2017 mk8 2.0 ecoblue rwd cooling problem

[Matt_814]

Hi All
II wonder if anyone can help me diagnose an issue with the cooling system on a mk8 rwd with 2.0 ecoblue engIne. RWD

Problem is that on a long run at motorway speeds the blowers start blowing cold air and the temp gauge hits max for a few seconds before dropping again. When it happens, there is steam coming out of the expansion tank. The hoses to the cab heater are both cold. The top and bottom hose are warm, but the top hose is not a lot hotter than the bottom hose. It seems to use a small amount of coolant on non motorway driving but not dramatic.

So far I have checked the expansion tank cap - it was not sealing well but after cleaning up its now holding 1.1 bar no problem. But the problem still happens.

Also changed the thermostat for a newer one without the second electrical connection.

Also checked egr cooler which holds pressure no problem. Did this because sniff test showed some colour change suggesting possible exhaust in coolant.

Any thoughts? Water pump or head gasket? Is there any way to diagnose head gasket beyond sniff test before I take the head off?

It's been a long time since I have posted here because I had a very reliable mk7 2.4, but that unfortunately is off the road for welding...
Thanks
Matt

[metalworker0]

Looks like you're on the right track with diagnosis

You've done the sniff test ..and the pressure tester.
With the sniff test showing positive. (you can also do this test at an MOT station with the exhaust probe in the header tank)

But as ive said many times, head gaskets are difficult to diagnose until they fail completely, they can go on for months sometimes over a year, tricking you and misleading you. confusing you. as the gasket can act like an intermittent one way valve into the cooling system of combustion chamber and act up at certain temperatures or conditions only

viscous fans
Not up to learning everything about these ecoblues .with it being RWD .does your engine have a viscous fan?

These can fail internally and fail to meet the speed of the engine when require

Takes a lifetime of being around viscous fans to really understand them ..me owning two cars with such units for 15 years each ..

This is how they will look, if they are good

...after initial couple hundred miles to take way the newness

Cold with engine not running can be spun by hand will rotate freely...but not super loose..will rotate perhaps one revolution when given a flick with the hand.

Engine just stopped after a period of running ...a few miles ...resistance to turn is felt

Bad one
Cold with engine not running can be spun by hand will be super loose and be able to turn several times with one push of the hand

Engine just stopped after a period of running, hardly any resistance to turn ..feels almost like its performing on the cold test..

in both instances when the engine is running the fan will appear to be turning

But a bad fan will not lock completely to the same speed as the pulley at higher temperatures as it should do, can be stopped with rolled up news paper.

in the winter ..tests like this can be flawed ..it may take 20 miles to function for the hot test.

Some traits of head gasket failures.
some here are what I've experienced:...not all at the same time ..different cars and engines:

Collapsed hoses when it cools down
Holding pressure when after its cooled down
Bubbling in the tank
Rock hard hoses
Weeping hoses at the joints
Temperature gauge going up
Temperature gauge going down if the sensor is high up in the system
Heater being inoperative is one of the first signs of it
Noise like whistle on a kettle as the thermostat opens.
Opening pressure cap on a cold engine results in sound like its under vacuum or sounds like pressure ..like opening a pop bottle, and lots of gurgling noises.l
Oil in the header tank
Coolant in the oil
Hard to turn over because of coolant or rust in the cylinders.
Loss of coolant
Gain in coolant ...due to oil
Gain in oil level on dipstick due to coolant in oil

I'm sure there are more I've forgotten about.

Loss of coolant can happen many ways.

Into oil in the sump, directly from the head gasket
From cracks in the cylinder head of cylinder sleeves
From heater matrix
From hoses
From EGR cooler directly into exhaust
From the core plugs

all the best.mark

[Matt_814]

Thanks Mark. I'm 99% sure it's the head gasket now. As you pointed out it retains pressure after stopping. Can also see the temp gauge both hitting max and then dropping below the normal level. I think this is because so much gas is building up in the system there is no circulation of fluid past the sensor. Weighing up doing myself but heard horror stories about injectors getting stuck.... thanks for your help