Car Overheating - Head Gasket Problems?

tober

Hi,
My 04 Polo has been overheating recently. When it occurs it generally happens about 10mins into a journey, can be on open road or in slow moving traffic. It doesn’t always happen (I have drove it for an hour without it occurring), an usually when I pull in for a few minutes it will be okay again. Generally when it overheats the water levels will drop a bit.
Mechanic looked at it first and did pressure tests etc and couldn’t find a problem. The second time he replaced the thermostat. Problem still occurring. He didn’t think it was a head gasket problem as I can drive it for longer journeys (1 hour) without it occurring. Any ideas?

analfabets

Airlock? Could be blocked radiator. Have you ever used any additives to stop leaks (Radweld etc)?

Means Of Escape

Get your mechanic to use his test kit for emissions in the coolant tank.

Flush the cooling system check for kinks in hoses.

make sure auxiliary fan is kicking in when the engine is hot.

If it starts to boil switch off allow to cool then check oil cap for water mixed w oil ,cream colour on cap.

Do you lose all heating inside the car when it gets hot?if so and you have checked the above the head is probably gone.

tober

No haven't used any additives.

Yes heating goes generally a minutes or two before the engine starts to overheat.

Means Of Escape

tober wrote: »

No haven't used any additives.

Yes heating goes generally a minutes or two before the engine starts to overheat.

Head cracked more than likely
you can buy an addative for about 18 euros
add to coolant system via thermostat hose.
No need to flush system out after use
can be got in all motor factors
might be lucky
cheaper than a skim.

Nissan doctor

me bolly wrote: »

Head cracked more than likely
you can buy an addative for about 18 euros
add to coolant system via thermostat hose.
No need to flush system out after use
can be got in all motor factors
might be lucky
cheaper than a skim.

A skim won't fix a cracked head anyway and if a head is cracked, bottles of gunk are a very temporary fix at best.


A failing head gasket can begin with the leak only happening at or above certain cylinder pressures i.e driving under load or up hills. If you drove for an hour at light engine load the problem wouldn't occur.

Your mechanic should know that a cooling system pressure test is generally an inaccurate way of checking for head gasket failure as if the the valves are closed in the effected cylinder(s) no pressure loss will be registered. Rotating the engine by hand when doing the test can get around this.

A cylinder leakdown test will show if there is an issue with any cylinder as a sniff test/combustion gas leak test also won't be accurate if the problem doesn't when the engine isn't under load(idle/high idle)

George Dalton

What engine is in it?

tober

It's a 1.2 litre petrol engine

Nissan doctor

tober wrote: »

It's a 1.2 litre petrol engine

What sort og driving does it happen in? Traffic, motorway?

tober

Nissan doctor wrote: »

What sort og driving does it happen in? Traffic, motorway?

It generally happens on main roads (100 kmph). It has occurred in slow moving urban traffic also. It always happens about 10 minutes into a journey so wherever I am then.

I don't think hills are an issue and the car would never be driving under any load.

George Dalton

I'm not sure if it fits the symptoms in your case but one common thing that happens to these is the plastic housing for the thermostat breaks internally. The reaction point for the thermostat breaks off and so it can't open. So next time the problem happens check the main coolant hoses running to the radiator to see if they are both hot or if one is cold. This will give you some idea whether the thermostat has opened or not.