fresh source of cooling water to successfully regulate the engine's temperature. The water tubs work Ok with small "air cooled engines" but bigger liquid cooled motors warm 'em up too quick. I guess they work as a muffler Ok, as long as you have a way to keep the overall temperature of the water down but that gets pretty tough.


Mike

[Fast Eddie]

Mike,

The tub has a garden hose attached to a fitting on the side, so it's constantly filling the tub with water. I ran the motor in the tub & also with earmuffs after letting the engine cool between tests. The results were the same.

This engine has got me confused. I replaced the bad t-stats and the thermo sensors, checked the PRV (is was fine), and replaced the water pump (everything not just the impeller) and now it is running hotter (at least the tell-tail ang the engine feel hotter) than when I started. I'm wondering if I have a bigger internal problem. The engine has less than 100 hours.

[Ken]

Eddie,
Your new thermostats should regulate at around 135 degrees f. - that's pretty darn hot when you touch it.
If your old stats were stuck open, then the motor might not ever come up to stat temp.
I would run the boat in the lake (bay) and see what happens. Assuming the thermo switches are good, if your motor overheats, they will let you know by sounding the alarm and the motor will go into rpm reduction. This happens well before any damage is done to the motor.
I would not go by what you are seeing on the driveway with the "flush bucket" or garden hose.
Run the boat in the water - if the alarm sounds, pull the hood and CAREFULLY feel of the top of the heads. You will know if you are gettng a false overheat alarm or not.
Again, the pee stream (in the lake) should not be but a little warm.
Good luck, let us know how you come out [img]smile.gif[/img] ,
Ken K

[Fast Eddie]

Ken,

Are the thermo switches and the thermo sensors the same item? The shop replaced the 2 round sensors that sit into indentions located at the top each cylinder bank. They have 2 leads coming from each one and you can pop the sensor in & out. They are not fastened to the engine.