With the Sirion 1.5sx at 5 years old I figured it was time to replace the coolant. The Sirion has also been taking slightly longer to warm up lately, so I have been wanting to swap out the thermostat so it seemed the time was right to just do it. Whilst I was at it I decided to change the Materia coolant too, although only 4 years old. Both engines are the same – 3SZ-VE.

To drain I set the heater to hot and opened the radiator drain tap. I whipped the thermostat out as well to help the drain-down. I stuck a hosepipe in the bottom of the radiator and back-flushed it, and I also pulled off a heater hose and back-flushed that and what came out was 100% clean – no debris or gunge. I have worked on cars for many years and I have never seen such clean systems.

The thermostats were visually like new and inside the bit of engine block I could see in the housing it was also like it had come from the factory. The radiator was also super clean.

Once ready to re-fill I nipped up the radiator drain tap, refitted the thermostat, and heater hose. Then it was just a case of pouring the new mixture in the top of the radiator until overflow, emptying the surge tank and refilling that with new coolant too. Next was running the engine until hot to self-bleed the system of air then fit the radiator cap and run some more, switch off and let cool, and then check and replenish all levels as required.

There are no bleed screws on these engines and just running them will drive all the air out. The heaters are pumping out gobs of hot air and there are no leaks so it all seems good. Refilling also took the requisite quantity of coolant, which is a good indicator the system is actually full. I am confident there is no air in the system.

The coolant used was Halfords pink pre-mix, which is an ethylene glycol, organic acid technology (OAT) mix – it is long-life (5 yrs) for modern engines with no copper coolant parts. I always use, and recommend, a pre-mix coolant because local water supplies can contain chemicals that are less than ideal when mixing up from a concentrate. The new thermostat was a Blue Print one stamped at 80 deg Celsius - same temperature rating as what came out.

I shall keep an eye on things for a week to make sure all is well. I will also be watching to see if the Sirion warm-up has improved.

So there we have it.

Phil