Coolant pressurising/overflowing. HG sniff test negative?

[Martin30]

Hi all,

My son's Peugeot 207 1.4 VTi (common engine with the BMW Mini) is pressurising it's cooling system, and coolant is overflowing out from the overflow tank. When the engine is idling and up to temp, you can see lots of bubbles making it into the overflow tank and the coolant level rises so much it overflows.

I assume the head gasket has gone, but I have used a chemical sniff test on the overflow tank and that is negative. No water in oil symptoms, no overheating. Electronic thermostat assembly, and overflow tank pressure cap have both been replaced as part of the diagnosis.

Before I start replacing the head gasket, has anyone got any other possible/simpler suggestions?

Thanks,

Martin.

[LordLoveLength]

Martin30 said:

Hi all,

My son's Peugeot 207 1.4 VTi (common engine with the BMW Mini) is pressurising it's cooling system, and coolant is overflowing out from the overflow tank. When the engine is idling and up to temp, you can see lots of bubbles making it into the overflow tank and the coolant level rises so much it overflows.

I assume the head gasket has gone, but I have used a chemical sniff test on the overflow tank and that is negative. No water in oil symptoms, no overheating. Electronic thermostat assembly, and overflow tank pressure cap have both been replaced as part of the diagnosis.

Before I start replacing the head gasket, has anyone got any other possible/simpler suggestions?

Thanks,

Martin.

Radiator blocked or water pump failed?

[Martin30]

LordLoveLength said:

Radiator blocked or water pump failed?

Thanks. I am confident in the WP as I replaced it 3k miles ago, before the coolant overflow issues. Not thought about a blocked rad, would that force coolant through the overflow tank?

Martin.

[NotGoingOut]

LordLoveLength said:

Radiator blocked or water pump failed?

Maybe heater matrix also. Worth a flush and recheck?

[LordLoveLength]

i imagine that without water flow it will boil somewhere in the system and force water out - does it do it when cold?
May not show as overheating depending on where temp sensor is.

[Martin30]

Thanks all for the continued suggestions, really appreciated as I would like to avoid an HG swap if it is not necessary.

I have replaced the coolant three times recently, once for the new water pump, and twice as part of fitting a new electronic thermostat housing.

I feel fairly confident that there is no blockage in the system, though I am all ears if there is a good way to test that.

To answer the other question, there is no pressurising /overflow when the engine is cold. Only when it reaches the temp to open the thermostat. I have had a live data scanner on the car, and watched coolant temp plus thermostat actuation data, and the car warms as expected over a few minutes - then I see the stat open and we start to get overflow shortly after.

Everything points to HG to me, but the negative sniff test (I did it twice) puzzles me.

Martin.

[VanDiesel99]

There must be some way of checking that the new Water Pump is pumping....perhaps by disconnecting a Hose somewhere (not one of those beyond the 'stat) to ensure you've got flow from the outset on cold start up.

I can't help thinking that there's a reasonable chance that the problem has been caused by a defective new WP, but you wanna be able to establish that without removing it and buying another.

Presumably once it warms up the pressure of the hot water 'll see to it that the water flows to some extent, but when cold if there's a problem the water within the engine block will be 'stagnant'

[phumy]

Expansion tank cap has gone weak.

[littleredrooster]

phumy said:

Expansion tank cap has gone weak.

It's been replaced, but I suppose it could be a very long shot. Wouldn't explain the bubbles, though.

[Martin30]

Thanks all for the continued thoughts. As stated, expansion tank cap has been replaced and I am feeling confident in the water pump - not least because I have no overheating issues (coolant temp monitored through diagnostics rather than the dash gauge).

Tempted to do a compression test, and maybe see if I can rig up a coolant system pressure leak down test. Not sure how conclusive (or otherwise) these would be of an HG failure though.

Martin.

[Mark300zx]

Air lock?

[rigga]

Mark300zx said:

Air lock?

My thoughts too, my mini needed a bit of a faff to bleed after the thermostat housing was replaced .
As you've done work to the cooling system previously, was it fully bled of air?

[julian64]

Martin30 said:

Thanks all for the continued thoughts. As stated, expansion tank cap has been replaced and I am feeling confident in the water pump - not least because I have no overheating issues (coolant temp monitored through diagnostics rather than the dash gauge).

Tempted to do a compression test, and maybe see if I can rig up a coolant system pressure leak down test. Not sure how conclusive (or otherwise) these would be of an HG failure though.

Martin.

I had this problem. I did a leakdown test on an old engine and got dubious results but not suggestive of anything other than an old engine or possible leak.

I then pressurised the coolant cap and got a very slow leak suggestive of a leak somewhere but not specific to the HG.

The fluid test colour change on the coolant was inconclusive.

What sorted it for me was a borescope. Cheap to buy. £20 attached to phone. slipped down a spark plug hole on my engine. Pressurised the coolant tank and voilla you could see small bubbles landing on the piston.

It had the advantage of actually knowing on what cylinder the head gasket had failed.