DannySutton

Morning all first post so apologies if it's in the wrong place. I wanted to do a full circle write up of an issue I have had over the last year with my 2012 CEGA 2.0 TDi octavia. The first symptoms were when driving home along the motorway, very occasionally the heater would stop blowing out hot air altogether, this started off by lasting about 20 seconds, but slowly got worse over time where the heater would stop working for a longer time. It got to the point where the engine would start to heat up past 90 on the dash just slightly and settle again, then evolved to me needing to downshift and floor it for a couple of seconds and that seemed like it shifted whatever was happening. The engine at it's worst point would just start heating and heating and sometimes there was nothing I could do, the coolant would be bubbling out of the expansion tank because of the pressure in there, and I had to keep constantly running an OBD reader to monitor the real time temperature instead of the indication you get on the dashboard. I initially changed the thermostat (never again, it is a horrible job). This was on the premises that it may be sticking shut and the increased water pressure from higher revs would force it open, but this didn't fix it. I then changed the water pump, as they are prone to expanding and then having the shaft spinning through the centre without the impeller moving. This didn't fix it. Next was a couple of partially related coolant hoses that had mini holes or splits in, these small leaks didn't sort the issues either although I was hopeful. At this point I am thinking in the back of my head that it is either a blown head gasket or a crack in the head of the block as some owners of CEGA cars have reported, but I was hoping it really wouldn't be this. Next to change was the heater matrix due to reports of sand castings being left in the coolant channels from factory, and how the problem all stemmed from the heater matrix sporadically not working. This didn't fix the issue. The actual fix came along when I fully blanked off the EGR, it had already had an EGR blanking plate inserted where the pipe meets the manifold, but I removed the pipe and blanked off the exhaust in and out from the actual EGR cooler unit behind the engine. My theory beforehand was that this is the only place other than the head where exhaust gases could be feasibly getting into the coolant system. After blanking off the EGR cooler from exhaust gases, it must be that there was a small crack which was letting the gases in to pressurise the coolant and stop it all from flowing when air pockets were locking out certain areas. I have now done ~3000 miles since the EGR blanks and have not had a single instance of overheating, and this has been up steep hills in the hot weather we have recently had, so I am classing this as a fix now. TLDR: Symptoms- Occasional lack of heat from heater matrix, climbing engine temperatures Fix- Blank off exhaust gas sides of EGR cooler Engine: 2012 2.0TDi CEGA