2010 a3 sportback overheating issue

[Nick parker]

Hi guys I hope someone can help

I have an A3 2010 sportback 1.6 tdi

Basically going around town perfectly fine even at temperature, it doesn't rise.

The minute I take it on the motorway after about 7 miles or so it starts to over heat. But its not loosing water if anything the light would come on the dash saying "no coolant please pull over" so I checked it but the coolant was higher than it normally was, so I thought it was the thermostat sticking so I had it changed, still the same issue, garage took it for a drive and advised that the radiator at temperature was stone cold , but at the same time told me its over pressuring pipes was so hard to squeeze, so I bought a new over flow bottle cap (cheap possible solution) and got the garage to change the rad as they explained it looked rusty.

Again still over heating with pressure in system.

Now they are advising it could be a split head, gasket , or might possibly the water pump

Had the water pump and Cambelt done 2.5 years ago and only done 15000miles since.

Downfall of the head and gasket is that I thought if that was cracked or gasket is going then surely I would be loosing water ? Which I am not ? And also if it was the head or gasket surely it would overheat straight away driving it around town ? It seems as if I put my foot down and go at a higher speed it pressurise alot In the system which causes it too over heat ?



Can anyone shed any light on this please or if they have come across the same issue as now I am completely stumped and really don't fancy forking out 1500 odd on having the head sent away to get checked and possibly skimmed and also all new gaskets.

 

[Retroman]

My guess would be the water pump. The fact that your radiator is staying cold suggests to me that it isn't receiving hot coolant to be cooled. It is known that with age, the water pump impeller can stop spinning or freewheel and so not keep pace with increased engine revs; and so not circulate coolant. Obviously regular and severe overheating can cause secondary damage of the type mentioned by the garage.

You're on your 2nd thermostat, I wouldn't suspect 2 on the trot to be faulty. In my many decades of playing with cars, I've only ever experienced thermostats sticking open and making the engine run too cold.

 

[Retroman]

I don't know your garage and they may be fantastic. Unfortunately, many high street garages are lazy, they don't want to spend too long diagnosing a problem and many are looking for costly (to you), relatively easy (for them) work. Water getting into coolant often shoes itself as a creamy "mayonnaise" on the underside of the oil filler cap. Garages can conduct a coolant pressure test which would show coolant dribbling from obvious cracks/gaps in a cylinder head. They can do a compression test and finally, they can do a simple "combustion leak" test.

Euro Car Parts Combustion Leak Detector Fluid 500ml | Car Parts 4 Less

 

[NHN]

2010 rad rusty, sounds very questionable, I've changed rads on 05 cars with zero rust & was just due to corner leaks a known problem, but yours sounds circulatory issue.

 

[ab1702]

I’d use a different garage if I were you, as said above there can be a compression test done to determine if the head has gone or not. You’d also really only change a radiator if it were blocked or leaking so that’s a waste of money.
My money would be on water pump or thermostat, if thermostat has been changed then make sure it were a genuine one

 

[samisnake]

You could have a gasket issue where the exhaust gases are going into the coolant, but then I'd assume you'd see other issues eg. Overflowing expansion tank, contamination of coolant.

They could do a sniff test on the coolant, removing the head for no reason is expensive and time consuming.

Best theory sounds like the waterpump.
Putting your foot down increases load, which increases heat, and the pump ain't pushing enough coolant round to cool it.
Does your cabin heater get warmer as you put your foot down?
When was the last time the belt and pump were changed?