What motor oil to use



I have a 2001 mitsubishi montero sport xls with 120K+ miles. I’ve had the oil changed regularly every 3-4K miles. Recently the oil light has been activating. It only activates after I’ve driven it for several miles and the vehicle is in gear and at a stop. It flickers at first and then is on continuous. When I flip it into nuetral, the light goes off after a few seconds. I run 10W30 oil and one mechanic tells me to switch to 10W40 and see if that eliminates it. Another wants to check the oil pressure but also said that 10W40 turns to mollasses in the winter. I live in Kansas City and it gets below 0 sometimes in the winter months. Does anyone have any insight on this issue. I’m having mechanic 2 look at the issue in the morning.


Your first mechanic SHOULD have checked the oil pressure. You know that you are supposed to stop the engine if the oil light is on. YOu can kill the engine if you continue to run it.


When the oil light comes on, do you hear any unusual noises from the engine? If not, maybe all that’s wrong is a defective oil pressure sending unit.



Good, having the work start tomorrow. It could be just an old oil pump or a bad sensor.


First off, 10W40 is the same base weight as 10W30 and neither turn turns to molasses in the winter. It dives below zero here in NH occasionally too. There’s a good primer on oils at www.carbibles.com.

Checking the oil pressure couldn’t hurt. Basically he’ll just connect a gage to the sender hole. That’s the correct approach. He may also want to check the idle speed to see if that’s too low. That’ll tell the tech whether the sender is bad, the pressure is dropping because the idle is too low, or the pressure is really low. From there he can consider the correct option. If teh pressure is really low, he may recommend going to a slightly thicker base weight oil.

The way the system works is that the pump forces oil under pressure through various spaces that need lubricating, like between the crank surfaces and the associated bearing surfaces. If the bearings get too worn down, the spaces become larger and the oil flows through too easily, preventing the pump from maintaining the pressure at idle speed. It’s sort of like trying to keep the pressure up in a balloon with a hold in it. A thicker oil doesn’t flow through the spaces so easily and the pump can maintain pressure.

The suggestion that you try a 10W40 was because the second number, the 30 or 40, designates the oil’s ability to maintain its resistance to flow when it heats up. That resistance to flow, particularly through the spaces, is what allows the pump to maintain the pressure.

Summary: first order of business is to check the actual oil pressure.
Second order of business is to determine why it’s low IF it’s really low.
Third order of business is to come up with an affordable solution.


mechanic says its the sensor, pressure was fine
thanks to everyone for responding
great feedback and advice