Right as I've had my fair share of problems with the g40 water/coolant system i thought i'd write up a helpful post, and there seems to be loads of threads at the moment too. During my G40 engine rebuild i replaced almost everything to do with the cooling system and then continued to replace other bits as money allowed and today finished off with a fresh radiator to complete the whole system. enjoy

Thermostat housing. Vag approx 28 quid. this over time cracks warps and becomes tired. if you replace it you will be best off replacing the thermostat within it (vag approx £7) and the 2 switch seals, and the housing seal. Easy job to do but make sure the mating surface on the head is clean.

G12/coolant/antifreeze. bought in 1.5 litre bottles, from Vag/gsf/ecp. Approx £6-7 for 1.5 litres. you will need about 1 bottle for a full system flush ( 2 parts G12, 3 parts water) basically it increases theboiling pont of water and reduces its freezing point, and contains ingredients which protect the water ways in the engine, if you do have a brown colour in the expansion tank, have you had the right amount of coolant?? rust from within the engine water ways. you can mix it at 50/50 but i prefer 2/3 after all its the water that keeps the system cool, an gnerally we dont live in a place that is minus 36 deg.

Expansion tank, not sure on price but unless yours is bust then you can actually clean yours to make it look new by simply removing it soaking it in hot water then filling it with rice. yes rice! basmati whatever it doesnt matter but the rice acts as an abrasive and if you shake it about the rice will remove that rusty shit from within. I takes some patience but believe me it will come out mint!!! make sure you get it all out when done before fitting!


Fan switch, located on the rad itself between the top and bottom coolant hoses. costs around £21 iirc from vag. if faulty this will cause the fan to kick in at the wrong time or not at all. dont be a dck and try to change it when the rad is still in, especially if the engine is hot as itll go everywhere, best thing to do if remove the rad flush it clean incase its blocked around that area and fit the fresh switch.

fan, G40/Gt's have a 2 speed fan, first sped should kick in at around 95 degrees and i think the faster speed around 110 deg. i bought one from gsf for approx £40. common problem is simple, bust bearing and an embarrasing screeching sound. To remove you will have to remove the rad, and undo the 4 screws holding it to the fan cowling then swap the cowling onto the new fan, a bit of a fuck on but an easy job just takes a bit of time.

Radiator, this was the root of all evil on my G and i wish i had chaged it earlier. from vag they're 81quid plus vat. but i honestly beleive that the common understanding that the g40/gt rad is a myth. yes there are 2 seperate part numbers for nz, aau, etc and py/3f but what is the difference? nobody knows! they're both 430mm and i have never heard /seen any hard evidence to prove the differences. even the dealers could not tell me. anyway, if blocked particulary on a G40 it will cause the car to overheat quickly. I'm convinced mine was blocked even after many a flush and the state of the sides there was a build up of white and coolant pink where it had obviouly been bleeding. its deffo bleeding now i stamped on the twat in the back lane but besides the point, gsf do a quality one for a reasonable 47 quid with CP discount of 10% ( a reason to re do your membership!)

On a G40 it is 10 times more awkward to remove then any of the other models because of the boost pipes. In my experience it goes like this.

remove grill
unplug fan
unplug fan switch
remove charger elbow to intercooler to increase room
undo boost pipe (on intercooler up and along front panel)
undo rad securing screws on front panel to push rad back to aid above.
undo coolant pipes on rad (top and bottom, or top and thermostat housing end)
lift rad out, (dont forget the 2 rubber bushes on the feet of the rad!)

fitting is reversal of removal.



Blue and black switches on thermo housing, price each approx £12.

black one - sends a signal to the dials and gives an approx temp
blue one - sends a signal to the ecu and regulates the engine management to adjust itself dependant on temperature.

the blue one is a common sinner often the root of poor idling, bad fuel consumption and general polo naughtiness. for the price its worth updating. again dont be a dick and change it whilst the engine is hot, the coolant is under pressure as the heated water expands. you undo the clip the sensor drops out and you get scalded in the face, not good! wait till the car is cold.

How do i flush the system?

Easy. when the car is cold. undo the expansion cap. undo the rad hoses and the coolant will begin to leave the system. use a reasonably sized bucket or pan to catch the stuff, its not good for the environment so try not to let it spill into the drains.
some of the coolant will still remain in the depths of the system so dont be a fruitcake get your lips around the expansion tank and blow. this will blow it all out. now use a hose and flush it all clean until clear water comes out of every open pipe. stick the hose into the top of the rad too and flush it seperatly.

