Coolant replaced...

[cps13]

Hi,

I have an MG TF with dreaded cooling issues. I had the coolant replaced in it recently and since then it seems to hotter than usual, but the strangest thing is this...

- when the car is cold the header tank is full of crystal clear water
- when the engine is running the header tank is empty
- when the engine is warm, take the cap off the header tank and it fills up with coolant, starts to bubble and boils out the top!

Can anyone shed any light on what is going on here?

Will the coolant and water seperate when it is cold?

Cheers,

[tristancliffe]

Sounds like an air lock somewhere. The header tank shouldn't ever become empty. The coolant can't separate from the water.

Somehow you need to pursuade the air out of the system - perhaps by removing pipes strategically whilst the engine is running (but cold!). Maybe the coolant pipes have air bleeds on them somewhere?

[NiceCupOfTea]

Air lock is the first think that springs to mind - how did you fill it? Is there a special procedure on the TF? Where's the rad?

IME the best way is just to fill up slowly with heater set to hot, then run with the expansion cap off for a few minutes, squeeze the pipes, top up as required. If there's a bleed screw then bleed it a bit. Never done a mid engined car though.

[lenientism]

It might have water added into the coolant, normally we only use the same type of coolant with one being used by radiator.

[tristancliffe]

lenientism said:

It might have water added into the coolant, normally we only use the same type of coolant with one being used by radiator.

What? Water added into the coolant, but the same as used by the radiator?

You are, surely, aware that the water and coolant mix together, and go in the pipes between engine and radiator, through the radiator and through the engine? What you stated is nonsense.

[Jack_and_MLE]

NiceCupOfTea said:

IME the best way is just to fill up slowly with heater set to hot, then run with the expansion cap off for a few minutes, squeeze the pipes, top up as required. If there's a bleed screw then bleed it a bit. Never done a mid engined car though.

I second that methode

It is what I do for my VVC and always removed any ailock with great success.

KJack

[skid-mark]

if i remember rightly they have a bleed screw on top of the radiator looks like a drain bung you should open this then start the engine,set the heater to hot with lowest fan speed, leave the expansion bottle cap off and wait for the coolant to come out the bleed bung if so nip tight, keep eye on coolant level if it shoots down add some coolant/water mixed 50/50 to the level line, keep eye on the temp gauge then keep going to the bleed bung and check no air is coming out if air is coming out just leave it open enough for it to escape then nip it shut when coolant comes out, check all coolant hoses are getting warm and give them a squeeze to push the coolant round.
when the radiator fans kick in its a good sign the termostat has opened, all coolant pipes should be hot, top the level up and now put the expansion cap on, you should now have warm air through the heaters and all should be ok.
if you keep getting the coolant shooting out the expansion bottle while doing this its down to trapped air in the system some times putting high reves on will stop this happening during the bleeding process but if it gets to bad put the cap on lightly and switch the engine off for a few minutes let it cool down and try the process agian, don't let the temp climb up to the red during any bleeding.
they can be a cow to bleed some people jack them up at the back to cause the expansion bottle to sit higher than the rest of the system cause the air travels to the top quicker, just be carefull you don't get burned.

[D1GGY]

There are four bleed points..

1 - side of the radiator at the front. Open this until coolant runs out without bubbles.
2 - Heater matrix, on the bulk head near the brake master cylinder, you will need to remove the black plastic moulding to access this one and is often forgotten about leading to air lock.
3 - Bleed screw on main water pipe on the passenger side of the engine bay, I would describe it as below the distributor but the TF does not have one....
4 - Coolant cap. Leave this off to begin with to assist with top up's etc. The cap should also be checked, they are known failure points, check to see if the brass nipple in the cap is in the center, if it is then it is OK. I would replace annually and treat it as a consumable item..

HTH

m

[lenientism]

tristancliffe said:

lenientism said:

It might have water added into the coolant, normally we only use the same type of coolant with one being used by radiator.

What? Water added into the coolant, but the same as used by the radiator?

You are, surely, aware that the water and coolant mix together, and go in the pipes between engine and radiator, through the radiator and through the engine? What you stated is nonsense.

I assumed the color substance of the coolant will go down when it is cold while the water will remain on top of the radiator tank. After three days of no use I find coolant on my car still green, although a half liter water was added into the tank previously. Perhaps it will make more sense if I put more water into the mixture, otherwise you may be right that coolant and water can't separate each other and my assumption was a nonsense...

[tristancliffe]

When the engine gets warms the level of coolant (coolant = a mixture of water and antifreeze) will go UP not down, as the fluid expands with temperature.

The antifreeze is mixed in the water, and doesn't separate. Think of it like adding water to orange squash (orange concentrate). You drink it, stir it, heat it and pour it, and the water and orange stay mixed.

Is that clearer?

[GreenV8S]

tristancliffe said:

When the engine gets warms the level of coolant (coolant = a mixture of water and antifreeze) will go UP not down, as the fluid expands with temperature.

The engine also expands, and if the system is pressurised the hoses will expand too. So it's possible for the level to go down as the system heats up.

[lenientism]

tristancliffe said:

When the engine gets warms the level of coolant (coolant = a mixture of water and antifreeze) will go UP not down, as the fluid expands with temperature.

The antifreeze is mixed in the water, and doesn't separate. Think of it like adding water to orange squash (orange concentrate). You drink it, stir it, heat it and pour it, and the water and orange stay mixed.

Is that clearer?

ok mate, i was wrong

[tristancliffe]

GreenV8S said:

tristancliffe said:

When the engine gets warms the level of coolant (coolant = a mixture of water and antifreeze) will go UP not down, as the fluid expands with temperature.

The engine also expands, and if the system is pressurised the hoses will expand too. So it's possible for the level to go down as the system heats up.

I'm pretty sure the coefficient of thermal expansion is greater for a water/antifreeze mixture than it is for cast iron or aluminium. Only if the engine cooling system was mostly rubber hoses would the level go down. If the hoses are flexing that much when pressurised, then there is something wrong with the hoses. There is no point pressurising the system if the hoses just flex a lot, so you might as well run at atmospheric.

Aluminium 23.1 µm·m−1·K−1
Iron 11.1 µm·m−1·K−1
Water ~69 µm·m−1·K−1
Rubber ~77 µm·m−1·K−1