Guide: Peugeot 306 GTI-6 Thermostat Change

In this post we will show you, step by step, how to change the thermostat in your Peugeot 306 GTI-6 and bleed the cooling system.

Incorrect running temperature can cause poor fuel economy and engine damage. Probably the most common and cheapest fix for this is to replace the thermostat which as we explained in this post, controls the flow of coolant to the radiator. A broken thermostat on your Peugeot 306 can cause both hot and cold running.

The parts for this job are very cheap, I recently bought a thermostat and seal from ECP for under £10 and don't forget to get some more coolant as well.

The Peugeot 306 GTI-6 uses an 83 degree C thermostat, before starting to take anything apart it is worth checking the new thermostat you have is correct - the opening temperature of the thermostat should be engraved into the metal body somewhere.

Unless you like 90 degree coolant on your hands make sure the car is cool before starting.

Follow the top hose from the radiator towards the engine block and you will come to the thermostat housing. To access the thermostat you will need to remove the black plastic right-angled hose thing which is held in place by 3 x 10mm bolts (B, C and D (round the back)). You won't be able to remove B without first removing the coolant hose. Pull the C-Clip off (A) and then the hose will just pull out.

 As you can see B and C are standard bolts but D is like the the un-labelled rusty nut with the thread sticking out and will require a deep socket or ring spanner.

Before doing this you might want to put a plastic bag or something over the loom and connectors which are below.

At this point I moved the throttle cable and zip tied the hose out of the way for easier access.

Once the 3 bolts are removed give the plastic housing a little tug and it will come off to reveal the thermostat which simply pulls out. When you remove this quite a bit of coolant will come out.

"Fitting is the reverse of removal"

Now it's time to refill the lost coolant and bleed the system of air.

Peugeot 306 Bleeding Coolant System Guide

First off make an extended header tank out of an old lemonade or squash bottle, this will help you to use good old fashioned gravity to do the hard work for you. Wrap the end in a cloth or tape so it makes a seal around the radiator filling cap.

Fill this header tank with coolant and open the brass bleed screw (E) to enable the trapped air to escape, now start the car up and let it get up to temperature so the thermostat opens up. As the engine is running you should notice the coolant in your header tank start to drop, carry on topping this up.

Periodically hold the revs at ~3,000rpm for about 15 seconds, you should find that doing this will cause bubbles in your header tank and it will also swallow lots of the coolant.

Once the car is up to temperature turn the fans to hot and full power, if you have done a good job so far the air should be nice and hot. If not there is still trapped air in the system. Check the thermostat bleed point again and if there is coolant running from it then gently nip it up.

If you are reading this post you might also be interested in our radiator fitting guide for the Peugeot 306 GTi.

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Answered: Peugeot 306 Running Cold

Q: My Peugeot 306 GTi-6 seems to be running cold, the water temperature doesn't seem to rise above 72 degrees, even when i've been driving for a good amount of time. Is something wrong?

A: Yes, but luckily it sounds like a cheap and easy fix. The water temperature is controlled by the thermostat which regulates how much coolant is allowed through to the radiator. When the engine is cold the thermostat should be completely closed and so water does not circulate around the radiator. As the car reaches operating temperature it will begin to open and as it starts to overheat it will fully open.

By opening and closing the thermostat should regulate the temperature and maintain correct coolant operating temperature.

If your car is running cold, the thermostat is stuck in the wide open position which means water is constantly running around the radiator which prevents it from getting up to the correct running temperature. If it is not stuck then the seal may be torn which will also allow water to pass through all of the time.

If this sounds like your problem then check out our easy to follow step-by-step guide on how to change the thermostat in your Peugeot 306 GTi-6 (all years).

Check out this article on "HowStuffWorks" which goes into further detail about how car cooling systems work.

One note is that this diagnosis assumes the temperature sender to your dash is working correctly, this temperature sender can be tested using a multimeter.