Now when you have replaced any parts needed, re-fit all the pipes, double check they're all tight and then begin pouring a pre-mixed amount of coolant using a jug into the expansion tank. i find it best to do 1 litre at a time.

Mix 400ml of G12 to 600 ml of water to get a 2/3 ratio of coolant and pour it in, add the next litre in the same way, at first it will disapear from the tank as it begins to fill the system. once you begin to see the coolant remain in the system start the car with the cap off. the water level will drop. before adding any more coolant. squeeze the bottom and top rad hoses to push any trapped air out. rev the car a little to get the water pump shifting the water and turn on the blowers inside the car. now under the black scuttle cover where the blowers are in the bay undo the yelow/white bleed screw so that a small amount of water is released. at first some air will come out but as it begins to flow freely shut it again. (it is the highest part of the system so air goes to that point to escape). Now add more coolant to the max mark, squeeze the pipes again and replace the cap.

After driving the car for a bit you may find the coolant level has dropped as it has found its way properly around the system. wait till the next morning when the car is cold and top it back to max, this will probably only be about 200ml so dont go mixing 1 litre of coolant!

Rad fan switch?
I cant elaborate unfortunatly as I'm no electrician but i had a switch fitted in my dash by using an extra rear heated screen switch in one of the blanks below the radio appature and had it wired so i can switch on the 2 speeed fan on the fast speed at any time. its an easy job for any auto electrian and cost me about 30 quid and is really professional you cant even see any of the wires going to the fan switch on the radiator. it brilliant for G40's which especially in the summer in traffic etc run scarily hot! fick on the switch and watch the temp come back down, phew! i use mine all the time in traffic just for peace of mind. worth doing on any G i think.

The above are just from my own experience, and other people will have their own ways and opinions but hopefully this will help with some of those questions floating around at the moment!

dan x

That's a brilliant idea, think it'd be great to keep this updated as well!

thats a nice write up dan

that switch idea is a life saver, I've been using mine for ages now...

Nice one Dan.

Bloodyhell Dan, that must have taken a while to type out. Good guide though, 1 tiny thing if I may, you dont need to take the radiator off to get the fan and cowling out. Just a bit of twisting and jiggery pokery.

Great advice there, thanks for writing that up

2 Minor things, if you don't mind:

G12+ is the best to use as it supposedly mixes with anything. Normal G12 can form a nasty brown sludge if mixed with other types iirc. I think G12 plus is all GSF sell, so you should be ok.

If you turn the heater to the 'hot' position when draining, it'll help remove all the coolant from the heat exchanger.

used this to flush out my cooling system on saturday before the 6 hour journey to ultimate dubs and back.

I also cleaned my temp sender and now my gauge works perfectly

Yup, have done all of what you've done on my GT dan!

Even down to the heated rear screen switch in the dash

Wicked write up and should help people in the future.

A good write up mate.

A couple of things I would add if you don't mind me saying.

Some GT's have a single speed fan.

I had two original SPI and GT rads next to each other to compare at one time. The actual overall size of the radiator was the same, but the cores were different. I think the new ones may be the same for the SPi and GT/G40 (in some cases) as it's easier and cheaper for radiator manufacturers.

I avoid buying non-genuine parts for the cooling system, be it blue/black temp sensors or thermostats. They have given me problems in the past.

When fitting a dash switch for the rad fan, I would make sure the fan still kicks in from the fan switch aswell.

Oh i did enjoy - out loud!

Just thought id highlight a few of my favorite bits - pure comedy genius

my fan switch is set up so it turns the fan on, on the faster of the 2 speeds. it cannot be turned on when the ignition is off and the fan can still turn itself on on its own accord if necessary. all these things were specifically asked for when it was fitted. worth highlighting the way it works to whoever fits it beforehand i think like i did.

Make sure you have a set of mole grips handy because it makes taking those annoying VW coolant pipe clips off a piece of piss. Easier than using the proper tool I find!

Long nose pliers work just as well - you can wedge one side through the gap in the clip, and get the other side round the other part of the clip... Saves having the grips slip off all the time!

or plumbers grips, easier to get around the engine bay

Another point to note when changing your antifreeze:

If you've flushed the block after draining the old stuff, you will need to increase the strength of coolant when you come to re-fill. The fresh water will remain in the block and dilute whatever you add. I forgot about this, and re-filled the system with the normal 2/3ds ratio. When I checked it with a hydrometer, it was too weak (only -15C protection).

I couldn't be pestered to drain it all and correct it, so I drained about 750ml from the expansion tank and refilled with neat G12+ which has gone some way to restoring it to the required strength of -25C.