3.0 temp gauge reading when ignition off

bobhol

Petty Officer 2nd Class
Joined
Oct 5, 2009
Messages
146
I have been chasing a temp problem all summer .My gauge reads 15 degrees higher than actual temp of motor according to IR gun. I have checked the gauge and it pins when grounded,the voltage is correct at the gauge and I have run wiring direct to the gauge from the sensor. Always the same result..it reads 180 to 185 but the IR gun shows 167 and lower all over the motor.When I turn off my ignition my temp gauge still shows the normal reading and drops slowly as the motor cools. The local marina mechanic says the gauge should turn off like the rest of the gauges and I have a problem ...anyone have an opinion on this ....thanks,Bob
 

zbnutcase

Commander
Joined
Sep 19, 2009
Messages
2,055
Re: 3.0 temp gauge reading when ignition off

The IR gun measures the OUTSIDE of the engine, the temp sender measures the INSIDE. Yes they ARE going to be different. I see no problem. Your gauge is simply getting 12v from a source other than the key switch, should be a simple fix.
 

bobhol

Petty Officer 2nd Class
Joined
Oct 5, 2009
Messages
146
Re: 3.0 temp gauge reading when ignition off

I appreciate your answer and I do agree to some extent ...but...other owners have noticed with a 160 thermostat that it runs up to 170 and falls when the stat opens ...mine is consistently 180 -185 I believe it read correctly from the factory and I would like to get it right again...so you are saying also my gauge should not read when the key is off?..I will try to chase that down with my meter...thanks.Bob
 

BAproject

Petty Officer 1st Class
Joined
Sep 2, 2009
Messages
276
Re: 3.0 temp gauge reading when ignition off

are you running in fresh or salt water? Which thermostat do you have a 140 or 160?

The IR gun to temp gauge on my boat runs about 10 degrees cooler then what the gauge reads. The sending unit could be faulty, but doubtful.

When was the last time you changed the impeller in your O/D?
 

Gary H NC

Fleet Admiral
Joined
Dec 1, 2005
Messages
8,972
Re: 3.0 temp gauge reading when ignition off

It could be the temp gauge is connected to the always hot side of the ignition switch.
If you can get under the dash see where it is connected.
For piece of mind i would change out the thermostat to a 160*....
 

bobhol

Petty Officer 2nd Class
Joined
Oct 5, 2009
Messages
146
Re: 3.0 temp gauge reading when ignition off

It is a new mercruiser stat 160 and I have 20 hours on the impeller.it did read between 190 and 200 with the old stat which I think was original....Bob
 

BAproject

Petty Officer 1st Class
Joined
Sep 2, 2009
Messages
276
Re: 3.0 temp gauge reading when ignition off

sounds like you're running ok to me
 

bobhol

Petty Officer 2nd Class
Joined
Oct 5, 2009
Messages
146
Re: 3.0 temp gauge reading when ignition off

Any other 3.0 owners out there? What temp is normal to you? ...Bob
 
Top