temp rising, temp sensor or themostat

[NGOLF.U]

hi guys, car is stating to over heat, the water pump was replaced 40,000kms ago.

its not over heating fully like it did when it was the waterpump, it will slowly increase 2-3 bars above the norm.

with the radiator one hose is cool one is hot.. so there doesnt seem to be a blockage.

on the freeway the car still overheats at speed.

what do you think?

[99gti]

The fuse hasn't melted on top of the battery has it that controls the thermo fans? Do they come on when it's overheating?

[NGOLF.U]

yeh fans are working they seem to be working overtime, doesn't seem to be coming on at the right time though ...

[ope126]

PM Jimmymac, he might be able to help you...

[Jmac]

Im afraid that does still sound like the impellar is spinning on your water pump. Try this start your engine , now you will need both hands - with your right squeeze the top rad hose and at the same time rev the engine with your left and you should feel pressure in the hose as the pump is forcing the coolant round the system - should feel like it wants to swell. If nothing then the problem lies in the water pump for sure. If it turns out to be the pump replace it with one with a metal impellar. Mate if it swells then we will look at something else , now the fact that it is doing it at speed tells me its not thermo fan related as such more engine as you should be getting good air flow to the rad.
Jmac

[NGOLF.U]

thanks jmac... ill see what happens tonight... it better not be the waterpump!
what do the metallic waterpumps cost?

[Jmac]

Mate you will pay Around $95 at Vw for the bakalite one and you will find you will pay around the same for the metal one. I just did a metal one for around the $95 mark, I trust you did your Timing belt and stuff then??? If not now will be the time.
CHeers

[NGOLF.U]

boys ended up being the thermostat $55

[Jmac]

Stuck closed hey - little bugger ah well not as bad as a pump - take it the pressure test was good pressure - thats good news mate.
Jmac

[NGOLF.U]

yeh thanks for you help man!!

[jDub]

Having the same problem.

Did the timing belt and water pump (metal impeller) at 120,000kms

Goes to 90 degrees within 5 mins of starting from dead cold then gradually rises up into the red zone.

I only recently replaced the plastic water flange and flushed it with fresh G12+ and only used distilled water.

My heater works fine and also get A/C as the fans do come on. Is this a thermostat issue? I have replaced the temp sensor and thermostat at 100,000kms. I am now at 145,000kms.

[dylan8]

Mk4 thermostats tend to jam open (letting too much cold in) rather the jam closed. So don't think it would be that.

[jDub]

Turns out to be the temperature sensor. Had replaced it before with the green top one a while back, guess it failed. Starting from dead cold it would read 130 degrees and the fans would turn on after 2 mins of driving as it was thinking the car was overheating.

Replaced with a genuine one. Now all good.

[dylan8]

was the one that failed genuine?

[jDub]

was the one that failed genuine?

The one I replaced was an aftermarket one. Made in Italy...