The performance service light came on our 2004 Chrysler Pacifica..we got an oil change like 3 wks ago...not sure what this means..

When you say the "oil light," do you mean the light that says "Change oil" or are you seeing the red light that indicates low oil pressure?

If you're seeing that red light, that likely means you have low oil pressure and should stop driving immediately, until the problem is diagnosed and repaired.

It's also possible to see the oil pressure light on when there's no issue with oil pressure, if the oil pressure sender has failed or there's a connection problem.

If the oil light you're referring to is the "change oil" light, you will need to manually reset it for it to disappear. Here's how (from Chrysler):

1. Turn the ignition switch to the ON/RUN position (do not start the engine).
2. Fully depress the accelerator pedal, slowly, three times within 10 seconds.
3. Turn the ignition switch to the OFF/LOCK position.
NOTE: If the indicator message illuminates when you start the engine, the oil change indicator system did not reset. If necessary, repeat these steps.

Yes, the oil cooler is water cooled.

https://www.google.com/search?q=2004+Chrysler+Pacifica+oil+cooler

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an oil change is not a service so get it done properly

This is the pressure light I think. Have that looked into RIGHT AWAY before you burn out the bearings in the engine.

most likely not the sensor; change the oil and use an oil of greater viscosity. which engine? how many miles?

Change oil and reset

Change oil and reset

No need to worry. It means it is time for Oil change, filters, coolant change. The "message" is just a reminder that it is time to have a scheduled maintenance done. What needs to be done is determined by the vehicle mileage and is set out in your owners manual.

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that light tells you that it is time for an oil change. make sure that they reset the monitor

It is for an oil change mainly and any other service your maintenance manual suggests at the mileage interval. It needs to be reset after each oil change to be accurate.