Mk4 Overheating & Thermostat Working..

[Pergs]

The Mk4 GTi has developed an overheating issue.

Last Friday AM, I drive 4kms which was enough for the engine to warm up and continue past its normal temp (90deg) to 120deg. The temp. alarm come up so I parked at work and turned the car off. It was a little dark under the bonnet to inspect but nothing seemed out of order. As expected the thermo fans started up to cool the poor thing down.

Friday PM, drove 5kms home, did not overheat... normal temps.

Saturday PM drove 10kms, overheating issue again, pulled over had a decent look/feel to notice the top hose where the temp. sensor lives to be HOT! The bottom hose connected in front of the thermostat was COLD.

Now, I only replaced the thermostat 2months ago, thinking it may be a stuck closed thermostat problem!

Today I pulled the thermostat out and put it on the stove in a pot of water. To my non-delight, the thermostat fully opened before boiling point .. Normal operation!

With the thermostat and coolant back in the car, we ran the car back up to operating temp. and more again!

Frustrating and hoping its not the water pump impeller..... ANY IDEAS ??

Have a day of site visits tomorrow too

[h100vw]

The Mk4 GTi has developed an overheating issue.

Last Friday AM, I drive 4kms which was enough for the engine to warm up and continue past its normal temp (90deg) to 120deg. The temp. alarm come up so I parked at work and turned the car off. It was a little dark under the bonnet to inspect but nothing seemed out of order. As expected the thermo fans started up to cool the poor thing down.

Friday PM, drove 5kms home, did not overheat... normal temps.

Saturday PM drove 10kms, overheating issue again, pulled over had a decent look/feel to notice the top hose where the temp. sensor lives to be HOT! The bottom hose connected in front of the thermostat was COLD.

Now, I only replaced the thermostat 2months ago, thinking it may be a stuck closed thermostat problem!

Today I pulled the thermostat out and put it on the stove in a pot of water. To my non-delight, the thermostat fully opened before boiling point .. Normal operation!

With the thermostat and coolant back in the car, we ran the car back up to operating temp. and more again!

Frustrating and hoping its not the water pump impeller..... ANY IDEAS ??

Have a day of site visits tomorrow too

You can hope it's not the pump but I am pretty sure that's what you'll find it is.

Gavin

[Pergs]

You can hope it's not the pump but I am pretty sure that's what you'll find it is.

Gavin

Thanks Gav,

How do the water pumps just fail?

Do i expect to find broken and mashed impeller fins throughout the coolant? There wasn't any today?

[h100vw]

Thanks Gav,

How do the water pumps just fail?

Do i expect to find broken and mashed impeller fins throughout the coolant? There wasn't any today?

The impeller splits and the shaft spins in the middle of it. Had it happen to my A3 years back. They don't crack and fall apart in my experience.

Gavin

[dylan8]

thermo stats normally open when they break, safety thing.
How many km on the car, and has the pump ever been replaced? usually in line with timing belts

[Pergs]

thermo stats normally open when they break, safety thing.
How many km on the car, and has the pump ever been replaced? usually in line with timing belts

149,900km on the car and I've been looking through receipts tonight and cant find a 'water pump' when the timing belt service was done.


Question is, should I do a timing belt, tensioner and roller at the same time?!

[adammm]

thermo stats normally open when they break, safety thing.

This could be why my GTI has suddenly started to run pretty much cold, takes an age to warm up, never hits operating temp unless im stuck in traffic, else, its always on the 3rd bar being cold!

[Pergs]

So I left work early today to take advantage of some sunshine... Floating impeller it is!

After taking out half of the engine bay, the water pump impeller is just happily spinning on the shaft!

Glad to confirm it as a replacement kit from ECS is already on the way!

[Pergs]

[Stan]

at least the mystery is solved!