You indicated you want no halt the first night — plan is to depart Pune at 18:00 and drive overnight directly to Kerala (suggested entry Ernakulam / Kochi) so you arrive early next day. Please confirm you are OK with 1 or 2 drivers rotating for safety during long night driving.
Before I produce the minute-by-minute day-by-day plan with bookings, I need you to confirm two things: 1) Must you be back in Pune by 2025-08-20 at 23:00 exactly, or is it acceptable to start the return from Kerala on the night of 20 Aug and arrive Pune early morning on 21 Aug? 2) Preferred Kerala entry city: Ernakulam (Kochi), Kozhikode (Calicut) or Thiruvananthapuram (Trivandrum)? Also confirm number of drivers for overnight legs (recommended 2).
I will use the following assumptions unless you tell me otherwise: diesel price = INR 100/L (approx.), car fuel economy = 21 km/L (you provided), no stays en route on first and last nights (you want nonstop overnight drives), and group of 4 people with standard mid-range hotels/houseboat. I will plan the detailed sightseeing hours once you confirm the two clarifications above.
Typical distances and drive-times between major points used in the planned route (approximate, by road): Pune → Ernakulam (Kochi): 1,180 km — ~16–20h. Ernakulam → Munnar: 130–150 km — ~4–5h. Munnar → Thekkady (Periyar): 90–100 km — ~3h. Thekkady → Alleppey: 140 km — ~3.5–4.5h. Alleppey → Kovalam (Trivandrum): 150–170 km — ~4–5h. Kovalam → Pune (return route via NH48/NH66 approximate): 1,180–1,300 km — ~18–22h depending on exact exit point.
If you follow the suggested loop (Pune → Kochi → Munnar → Thekkady → Alleppey → Kovalam → Pune) approximate total driving distance ~3,000–3,300 km (including transfers between sights). At 21 km/L that is ~143–157 L diesel. At INR 100/L fuel only ≈ INR 14,300–15,700. Add tolls and parking for the whole trip estimated ≈ INR 6,000–9,000 depending on exact roads. These are ballpark numbers — I will produce leg-by-leg fuel math when you confirm the return-time constraint.