Hello, I have a Problem with the temperature, gasoline an oil pressure gauge. They do not work. When I fill up the fuel the fuel gauge just shows that the tank is below 30%, temperature an oil pressure do not work at all. what can be the problem ?
Sorry for my poor english, but I am from Germany and my vocabulary with this special problems is not that good, but I try to get better.
Thanks for help
Harry
It sounds like a bad float or worn out fuel sender.
I’d bet that the Temp & Oil senders are for lights, not gauges. The senders could also be for ‘modern’ (post 85 or so) gauges that use the 150 ohm range instead of the classic 73 ohm range. Both of those are common mistakes.
Rather than retype it all, here’s a link to understanding how the gauges work: http://www.classiccougargarage.net/showthread.php?tid=186
Hopefully that info will be helpful to you.
I’m thinking perhaps a bad Instrument Voltage Regulator (since all three of these gauges use it as a power source). The IVR (sometmes called CVR) is located on the back of the instrument cluster and is a small metal can.
My first thought was the regulator, but I opted for senders when he said that the fuel gauge does go to 30% when full. If the gauge is moving the regulator is regulating. I had also considered a bad printed circuit, but his Cougar is a '68 so that wouldn’t apply.
IVR could be way out of whack (so wrong effective voltage), so while it may be doing something, it may not be regulating.
The fuel gauge probably works slightly even with a low voltage from a bad CVR because with a full tank, there is only 10 ohm or so resistance through the sender. The resistance at the other senders is likely high enough to prevent the needles from moving. I’d try grounding the oil pressure and temperature sender lines and see what the gauges do. If they also move part way then I think the CVR is the culprit.