Header Tank level

[shrig1969]

Evening all

I have recently changed my coolant and am finding the header tank level is not rising or dropping .
I had hoped it was the expansion cap so replaced that with a new one from brickwerks but still the level remains the same.
I can confirm there is no blockage in the hose from expansion to header.
I've had one long trip in her since and plenty of short journeys.
Everything else seems normal, Temp gauge is sitting where it was prior to the change, radiator is hot to touch at the top and all air has been bled.
Prior to the above there was a noticable rise and fall of the levels in the header tank.

Is there anything else I can try?
Wouldn't normally bother me but now its in my head I can't stop looking behind the flap. 
 

[cobblers]

Header tank should stay full, it's the expansion tank that goes up and down. Sounds like that's what you mean, though,

If the header tank is full, there's probably a small pocket of air somewhere limiting the pressure rise. It'll burp itself out eventually. Or it might not. 
If you want to be super happy everything is OK, you can get a coolant vacuum fill and pressure tester off amazon for about 65 quid, then you can stress test it by pumping it up to 17psi and see that it holds pressure over time and look for any leaks etc.
 

[shrig1969]

Thank you for the reassuring reply.
Was hoping that it was potentially that.
I will keep an eye on it and bleed all the high points next time I return from a decent run.

[cobblers]

Yeah, I wouldn't worry about it. Keep an eye on the header tank level and top it up if / when the air bubble works it's way round and the level drops.

The reality is that 95% of the T25s on the road are running around with slight leaks causing the header tank to always end up half full of air, to no ill effect

[icosahedron]

It all depends on how you choose to run your cooling system. If you run it as an expansion tank, the level must be above the "min" mark on the front of the tank. As the coolant temperature rises, it expands, which causes the level to rise in the tank. This in turn compresses the trapped air inside the tank. The compressed air acts like a "spring," which keeps the cooling system under pressure. It is called an expansion tank as it accommodates the increased volume of expanded coolant. If you have a minor coolant leak, coolant is replenished from the "overflow" or replenish tank as the trapped air pressure equalises with the outside air pressure when it cools. The level in the tank will be lower due to the leak, and the trapped air pressure will therefore be lower than the outside pressure, which will force in coolant from the replenish tank via the one-way valve. The amount of trapped air controls pressurisation, more air equals less pressure; therefore, it is important to keep the level above the "min" mark.

In "header" tank mode there is no trapped air in the system. Unlike air, a liquid can't be compressed and act as a "spring." The cooling system is thus inflated by the expanded volume of coolant, which over-pressurises it. This turns your vehicle into a "wasser leaker." If you do manage to contain all the leaks, the "header" tank eventually cracks, being the weakest link, and has to be replaced. When I was using mine as a daily in "header" tank mode, I had to replace the tank annually. I haven't done this since figuring out the problem many years ago.

I've found that the blue tank cap rapidly turns my expansion tank into a "header" tank. Under pressure, the trapped air in the tank leaks through the one-way valve and is replaced by coolant. I didn't have this problem with the original black cap.

From past experience on this forum, the members with high post counts will unite behind "header" tank mode. This is fine by me, but it doesn't change the fact that when new, my van was fitted with an expansion tank and replacing the black cap with a blue one turned it into a "header" tank with its problems.

[maxstu]

Aside from the answers above. Did you rev engine to the moon on your final fill?
Cold start with blue cap removed. Get a little warmth in the engine. About 30 seconds. Then watch the coolant in tank drop as a pal revs engine past about 3k and keeps constants revs going. Add coolant to brim. Replace cap. Let it idle.
If you drop revs while cap is off, coolant with spill over.

[shrig1969]

 It all depends on how you choose to run your cooling system. If you run it as an expansion tank, the level must be above the "min" mark on the front of the tank. As the coolant temperature rises, it expands, which causes the level to rise in the tank. This in turn compresses the trapped air inside the tank. The compressed air acts like a "spring," which keeps the cooling system under pressure. It is called an expansion tank as it accommodates the increased volume of expanded coolant. If you have a minor coolant leak, coolant is replenished from the "overflow" or replenish tank as the trapped air pressure equalises with the outside air pressure when it cools. The level in the tank will be lower due to the leak, and the trapped air pressure will therefore be lower than the outside pressure, which will force in coolant from the replenish tank via the one-way valve. The amount of trapped air controls pressurisation, more air equals less pressure; therefore, it is important to keep the level above the "min" mark.

In "header" tank mode there is no trapped air in the system. Unlike air, a liquid can't be compressed and act as a "spring." The cooling system is thus inflated by the expanded volume of coolant, which over-pressurises it. This turns your vehicle into a "wasser leaker." If you do manage to contain all the leaks, the "header" tank eventually cracks, being the weakest link, and has to be replaced. When I was using mine as a daily in "header" tank mode, I had to replace the tank annually. I haven't done this since figuring out the problem many years ago.

I've found that the blue tank cap rapidly turns my expansion tank into a "header" tank. Under pressure, the trapped air in the tank leaks through the one-way valve and is replaced by coolant. I didn't have this problem with the original black cap.

From past experience on this forum, the members with high post counts will unite behind "header" tank mode. This is fine by me, but it doesn't change the fact that when new, my van was fitted with an expansion tank and replacing the black cap with a blue one turned it into a "header" tank with its problems.

 

[shrig1969]

Aside from the answers above. Did you rev engine to the moon on your final fill?
Cold start with blue cap removed. Get a little warmth in the engine. About 30 seconds. Then watch the coolant in tank drop as a pal revs engine past about 3k and keeps constants revs going. Add coolant to brim. Replace cap. Let it idle.
If you drop revs while cap is off, coolant with spill over.

Only revved as much as I dare, on a Sunday, as all the neighbours were sunning in the garden.
Will monitor levels as I go... 
 

[maxstu]

Aside from the answers above. Did you rev engine to the moon on your final fill?
Cold start with blue cap removed. Get a little warmth in the engine. About 30 seconds. Then watch the coolant in tank drop as a pal revs engine past about 3k and keeps constants revs going. Add coolant to brim. Replace cap. Let it idle.
If you drop revs while cap is off, coolant with spill over.

Only revved as much as I dare, on a Sunday, as all the neighbours were sunning in the garden.
Will monitor levels as I go... 
 

It's the only way it works. Otherwise you will be constantly topping up