Expansion Tank Higher Pressure Problem

[Erceste]

Dear Forum Users,

I have DS5 2016 model 2.0 BlueHdi diesel 180 HP automatic car.

I need your advise regarding my higher pressure problem on expansion tank. Maybe I top up 750ml coolant every day due to expansion tank higher pressure issue.

1. There is no overheating issue and 90 degrees settling always when I drive.
2. Heating fans works well.
3. Sometime radiator is hot sometimes cold.
4. AC fans works well.

So far replaced bellows.
1. Expansion tank and cap replaced.
2. Air bleeding done.
3. Steel seal applied.
4. Cam belt and water pump kit replaced today.

But still I have same issue.

Is it possible radiator blockage or flashing issue ?
Or thermostat issue ?
Or head gasket issue ?

Please can you advise action plan if you had experience before?

[RichardW]

If it's not overheating, but the tank is over pressuring and blowing out coolant, then odds on the head gasket is gone. Does it pressurise quickly from cold (i.e. before it gets hot) / does it retain pressure overnight?

[andyandjulie]

I'm with Richard on this one. I had same thing happen on a 240Z back in the day. My brother and I did it on a Sunday afternoon but cars were much simpler then.. It sounds like the gasket has failed between a waterway and a cylinder. An exhaust gas analyser wafted over the expansion tank might confirm. Hope I'm wrong.

[myglaren]

There are kits available for detecting exhaust gas in the coolant, one here from Amazon.
May be cheaper elsewhere.

[Stickyfinger]

There are kits available for detecting exhaust gas in the coolant, one here from Amazon.
May be cheaper elsewhere.

This....they work very well

[Muir]

If it ingests 700+ ml of coolant per day you should be able to see and smell by the exhaust - does the exhaust smoke perpetually or does it smell sweet?
Is there any black gunk in the expansion tank?
Can you confirm it's leaving by the expansion tank, any residue/dipple near it?
How did you comfirm the coolant system is overpressurized, just curious?

Might be worth dropping the lower plastic engine guard and look for coolant residue.
I honestly think it's much too early to target the headgasket, could be a simple leak.

[Stickyfinger]

If it ingests 700+ ml of coolant per day you should be able to see and smell by the exhaust - does the exhaust smoke perpetually or does it smell sweet?
Is there any black gunk in the expansion tank?
Can you confirm............................

Might be worth dropping the lower plastic engine guard and look for coolant residue.
I honestly think it's much too early to target the headgasket, could be a simple leak.

Or the gearbox is getting it via the box oil cooler (if it has one)....

[Muir]

If it's the DW10FC engine yeah it has a small trans cooler on the gearbox.
Though I reckon the box would have seized already if it had that much coolant in it