miamioffshore

Ok, so I recently changed my impellars & housings on both engines (1999 carbed HP500's). After completing the job we fired up the engines on the hose and 1 of my engines after warming up the engine overheat buzzer is sounding. I know for sure its the engine temp sensor, as soon as you umplug it alarm stops, plug it back in, alarm back on. Temp gauges do not indicate a problem (never over 150 degrees). Disassembled thermostat housing to check for impellar pieces, none found, same thing with checking ball valves, backflushed entire system for the second time. Problem still there. Then got curios what water temp was leaving engine, so we put the temp sensor from the thermostat housing in the hole where the alarm sensor goes, fired up engine and water temp there is 195-200, then I took exact same temp sensor and put it in non-trouble engine, reading from alarm sensor location(leaving the engine, not at thermostat) was 200 steady after warmup, held for 10 minutes. so then I'm thinking alarm sensor must be faulty, so I take the alarm sensor from good engine and put it in trouble engine, alarm still goes off!! Alarm sensor must be good. Removed thermostat from trouble engine and ran, problem is still there!! The alarm doesnt go off until engine gets up to temp, so its not like the sensor or wire somewhere is grounding out. Takes about 10 minutes of idle run time for alarm to sound. What could this be? I had hose on flush kit and a second hose with ears on drive pickups just to make sure it was getting enough water, which they obviously are as temps level off where they should, correct? What do I do now? I dont know what else to trouble shoot? Plenty of water flow out of exhaust also.


re-cap:

-both engine temps same at thermostat housing (150) and at location of warning alarm temp sensor(200)

-full water flow from exhaust

-alarm sensors swapped and same engine sounds alarm, sensors must be good correct?

HELP!!!!

sandcraft

Sounds like you've narrowed it down to the alarm circuit. I'm pretty good with engines, but I admit to be a little weak with electrics. Is it possible to make a jumper from the good engine sender wire to the trouble engine sender? Make sure you have good grounds and maybe even try making a jumper from the trouble engine sender wire to the good engine. I may be way off base but it sounds like anythings worth a try.....Casey

miamioffshore

I"m going to try that. Somebody correct me if i'm wrong but isn't the overheat alarm just a sensor that closes a circuit if it gets to hot? Thus sensor is just a circuit that closes causing there to be a ground and set off the buzzer? Or is there more to it?

Wobble

what temp are your t-stats and are they marine ones? Is this a closed cooling motor?

Try switching the t-stats or replacing them.

Raw water cooling, there is a rod with two nylon balls on it that goes through the t-stat housing between the two small hoses on the top and allows water to flow before the t-stat opens. Make sure it is free and that all passages through the t-stat housing are open and not corroded up.

miamioffshore

Yes, I check the nylon ball valves, they're good. T-stats are new with less than 5 hours on them, they should be marine, were installed by TNT, although they dont have a hole in them, should they? Not a closed cooling motor, temps settle at 150 so i'm assuming they're the correct 140 degree t-stats. I even tried removing the t-stat after engine was already hot, alarm STILL goes off

Wobble

Thinking out loud..

you have checked the switch by swapping it to the other motor.

your temp gauge reads ok.

all passages are open.

good water flow out both exhausts.

the switch ( which is the bigger of the two and has the tan/blue wire) causes the alarm.

the alarm can be stopped by disconnecting the tan/blue wire from the switch. You should be able to cause alarm by connecting touching that wire to any ground

if you remove the switch and start the motor do you have water coming out the hole?

try sandcraft's idea, if that solves it you have a fault in the alarm circuit on that engine.

A hole in the t-stat is not going to work if the alarm sounds with no t-stat.

maybe the easiest thing would be to start loosening hoses and checking for flow...

do you have good water flow when using only the muffs? if not then is it possible you got the hoses reversed on the raw water pump and the flush system is disguising the problem ( I ask because I don't know what kind of flush system you have)

boomer

If you have a fresh water flush valve on the boat check the T connection it has a springloaded valve that can get stuck and not allow enough water into the engine.

Wobble

so, what did you find out?

ActiveFun

What is the T connection springloaded valve? Is that in lieu of having a manual valve at the fresh water input to open and close off the flush?

Vmax

The overheat alarm is the same as the drive oil reservoir sensor. I would check to see the reservoir is not low or drive oil sensor is bad.