Octavia Mk1 1.9TDi overheating

[ModernAndy]

greetings VAG brethren,

I'm having a cooling issue saga with an Octavia I own (1.9 TDi 110 PD). At the moment it keeps overheating (up to just under the 130 redline). Normally it will sit at 90 but when pressing on a bit or after about 5-10 minutes of sitting at the national speed limit, the needle gradually nudges up from 90 to at least 110.

A couple of months ago the radiator suffered the usual problem of a hole in the bottom corner and I replaced this and while I was there, fitted a decent thermostat as well.

Here's a list of the symptoms:

-the car is losing coolant at a rate of a litre per 30-50 miles, have been topping up with water (and I am aware this isn't great for the engine but it's an old car that I'm not too bothered about)
-making the coolant concentration stronger recently seems to have actually made the problem worse
-the oil cap is clean, no sign of water and oil mixing
-radiator is getting warm
-bottom radiator pipe is getting warm after a bit of driving
-the interior heater heats up great when the car is topped up with coolant but will go cold in the space of 5-10 mins
-the coolant system is pressurising
-the system has been bled properly
-the water pump is sending the coolant round the system fine as far as I can tell
-the temperature isn't spiking as you'd expect if the guage was faulty so I haven't replaced the temperature sender yet. The heating up and cooling down is gradual as normal
-the smaller air-con fan behind the radiator works but I think the larger main fan is f***ed. The car is normally on the move most of the time though so I would think the air cooling would be taken care of by the air being blasted in the front at 50-70mph. It doesn't make any difference at all to the temp guage whether or not the air-con fan is on. I did have a Pug HDi where the fan didn't work and it was only ever a problem in slow moving stop-start traffic.

I'm thinking that a hole in the coolant reservoir could be letting steam escape but this is just a theory at the moment.

All ideas most welcome. Thanks.

[Spangles]

If you're losing that much coolant and you can't see a puddle on the ground then your head gasket has gone.

[ModernAndy]

yeah, starting to look that way but some of the symptoms don't add up. I can't see any evidence of water and oil mixing for a start, there's not really any white smoke and no real loss of power. The engine will have a grumble at idle occassionally like it's struggling to keep going though. I think I'm actually losing more coolant than I estimated in the first post which, if it is going into the engine, I'd imagine should have a more noticeable effect. Add into that, I'm now starting to suspect that the water pump may not be operating particularly well.

I have heard that tightening the head bolts on these can be required after a bit of mileage is racked up as they can stretch a bit. My one is sitting at a bit over 232k so probably worth a shot.

No big deal if the car needs scrapped but for my own knowledge, I would like to diagnose and fix it.