'94 150HP Ocean Runner, overheating horn

[Gulfsurfer]

When I run over 3200 rpm, overheat horn goes off after approx 5 min run time. Staying at 3200 extends the run time to maybe 10 min, but it still overheats. At first, I would let it cool for 5-10 in then start again and blast off. Then I found that raising the motor and letting the water drain out would quicken the process. maybe I'm draining the hot water out the power head? Anyway...

First off, I have replaced the water pump fairly recently (3 yrs ago), housing impeller, all seals & o-rings. I plan on dropping the lower unit to check the impeller but really expect to find nothing out of the ordinary. I have not pulled the plugs (I will though) or done a compression test to rule out head o-ring leaks.

My direct question is, has anybody seen these symptoms on a 60deg block (150-225hp)? Is there any anomaly with these motor's cooling passages which might cause blockages that are not readily apparent?

Thx in advance for any replies!

 

[Joe Reeves]

Re: '94 150HP Ocean Runner, overheating horn

Are you sure that the engine is overheating or just assuming it is because the overheat warning horn is sounding constant and steady?

The reason I ask is that your engine has the same identical horn warning should a fuel restriction take place. Should this happen, the fuel primer bulb normally starts to be drawn inwards (collapsing), and the usual cause is as follows:

(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.

 

[Gulfsurfer]

Re: '94 150HP Ocean Runner, overheating horn

Thank you Joe for your quick response. Actually I do not know if it's a fuel starvation issue. I was under the impression that fuel starve/steadyhorn would not initiate the 2000rpm limit function. Thought only the overheat/steady horn condition would do that.
Wish I would have thought of checking the fuel bulb as the horn goes off!

But in retrospect, the rpm drop isn't like you would expect from fuel starve, it doesn't slowly lose power from one or more carb fuel levels dropping low; it just cuts off as if the ignition cuts out completely. As the rpms drops below 2k, the ignition cuts back on... in a staccato fashion as long as the throthtle is held above that necessary for 2000 rpm power. Capish?

I suppose I can launch again this weekend and run through the scenario again and verify fuel delivery.

 

[Joe Reeves]

Re: '94 150HP Ocean Runner, overheating horn

Thank you Joe for your quick response. Actually I do not know if it's a fuel starvation issue. I was under the impression that fuel starve/steadyhorn would not initiate the 2000rpm limit function. Thought only the overheat/steady horn condition would do that. Wish I would have thought of checking the fuel bulb as the horn goes off!

Yes, of course you are correct in that a fuel restriction would not cause the S.L.O.W. feature to engage... BUT it would certainly cause a drop in rpms due to a lack of fuel. If memory serves me right (it does occasionally), the S.L.O.W. feature drops the rpms to 2500 and keeps it there until you shut the engine down, then restart it... that is if you wanted to push the envelope, you could shut the engine down, then 5 seconds later, start it up again and full throttle would be accessible... for a short time anyway.

Let us know what the fuel primer bulb does when you retest this problem.

 

[Gulfsurfer]

Re: '94 150HP Ocean Runner, overheating horn

Ok, ran motor yesterday, re-created problem. Checked fuel primer bulb, it was firm, not flat. Raised motor and checked temps w/ infrared thermometer. All 6 cylinders were in the 150-160 degF range; not near overheating. I changed the fuel filter for good measure. problem still there.

What's odd is that if I let it idle, horn goes away but if I then nail it, horn sounds and SLOW activates. Shutting off key and re-starting allows normal operation for a while, until the overheat horn and SLOW occurs again.

Right now, I`m thinking, in order of likelihood:
1) loose thermostat connection or wire splice
2) faulty thermostat
3) faulty logic solver (what ever takes all the inputs from sensors and sounds horn)

 

[Joe Reeves]

Re: '94 150HP Ocean Runner, overheating horn

After reading all the posts above over carefully, it does sound like the S.L.O.W. feature is cutting in and that is puzzling as the thermostats open at roughly 143 degrees or so, and your engine is running in the 150/160 degree range so as you state, it's not in the overheating range.

Also to support the S.L.O.W. problem, you state (in not so many words) that the rpm drop off is more of an instantaneous drop of rpms as per an ignition loss... rather than a gradual drop one would experience with a fuel loss.

Unfortunately I retired in 1991 so I'm somewhat unfamiliar with the circuitry of that model. This being the case, I will back out of here and let the more knowledgeable members jump in here with their views on the problem.

 

[clanton]

Re: '94 150HP Ocean Runner, overheating horn

I`m not clear on your post. Do the rpms drop back to 2500 rpms?

 

[Gulfsurfer]

Re: '94 150HP Ocean Runner, overheating horn

I`m not clear on your post. Do the rpms drop back to 2500 rpms?

Yes, absolutely, the rpms drop very abruptly as soon as the horn starts to sound.

 

[boobie]

Re: '94 150HP Ocean Runner, overheating horn

I've heard of some bad power packs doing this.

 

[Gulfsurfer]

Re: '94 150HP Ocean Runner, overheating horn

Oops: revised...

Right now, I`m thinking, in order of likelihood:
1) loose hi temp switch connection or wire splice
2) faulty hi temp switch
3) faulty logic solver (what ever takes all the inputs from sensors and sounds horn)

Noticed I had written 'thermostat" instead of hi temp switch before as I was looking to see how much the cost was going to be for the hi temp switch. $65, so I'll take it out of the circuit (disconnect and test again before I order a new one.
There's nothing wrong with the thermostats and even if there were, they would cause an overheat condition at very low engine rpms. They are spring loaded in the top of the head. As the water pump picks up discharge pressure (higher engine speed), the force of the cooling water pushes the thermostat against the spring, bypassing them completely. A bad thermostat cannot cause overheating at the speed when my warning horn is sounding.

 

[Gulfsurfer]

Re: '94 150HP Ocean Runner, overheating horn

I've heard of some bad power packs doing this.

Gee, I hope not; I replaced the power pack 2-3 yrs ago due to intermittent ignition loss. As I remember it, it cost a couple of hundred...

 

[Gulfsurfer]

Re: '94 150HP Ocean Runner, overheating horn

OK,, update in case anyone has a similar issue. I think it's fixed (unless it is an intermittent problem w/ the power pack as suggested by 'boobie').

I pulled the lower and changed the impeller. Didn't really find much wrong with the old one, it had taken a set but wasn't cracked or anything. The plate had some grooves from the times I used it to pump mud and sand but I didn't have a new one. Next service will be a complete kit. I flushed the block using a hose, didn't see much crud come out though.

Ran yesterday for several hours fishing, up to 4500 rpm. No high temp alarm or SLOW function!

My hypothesis is this: the thermostats on this engine are spring-loaded and are bypassed at higher rpms when the water pump pressure overcomes the spring pressure and then water that has flowed around the cylinders is allowed to flow past the stats to heads (where the temp sensors are located) before exiting the engine. Maybe, for whatever reason, the discharge pressure of the water pump was borderline unable to buck the spring pressure of the stats so the heads wouldn't receive enough water to keep them cool. The temp sensor would then trip on overtemp, the alarm goes off and the SLOW protective function would kick in.

??? I hope it's fixed, I use it every weekend so I'll know soon enough. Thx to everyone who replied this thread. Now to fix the oil tank level sensor.