View Full Version : Wierd electrical bug, Temp gauge

07-21-2005, 08:58 AM
I've got a really strange problem with the temperature gauge on my '93 Prostar 190.

Most of the time the gauge works perfectly fine, staying right around 160*. However, if I have the blower running and the nav lights on, the gauge reads slightly higher, about 180*. Then if I leave the blower and nav lights on and turn the engine off, the temp gauge steadily climbs until it is pegged above 240*!!!

As soon as I restart the engine, the gauge returns to 180* and if I turn either the blower or nav lights off, the gauge settles back to 160*.

I've checked the impeller (which was new this spring) and I replaced the thermostat last year. I have a feeling this is going to be one of those electrical gremlins that is impossible to find. Just thought I would post this to see if anyone has any suggestions about where to even begin looking.


07-21-2005, 09:23 AM
Sorry to hear about the issues, Brian. Sounds like you're right, it may be a electrical issue that's tough to diagnose.

My first thought is that some of the rising temps after shut down can be attributed to heat soak, which is normal. Getting as high as 240 on the guage isn't, and most likely is impossible for the actual temps to be reading that high.

On my '88, the needle jumps a bit (10 degrees) when I turn on the blower as well, and I think it has something to do with the change in draw from the electrical source. Wish I could be of more help, but I'd pull the dash, and check voltages running to the temp gauge when the blower is on, and off, and then check continuously when the nav lights are on, with the blower on and the engine off, to see if the voltages keep changing.

While the dash is pulled, I'd keep checking voltages from various wires to see if there is a weird short someplace. If you find one, you may be able to to jumper out the wire in question to see if anything changes on the temp guage. Hope that helps.

Kevin 89MC
08-12-2005, 11:42 AM
Also look at all the grounds. Electrical issues can be tough to chase. If the needle jump is instantaneous with the flip of the switches, it is likely electrical. If it is gradual, then it could be the actual temp increase. 240 is too hot, so if that is the actual temp, you'd better get that looked at ASAP. If your impeller and t-stat are good, next thing to check is the pump, and then the hoses. Also look at the screen at the water pickup back by the trans. I'd also try another temp gauge if you can get access to one.
Good luck,

08-12-2005, 12:16 PM
I am having the EXACT same issues with my '89. Also, when I turn on the blower or bilge, I get a high pitch screech from the dash. I know it isn't the bilge or blower because I traced the sound. It almost sounds like a dial-up modem connecting but not as lound. If I turn the switch on and off a couple of times the sound goes away.

08-12-2005, 12:24 PM
brians, as an electrician, I agree with kevin....it sure sounds like a ground problem; those gauges see low resistance to ground as a high temp=check all connections for corrosion/tightness, I think this will solve your problem

09-01-2005, 07:31 PM
I had the exact same problem with my 1990 PS 190. It was a grounding issue. You should be able to fix it by either cleaning the existing grounds or, what I did, installing new ones. I believe the high pitch squeel you are hearing is a high temp alarm triggered by the guage reading high. The guages are very sensitive to changes in current and DC voltage is famous for 'hunting for ground' causing it to route through areas where it's not really supposed to go due to finding a better ground. My temp guage sits at 160 all the time but if I turn the blower on it will jump a few degrees still. Before I installed the new grounds it would do exactly what yours is doing and go up till it was pegged.

Hope that helps.


09-01-2005, 07:34 PM
The 240 temps are most likely due to heat soak. ie; the engine is hot & there is no cool water flowing thru it any more, so the water in the engine tends to climb. 240 is a bit high, but 200 is common. So maybe the ground problems mentioned above are contributing also.