Q. My husband and I had to replace the engine in our 1997 Saturn SC2 because we had driven it with no oil (oops!). While we weren’t totally on top of checking and changing the oil, we were very surprised that the oil light never came on to warn us of an impending problem.
We asked the dealership to check the oil light when they replaced the engine and they told us that it wasn’t designed to ever come on while the engine was running (which surprised us even more).
Is this true, and if so, what good is the oil light if it doesn’t help protect against low engine oil? Or did we misunderstand what we were told (or maybe the message got garbled between the mechanic and the repair manager?) Any help you can give us in understanding what went wrong would be appreciated.
— Katherine F., Seattle
A. Ouch! Writing that check was a tough way to learn the importance of maintaining proper engine oil level. Sharing your experience might save others from the same fate.
Your Saturn’s oil-pressure warning light (like most others) is designed to illuminate any time the ignition switch is on and engine oil pressure is below about eight psi (pounds per square inch). (It normally is 30 to 60 psi).
Under normal conditions the light should glow as the key is turned on, but go out and stay out after the engine has been started.
If the light flickers on during braking or comes on steadily (with the engine running), this indicates dangerously low oil pressure.
Oil pressure provides the essential lubricating film between moving engine parts and draws heat away from critical areas. Insufficient oil level is the most common cause of low oil pressure, although diluted oil or worn engine parts also can cause the lamp to glow — usually at warm-idle.
The scary thing about oil-pressure warning lights is that by the time they come on, engine damage might have already occurred.
A low oil condition might allow air to be gulped into the oil pump pickup screen, reducing oil pressure (but not yet to the point of turning on the light).
Also, when there are only 1 or 2 quarts of oil doing the work of 4 or 5, oil temperature can soar, reducing pressure and damaging the oil.
With our busy schedules, it’s difficult to remember to stay on top of everything we should. Most engines use a quart or so of oil between oil changes, while others might consume far more.
Once you learn your engine’s consumption rate, you can designate an inspection schedule — perhaps every other tank of gas, or the first Saturday of each month.
I like the Saturday plan, and I devote five minutes to checking the oil and other under-hood fluids as well as checking tire pressure and looking for fluid leakage, frayed belts or other signs of trouble.
Today’s tip: Whenever a "V" or serpentine drive belt is replaced, hang on to the original for an emergency spare. A roll of electrical tape also can come in very handy to repair a split cooling system hose. Next week we’ll put together a complete roadside trouble kit.
Brad Bergholdt teaches automotive technology at Evergreen Valley College in San Jose, Calif. E-mail him at under-the-hood@juno.com or write to him in care of Drive, Mercury News, 750 Ridder Park Drive, San Jose, Calif. 95190. He cannot make personal replies.
