QuestionI've had issues with the oil light coming on when stopping or when the car is idling but it does not come on until after the car warms up. I also have an issue with the check engine light and was informed that a oxygen sensor needs to be replaced. Would this issue also be causing the oil light to come on or is it something else that will need to be repaired. What should I expect in terms of cost of repair for both these issues.
AnswerHi Damien,
I don't believe you have a costly repair issue here. The oil light coming on at idle after the engine is warm is quite common. It is due to the combination of the oil being easier to pump when it is hot, and also with the oil pump running slowly when at idle. The pressure switch that turns on the light is probably just a little pessimistic because the specification only requires a pressure of about 4 psi to keep the engine safe at idle from excessive wear but the switch may be set to turn on the light at 8 or so psi, for example. As long as the light doesn't come on when you are running the engine at more that 1200 rpm I wouldn't bother changing the oil pressure switch. It is an inexpensive item and shouldn't take more than 10 minutes to change nonetheless.
If you want to be certain that there is nothing wrong with the oil pressure you can have the mechanic screw in a calibrated pressure guage in place of the switch and actually see what it is reading at idle and at 2500 rpm to compare that with the specs. Tell me what engine you have and I'll tell you the pressure specs. Another way to eliminate the issue is the raise the viscosity number of you your oil one step. That will raise the pressure at a given rpm and likely eliminate the light as an issue.
On the oxgen sensor, it is a more espensive part, around $100, and it too is pretty fast to change (maybe a half hour). There are probably two or even four sensors on the engine so you should try to find out what the exact fault code was that led a mechanic to tell you about the sensor. The code will specify which sensor has gone bad. It is similar mechanically to a spark plug, so except for getting to it which might involve putting the car on a lift, and putting some penetrating oil around its threads, it is a quick unbolt and bolt item.
The only way these two issues would be interrelated is if the oxygen sensor malfunction was causing a too low idle speed. If you have a tach, most engines should idle around 800 rpm. If your is lower, that would lower the pressure and probably turn on the light. But most engines will compensate for low idle and increase it automatically.
Roland
