Gauge making me crazy

[Timbolex]

I recently purchased a 2003 Chaparral with a Mercruiser 350 mag MPI the temperature gauge was reading 210 degrees Plus so I changed the impeller I changed the thermostat still getting a high reading, checked with an IR thermometer and it seems to read correctly around 160° close to the temperature sensor and around 180 on the manifolds I changed the temperature sensor and while running at the dock it seemed to work perfectly but once I got it out on the water it again creeped up to 210, even though my IR was still reading normal? Any ideas?

 

[Searay205]

make sure when you guys use the less than $20K IR guns you get as close as possible to what you are trying to get temperature. that little dot is not what its reading it reading an average over 5" at 1 foot. Also they are set for emmisivity value of 1 which is dull black color. not shiny aluminum.

 

[Lou C]

I've never checked temps on a Merc but on my OMC with the OMC/Volvo style stat housing & 160* stat, it reads closest to the dash gauge temp when I take a reading of the intake manifold right under the stat housing. The gauge will read 160-165 and the intake will read 145-150 or so. The stat housing itself is a good bit cooler like 120-130.

 

[ROY WILLIAMS]

the water engine temp is 210F the temp sender in the engine .. then the temp gun is outside the metal engine 160F .....
I would be the 140-150F temp sender on the spec temperature ..

 

[Bt Doctur]

does the gauge go to zero when you remove the wire? does the gauge go full hot when you ground the wire? Check the voltage, ground, and sender wire at the rear of the gauge.

 

[Timbolex]

The IR was 40 and has been pretty consistent, I take readings all over the motor, simply from fear of over heating, but never had a reading Over 190 on any part of motor, still scary to see the guage that high, driven 35 minutes at 4000 rpms with guage that high and it ran great, no smoke, oil looks good, I would hope an alarm would have sounded if is was that hot

 

[Timbolex]

does the gauge go to zero when you remove the wire? does the gauge go full hot when you ground the wire? Check the voltage, ground, and sender wire at the rear of the gauge.

How do I check? Do I remove wire to sender, put a wire in it and then touch to ground? If pegs high, then guage is working?

 

[ROY WILLIAMS]

How do I check? Do I remove wire to sender, put a wire in it and then touch to ground? If pegs high, then gauge is working?

yes the wire sender is on the block ground then the sender is 260F....
gauge you did it is correct ...
the temp gun is outside the engine .....drops the temp metal outside..
I know the water flow parts are changed ...

 

[tank1949]

I recently purchased a 2003 Chaparral with a Mercruiser 350 mag MPI the temperature gauge was reading 210 degrees Plus so I changed the impeller I changed the thermostat still getting a high reading, checked with an IR thermometer and it seems to read correctly around 160° close to the temperature sensor and around 180 on the manifolds I changed the temperature sensor and while running at the dock it seemed to work perfectly but once I got it out on the water it again creeped up to 210, even though my IR was still reading normal? Any ideas?

Perhaps former owner replaced sender or helm gauge, which was the incorrect impedance?

 

[Timbolex]

Perhaps former owner replaced sender or helm gauge, which was the incorrect impedance?

I just replaced the sender and seemed to work while at the dock, but once on water, it went up again, but slower than prior to changing sender

 

[tank1949]

I just replaced the sender and seemed to work while at the dock, but once on water, it went up again, but slower than prior to changing sender

But are they "balanced? This is simple to check and will rule out impedance as the problem. Been there!!!!!!

 

[Timbolex]

But are they "balanced? This is simple to check and will rule out impedance as the problem. Been there!!!!!!

How do I tell if balanced?

 

[Timbolex]

How do I tell if balanced?

The gauge went up, but the IR stayed consistent

 

[Timbolex]

and ONE more thing, the alarm everyone talks about, is it the alarm I hear when I turn the key on, or is it the horn?

 

[tpenfield]

There is an overheat alarm and it will use the obnoxious buzzer.

See if you can find the 210˚ F somewhere around the engine. Make note of the temperatures at different spots. Where you are holding the IR gun in the picture is right where cold water comes in from the outdrive, so you are not getting the whole story.

 

[Timbolex]

I checked the sides, that hit around 175/180 , the block was 140ish couldn't find anything on motor above 180

 

[Timbolex]

There is an overheat alarm and it will use the obnoxious buzzer.

See if you can find the 210˚ F somewhere around the engine. Make note of the temperatures at different spots. Where you are holding the IR gun in the picture is right where cold water comes in from the outdrive, so you are not getting the whole story.

 

[dingbat]

Bi-metal temp sensors can and do fall out of calibration/linearity.

Have you done any testing to confirm that the temp sensor is performing to specification?

Testing harness:

1. Pull out the harness connected to the sensor, to reveal the connection point, between the harness and the sensor.
2. Turn the ignition key on, without starting the engine.
3. Connect the red clip to terminal two, while grounding the black clip.

• Should read 5 volts or less if the harness is in tact.

Ohm Testing:

1. Attach an ohmmeter, across the sensor’s terminals.
2. Measure the sensor’s resistance and record the reading.
3. Reconnect the sensor wiring connector
4. Start and run the engine for two minutes, then shut the engine off.
5. Disconnect the sensor wiring harness and take an ohmmeter reading, across the sensor’s terminals.

• Should be at least a 200 ohm difference in readings

Voltage Testing

1. The reference voltage to the sensor from the (PCM), should be @ 5-volts.
2. The return voltage signal, should be 3 to 4 volts, when the engine is cold.

• This should gradually drop to 2 volts or less as the engine reaches normal operating temperature.

 

[tpenfield]

Your starboard exhaust manifold is 165. What about all the other parts of the engine?

Top of elbow
Recirculating pump hose
Bottom of thermostat housing were it meets the intake manifold
Water duct in the front of the intake manifold

Any chance you are using a European sender and a USA gauge?

 

[tank1949]

How do I tell if balanced?

documentation should tell impendence. Perhaps on gauge and sender??? If not do a web search for specifications.