False overheating signal

"I hope someone can help me wi

"I hope someone can help me with this. I have a 1990 GT150 hp i just installed on a boat. When I purchased the motor I was told the overheating alarm would go off and we all assumed it was just the water pump. I replaced the pump, with help from this forum, I disconnected the VRO by plugging the inlet and disconnecting the wire going to the VRO and all seemed well. Now, after running for 3-5 miles at 3800-4000 rpm an alarm goes off. If I reduce the rpms the alarm fades off. I've removed the cowling when the alarm goes off and the hottest pistons are the top ones of the powerhead, I can easily keep my hands on the top pistons for 10 or more seconds and they get cooler as I go down the powerhead. I have water coming out of the tell tale and all seems well except for the alarm. Any suggestions are welcome. John"

"If it were mine, I would loca

"If it were mine, I would locate the head sensor on each head. Note the plug where they connect. Next time the alarm goes off, disconnect them in sequence, so that you know which one is setting off the alarm. I would then replace that sensor. If the alarm still goes off, then you can be fairly sure you have an overheating problem as opposed to a false alarm."

"This may not be a temp proble

"This may not be a temp problem, but a voltage problem. Do a test as follows: Take it out until the alarm goes off, then use the trim in and out to make a voltage drop in the system and see if that stops the alarm. In That case it may be a defective alarm horn or a defective voltage regulator. You may even hook a volt meter o the battery and check the voltage when the alarm goes off. If a temp sensor, the alarm would not 'fade' but shut off. Note that the operating temp on theese engines are higher at idle than above 2500-3000rpm providing the relief valves in the cooling system works!"

"Morten and Sleeper thanks for

"Morten and Sleeper thanks for responding. I tried your recomendations without a conclusion. Sleeper, one at a time I disconnected the tan wires running to the temp sensors when the alarm went off and there was no difference. Morten, when the alarm went off I tried the tilt\trim and nothing changed, voltage stayed at 14.8-9. I haven't hooked up a voltage meter but I was wondering is this the same as the voltage meter that is hooked up to the motor and mounted on the boat, or the reading I am getting out of my depthfinder? One thing that was different today was it didn't take but a minute for the alarm to go off and even at a very low rpm the alarm would go off, 1000+. I could still keep my hand on the powerhead for 10 secs. plus. Hope you have some solution. John"

"Try to unhook the brown wire

"Try to unhook the brown wire going in to the alarm horn. If the alarm still goes, horn defect.
Have you taken out the VRO tank and removed the alarm cable from the tank?"

"Hey Morten, thanks for the re

"Hey Morten, thanks for the response. I have taken the VRO tank out and removed the alarm cable. I didn't unhook the brown wire but something else happened. I was reading some previous posts about alarms going off and some stated a gas starvation situation. My fuel gauge is not very accurate at low volumes and it read just above empty. I went out and got 12 gallons of fuel, ran the boat at 5000 rpm for over 3 nm with no alarm or problem, then ran it another 4 nm at 4200 rpm and no problem. What do you think the chances are that this was the problem, or may they just be coincidental. Do you think I could have just been running out of fuel yesterday when even at 1000+ rpm the alarm was going off, and now that I think about it there was a hesitation in the motor. John"

"I do not quite remember if Yo

"I do not quite remember if Your engine has a 'vacum' switch in the fuel system. However the switch will not be activated by running out of gas, but if the vacum gets too high on the suction side like a clogged filter, to small fuel lines or other blocking. If there is a vacum switch it is just before the vro in a T connection to the fuel line and grey of color."

"Morten, I have just run 30 nm

"Morten, I have just run 30 nm on the outboard and had the alarm go off two times, both times I reduced the rpms, primed the bulb which was soft, and the alarms didn't come back on. This is at a cruising rpm of 3800 and a max of 5500 rpm. Tell me if I'm wrong but I am ruling out overheating. It really seems to be in the fuel supply. Oh, I added another 12 gallons of fuel. I haven't checked for a vacuum switch yet but I will. John"

"If You are running on a separ

"If You are running on a separate tank You probably have a 5/16 fuel line,the engine requires a 3/8 all the way. This may be the problem, hopefully You find a vacum switch."

"Morten, I've been working

"Morten, I've been working a lot over the past week and haven't had much time for the boat. The engine is running fine now with no alarms at any rpm. I checked and all the lines are 3/8, replaced one filter that is a see through and had some debris in it, I'll be looking for that vacuum switch this weekend and I plan on changing the fuel filter that is mounted on the powerhead. Thanks for your help. John"

"One 'item' that has c

"One 'item' that has caused me quite some head ache and ruined more engines than they have saved is the 'anti siphon valve' that seems to be a standard on most US boats, mountet on the tank top (fuel pick up). A spring loaded ball valve supposed to prevent the tank from self siphoning if there is a leak in the fuel system below the tank top! Some are made in aluminum with a stainless steel ball and spring, a litle moisture in fuel, and it starts sticking. Check that out and replace if needed or dispose of if not needed!"

"In agreement with Mort, I wou

"In agreement with Mort, I would add:

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vaccum 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."

"I hope someone can help me wi

"I hope someone can help me with this. I have a 1990 GT150 hp. I had the water pump, thermastats and varnathers replaced at an authorized dealer this spring after an unfortunate grounding. The mechanic who performed the repair stated that he cleaned some sand that had gotten into some of the jackets as well . Now, after running for 3-5 miles at 3800-4000 rpm an alarm goes off. If I reduce the rpms the alarm goes off. I've removed the cowling when the alarm goes off and the hottest pistons are the top ones of the powerhead, I can easily keep my hands on the top pistons for 10 or more seconds and they get cooler as I go down the powerhead. I have water coming out of the tell tale and all seems well except for the alarm. We have performed all of the trouble shooting steps recommended on this site (includng but not limited to the anti-siphone valve and vacumm fuel valve on the engine). We have isolated the problem to a heat sensor on the right side powerhead. Our last project is to replace the sensor to rule out a bad relay verses overheating.
How difficult is it to replace the sensor on engine? Can it be done without special tools or consideration?"

"I have a 1989 60 hp Evinrude

"I have a 1989 60 hp Evinrude outboard with very few hour (less than 100) It came from Wisconsin to Montana 3500ft elevation and has not been rejetted. My questions are does anyone know what jets I may need to go to?
It currently has a 17" prop running at 4900 rpms and was thinking of going to a 15" prop to increase the rpms to around 5600 rpms. And last would these conditions create the overheat warning horn to sound under a heavy load? It has went off a couple of times but only if the boat was heavily loaded. I thought I had seen a recall notice on this over heat sensor and a fix on this particular motor, has anyone seen it."