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Warning horn question

N

navchapdoc

Member
"1994 90 HP Merc. Is a steady

"1994 90 HP Merc. Is a steady un-interrupted horn oil or overheat? It only comes on at 5000 rpm and stops when I drop to 1000 rpm. I can run at 4000 rpm all day with no prolbem but, once I hit 5000 it goes off. This is NOT a beep-beep-beep it is a steady horn.Is it oil or overheat?
Thanks,
John"
 
That's an overheat alarm.

That's an overheat alarm.

So either:

your sensor is starting to go

your impellor is getting "done"

your poppet is starting to lose it

you have a gasket going somewhere

or you are developing a blockage/build up in the water channels
 
"Thanks Graham. I do have a te

"Thanks Graham. I do have a temp gauge and when the alarm goes off, I dont see it rising above 120-140 degrees. As a matter of fact, now that I think about it, I believe the temp warning switch that was bolted near the top cylinder is disconnected. I have a ton of pressure on my water pressure gauge as well. The P stream is like a pressure cleaner. Any thoughts?
John"
 
Could be the warning module it

Could be the warning module itself that is going.

Confirm that the temp sensor is not connected to the module.

Should be a black wire going from the temp sensor to a small gang connector. From the gang connector there is a tan/blue stripe wire that goes to your harness to feed your temp gauge on the dash.

Also from the gang connection you will have an all tan and all black wire that will go over to the warning module.

If the black and tan wires are disconnected then it is probably your module that is bad. If the sensor itself was bad you would be getting some funky readings on your gauge as well....
 
"Graham, thanks again. Let me

"Graham, thanks again. Let me ask you (or anyone eles) a question, how much water pressure should I see on the gauge at full throttle (5000 rpm). I spoke to someone who said that if the poppet was bad I would have alot of pressure at the guage and not enough circulation through the block to cool it. They also said that the P stream would be really strong if that were the case. Do you agree?
John"
 
"The service manual says 10-15

"The service manual says 10-15 psi at 5250.

In general from idle to about 1500-2000 rpms your water pressure may be up to 4 psi with the thermostats looking after the cooling.

Between 1500 and maybe 4500 rpms the psi should be 4-9 psi and the poppet is doing it's thing.

At wide open, both the 'stats and the poppet are bypassed and the water just flows uninterupted through the head with psi above 10...."
 
"Graham,
So do you agree or

"Graham,
So do you agree or disagree that the poppet may need to be replaced. I never really paid attention to what the gauge does between 2000-4000 rpm but I can tell you it is above 15 at wide open. Should I change my poppet?
John"
 
"If you can run it at 4k all d

"If you can run it at 4k all day without an alarm, sounds like the poppet is working. Wide open it shouldn't be the issue because the pressure is bypassing it all together.

I would test the sensor (temp sender) first. You can remove it and test with a pot of water on the stove, a thermometer and an ohm meter. They sell for about 50 bucks at a Merc dealer if it's the problem.

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"
 
"Thanks again Graham. So if I

"Thanks again Graham. So if I am understanding this, if I get resistance before 190 degrees than the sending unit is going bad? In other words it is making contact before it should?
John"
 
"Yes, exactly and that is a ve

"Yes, exactly and that is a very common problem with these sensors. But if you get resistance (no connectivity) it's working ok - if you have NO RESISTANCE, the circuit is closed. They read 190 degrees when in fact it may only be 150.

When they "think" it's too hot, the circuit closes (switches on) which allows the current to pass to the horn and beeeeeeeeeeeeeeep"
 
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