Land Rover Repair: Land Rover Freelander 2002 - low oil pressure sign at idle, land rover freelander, 2002 land rover freelander

Question
2002 Land Rover Freelander with ~93K miles.  Recently I saw its low pressure light flicker at idle.  It comes on after the car has driven 40-50 miles (so the engine gets quite warmed up).  A similar problem happened around 88K miles and I got an oil change at Jiffy and the problem went away.  The guy at Jiffy also mentioned some gunk in the engine and cleaned the gunk by passing some gunk cleaner.

I have been using Mobil 1 0w-40 (synthetic).  Should I be using a more viscous oil now?  Can gunk cause low oil pressure?

The recommended service interval in the car is 12k miles and I have followed it very religiously.  I follow my car's service manual on all recommended services.  

Not sure whether this is related or not, but there is a slight coolant loss also in the engine.  I have to top off the coolant every 300 miles.  

Answer
If the car loses oil pressure after 50 miles that's a sign of a serious internal engine problem.  The coolant loss may signal a leak or something more.  I suggest you have it checked out, and see if the oil pressur eproblem is real, or if you have a problem with the gauge/light instead