As you may know, there was a trip computer (TC-6 and TC-6P) made specifically for Skoda Felicia 1.3 and 1.6. According to user manual, the fuel consumption of a Felicia 1.3 warmed-up engine at idle is 0.8 liter/hour.

 

What do you think of that value? To me that looks way too low. Do you have any measured data?

My Czech friend Lugosy sent me the following results displayed by his onboard computer at idle:

I hope this helps you to understand why a stuck open thermostat (or no thermostat) increases the fuel consumption by up to 100%.

 

1) Engine cold:

• during summer: 3,5 - 4 liters / hour then going slowly down
• during winter: 4 - 6 liters / hour then going slowly down

2) Engine warmed up: 0.7 - 0.9 liters / hour

 

3) Waiting at traffic light:

• slow traffic: 1,1 to 1,8 liters / hour then going slowly down
• quick traffic: 0.7 - 0.9 liters / hour