Temp Gauge indicates Hot, But engine is Not Hot

ShoreFlyer

Recruit
Joined
Oct 2, 2011
Messages
3
I have a 7.4L EFI Horizon Mercruiser Raw Water Cooled. The temperature gauge has been warming up to about 200-220 deg.

1. The computer indicates is running at 158-163 deg. (mercruiser scan tool)
2. I have changed the sending unite twice.
3. I changed the Thermostat.
4. Changed the Thermostat gasket twice, it does have the brass rivets in it.
5. Changed the gauge twice.
6. Hooked the gauge up directly to the battery using new wires. New wires to sending unit. by passing he harness.
7. Engine is normal to the touch.
8. Used an Infrared gun to take temps. Seems normal
9. Manifolds and Risers changed last year
10. New Water pump last month. It had broke.
11. The Alarm doesn't go off.

The engine doesn't appear to be overheating, as confirmed by the mercruiser scan tool. I believe its an issue with the wrong resistance going to the sending unit from the block. But I can't pinpoint what would be causing this.

Andy ideas ?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,296
Bad gauge or bad sender or bad signal wire
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
There are 2 temperature sending units, one for the gauge, one for the ECU. Silly question, you are changing the gauge one aren't you.
 

ShoreFlyer

Recruit
Joined
Oct 2, 2011
Messages
3
Changed the sending units twice, gauges twice. same result. Even took the gauge out of the dash and ran separate wires from the sending unit to the gauge and battery direct to test for a bad connection. Computer sending unit says 158-163deg.
 
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