Car has 103,000 miles. I live in Wisconsin, where it can get very cold. This only happens when the outdoor temperature is below freezing and the car has had time to warm up: the oil light will come on when the car is idling or driving at very low speed, such as at stop lights. The oil light never blinks, just stays solid, and always goes away when accelerating over 5 or 10 mph. This started last winter and it’s happening again this winter. Never happens in warmer temperatures. Last winter, my uncle suggested I put a heavier oil in the car. I did this and the problem went away (although, coincidentally, it stayed relatively warm the rest of the winter). I don’t remember my uncle’s reasoning. This winter I have gone to two different shops to get an oil change with a heavier oil, and both times I was laughed out of the shop. Neither shop felt it would benefit my car to put a summer oil into the car during cold Wisconsin winter months. So, I’m wondering what is wrong with my car, if it’s going to become a serious problem, and if the oil change with a heavier oil is a simple solution. It’s about due for the timing belt replacement. Is it worth dumping more money into this car or is it going to die soon?
The heavier weight oil is allowing your engine to better maintain oil pressure. The symptoms suggest that the engine is well worn.
Pressure is created by the oil pump having to force oil through the small spaces between the wear surfaces and the sleeve bearings, and as wear opens these surfaces up the oil flows through too easily and the pump starts having trouble keeping the pressure up. Heavier oil is harder to push through and allows the pressure to be more easily maintained. Yours may be happening only in cold weather because of varying coefficients of thermal expansion in the internal parts. They change size and shape when they get cold.
The oil light is not good. It means that the pressurized barrier between the wear surfaces is not being maintained. I’d suggest staying with the heavier weight oil. If you do not do this, the engine may die soon of oil starvation of the bearings. If you do this and it continues to work, you may get many more years of service from this vehicle.
You could if you like have a compression check done of the engine just to get a feel of the overall wear, but that won’t tell you what the bearings are doing or how long the engine has to live.
Try having the oil pressure sending unit replaced. Out of all the vehicles I’ve had come in with this problem, 99% of the time it was because of a defective oil pressure sending unit.
And as far as using a heavier oil in winter? Don’t do it. A heavier oil flows far too slow in cold temperatures to protect the engine during cold starts. And doing this is an excellent way to rapidly wear out the engine.
+1 on the sender/sensor. It’s probably reading out of range. If there was a true pressure issue …the last place it would show up is when it’s cold.
One possible (and obscure) issue could be a scored or slightly leaking pressure relief valve in the oil pump. That COULD match the conditions that you cite, but it would still be a very narrow set of circumstances for it to show up only in cold weather.
Consider using Auto-Rx (google it) for one oil change on conventional oil. It will assure that any fouling material is removed from the engine.