False overheat. Temp gauge affected by dash lights

[Babeliner195]

I have a 2001 Bayliner 195, 4.3L engine. I've been chasing an overheating problem for two years now.
The boat would occasionally show an overheat situation in the evening, after a day of running fairly hard. I replaced the impeller and thermostat so I knew they were good, and it was time anyway.
I suspected a short since the engine never really seemed hot, but could never find it. Last evening coming back to the dock, the temp starts climbing and the alarm goes off. The only thing I could think of that I changed before the overheat situation surfaced was to turn on the bow lights. I shut off the lights, and the temp starts to drop. I turn them back on and the temp slowly starts to climb.
Bingo! I found the what causes the problem, but am baffled because the temp sending unit is ground based, and the bow/dash lights are always grounded, and the switch cuts/sends 12v current. How are the two systems related? I'm thinking the problem is likely at the temp gauge, since that is the one place where the dash light and the temp sending unit wire would be in the same vicinity, attached to the back of the gauge.
Anyone have any thoughts on this one?

 

[oldjeep]

Re: False overheat. Temp gauge affected by dash lights

My guess would be that you've got a bad ground on your lights and it is somehow using the sensor or the gauge as a path. I'd clean all the connections you can find and use some dielectric grease on them.

 

[Bondo]

Re: False overheat. Temp gauge affected by dash lights

Ayuh,... Welcome Aboard,.... It's Gotta be a Groundin' problem,...

Either the lights, the dash, or I suppose, the motor/ battery,...

 

[glenn property of pam]

Re: False overheat. Temp gauge affected by dash lights

boat builders are cheap so they didn't run the bow light ground all the way back to the battery they instead ran it close to the dash and used the same ground block your gauges are connected to so if the large cable from the ground block to battery is higher resistance (dirty connection) then it will use any ground that is lower resistance and like you pointed out the temp is a grounded sensor. It may not be the problem but its the first place you should look.

 

[Babeliner195]

Re: False overheat. Temp gauge affected by dash lights

Thanks for the replies. I haven't been idle.... I go out to the boat in the evenings and have been cleaning all the connections, looking for the obvious problem, but so far have only been finding 'maybes'.

Interesting thing that I have found - the problem only surfaces when the engine gets near normal operating temp (175-180*). When the engine is cold, it won't register an overheat even if the lights are left on for a while. And, it's related to the dash lights only. The bow light is on the same switch, but is fed by a different 'hot' wire from the switch and so does not affect the temp at all.

The bummer - the dash/gauges are a solid state unit. Once the wiring harness plugs into the back of the dash, it's all circuit board and solder. No wires that can be disconnected or re-run for testing or a better ground. If a gauge goes out, the entire operation has to be replaced as a unit. (bummed face):grumpy:

On with the search. I will find it, one way or the other. The other is always more expensive.

 

[achris]

Re: False overheat. Temp gauge affected by dash lights

My philosophy has always been to keep engine electrics (which includes engine gauges) and non-engine electrics completely separate. And now you see why. If you would like to fix the problem properly and avoid any problems like this in the future, now is the time. But it will take quite a bit of work.

What I do is run a pair of heavy gauge wires, one red one black, from the battery switch up to the dash panel. There I mount a red and a black terminal block, and secure the incoming power wires to each of those. Now, any thing that is not part of the engine, nav lights, radios, depth sounders, GPS, cabin lights, etc comes from those 2 terminal blocks. Everything that IS engine, stays engine. The only exception I would include would be the fuel gauge, only because it (and the tank and the fill point) should be grounded all the back to the engine block.

HTH,

Chris.....

 

[glenn property of pam]

Re: False overheat. Temp gauge affected by dash lights

Thanks for the replies. I haven't been idle.... I go out to the boat in the evenings and have been cleaning all the connections, looking for the obvious problem, but so far have only been finding 'maybes'.

Interesting thing that I have found - the problem only surfaces when the engine gets near normal operating temp (175-180*). When the engine is cold, it won't register an overheat even if the lights are left on for a while. And, it's related to the dash lights only. The bow light is on the same switch, but is fed by a different 'hot' wire from the switch and so does not affect the temp at all.

The bummer - the dash/gauges are a solid state unit. Once the wiring harness plugs into the back of the dash, it's all circuit board and solder. No wires that can be disconnected or re-run for testing or a better ground. If a gauge goes out, the entire operation has to be replaced as a unit. (bummed face):grumpy:

On with the search. I will find it, one way or the other. The other is always more expensive.

kinda makes sense as the temp rises the resistance on the temp switch drops which makes the ground path more attractive. Try some thing like a spray on contact cleaner and clean the harness plugs then use a small amount of grease before reconnecting. Also check the main ground cable at the motor and clean the terminal and the area its bolted to.

 

[JTwelve]

This is interesting. I found this forum post because I have this same problem, except for me the overheating gauge rises when I turn the "Nav lights" switch on. Boat runs fine all day. In the evening on the way back to the dock I turn the nav lights on and the temp gauge rises immediately throwing the temperature alarm.

Interestingly, I ALSO have a 2001 Bayliner 192 Cuddy Cabin. So I'm assuming this is the fault of Bayliner and they way they ran these wires.

Did the OP find resolution? Other than cleaning connections, any other suggestions?