Got a pressure build up in coolant system.  It doesn’t appear to be loosing any coolant (negligible at least) and no white smoke, no loss of coolant or power and no mayo in oil. 

Coolant at max at normal pressure and  drops below min when hot and stays there even when cold.  Returns to max when reservoir cap opened (when cold!!).  Replaced cap and still does it.

I suspect head gasket but is there any easy way of ruling out egr oil cooler issue?  
 

Thanks

Coolant level dropping when hot is usually just the sign of an airlock.  Air can be compressed, liquid can't.

You can use a CO2 sniff test to confirm exhaust in the coolant, though that won't distinguish between headgasket or EGR cooler.

21 minutes ago, TomsFocus said:

Coolant level dropping when hot is usually just the sign of an airlock.  Air can be compressed, liquid can't.

You can use a CO2 sniff test to confirm exhaust in the coolant, though that won't distinguish between headgasket or EGR cooler.

I don’t think it’s airlocked. Steady stream of gas for about an hour last night. Coolant is a bit murky as well so I think something else is going on.   That said I’m going to have another play today just in case.

it’s definitely not overheating which is good news.
 

Got a sniff test on order so should be with me by Weds I hope.  

I'm afraid that I'm with Tom on this one. Your cooling system has most probably got an airlock.

With the engine cold remove the filler cap and leave it off. Start the engine and allow it to reach normal operating temperature, and let it idle for 10 minutes at temp. Switch off and let it cool down, topping up the expansion tank as required. The only other option is to drain the system and refill it under vacuum which is the correct way but most people don't have the equipment needed to do that.

So I jacked up th passenger side and undid the expansion hose clip on the top right of radiator.  Ran with the cap off and there is no doubt it was full of air as the resovoir dropped to virtually empty.

Refilled till there was good flow out of the radiator, bled the thermostat replaced expansion hose clip on radiator.

Initially it looked like that was the problem as there was no more perceivable bubbling in the expansion tank.

Took the car for a run and the expansion tank is virtually empty again. 
 

Looking at the oil again, I’m not convinced it’s the right colour.  It’s not mayonnaise, but it has a brown tinge to it and feels slightly watery.  Also vapour when removing oil filler cap when hot.

 

Some moisture in the oil is to be expected from damp in the air, that's not a concern in itself.  Ideally engines should be fully warmed up every time to burn it off, but that's not practical for most of us in the UK.  There will also be some diesel thinning the oil on these engines from DPF regen, as well as a bit of soot to darken it on any diesel engine.

I'd top up the coolant again and see how it goes for now, there may just have been another bubble in there from the pipe that was disconnected.  Though a large amount of air in the system probably does mean a leak somewhere.

1 hour ago, TomsFocus said:

Some moisture in the oil is to be expected from damp in the air, that's not a concern in itself.  Ideally engines should be fully warmed up every time to burn it off, but that's not practical for most of us in the UK.  There will also be some diesel thinning the oil on these engines from DPF regen, as well as a bit of soot to darken it on any diesel engine.

I'd top up the coolant again and see how it goes for now, there may just have been another bubble in there from the pipe that was disconnected.  Though a large amount of air in the system probably does mean a leak somewhere.

The strange thing is, once the engine had cooled I undid the expansion tank cap and the reservoir filled up again to max, which is what it did before.

im sure this isn’t normal behaviour but I’m at a loss to know what’s causing it.  Surely the cap (brand new) should vent and prevent this behaviour whatever the cause?

That is very strange, but means there is still air in the system.

The cap doesn't work in quite the way you're thinking.  It's not 'squashing' the coolant. It's designed to hold some pressure (maybe 1.4 bar) to raise the boiling point of the coolant above 100c.

If the pressure exceeds that, the cap should open to vent the excess.

However, during normal use, the air gap at the top of the reservoir is what allows the coolant to expand and contract through heating and cooling cycles.  That's why it should only ever be filled to max instead of right to the top.

As coolant cannot be compressed, the only place it can disappear to, before refilling itself, is an air lock within the sealed cooling system.

If you can't see any external leaks, it's worth checking the interior carefully as a minor leak on the heater matrix could cause an issue like this.

Carpets are bone dry.  
 

Another bubble check an at idle there are none.  Steady stream at 2500rpm though.

Radiator seemed full, but a load of air came out of the thermostat bleed valve when I bled and topped up again.  Went for another run and the reservoir was empty again.  
 

Maybe need to get the car jacked up and take the covers off and have a good look for leaks under load.  
 

With the amount of water that it seems to be losing I’m pretty sure there would be mayonnaise or white smoke if it was a gasket issue.  

Well that was pretty conclusive. 😭

Hi wheezywez

i have exact same issue now with my focus 1.6 diesel duratorq, vacuum being created, i have done co2 test it has failed, this is where i have stopped was your problem the Head gasket, actual head or egr cooler.

Kind regards

shaun

I have a similar problem with my 1.6 galaxy.. it runs really well, no white smoke but it keeps pressuring and pumping the coolant out.. could it be the egr cooler? We did a sniff test but not really convinced with the results 

11 hours ago, puddles 01 said:

I have a similar problem with my 1.6 galaxy.. it runs really well, no white smoke but it keeps pressuring and pumping the coolant out.. could it be the egr cooler? We did a sniff test but not really convinced with the results 

The cooler is bypassed under some engine conditions, so may not always show up on a sniff test, especially if done cold.

The alternatives would be a cracked head or failing headgasket, so EGR cooler is the cheapest thing to try first if you haven't got any hard evidence to go on.

On 9/22/2025 at 7:30 PM, Prawn said:

Hi wheezywez

i have exact same issue now with my focus 1.6 diesel duratorq, vacuum being created, i have done co2 test it has failed, this is where i have stopped was your problem the Head gasket, actual head or egr cooler.

Kind regards

shaun

Apologies for the late reply.  Yes, was the head gasket unfortunately.