Coolant.

[Max_Headroom]

I noticed the other day there is an old school radiator cap (see picture below) in the engine bay next to it is a black filler cap which i assume is the header tank what i found strange is the header tank cap is not threaded it pops off like the screen wash filler cap so how does that work surely there must be pressure in the header tank but it would seem not.

I also fond it near impossible to see the level in the header tank i think there is the work level or something on the side of the tank but its very hard to see, has anyone else found this?

 

[APS]

Yes, that would be the header / expansion tank. An expansion tank is just an overflow to take the excess coolant as the engine warms up and the coolant expands. It does not hold any pressure. There will be a high and low mark on the expansion tank. The level should be above low when cold.

[stantheman1]

Read this for a better understanding.

https://innovationdiscoveries.space/how-do-you-know-if-your-vehicle-radiator-cap-is-bad/

[Max_Headroom]

3 hours ago, APS said:

There will be a high and low mark on the expansion tank. The level should be above low when cold.

Thanks,  that's the problem as looking from above its almost impossible to see where the level is i am wondering how members view it.

[APS]

41 minutes ago, Max_Headroom said:

Thanks,  that's the problem as looking from above its almost impossible to see where the level is i am wondering how members view it.

In don't know exactly how it is mounted on the Yaris, but generally on Toyota's the tank sits between the radiator and the engine. So, yes it can be a bit of a squeeze to see anything. The tank is often dirty and not clear, making it harder. What I'd normally do is pop the cap off the expansion tank and shine a strong light down the filler neck and rock the car gently. Then it's a little easier to spot the level. On a relatively new car like yours I'd be surprised if the level was anything but normal. 

[Max_Headroom]

14 minutes ago, APS said:

On a relatively new car like yours I'd be surprised if the level was anything by normal. 

I agree, i will give the torch trick a go and see if it helps. 

[forkingabout]

 We use the torch trick on the Toyota Tonero to check the expansion bottle level.

 

 

[Max_Headroom]

Thanks F i will try that.

[TonyHSD]

One thing to point, on cars with radiator cap coolant level should be checked and topped up directly into the radiator. When changing the coolant the old one from expansion tank should be sucked out with pump or large syringe, susytem drained and when filling up with new coolant the expansion tank should be filled separately to the max. On air bleed procedure the coolant from expansion tank will be sucked on opening of the thermostat at the required temperature and radiator fans activated. Then the tank should be topped up again. 
One cars without radiator cap all fills happens directly into the coolant reservoir. 👍

[Derek.w]

If for any reason you remove a radiator cap then take some liquid out of expansion bottle and drop it into the radiator.

If radiator is overfull no problem extra is pushed back into expansion tank.

If radiator has a air lock created when cap was removed then at some point it will boil dry blowing the head gasket but the expansion tank will fail to do its job because of the air lock.

[Max_Headroom]

8 hours ago, Derek.w said:

If radiator is overfull no problem extra is pushed back into expansion tank.

When I took the cap off the coolant was at the top (you couldn't have got more in) so I assume that counts as overfull. 

[TonyHSD]

55 minutes ago, Max_Headroom said:

When I took the cap off the coolant was at the top (you couldn't have got more in) so I assume that counts as overfull. 

Radiators can’t be overfilled. , they should be always full with coolant and no air. When open to check level make sure you do so on cold engine or wait 10 min after you had turned off the engine.  wearing gloves also recommended. Coolant it’s under pressure when hot and can blow onto you when you undo the cap. 

[Guest]

7 hours ago, Max_Headroom said:

When I took the cap off the coolant was at the top (you couldn't have got more in) so I assume that counts as overfull. 

That's full Max, as Tony writes.

However, Tony's "no air" applies to cooling systems with a separate non pressurised overflow/expansion tank.

Without an expansion tank the radiator should never be full to the top with coolant. Air space above the coolant will allow for expansion. If filled to the top, when the temperature and pressure increases, the cap seal will lift and coolant expelled through an overflow pipe open to atmosphere. 😎

Some systems have a separate tank which is pressurised with a pressure cap fitted. Same precautions as removing the cap from the radiator. That tank also allows for expansion.

It would appear Toyota have made further "improvements", over the years, on the visibilty of coolant expansion tank level!🙄

Note Blueprint "Made in England"😲 radiator cap Tony.👍

[Derek.w]

You cannot overfill a radiator if its up to the expansion tube fitting then it just pushes it back into the expansion tank.

Thats what you want no air blockage so expansion tank reading will work giving a correct reading.