7.4L Over temp alarm on monitor panel - but no overheating evident (330DA 96)

[testlab]

Hi,

I have a 330DA with 7.4L carb (FWC) Bluewater Inboards with ZF630 V-Drives. Today the water temperature alarm went off on the port engine, or at least according to the system montor panel (I have the boat shaped one with the LEDs).

The water temp gauge was rock solid at 160F as it always is (both engines are always within 5-10F) and the elbows seemed to have similar temperatures between the two engines. I could not find an obvous over heat problem and everything I checked by comparing port and starboard was similar. Water pumps, heat exchangers, manifolds and elbows all been inspected and replaced within last 20 hours. Everything runs great (I must buy an IR gun to leave on the boat). Even after 40 mins with both engines off (and both port and starboard gauges showing 130) the port water temp monitor continued to illuminate and buzz.

With the ignitions on and engines off, both oil alarms work and the starboard temp alarm is off - the port one however is lit. The test switch seems to do what it should.

I went over the system with a voltmeter and I have a few questions (to start with):

1. Is there separate temperature senders for the gauge and the overheat alarm? I found one (tan wire) on the thermostat housing which goes to the gauge (disconnecting it sent gauge to minimum) but I couldn't see another near there that might go to the alarm monitor.

2. When measuring voltage at the systems monitor input circuit board, the port water temp terminal is 0V and the starboard is around 12V. This says to me:

A) I have a dud overheat switch (assuming separate sensors) or
B) The monitor input circut has gone short circuit (but if it did, and there was only one sensor, the gauge would read high too), or
C) The wire (#326) from the monitor input to the sensor or gauge is open circuit.

Am I on the right track?

I keep coming back to thinking its A or C but with wife and kids waiting I had to pack up and go home as watching me scratch my head and say 'what if' is a tad boring (or so I am told).

3. Can anyone point me to the overheat switch if it exists. I did see a sensor nestled down to the left of the distributor but didn't have time to check it... is this it or is that the oil pressure sender?

I hope too much info doesn't confuse the issue.... is there an overheat switch... if so, where is it????

Thanks and regards
Dave.

 

[rpeterson]

Dave, I have a similar problem that I am just getting into, where did you find the "imput circuit board" for the monitor. What does it look like?
Ron P.

 

[northern]

On my 454s there are two sensors fot temp one for gauge reading theother for high temp alarm.They are located on the port side of the engine towards the rear just behind and below the manifold.

 

[rpeterson]

Northern I am looking for the "imput circuit board" not the actual sensors. It should be a black or grey box oblong, usually mounted on the bulkhead with the coaxial cable going to the unit itself on the instrument panel.

 

[northern]

My motors are 1989 not to much in the way of new electoronics. I think most sensors are hard wired to the gauges.

 

[Jimmy Buoy]

A friend with twin 454's had his engine continually go into limp mode due to overheating. The engine was not actually overheating. the transmission was overheating. Apparently the prop shaft was a bit bent and caused the output gears to bind enough to heat things up and trigger the engine to signal an overheat/limp mode.

Just a thought...