GT'ing around in my VW Polo TSI | Update: SOLD! (2024)

Update:

My little Polo is inching closer to the 40,000 km landmark, and if it wasn’t for the lockdown, I would have easily breached the landmark before July.

The changes made to the car, specifically the downpipe and the divorced coolant circuit, have transformed it, and the driving experience it delivers is nearly flawless.

I say nearly, because fiddling with the coolant lines has resulted in a slight vibration that can be felt through the pedals. Diagnosing the problem has revealed that the coolant lines are now vibrating against certain components only when the car is stationary and idling, consequently causing the rattle. Personally, it does not bother me too much and I am relieved that it’s not a serious issue. Venkat has nonetheless promised to rectify it.

Venkat has also been exploring options that could, potentially, further improve upon the divorced coolant circuit mod. He had something of a eureka moment in June, and immediately swung into action.

The idea: Incorporate an additional radiator – in series - along with the existing one that services the charged-coolant line.

Adding an additional radiator in series with the exiting one would not only increase the surface area for improved cooling of the errmm.. coolant () flowing through them, it would also expand the capacity of the coolant for the charged air. The goal is to further reduce the IATs, if possible.

It was decided that a new radiator will be used, identical to the secondary radiator, to achieve this.

Venkat pulled a few strings and managed to source the secondary radiator over the counter, and after picking up the part, I headed straight to his workshop to get it fitted. The cost of the new radiator was around 13k.

Parallelly, Akshay from GT Tunerz sent across a Borla ProXS muffler as I was looking to address the exhaust note with an aftermarket end-can. I found the Borla muffler to be reasonable, and based on feedback from others, I as told that it’s designed to be on the quieter side.

I arrived at Blackworks nice and early, and Venkat immediately removed the front bumper and inspected all possible mounting points, brackets, room available for the additional radiator, etc. The plan was to initially mount the new radiator above the existing secondary-one, but space constraints forced him to explore other options. After carefully studying the bumper and the frame behind it, he concluded that the best option was to mount the new radiator in front of the old one, as the bumper had sufficient room to accommodate it.

We also realized that mounting the radiator did not require a lot of work as the unit is quite light to begin with and will not need heavy-duty mounting points or brackets. Even though the necessary brackets were prepared, we did not use them.

So, how was this executed? Here are the highlights:
1)The front bumper was removed, the area was inspected, and it was settled that the new radiator can be mounted in front of the existing one.
2)Venkat used rubber hoses, similar to the ones used for the coolant lines, to run the new radiator in series with the secondary one. Initially, we were looking at getting a custom U-shape silicone hose but finding one on short notice proved to be impossible. We found the rubber hoses lying around the workshop that did the job just as well.
3)Since the new radiator was is super light, we did away with the heavy-duty brackets for mounting and utilized the frame behind the front bumper (that houses the primary and secondary radiators) to mount the additional radiator onto it.

Installing the additional radiator did not take more than a couple of hours.

First, the front bumper was removed, and the location for the new radiator was finalized:

Once positioned and marked, the plastic frame that houses the primary and secondary radiator was trimmed to accommodate the additional plumbing.

The other end of the radiator with the dummy plastic housing also required a little trimming to accommodate it in the space available behind the front bumper.

The bumper too required a little trimming to ensure that the new radiator does not foul with the bumper (notice the small bits of bumper on the floor)

The stock radiator hoses:

The re-routed plumbing now consists of one additional U-shaped rubber hose that connects the exit point of the original radiator to the entry point into the new radiator.

Photograph of the new radiator mounted in series with the secondary radiator and positioned in front of the secondary radiator:

After the installation, we took the car for a spin, hooked up VCDS to the OBD and noticed something extremely unusual after about 15 minutes into the drive: The IATS had shot up to 85 degrees! We pulled over to the side of the road immediately, inspected the plumbing (which appeared to be fine) opened the secondary reservoir and noticed that the coolant level had not dropped at all and in fact, the coolant was cold – a clear indication that the coolant is not doing its job of absorbing heat from the charged air.

Unfortunately, we had wrapped up at the workshop as it had gotten late, and I decided to drive home gingerly to avoid causing any damage. The plan was to drive again to the workshop in two days to diagnose the issue.

Two days later, upon a detailed inspection at the workshop, we realized that the coolant from the secondary reservoir is now being circulated through the lines – something that was not happening after the install two days earlier. We attributed this to an air-bubble somewhere in the circuit that caused the circuit to be blocked. Perhaps the drive back home that night had shaken the circuit a little causing the circuit to burp the air out and allowing the coolant to finally circulate through the lines. After the drive back home, I also noticed that the coolant level in the secondary reservoir had dropped quite a bit and I topped it up with water – about 700 ml to be precise.

The results:

On the day when I had gone back to Blackworks to diagnose the issue, Venkat hooked up the VCDS to the OBD and a few hard runs revealed that the IATs has dropped by a few degrees to around 40 degrees. WOT runs resulted in a temperature spike to around 50 degrees. At first it seemed like the slight drop in IAT was marginal and that there was no real benefit of the additional radiator, but Venkat then noticed that immediately after the WOT run, the IAT which had creeped up to 50 would now fall to the early 40s in a matter of 3 seconds. Before the installation of the additional radiator, any spike in IATs would take at least 30 seconds to about a minute to fall back to acceptable levels.

So, although this modification has not resulted in a huge drop in IATs, it has resulted in:
a.Recovery rate of IATs after WOT runs has improved drastically. In essence, the IATs now take just a few seconds to recover after wide-open-throttle runs instead of taking 30 seconds to recover. This effectively ensures that the engine can now deal with sustained flogging without having any impact on performance at all.
b.The divorced circuit and secondary reservoir can now hold a much larger volume of coolant-water mixture since the new radiator has expanded the volume of the circuit.

In the real world, the car now pulls quite strongly in the mid-range and it feels like some additional horses have been unleashed. In fact, during one particular pull on an empty stretch in the city, I was surprised by just how incredibly punchy the engine felt in the midrange that I cannot wait for a revised Quantum map to exploit the potential unlocked by Blackworks and the revised coolant setup. The timing of this modification, with the impending monsoon season, couldn't have been better. Now that the IATs are in check and the new radiator has been installed, and with Bangalore ambient temps hovering in the mid-20s, the car feels like it's running on steroids!

A note on the Borla ProXS muffler:

Venkat swapped the stock muffler for the Borla unit, and I have to say, it’s not as impressive as I thought it would be. There is just bass now, a lot of it in fact. There is no tone or note as such. Delving into the details made me realise that the ProXS muffler may perhaps be a tad too large for the small-capacity 1.2 TSI, which is the reason for the only-bass-no-pitch exhaust note. Deleting the resonator further compounded the issue as it not only got a whole lot louder, but the drone at 3k RPM was more than apparent and intrusive. It was an absolute pain in the city, and I’m sure I would lose my mind on the open road and highway drives.

The search for a suitable muffler and a nice exhaust note continues, unfortunately.

Stay tuned for more updates.