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mmt

Wrong Air?

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mmt

Hi guys, 


My cooling is not what is should be.

 

At idle in the garage with fan on. Temp at thermostat housing is 90c the lower hose on the radiator is 80c however at the top hose/top of the radiator I read 50c could this be a sign of having Air in the radiator? 
 

brand new radiator and thermostat. 
 

thanks. 

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Thijs_Rallye

Have you bled the system? It sounds like an air pocket to me.

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mmt

Thanks - I have (tried) to bleed the system. 
 

any general pointers on How to bleed ? I have used all my tricks and it seems not to be enough. 
 

When it is hot it hisses from the expansion tank - should it be doing that? 
 

much appreciated. 

Edited by mmt

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DamirGTI

Hissing from the closed expansion bottle means - bad/leaky expansion bottle cap or cracked/leaky bottle (or leaky hoses/joints which attaches on the ex. bottle) .

If it is indeed the expansion bottle cap (or bottle itself) , need to replace it (sooner the better) as it keeps the system pressurized , so that the coolant doesn't boil off when you switch off hot engine (if it starts boiling , steam pockets will form inside the system , and especially nasty around the cylinder liners and exhaust valve seats which can and possibly will result with thermal stress/metal cracking) .

 

Mix some dish washing liquid or similar , and spray on the the expansion bottle .. when you hit the leaking spot it'll start bubbling .

But my guess is either bad cap or bad/cracked expansion bottle .

 

Cooling system bleeding is easy on 205's with XU engines , they pretty much "self bleed".

 

Initially (engine off) , open up the bleed nipple on the heater matrix hose , fill up the system with coolant until it starts to flow through the bleed nipple , when it does , cap it off and fill up the expansion bottle (almost) to the top and leave it open .

Put the heater on fully hot , start the engine and let it idle for around 10min. (periodically reving it while doing so) until the cooling fan kicks in , both top and bottom radiator hoses should be warm to touch then and cabin heater blowing hot air , at this time put the cap back on the expansion bottle and switch engine off .

After about 30min. up to one hour cooling down period , check the level inside the expansion bottle and add/top up if needed .

 

But , fit new expansion bottle cap or new bottle first (fix that pressure leaking)  .. then re- bleed , if still no good try without the thermostat , new doesn't mean its good , could be faulty thermostat .

 

D

 

Edited by DamirGTI

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mmt

Thanks Damir. Very helpfull. The expansion tank is also new so indeed new doesen’t mean good! 
 

I Think it is the cap which is faulty. Coolant come out the bled Hole instantly and the top hose goes warm after the thermostat has opened at approx. 82c. However the top of the radiator is not more than 50c. Oil cooler is also hot. 
 

could faulty spark plugs cause overheating. It runs bad /misfireing untill I rev it a little. 
 

thanks again

/M

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DamirGTI

Very likely , it'll be the expansion bottle cap ... common problem .

 

Get the new metal cap , there's plastic and metal variants - pick metal , as plastic caps usually don't seal so good on a 205 expansion bottle as metal ones do .

 

I'd try without the thermostat to be honest ... sounds like it's faulty . Simply remove it out and re-bleed , see what happens . If good afterwards then you've found the problem .

 

Spark plugs , no unless they're way out from the specified heat range (up to the chart hottest plugs) .. even then aside overheating you'll probably just hear "ill" combustion/mixture igniting , pinking detonating etc. which will eventually pop the head gasket .

 

Misfiring or kinda "running on 3 cylinders" is often sign of a blown head gasket , especially if it manifests on/during the cold start .

 

D

 

Edited by DamirGTI

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Thijs_Rallye

I usually bleed them like Damir says, but to add to that I also bleed it at the thermostat housing. Assuming it is an eight valve engine, very near the "bend" in the spark plug cable there is a allen head bolt which bleeds the thermostat. You do not need to remove that fully to bleed, because the bolt is slotted. Setting the heater to hot is unnecessary since the 205 doesn't have a valve for the heater matrix.

 

Officially the PSA procedure wants you to bleed during and after the fans have kicked in three times.

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mmt

Sorry my bad. Gti6 engine. 
 

ran it hot with cap off - started boiling over when I turned the engine off again. I’ll let it rest for a few days and see if it behaves then. 

/M

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