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Old 10-02-2012, 04:12   #1
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Operating Temp Coolant v Metal

hi im having some problems with overheating with a nanni 85 hp.
alarm comes on after about 20 mins at full throttle.i have replaced heat exchanger and tubes .so im thinking it just maybe a bad sender unit?but quite expensive as i need the behind the dash electrics to go with sender.
now i have seen a digital temp alarm on ebay from the states that the sender unit just bolts onto any bolt near the cylinder head.
now my question?could getting a reading from a bold near the head be true operating temp as apposed to reading from coolant.
DIGITAL TEMPERATURE GAUGE ENGINE ALARM RACING OVERHEAT | eBay

thanks for any info.gaz.
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Old 10-02-2012, 09:12   #2
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Quote:
Originally Posted by fishingaz
hi im having some problems with overheating with a nanni 85 hp.
alarm comes on after about 20 mins at full throttle.i have replaced heat exchanger and tubes .so im thinking it just maybe a bad sender unit?but quite expensive as i need the behind the dash electrics to go with sender.
now i have seen a digital temp alarm on ebay from the states that the sender unit just bolts onto any bolt near the cylinder head.
now my question?could getting a reading from a bold near the head be true operating temp as apposed to reading from coolant.
DIGITAL TEMPERATURE GAUGE ENGINE ALARM RACING OVERHEAT | eBay

thanks for any info.gaz.
I'd suggest if you really think its a sender. Why not get another replacement sender for the engine.

Is the full throttle under load. The raw water system may just not be up to it. I know several
Boats that can't operate at flat out throttle for 20 minutes.

Also is the cylinder head gasket leaking. , theres no water in the oil etc. nanni are aluminium. So a wrapped head can be a problem.

Dave
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Old 10-02-2012, 09:19   #3
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Re: Operating Temp Coolant v Metal

We've got a 28 hp Phasor that won't operate at full load for more than about 15-20 minutes. the heat exchanger just isn't up to the task in tropical waters. But winter water temperatures in Houston poses less of a problem.
Is this a new problem?
Have you tried an infrared thermometer to confirm it the gauge/sender are correct?
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Old 10-02-2012, 09:51   #4
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Re: Operating Temp Coolant v Metal

See Basic Troubleshooting of Gauges:
Basic Engine Gauge Theory and Testing

For All Gauges:

1. Remove Sender Wire from “S” Terminal on Gauge, and Turn ON Instruments Circuit.

2. Test Voltage between “I” Terminal (External Power Supply) and Ground Terminal “G”.
Tested voltage must match nominal voltage of the Gauge (ie: 12V Gauge must test between 10 - 16VDC), and the Battery Voltage.
If no voltage - check Ignition or Instrument Switch(s) and/or Fuses.
If tests less than battery voltage, repair or replace (Violet) wire from Ignition or Instrument Switch.

If a Sender fails “Open” (Infinite Resistance), one or both (if Dual Station) Gauges will read Zero Scale.
If a Sender Fails “Closed” (shorted - Zero Resistance), one or both Gauges will read Full Scale.

Other confusing Ohmmeter results, such as readings lower than expected, could indicate a poor Ground Connection at the Sender Body (Sender to Engine Block). Check for pipe dope or tape on Sender Threads.

Testing Temperature Gauges:

1. Disconnect Tan Sender Wire from Gauge (Terminal “S”) and turn Instrument Power ON.
The Temperature Gauge should indicate ZERO Scale (< Low Temperature).

2. Short the Gauge Sender Terminal “S” to Ground Terminal “G”.
The Gauge should deflect to FULL Scale (> High Temperature).

3. Measure Resistance from Tan Sender Wire (disconnected from Gauge) to Ground.
American Temp. Senders will read: 450 Ohms (Engine Cold @ 1000F)
or 29.6 Ohms (Engine Hot @ 2500F )
European Temp. Senders will read: 281 Ohms (Cold @ 40 0C) and 22 Ohms (Hot @ 1200C)

4. Disconnect Tan Wire from Sender on Engine Block.

5. Test continuity of Tan Wire.
Zero Ohms from Block End to Gauge End - If not, repair or replace Wire.


6. Measure Resistance from Sender Terminal (on Block) to Ground on Block.
Should read as per (3) above - If not, replace Sender.
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Old 10-02-2012, 20:31   #5
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Re: Operating Temp Coolant v Metal

thanks for all the good info.
the impeller is newish.there is no water in the sump.and the heat exchanger is brand new.
and Gord i would have no idea where to start with that?but im sure many on here understand all that.but thanks again.
just like to know would that digital gauge read the true operating temp?

gaz.
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Old 11-02-2012, 07:19   #6
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Re: Operating Temp Coolant v Metal

Quote:
Originally Posted by fishingaz View Post
... just like to know would that digital gauge read the true operating temp?
gaz.
Not exactly.
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Old 11-02-2012, 08:42   #7
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Re: Operating Temp Coolant v Metal

Quote:
Originally Posted by fishingaz View Post
thanks for all the good info.
the impeller is newish.there is no water in the sump.and the heat exchanger is brand new.
and Gord i would have no idea where to start with that?but im sure many on here understand all that.but thanks again.
just like to know would that digital gauge read the true operating temp?

gaz.
NON CONTACT INFRARED THERMOMETER IR LASER Temperature GUN WITH TC SENSOR DIGITAL | eBay


This would be a far better use of your money than some overpriced bolt on temp sender. If you really have a problem you should fix it, once the problem is fixed this can be used for all sorts of things, like seeing if you're drinking beer fast enough(by measuring the temperature of your stomach and your friends!)
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Old 12-02-2012, 04:24   #8
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Re: Operating Temp Coolant v Metal

thanks again for all your info.
i do have a infrared temp gauge and today i did use it.i came home from fishing and had a run of 35 to 40 mins but i reduced the revs to 2300 from 2800 rpm.when i got back to the bay i quickly checked with the infrared and the highest temp i got on any metal around the head area was 80c.
the ocean temp here is 25c.
so maybe lower the revs in summer time is the only thing i can do.next week ill try the revs at 2500 and see how we go?
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