QuestionQUESTION: '02 Jeep Liberty (160k miles) oil light kept coming on but no outward loss of pressure nor oil, no clacking, nothing of the sort. Scope showed nothing so the Service Center then did a manual test and determined that it was most likely the Sending Unit so we had it replaced. However the Oil Light still comes on. The same Service Center now says well there's probably something going on with internal engine. Can you offer any other explanation(s)? Thank you!
ANSWER: Hi John,
You didn't say whether the oil light was coming on at idle or when the rpm was over 1,00 rpm (e.g. while you were underway). The question just before yours was the same, so here my answer if the light only comes on at a stop:
This is fairly common with all makes/models. Your idle rpm is a little on the low side which means the pressure is going to be low enough to turn on the light after the engine warms the oil, which also lowers the pressure a bit. The actual minimim oil pressure is 5 psi so if you wanted to check this out you could have it measured with a gauge at a shop or buy a gauge and substitute it for the oil pressure light sensor located next to the oil filter.
But in my experience I would not be concerned for the moment, but rather the next time you change the oil increase the 'weight' by one step*, which increases the viscosity and thus will raise the pressure at idle so that the light will usually not come on anymore. Another approach would be to buy a new sensor for the light and replace the present one which may be off-value. Either of those approaches don't have any labor charges if you do it yourself.
The only time you really have to be concerned is if the light comes 'on' when you are driving and the rpm is higher than about 1,000 rpm as that could mean there is insufficient oil reaching all the moving parts.
Roland
*If you have been using 5W-20 try instead 10W-30 for example. Also it is the case that if you are using a synthetic oil that too will have a lower pressure at a given temperature and rpm than conventional oils. But again, I would not be concerned except as you note were it to come on when you are driving and at rpms above 1,000.
Let me know if this answer doesn't apply to your situation.
Roland
---------- FOLLOW-UP ----------
QUESTION: I'm sorry Roland, the light comes on while driving...on the highway and around town. I think she's (my wife drives this vehicle), been using a synthetic oil for high-milage vehicles from the local Jiffy Lube ...if that has any bearing.
AnswerHi John,
I trust that the light comes on at relatively low rpm if you are moving, and not while you are cruising down the highway at 55 mph+.
If that were not the case, and you have a new sensor, then I would nonetheless be inclined to check the wiring from the sensor to make sure that you don't have an electrical problem that causes the light to come on. Do you have an oil pressure gauge on the dash, and if so what is it showing? The type of electrical problem that would falsely cause the light is if the wire from the sensor had a break in its insulation so the conductor would touch a metal surface, which is what is required for it to come 'on'.
I would suggest barring a false alarm, that you follow my suggestion about not using synthetic or high mileage oil (which is more intended to reduce leaks from worn oil seals), rather to use conventional oil and use the next higher viscosity grade. This will likely cause the pressure to increase sufficiently as to circumvent the warning light. When you had the sensor changed, did they happen to measure the psi at idle and at 3,000 rpm? For most engines you want that to be 5 psi and 30 psi at idle and at 3,000 rpm respectively.
Roland
