Heat buzzer going off but plenty of water

[Cdogtx]

I have a 90 model Johnson GT150 that is driving me crazy. At wide open throttle the buzzer in the control box goes off. I can slow down and it stops. After being out for hours it get worse, and starts buzzing at 1/2 throttle or so. I can find no evidence that it as actually getting hot. Is there anything else it could be?

Here is what I have done

1st - not sure if it used the same buzzer, but the oil injection is not used or connected.

I've replaced the water pump impeller
I pulled the heads and replaced the deflectors and head gaskets
Put the thermostats in hot water to make sure they are opening
I even unplugged the heat senors on both heads

I have a steady stream of water out the tattle tail and 16-17lbs of water pressure on the gage

I'm stumped

Charlie

 

[Joe Reeves]

Re: Heat buzzer going off but plenty of water

Fuel restriction:

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

NOTE: There has been cases when the output valve in the fuel primer bulb would come apart, and the inner portion of the valve would actually reverse itself and be drawn back into the primer bulb's output valve body. This in effect would create a shut off valve and result in a fuel restriction. If this is the case, you should be able to feel something laying in the bottom of the primer bulb when held horizontally.

 

[Cdogtx]

Re: Heat buzzer going off but plenty of water

Thanks Joe, I will look at fuel flow and let you know. I appreciate the response.

 

[metriccrescentwrench]

Re: Heat buzzer going off but plenty of water

OK, this is one of those rare rare occasions when I'm going to take exception to something Joe posted. The purpose of the anti-siphon valve is to prevent fuel from siphoning out of the tank and into the bilge in the event of broken/damaged fuel line. (Obviously this can only happen in a section of fuel line that's below the level of fuel in the tank.) The Coast Guard requires an anti-siphon valve on all installed fuel tanks except where all fuel lines are secured above the top of the fuel tank.



(I looked all this up to determine if I needed an anti-siphon valve in my Checkmate when I was rebuilding it. I secured all my fuel lines above the top of the tank with Adel clamps, so therefore I didn't need one.)

 

[emdsapmgr]

Re: Heat buzzer going off but plenty of water

I've had problems with my anti-siphon valve sticking. My V6 engine would not run at max rpm's. Pulled the valve apart and found a few grains of sand stuck to the ball valve. That sand was just enough to inhibit full movement of that ball valve and reduce fuel flow to the engine. Pull your anti-siphon valve apart, clean it well with some carb cleaner and reassemble. See what you find in yours. An engine running at WOT and lean on fuel is a potential for a cooked powerhead. Double check to make sure you are using the correct size valve. Should be a valve that will accommodate 3/8 hose.

 

[Joe Reeves]

Re: Heat buzzer going off but plenty of water

OK, this is one of those rare rare occasions when I'm going to take exception to something Joe posted. The purpose of the anti-siphon valve is to prevent fuel from siphoning out of the tank and into the bilge in the event of broken/damaged fuel line. (Obviously this can only happen in a section of fuel line that's below the level of fuel in the tank.) The Coast Guard requires an anti-siphon valve on all installed fuel tanks except where all fuel lines are secured above the top of the fuel tank.

I was aware of that as I assumed that everyone else is that a liquid will siphon if a open hose is lower than the liquid level. My post/reply is simply to advise them of additional problems with a anti siphon valve that would lead to engine trouble.

Nobody ever asks why their bilge is full of gasoline.

 

[Cdogtx]

Re: Heat buzzer going off but plenty of water

The thing that is not making since to me is that there is not an RPM drop. It will run wide open, but the buzzer just goes off. I don't believe it is running out of fuel, but looking at the plugs it looks a little rich, not lean. The longer I am running it, the lower RPM the buzzer goes off. I ran around for an hour at 3/4 throttle with no buzzer. Then when it started going off, it just kept getting worse, until even at less than 1/2 throttle it was sounding

 

[Joe Reeves]

Re: Heat buzzer going off but plenty of water

In the engines present condition, VRO disconnected etc as per your post #1... has this engine performed perfectly or has this horn problem existed immediately from that time on?

Have you noticed the fuel primer bulb attempting to be drawn flat if you continue to run at the higher rpms with that horn sounding?

The TAN wire on the horn must be connected to the terminal closest to the horn's black built in ground wire. If not, weird things will happen.

If wired properly, when the horn is sounding, remove the TAN wire from the horn. If the horn continues to sound with that TAN wire removed, the horn is faulty.

Let us know what you find.

 

[toddschubert]

Re: Heat buzzer going off but plenty of water

Another idea: I had placed a thermal sensor on the thermostat housing with gauge so I could monitor exact temp of combined heads. It is a somewhat easy way to take some guesswork out of the equation.
Just a thought

 

[RMNS1013]

Re: Heat buzzer going off but plenty of water

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.


What year do you think this began? I have a 1996 model does the same thing.