I believe this is the Owner's Manual for this vehicle:
Apache RTR 160 Manual
On page 32 is calls for "SAE 10W-30 API-SL JASO MA2" specification oil. I did not find 20W-50 listed as an acceptable alternative.
So NO, you should not use 20W-50 in this bike.
Disclaimer: I've never tried this myself.
Is it close to being time to change the oil filter? Depending on its position, you should be able to spin it off without losing much more than the oil contained within (which should be ~0.5-0.75 litre). Replace it with a new (empty) one and run the engine for a minute or two then recheck the oil level.
That's the crankcase vent hose. It provides crankcase ventilation by relieving pressure and scavenging fumes from the crankcase then recirculating them through the air filter. A 5/8" or 3/4" (depending on the ID of the original) heater hose should do in a pinch for a replacement but an OEM product seems readily available.
The images above are for a 03-...
There is no need to change it immediately IMO.
The main difference between B3 and B4 is that the TBN number is higher for B4, which gives more capability of neutralizing acidic contaminants in long-oil-life or high-performance situations.
Whether you need to make the next oil change sooner (and how much sooner) is hard to say. It depends a lot on the ...
You might want to read the article here:
But the key point on too high a TBN number is:
So should we all use a High TBN oil? There are advantages, but there
are also disadvantages of using a High based TBN oil (known as High
Overbased Sulphonates) it's not just because the price is much higher.
High TBN oils can produce high ash ...
There's a very straightforward answer to this question: Water has a much, much higher capability to transfer heat than oil.
Even if you were able to overcome the safety and design issues brought up in other answers, you'd still have to overcome the fact that water has a huge performance advantage at transferring heat compared to other common fluids (...
Water has the nice property that it boils at a fairly low temperature, so the vapour pressure rises quickly with temperature and it is easy to design fail-safe over-pressure protection (a simple spring-loaded filling cap). Also, water is not flammable.
Oil does not have those nice properties, and a cooling system failure which released high pressure, high ...
Oil has been used as a heat transfer fluid in many applications (especially high temperature ones) but in engines the higher viscosity will require more pumping power, which means more driving power from the belt and so more power from the engine.
Then there are the issues of cost... and, of course, issues with replacing fluid if you are far from an auto ...