Pressured by Faulty Oil Indicator
Question: While returning from vacation in my 1987 Thunderbird, the chime on the dashboard sounded and a picture of an oil can lit up. I pulled off the highway and checked the dip stick, which read full, and the coolant, which was full. I continued home, but this condition occurs often now. It only lasts for a few minutes. The Ford dealership is unfamiliar with this problem. Can you offer any ideas about the cause?--K.O.
Answer: It’s a risky proposition to fool around with a low oil indication, since low oil pressure or low oil level that causes a loss of pressure can ruin your engine. Low pressure is often accompanied by high engine temperature, loud knocking noises and eventually a seizure in which engine parts become welded together.
The dashboards of most modern cars contain lights that alert the driver to a problem--unfortunately after it has already occurred. At one time, most cars came equipped with oil pressure gauges that provided a continuous readout. They were replaced with the lights, which immediately became known as idiot lights.
These dashboard lights have partially redeemed themselves in recent years, though. In the past, idiot lights have signaled only that the pressure in the lubricating system was below normal. But newer cars, including your Thunderbird, have a sensor that will activate the dashboard warning if the oil level drops too low. That way, if you have neglected the onerous job of checking your oil dipstick, your engine will be saved from ruin.
The Thunderbird chime and light go on simultaneously when the oil pressure drops to about 50% of normal. At idle, for example, normal oil pressure should be 30 pounds per square inch; the oil light indicator will light up at 15 pounds per square inch.
There are many specific causes of low oil pressure, but general causes include a faulty oil pump, a malfunctioning oil filter, grossly worn out parts in the engine or low oil.
The mechanics at your dealership should have been able to determine with certainly whether you have low oil pressure or not. It is possible to attach a mechanical pressure gauge to engine that should provide an exact reading of your pressure.
Possibly, either the pressure sensor or the level sensor is malfunctioning. One distinct possibility is that the level sensor is faulty, since it can become contaminated with engine deposits, such as tar. Unlike the pressure sensor, the deposits can cause an intermittent false alarm. If this is the problem, the fix will be inexpensive.
