Mysterious coolant loss

[JohnLuke]

I have owned a Seat 1.9 TDI 110 for two years covering 14K miles. Initially it ran round locally without problems, but on long journeys it overheated and needed a few litres of coolant to replace that lost. The header tank cap was replaced which stopped the coolant loss. However, as time passed the car still lost coolant on longer trips. The thermostat was replaced, but still the over heating reoccurred. The cooling system was flushed a number of times. It transpired that the heater matrix was clogged and the over heating stopped.
The problem remains of needing to top up the coolant every couple of days with up to half a litre approx. each time. There is no visible sign in the engine bay of a leak nor under the car. The header tank was checked for leaks, non found. I thought it was perhaps the cylinder head gasket, even though no steam from the exhaust, no apparent loss of power. A friend of a friend experienced with diesels, after checking it, dismissed possible head gasket failure.
Some coolant has made its way into the engine, I have seen droplets when I took off the oil filler cap, but the under side of the cap was not a creamy colour. Is there another way coolant can enter the engine other than the cylinder head gasket? I think it is when the cooling system is under pressure that the leak occurs.
Furthermore, there is now a problem starting. On turning the key the starter motor tries but fails to turn the engine over. Then, by moving gear leaver through the gears it starts as normal.
I would be grateful for your advice.

 

[csstevej]

Welcome . How many miles total on the car?
The over heating , does it happen when your aggressive on the throttle or leisurely driving?
Has the coolant in the bottle have any dark flecks floating around?
It sounds like a leaking head gasket……probably leaking under boost.

 

[JohnLuke]

Thank you, CSS, for your prompt response.
It ceased overheating after the cooling system was very thoroughly flushed out, even using some cola in the system for a couple of days, which cleared the system.
The Seat Leon has covered 101K miles.
I have not seen anything at all in the header tank water (I'm using rainwater because of the quantity of coolant needed to top up).
I think the fluid loss occurs after the motor has warmed up, the system becomes pressurised.
I thought it was the cylinder head gasket, but an experienced guy said he thought it wasn't.
I think the earlier period of overheating may have weakened a seal or gasket. Perhaps a pressure test would give an answer, but I don't have the tool for that.

 

[Tdijarhead]

There are a couple of spots that leak coolant and can be difficult. Is the area on top of your transmission damp? The coolant flange on the right side of the head as you’re standing in front of the car is prone to weep. Put you hand under the flange wipe it around a bit and pull your hand away, is there any moisture?

The oil cooler can dump coolant into the sump. Is your oil level rising?

At the bottom of your timing belt cover, is there and drips?

 

[r90sKirk]

I agree, it sounds like a HG. Typically when the HG leaks it gets the hot compressed exhaust gases by the HG and into the rear coolant passages in the block. The system then is way over- pressurized, you can see/feel hard coolant lines to and from the radiator including the smaller ones to the cylinder head. Most of the time, you'll see a reduction in cabin heat due to the lousy transfer of heat from the coolant because of all the microscopic air bubbles in the system. Sometimes the coolant overflow reservoir ball/tank will get a darker discolored appearance on the inside (again from the hot carbon gases in the system), and lastly since the system is over-pressurized all the time, you will leak coolant out the overflow (slowly) everytime you shut the engine down. This results in a loss of coolant over time that sometimes is hard to see anywhere. If you can see it, the coolant will make it's way to the ground just below the passenger side footwell closer to the pinch joint in the body.

 

[JohnLuke]

Thank you Tdijarhead and r90sKirk, I will get back to you. Although the oil level has not raised, the oil itself is seriously degraded, I don't want to start it until the oil and filter are changed. Hope to do this asap. Using another car (old Peugeot diesel) for daily trips.

 

[r90sKirk]

the oil level will not raise, with a HG issue on an ALH engine, you are not getting coolant in with the oil or vice-versa, ONLY hot exhaust gases into the cooling system.