cooling issue

Chat about your MKV (6N2) Polo GTi
m3ag
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cooling issue

Post by m3ag »

Separate thread for my cars issue, and its no doubt been covered before

6n2 GTi issue is:

Bought it as a car that had suffered an overheat a few months ago, we inherited a damaged header tank (looks to have been butchered) and very little coolant, apparently the car was left standing for 30mins ticking over, no fan kicking in meant it boiled over.

So, the fan didn't run, but does now (new fan), new header tank and cap, flushed the system best we could.

Symptoms now are

Refill the cooling system via the header tank, run the car up to temp, top hose getting hot, heater blowing hot, bottom hose still cold/barely warm. Can feel pressure in the hoses, and the return feed is pumping through into the header. After about 15mins running at approx 2k the coolant starts to boil in the header tank and starts to escape via the tanks outlet point. Bottom hose still not hot but coolant warning light comes on.

The cars history shows it had a new VAG thermostat in Sept 2018, but not the housing. Not fitted by VW but by a local garage.

So we'll pull the stat out and re-run the car without to see if this resolves the issue.

Engine runs nice, no mayo, oil is clear.

So we believe the stat isn't opening for whatever reason or is stuck as such its boiling up. I can't add any more coolant in either and we're running it with the cap on now as coolant was just spurting out with it off.

Could the car overheating like it did damage the stat?
Is it best to replace the stat and the housing at the same time, obviously best off using genuine vw parts, or could we just have a major airlock, if so so how does that get shifted?
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937carrera
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Re: cooling issue

Post by 937carrera »

It sounds like the coolant isn't circulating, I doubt it's an airlock.

Time to check water pump and for blockage in the radiator, did you flush that through properly ?

Be careful with removing thermostats, sometimes the design of them means that coolant does not circulate as well when they are removed, but you already have a problem.

I haven't seen any signs of a blown HG from your description, so I doubt the overheating has caused major damage
m3ag
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Re: cooling issue

Post by m3ag »

flushed it again and runs clear however we took the stat out. OMG talk about ruined, the bridge has failed and the stat has fallen apart so new parts ordered from vw for fitting later today. The original would not be letting anything through in a hurry.
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937carrera
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Re: cooling issue

Post by 937carrera »

:D

I read above it had a new VAG thermostat last year, but maybe it wasn't VAG ?

Anyway, looks like you have identified the problem. Nice cheap fix and GTi :D :D :D
m3ag
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Re: cooling issue

Post by m3ag »

yes, found the receipt, Vindis VW. Supplied Sept 2018, fitted a week later and the part number matches up OK but looking at the flange/bridge etc that doesn't appear to have a part number and thats the part that has caused the issue I think.
m3ag
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Re: cooling issue

Post by m3ag »

all sorted, it was the stat and the housing, car running great so happy bunny.

Thanks for the pointers and the suggestions, all helps you know....
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937carrera
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Re: cooling issue

Post by 937carrera »

It's a pleasure, time to put some pictures up :wink:
connerallier
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Re: cooling issue

Post by connerallier »

Hi looking for some help my fan wont kick in I have replace the radiator switch and the fan control unit also took the plug off the radiator switch and bridged 2 and 3 and the fan kicks in at high speed but nothing if I bridge 1 and 2 or 1 and 3 any help would be much appreciated cheers.
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937carrera
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Re: cooling issue

Post by 937carrera »

If 1-2 doesn't put the fan on low speed the resistor has corroded and broken, you need a new fan

viewtopic.php?f=23&t=73875 if you want to see what has failed
connerallier
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Re: cooling issue

Post by connerallier »

Thank you will try that next was thinking it was fan was just confused how 2-3 on the plug still kicked the fan but makes sense now.
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Re: cooling issue

Post by connerallier »

Hi guys I posted back in December about my fan not kicking in still having trouble getting it to kick in I have replaced the radiator switch fan control unit and the fan it self I have also bridged 2-3 on radiator switch get high speed all good also bridged 1-2 get low speed also all good so very confused to what it could be any help much appreciated cheers
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937carrera
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Re: cooling issue

Post by 937carrera »

Well, if the fan kicks in when bridging the terminals, that just leaves the fan switch that's screwed into the radiator. They can fail too.
connerallier
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Re: cooling issue

Post by connerallier »

Yeah that's what I come down too but that's been replaced very confused to why it's not working
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937carrera
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Re: cooling issue

Post by 937carrera »

Ah, missed that, so you need to get a meter and check the contacts on the thermoswitch at different temperatures.

Can you borrow a type k thermocouple and see at what temperatures the switch opens......... and even if it is getting hot enough to
connerallier
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Re: cooling issue

Post by connerallier »

I have just ordered another fan switch just to see maybe the one I have is faulty but not to sure what a type k thermocouple is but I will look into it
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