Hello everyone!

I have a mk1 Octavia 1.6 petrol, 102 hp, BFQ engine. I'd like to ask the following:

At what temperature is the thermostat supposed to open? I had mine replaced when I purchased the car and from what I can tell, my current thermostat opens at 105 C. When I run a diagnostic tool I can see that the coolant temperature is 109-110 C. These temps seem pretty high to me. The gauge on the dashboard stays at 90 the whole time and doesn't move at all.

I haven't had any real issues (been driving it for 1 year now), except that sometimes during the summer the fan would kick in about 3-4 minutes after I shut the engine off and it can't stop until I start the engine just so that the coolant will move a bit. While the engine is running the fan will kick in and turn off as on any car, mostly when I'm stuck in traffic, from which I can tell the cooling system is working properly. I started wondering about the thermostat when I saw 2 types of thermostats in autodoc - 1 opens at 105, the other at 87.

So basically, is the thermostat supposed to open at 105 C, and is 110 C the normal operating temperature?

Thanks,

Yasho

On 24/10/2025 at 15:05, Yasho said:

Hello everyone!

I have a mk1 Octavia 1.6 petrol, 102 hp, BFQ engine. I'd like to ask the following:

At what temperature is the thermostat supposed to open? I had mine replaced when I purchased the car and from what I can tell, my current thermostat opens at 105 C. When I run a diagnostic tool I can see that the coolant temperature is 109-110 C. These temps seem pretty high to me. The gauge on the dashboard stays at 90 the whole time and doesn't move at all.

I haven't had any real issues (been driving it for 1 year now), except that sometimes during the summer the fan would kick in about 3-4 minutes after I shut the engine off and it can't stop until I start the engine just so that the coolant will move a bit. While the engine is running the fan will kick in and turn off as on any car, mostly when I'm stuck in traffic, from which I can tell the cooling system is working properly. I started wondering about the thermostat when I saw 2 types of thermostats in autodoc - 1 opens at 105, the other at 87.

So basically, is the thermostat supposed to open at 105 C, and is 110 C the normal operating temperature?

Thanks,

Yasho

i have the same overly complex engine 105-110 is perfectly normal for that engine it uses map controled thermostat. Switch to full heating or go full trottle of u want it to be 95-100. As for the fans kicking in randomly try changing the sensors one is in the middle of plastic housing on the right side of the block and the other one is on the lower right side of the radiator. 87c thermostat dosnt fit from what i figured out thats for avu engine code.

Also dont use regular watter for coolant, heater core is prone to cloging and u need to take out the whole dash to change it.

If ur changing sparkplugs change the leads aswell so u dont have to take off/pay someone to take off the whole intake manifold 2x.

On 29/10/2025 at 00:28, LeadDiplomat said:

i have the same overly complex engine 105-110 is perfectly normal for that engine it uses map controled thermostat. Switch to full heating or go full trottle of u want it to be 95-100. As for the fans kicking in randomly try changing the sensors one is in the middle of plastic housing on the right side of the block and the other one is on the lower right side of the radiator. 87c thermostat dosnt fit from what i figured out thats for avu engine code.

Also dont use regular watter for coolant, heater core is prone to cloging and u need to take out the whole dash to change it.

If ur changing sparkplugs change the leads aswell so u dont have to take off/pay someone to take off the whole intake manifold 2x.

Thanks :)

Anti freeze / Summer Coolant does not just contain anti corrosion ingredients, it alters the Boiling point of H20 and the freezing point.

So use the correct strength of Coolant / Antifreeze.