[asit.kulkarni93]

With the new radiator, Did you replace the radiator cap too?

You will have to diagnose this systematically. I would first suggest you check the electricals like the temperature sensor and fan motors. Then you can put in a new thermostat considering the car has done 186k kms or just eliminate the current thermostat and direct the cooling system to check if the thermostat is the actual culprit. Finally you can have a look at the water pump and it's pulley. If all these things don't yeild any results then you will have open up the engine.

[OpenRoads]

This forum is pretty much the gold standard for troubleshooting.

Full disclosure: I have very limited knowledge. However I faced similar issue with i10 and found the radiator fan motor to be the issue.

The second one might be the water pump motor which might not be performing to its fullest efficiency. In this case the bearings are the root cause. You might need to replace it which can cost ~ 4-5K.

[Kaumad]

The old girl is back home after spending 2 months in the workshop!!
Unfortunately, as luck would have it, the worst possible scenario and my gut feel came true.

Originally Posted by Kaumad

My gut feel and hypothesis
• Cause 1 – there is a physical blockage / restriction in the engine block water jacket, which is causing the ‘discontinuous’ flow. This is my top concern as I really don’t want to dismantle the block jacket to diagnose the restriction.

Raghav from IgNite has been looking after my vehicle for the past decade and more and 2 months ago, we both decided it was time to see what was happening inside. The whole engine was dismantled - lo and behold, the amount of gunk that was accumulated over 16 years was astonishing!!

The block was separated and subject to an alkaline bath and subsequent cleaning of the jacket. We also discovered that the block and head had warped every so slightly and a proper seal was not being achieved. Off they went to a reputed machinist for a surface skim.
After a couple rounds of assembling, all leaks were arrested and finally the engine was running as it should.

In the process, got a lot of things changed as part of maintenance - new pistons, rings, timing chain & kit, clutch, water pump and all small bits with the engine.
The engine drives well now - did a drive to Mahabalipuram over the weekend and there were no signs of overheating whatsoever, even with some bits of spirited bursts. I am hoping this will take me through a couple more years with ease, without having to worry about what will fail with the engine.

Attaching a few pictures and videos for reference.