I too have a 175 hydro and it has been a great little lawn tractor. I mow about an acre with mine. The Fram equivalent oil filter is PH4967, about $4-5 at Walmart. NAPA should be able to cross the Fram number.
Or Purolator L14476.Look for a NAPA 1394.
Dieselfuelonly -
Great looking machine you have there. I have had a 185 for almost 20 years with no mechanical problems. Here is what the manual says regarding your questions:
First, the lights. On the left is oil pressure and on the right is battery.
Don't know about the NAPA filter, have always run the JD filters.
For oils it says "John Deere PLUS-4" recommended. Other oils may be used if they meet API Service Classification SF or SE. Goes on to say, 5W30 between -31 to +50 degrees, SAE 10W -4 to +50, SAE 10W30 -4 to +86, 10W40 -4 to +104, SAE 30 +32 to +122.
Transmission uses SAE 30 engine oil with API Classification of SE, CC or CD. Also, it says "IMPORTANT: To preven contamination in hydraulic system, DO NOT drain or change hydrostatic transmission fluid."
To check the tranny oil on the 175, it says to park on level surface and remove the tranny oil cap (under the seat). The level should be just above the screen in the bottom of the reservoir, or, 5.5 inches from the top of the reservoir fill tube. If oil level is low, add just enough to bring the oil level to just above the screen.
Differential should be checked to the level of the plug on the back of the diff. It uses SAE 90 gear oil.
I have had one electrical issue so far related to the brake pedal/starter interlock switch. This keeps the tractor from starting unless the brake pedal is pushed down. If it is bad, the tractor will do nothing when you turn the key (except the dash lights will come on). The interlock is located behind the plastic valence panel below the dash, on the left hand side. On mine, the problem was just corrosion on the spade terminals. I cleaned them up and it was working fine again.
Best of luck with your tractor and I wish you many happy hours of mowing.
Oh, by the way, don't forget to grease the mower spindles.
Runner