Temp Gauge

[joseph m. hahnl]

My temp Gauge stops working when the motor is running. But works with the ignition on and the engine off??????????????????????/

any suggestions?????????????????????????????????

[VetteLT193]

maybe a bad ground. have you poked around behind the dash to make sure everything is tight? the factory connections are slip fit

[mrfixxall]

My temp Gauge stops working when the motor is running. But works with the ignition on and the engine off??????????????????????/

any suggestions?????????????????????????????????

could be your thermostat is stuck open,when your engine sits after its ben running for a whyle the water in the block warms the water.. when you start the engine it sucks in the cool water and cools off the coolent temp sender because theirs no closed thermostat to restrict the water ..

[joseph m. hahnl]

. when you start the engine it sucks in the cool water and cools off the coolant temp sender ..


It has a full cooler on it. The coolant is always hot. the thermostat is a 150 degree .It does grows hotter without the coolant circulating and drops back to a continues 150 when you run it. "shut off ignition on"

.It almost seems like the gauge drops 50 degrees when running. but I cant be sure. The gauge starts at a 100 degrees..

It really seems to be electrical.

Does the current Switch to the alternator ? Could this be where I should start?

[VetteLT193]

It has a full cooler on it. The coolant is always hot. the thermostat is a 150 degree .It does grows hotter without the coolant circulating and drops back to a continues 150 when you run it. "shut off ignition on"

.It almost seems like the gauge drops 50 degrees when running. but I cant be sure. The gauge starts at a 100 degrees..

It really seems to be electrical.

Does the current Switch to the alternator ? Could this be where I should start?

Does the gauge have power or not? Meaning as soon as the boat starts does it instantly drop or does it slowly drop?

If it slowly drops, I'd check the T-stat. It could be stuck open like fixxall said.

If it instantly drops it is probably a ground.

[joseph m. hahnl]

If it instantly drops it is probably a ground.


Yes it instantly drops. the needle still seems to have power.But no actual reading

[VetteLT193]

do you have an ohm meter?

First place to check is on the engine then work yourself to the gauge. I am going to take a guess that pulling the sensor and putting it back in might fix the problem. it's right up top on my boat, so probably the same on yours. it has to be the easiest part to get to...

[joseph m. hahnl]

it has to be the easiest part to get to...



OH MY, NO:shocking:!!! The full cooler is the way of the lower heat plug.
The cooler has to come off to change it.

The upper heat plug is a tight squeeze but I think doable.



So that leads to another question??????

2 plugs.

Which one is the gauge "TAN"???????????????

Which one is the warning "tan & blue"??????????????

[VetteLT193]

OH MY, NO:shocking:!!! The full cooler is the way of the lower heat plug.
The cooler has to come off to change it.

The upper heat plug is a tight squeeze but I think doable.



So that leads to another question??????

2 plugs.

Which one is the gauge "TAN"???????????????

Which one is the warning "tan & blue"??????????????


closed cooling? can you post a pic? I gotta run out to see mine now...

[VetteLT193]

mine has a purple wire off the sensor and on the back of the gauge.

On second look, it might have been moved on my boat. it is in the manifold, on top, to the left of the Thermostat housing.

the tan/orange/earth tone wires all go to the buzzer box

[VetteLT193]

OH MY, NO:shocking:!!! The full cooler is the way of the lower heat plug.
The cooler has to come off to change it.

The upper heat plug is a tight squeeze but I think doable.



So that leads to another question??????

2 plugs.

Which one is the gauge "TAN"???????????????

Which one is the warning "tan & blue"??????????????

oh, and as far as I can tell 98% of the wires Donzi used are TAN.

and, more important, BLUE (kinda lightish blue) is oil pressure, so I have to assume you are looking at the wrong sensor at the end of the blue wire...

[VetteLT193]

here is yet another reply because I found this pic on hand from when I pulled my dash.

The gauge on the top left is oil pressure, top right is oil temp... notice the 367 tan, gray, and white wires :smash: after you weed those out, notice the purple wire and blue wire. and, oh crap, there is another purple wire going to the pressure gauge.

well, maybe this will help you :crossfing:

[joseph m. hahnl]

here is yet another reply because I found this pic on hand from when I pulled my dash.

The gauge on the top left is oil pressure, top right is oil temp... notice the 367 tan, gray, and white wires :smash: after you weed those out, notice the purple wire and blue wire. and, oh crap, there is another purple wire going to the pressure gauge.

well, maybe this will help you :crossfing:

I was talking about at the engine. I believe the purple wire(s) at the dash are for the audio warning from all of the sensors. All the gray & white wires are daisy chained illumination wires.

I will rephrase. The upper heat plug ,which I believe to be the warning indicator has a Tan with blue stripe.



The lower heat plug has two wires straight tan and also a black wire on it. ( the black could be residual engine enamel paint or even shrink tube )They seem to lead back into the alternator wire harness . The two wires are real short coming out of that wire cluster. Just enough to connect to the heat plug.

I'm thinking it switches circuits to the alternator when running.


I did replace the alternator last season. But I'm thinking the problem started before that. I used the GM instead of The Mondo.