Coolant goes back up when cap removed

[Aaron2410]

23 minutes ago, Martin-Fiesta-MK6-1.4 said:

Correct antifreeze mixture? off the shelf antifreeze is pre mixed isnt it? https://www.eurocarparts.com/p/triple-qx-red-ready-mixed-antifreeze-coolant-5ltr-523770511

Yeah he used pre mixed off the shelf blue, I’ve checked it again this morning and it seems to be now between the min and max level which I’m happy with, going to let it cool and check again later

[TomsFocus]

1 hour ago, Martin-Fiesta-MK6-1.4 said:

Is running the engine with the coolant cap off not common practice to get rid of air bubbles after a coolant change mate? need to do ine and most sources say that its fine?

It used to be, but with cooling systems getting more intricate nowadays and heater hoses sitting at a similar height to reservoirs, it's more difficult to self-bleed.

Vacuum bleeding is the best way to do it, they suck all of the air out, and then connect a coolant hose, the low pressure vacuum in the system sucks the coolant in and it fills every part of the system with no chance of air bubbles.

Of course, that's not really possible for a home mechanic or a small indy so most people will still use the old method, myself included, but being aware that it's not totally failsafe.

[fleamoo]

5 hours ago, TomsFocus said:

So much confusion over a simple system!  I take it none of you are plumbers or heating engineers?  It works exactly the same way as your hot water tank or central heating radiators at home.  

It's simple physics:

1. Hot water expands

2. Fluids can't be compressed, but gasses can.

 

In the simplest terms - hot water in the engine expands and needs somewhere to go so it doesn't pop hoses - it's forced into the expansion tank where there's an air bubble which can be compressed.  The level in the tank rises slightly.  It's that simple.  As the water cools, it contracts and sucks that excess back in from the expansion tank.  The level drops back to original line.

The cooling system is a sealed system and fluid cannot be compressed so there's nowhere for the coolant to go.  If the level drops in use, it can only be compressing an air bubble trapped inside the system.

 

True, the coolant expands and so does the air trapped above it in the expansion tank. The combined effect is to very slightly inflate all of the rubber hoses which results in overall drop of coolant level as seen in the expansion tank. Remember the whole system is under pressure ultimately limited by the pressure cap valve. 

[Eng_Ahmad1986]

what is normal is the coolant rising as you open the cap , the decrease in pressure will make the coolant expand and rise in level , although this is dangerous for both you and the engine, as for the engine, the hot coolant now is not pressurized , this will allow the coolant to boil inside the system, a boiling coolant is a bubbles forming coolant, bubbles would create air pockets inside the engine, those air pockets would create hot spots ( as air is not good at heat transfer ) resulting in unnecessary engine overheating, never do this again 🙂 

now lets come to what is not normal , which is the coolant being below the min level when hot ( while the cap is still on ) , normally when the engine is cold the level should never be below minimum, it should be somewhere between minimum and maximum, as the engine warms up the coolant rises a little bit to be at max or above max by little, if this is not the case there are only two aspects, either there are already air pockets inside the system due to bad draining procedure performed during thermostat replacement, or a faulty coolant cap that doesn't allow excess pressure to escape to get the system in equilibrium state.

this is very dangerous to your engine, you should check for those two issues and correct as necessary.

if its ecoboost then its worse, ecoboosts are known to be not tolerating a slight overheating issue , take care 🙂 

[Aaron2410]

14 hours ago, Eng_Ahmad1986 said:

what is normal is the coolant rising as you open the cap , the decrease in pressure will make the coolant expand and rise in level , although this is dangerous for both you and the engine, as for the engine, the hot coolant now is not pressurized , this will allow the coolant to boil inside the system, a boiling coolant is a bubbles forming coolant, bubbles would create air pockets inside the engine, those air pockets would create hot spots ( as air is not good at heat transfer ) resulting in unnecessary engine overheating, never do this again 🙂 

now lets come to what is not normal , which is the coolant being below the min level when hot ( while the cap is still on ) , normally when the engine is cold the level should never be below minimum, it should be somewhere between minimum and maximum, as the engine warms up the coolant rises a little bit to be at max or above max by little, if this is not the case there are only two aspects, either there are already air pockets inside the system due to bad draining procedure performed during thermostat replacement, or a faulty coolant cap that doesn't allow excess pressure to escape to get the system in equilibrium state.

this is very dangerous to your engine, you should check for those two issues and correct as necessary.

if its ecoboost then its worse, ecoboosts are known to be not tolerating a slight overheating issue , take care 🙂 

Having checked the coolant over the last couple days it seems to have sorted itself out, I haven’t removed the cap after driving since instructed and definitely won’t now because of what U have said, only when the engine is cooled down I have removed the cap. Hopefully it has been rectified thank you for your instructive description

[Rat Park Refugee]

I have a leak in mine, or something is wrong with it.  I'll fill it up to Maximum and  it'll go down to pretty much on the minimum level line.  I can't remember which temperature though, I know it was just on the minimum line when the car was cold. I also have a fault code p1025 (the coolant temperature did not reach the correct level) error. I figured either the thermostat is faulty or the housing is leaking but I haven't actually checked it for evidence of a leak yet.

I wonder if it's worth doing the air bleed procedure (running it for 20 mins with the cap off and refilling it).   2 years ago I bought a new expansion tank cap, and a month later the p1025 went away and the EML went out.  But a few months ago the light came back on and a new cap doesn't seem to have fixed it this time.   

[st line x 140 driver]

2 minutes ago, Rat Park Refugee said:

I have a leak in mine, or something is wrong with it.  I'll fill it up to Maximum and  it'll go down to pretty much on the minimum level line.  I can't remember which temperature though, I know it was just on the minimum line when the car was cold. I also have a fault code p1025 (the coolant temperature did not reach the correct level) error. I figured either the thermostat is faulty or the housing is leaking but I haven't actually checked it for evidence of a leak yet.

I wonder if it's worth doing the air bleed procedure (running it for 20 mins with the cap off and refilling it).   2 years ago I bought a new expansion tank cap, and a month later the p1025 went away and the EML went out.  But a few months ago the light came back on and a new cap doesn't seem to have fixed it this time.   

 

[st line x 140 driver]

No harm trying for cheap fix insure heater is on full and keep an eye on engine temp if *overheats could well be the thermostat not opening/faulty. Be careful you will warp head if engine gets too hot so keep an eye on temperature gauge.

[Rat Park Refugee]

20 hours ago, st line x 140 driver said:

No harm trying for cheap fix insure heater is on full and keep an eye on engine temp if *overheats could well be the thermostat not opening/faulty. Be careful you will warp head if engine gets too hot so keep an eye on temperature gauge.

Yeah I will try it this weekend I think. It was boiling/forcing air out the cap last night when I took it home..  I am hoping that is just due to me putting coolant in it for the MOT.  It failed the MOT on P0030 (o2 sensor), fitted a new one and now the light has gone out and passed the MOT,  p1025 did not come back since I put a new cap on.  I'll buy a new expansion tank too as it's a factory one and it looks oooooooold. 

Plus my coolant is more water than coolant, I had been topping it up with water only  during the summer which was a very dumb thing to do. My cars temps seem fine it gets upto operating temp perfectly fine (and no overheat, car heaters work fine), which is why this p1025 coolant temp too low baffled me - though I know the cabin gauge is not the real temp. (I'll learn how to use this ODB2 forskin software I think)

[st line x 140 driver]

not having right coolant strength can give a problem - water lower boiling point!

[arslan zafar]

Same problem in ford focus 2014. Do you guys found any solution?

[arslan zafar]

Same problem ford focus 2014. Do you guys found any solution.