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[zippo]

whats the temp gauge doing ?

a steady 85

If the temp is a steady 85 it is at normal operating temperature and is not being affected by any contact with combustion as I stated earlier due to your misleading description of "boiling".

whats misleading about boiling , that's what is happening

[Kevin Wood]

whats misleading about boiling , that's what is happening

I think there are 2 possibilities though. If the cap is on the expansion tank and the coolant boils, the pressure builds up until the pressure relief valve in the cap blows at which point you get a sudden release of steam and water from the expansion tank cap as it vents. The coolant needs to be at at least 120 degrees C to do this, IME, which means the engine is overheating (gauge would be in the red).

The second possibility is that the coolant boiled over with the expansion tank cap removed, which is normal.

Do you have cracks around the filler neck of the expansion tank? Could be that it''s leaking around this area and not holding enough pressure. Do the radiator hoses get pressurised so they're firm when squeezed when the engine is up to temperature? Does the cooling fan run when the temperature gets up to just over 1/2 way up the gauge?

Sounds like the cooling system could at least do with a thorough flush and some fresh coolant.

Kevin

[Entwood]

whats the temp gauge doing ?

a steady 85

If the temp is a steady 85 it is at normal operating temperature and is not being affected by any contact with combustion as I stated earlier due to your misleading description of "boiling".

whats misleading about boiling , that's what is happening

The coolant in the header tank can't boil on its own ... the whole system boils or it doesn't ... and water can't "boil" at 85 degrees (unless you have transported to the top of Mount Everest) .. it "boils" at 100 degrees !!

So .. enough of the physics lesson ...  

As previously stated ... possibilities IF you didn't touch the cap...

leaking cap
leaking "neck" of expansion bottle .. known to crack.

Both cause low pressure in the system and MIGHT (?) lead to localised "boiling" and agitation of the system enough to stir up sediment

Failed water-pump may lead to localised "boiling" and agitation of the system enough to stir up sediment.

Thermostat stuck closed may lead to localised "boiling" and agitation of the system enough to stir up sediment but I would expect  this to be accompanied by a high temp

IF this happened when you removed the cap from a pressurised system then localised "boiling" and agitation of the system enough to stir up sediment is highly likely.

See a common thread here ??

Solutions offered :

1. Give the system a damned good flush, several times over several days with decent runs in between - this should hopefully remove all sediment.

2. Check expansion tank for cracks

3. Check expansion tank cap for pressure relieving too early

4. Don't remove cap of pressurised system

5. After flushing and finding /fixing problem fill with 50/50 antifreeze/water mix.

HTH  

[zippo]

thanks folks "i'll leave as is" for the time being .
Daz

[FRE07962128]

Right

A few hints here.

Water boils at 100degC unless its under pressure as in a well maintained engine cooling system.

So, release the coolant cap on a hot engine and the water will boil!

What you can also get is any sediment in the system may be disturbed in the process causing gunk to be thrown out at the same time.

Also be aware that the 4 pots do not have the same sort of oil cooler setup as the V6, only the 2.2 has a small oil cooler which is sandwiched between the oil filter and oil pump and is not known as a failure item.

If the head gasket was gone, I would expect rough running, particularly when the engine was first started as its likely that one of the bores would be full of water!

Thanks Mark & Entwood.  A good tip for all of us, and especially me who jumped too quickly to the wrong conclusion!   It is all too easy to do without the car in front of me to investigate!  

[zippo]

Quick update
 fitted a new expansion cap and that seems to have cured the problem .
thanks again for the help

[albitz]

result

[zippo]

A quick update
 tried to empty the radiator as per Tunnie's excellent how 2 and nothing came out ,not even a drip .Any ideas folks , or could the bottom of the rad be clogged so full of sediment,  w.h.y. that the coolant isn't getting there

[Kevin Wood]

Sounds like the drain tap is blocked. I would remove both radiator hoses and drain the system that way, then see if you can backflush the radiator with a hose pipe until the water runs clean. If the coolant has revealed brown goo the system needs a flush and some fresh antifreeze.

Kevin

[zippo]

Sounds like the drain tap is blocked. I would remove both radiator hoses and drain the system that way, then see if you can backflush the radiator with a hose pipe until the water runs clean. If the coolant has revealed brown goo the system needs a flush and some fresh antifreeze.

Kevin

can i do that with the radiator in situ Kevin

[Kevin Wood]

Sounds like the drain tap is blocked. I would remove both radiator hoses and drain the system that way, then see if you can backflush the radiator with a hose pipe until the water runs clean. If the coolant has revealed brown goo the system needs a flush and some fresh antifreeze.

Kevin

can i do that with the radiator in situ Kevin

I'd certainly try, at first. If it's really filthy you can do a better job if you take it out and shake it around but, assuming you haven't had problems with poor cooling a flush in-situ will probably be fine.

Kevin