Ford focus tdci - coolant pressurisation

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Sun 10 Oct 2010 21:31
Ford focus tdci - coolant pressurisation - APG

I had a major breakdown recently and i have had to have a bent con rod replaced. Also as the engine was in bits i had a new clutch and timing belt fitted as well as all the usual stuff replaced asociated with that kind of rebuild.... gaskets and alike... About a week after that i had an temerature spike and after further examination i found the thermostat was stuck shut so i replaced that.... But, i have since realised that the cooling system is becoming pressureised as the water isn't hot and the water resavoir releif stopper is releasing the pressure and the coolant is now a rusty colour..... ive taken the car back to the garage that did the work but he is telling me he cant detect a problem......

Edited by APG on 10/10/2010 at 21:32

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Sun 10 Oct 2010 22:33
Ford focus tdci - coolant pressurisation - Collos25

The cooling system is a pressurised system you only have to worry if the actual coolant is being forced out of the system or its boiling away.If the level is staying constant and the temp gauge is normal you probably have nothing to worry about.

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Mon 11 Oct 2010 00:59
Ford focus tdci - coolant pressurisation - mikej

Also, be aware that the rusty colour you're seeing may not necessarily be due to rust - Ford/Motorcraft coolants come in various colours, including orange, purple and blue.

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Mon 11 Oct 2010 21:14
Ford focus tdci - coolant pressurisation - APG

Hi there, thanks for your reply. Yeah.... I have realised that there are different coloured coolants after looking at my brothers focus and found it to be a bright orange... and a neighbours was blue. But this coolant contains rusty deposits as once the liquid has gone there is a distinct orange powdery residue.

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Mon 11 Oct 2010 21:10
Ford focus tdci - coolant pressurisation - APG

Thanks for your reply. The coolant is actually coming out of the reservoir filler cap after short to medium journeys. And inspecting the fluid level during the journey, the coolant isn’t that hot as the thermostat has been removed.... so it can’t t be boiling.....

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Mon 11 Oct 2010 21:47
Ford focus tdci - coolant pressurisation - Railroad.

It sounds to me like you have a head gasket problem. The cooling system is sealed, but it is not the water pump that creates pressure. If your system's pressure is rising rapidly when the engine is cold it's because you have an internal leak from one or more cylinders.

When the engine is cold the pressure in the cooling system is equivalent to atmospheric pressure. As the engine warms up the coolant circulates the engine via a two-stage thermostat. A two-stage thermostat allows coolant to actually circulate rather than remain still. This is to prevent hotspots forming and uneven cooling. The coolant warms up with the engine and in doing so begins to expand. The pressure therefore begins to rise. Eventually the engine gets too warm and the coolant can no longer have a cooling effect, and so the thermostat opens allowing coolant to pass through the radiator dissipating its heat into the air which passes through it. The engine now begins to cool again and the pressure falls. If the engine gets too cool the thermostat closes and the process begins again. The pressure in the cooling system is directly proportional to the temperature. The higher the temperature the higher the pressure and vice-versa. If the engine gets too hot the cooling fan cuts in to generate airflow through the radiator. The pressure cap acts as an overall safety valve in the event of the pressure getting too high. Most caps release at about 15psi. The cap has a second valve, the purpose of which is to allow air into the cooling system as the engine cools down and the coolant contracts. If this wasn't the case the cooling system would be a partial vacuum after the car had been stood overnight.

It is the temperature of the coolant that regulates the pressure. If your engine’s cooling system has a high pressure at low temperature then you quite definitely have something wrong.....

Edited by Railroad. on 11/10/2010 at 21:58

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Mon 11 Oct 2010 22:21
Ford focus tdci - coolant pressurisation - APG

wow... Thanks for such a a concise text book description of how i thiught the cooling system worked..... god i feel sane again. The trouble is that the garage that rebuilt he engine is saying they can find nothing wrong and they would do wouldnt theyy as they would have to put the problem right. By saying they cant find a problem, i have to i have to take it for an indipendant diagnosis to prove it might be something they might have done then legally get them to do the right job. Up to now im £1875.63 into getting the thing good and going grey. Thanks for the info though..

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Tue 12 Oct 2010 21:10
Ford focus tdci - coolant pressurisation - kithmo

Have you tried a new reservoir cap ?
the seal may have gone in the cap's valve.
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Tue 12 Oct 2010 21:16
Ford focus tdci - coolant pressurisation - bathtub tom

Why has the thermostat been removed, perhaps to try and mask another problem?

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Wed 13 Oct 2010 22:47
Ford focus tdci - coolant pressurisation - APG

I removed the thermostat as i had a temperature spike light on the dash so i checked it and found after boiling remained stuck shut...

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Wed 13 Oct 2010 22:45
Ford focus tdci - coolant pressurisation - APG

You know.... as i was typing my reply yesterday i tghought to myself, ''I wonder if the cap's pressure threshold is redused and maybe i ought to try a new one....lol. But what can the rusty water be..... its gotta be something more.

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Thu 14 Oct 2010 00:21
Ford focus tdci - coolant pressurisation - Railroad.

You should not remove a two-stage thermostat. It's purpose is to allow coolant to run round a by-pass when the thermostat is closed. This ensures even cooling and prevents hotspots forming. When the thermostat opens the by-pass is closed off. Coolant then has no option but to flow through the radiator. It is acceptable to jam the thermostat open as a temporary repair because to do so would close the by-pass, but to remove it means the by-pass is always open, and coolant will take the easier option of flowing via the by-pass rather than through the radiator. This will result in engine overheating.....

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