Hello

I have 1998 Grand Cherokee 5.9l it has 280k km or 170k miles.

1. It takes only 4liters of oil so about 4 quarts to the FULL mark from the moment I bought It, It should have 4.7L The dipstick has the right numbers so it is original, I am thinking maybe someone changed the oil pan before ?? Will it hurt riding like that, I change oil every 3000miles 5000km.

2. Is it a good idea to change to 5w40 for this engine (5.9 Magnum) should be 10w30 but in Europe 10w30 is a very rare oil so I use 5w30 ? it takes a little oil about 1/2l for 5000km. I am mostly thinking about engine protection.

3. My charging voltage is constantly 13.6v to 14v all the time mostly 13.8v few times I seen it go to 14.2v, under FULL load drops 0.1-0.2v ( when everything is ON) I checked voltage losses on cables its 0.2Volts so cables are fine so Is alternator, Battery is fine too. Do this cars have normaly this voltage or is something wrong ??

4. I have a problem with battery drainage when car is shut off, I installed a Power off switch to go around this problem so my battery wont go dry in a week. Checking OBD only thing that has an error is "park lamp relay open" but parking lamps work fine. I noticed the battery gets drained from time to time its not a constant drain, car sits it has 12.6v and suddenly it drops to 11.7 cause something is draining it.

5. Can I use 75w-140 Gear oil only ??? I used 80w90 but it had a whine in the back, I tried 75w90 it was even worse, so I moved to 75-140 and it is better, I am currentlly rebuilding new set of differentials with new parts, But would like to hear an opinion can I use 75w-140 from the start ???

Actually car rides and goes it has some small quirks and I installed LPG in it so it is quite a decent ride.