Thanks @toxicdevil and @arzaam.bhatti. Yes that's O2 sensor, haven't opened it yet. Just reading stuff about how to clean it.
@arzaam.bhatti yes you're right. One should not mess if car is running ok.
As my Pajero Mini is giving about 7kmpl and after service it seems to be a bit better, 8kmpl or maybe more.
My aim is to get at least 10kmpl, so trying the most easy accessible components serviced myself.
I have an ODB2 scan tool Chinese made, however it didn't detect my vehicle. Also tried on cultus and HiJet cargo. Maybe the scanner is bad, or these vehicles don't support ODB2. Online most sites say 1996+ models have ODB2.
For Pajero Mini 1995 model, I can't confirm online that this one supports standard ODB2 or proprietary protocol. I will try to find a shop where they can just scan and show me data directly.
Yes there's thermostat installed as you can see two sensors near radiator pipe. Idle RPM is about 850/900. I adjusted it with throttle setting screw it was about 600 when I got the car. The fan is not locked, as I can spin it when engine is off.
There's something with the temperature. I run this car at less than 4k RPM, change gear around 3.5k RPM. The temperature needle mostly stay at 1/4 of the range. When I get stuck in traffic it gets a bit higher but not to normal (just a bit lower than half) position, even with AC on. I think either temperature sensor is not good or car is cooler because it's high RPM engine and one should be going at 4k-5k RPM normally?