Coolant system issues

[Richie302]

I have been having some problems with the cooling system in my mk6 GTD… I brought it a few months ago and took it for a test drive and everything seemed perfect but once I started to drive it I noticed when I put my foot down the water temperature would rise above 90° and then quickly return back to 90°

I started by changing the thermostat and secondary water pump (it was causing an intermittent DTC), this changed nothing so I changed the two water temperature sensors, again this did nothing so I changed the radiator and the heating matrix because after changing the sensors I couldn’t get any heat inside the car, these both had grit inside them, just small bits of what looked like sharp sand.

I then changed the water pump and cam belt, the water pump was rusty

I then started to pay attention to the oil temperature, which was getting all the way up to 135°, so I decided to remove the oil cooler, this was blocked solid with the same sand looking grit, after changing it for a new one the oil temperature dropped to max 110°, still too hot so I removed the oil cooler again and it was full of grit again, so I used a wet and dry vacuum to suck everything I could from the engine, again got lots of grit in the vacuum so I put a litre of Prestones water system flush in and topped up with water, I let this in for 3 days while running the car normally.

When I dropped this water out it was dark grey and nasty looking, I filled it back up with antifreeze and water (50/50 mix) but it is still got the same high oil temperature of 110° and I can hear the water is still not circulating properly, everytime I remove the oil cooler it’s blocked solid with this same grit! How do I get rid of it completely?

Please any advice would be greatly appreciated, the car is driving me nuts, I’ve had a lot of golfs and never seen anything like this in the water system

[Richie302]

After looking at this grit underneath a microscope I’m starting to think it’s catalyst… There seems to be little bits of metals, gold, silver and white looking bits… if a past owner has tried to knock the catalytic converter through how would this find its way into the water system?

















I’ve ordered a new cat and down pipe but how would this possibly get into the water system? Thought the DPF or Cat? Are the systems connected in a way that would allow cross contamination?

I have a feeling the last owner tried to knock the catalytic converter though…

How did this catalyst get into the water system?

[Nino]

Holy moly! 

I have never seen anything this bad before.

You have done some extensive investigation too.
I am wondering if previous owner has used some kind of Stop leak in the system and its compeltely blocked it up.

I cannot see how the cat would get in there but then im no expert ether.
It might be worth pulling the heater core out again, flush it, flush the oil cooler, flush the themo, waterpump (again) run a hose into the inlet and let it overflow out of the engine while everything is disconnected if this is even possible to flush out anything that is left in the engine.

Put all your parts back on nice and clean (again) with your new cat and downpipe, Id also do a full service while your there as well.

How is the turbo looking?

[Snoopy]

As above I would flow water through it for a while and do some research on what else is water cooled that could cause this. Is the dpf water cooled on the gtd?

[doberman19]

Hi, I'm no expert either but from what I've read, the heater not functioning properly could be an air lock, I also don't think that the stuff got in their accidently either. Could I suggest removing the thermostat and if the hosed water doesn't flow freely while your stripped down you may have an issue with the water jackets around the cylinders being silted up' if a strong flushing agent is unsuccessful it may be a major strip-down. Regards.

[Richie302]

Thanks Nino and Snoopy for the reply, I just spent the week stripping it down completely and you are absolutely spot on. The head gasket was completely blocked with a sealant, possibly K-seal…









I had the head skimmed, pressure tested and the valves and seals reseated, I have replaced every gasket and literally scraped 90% of the remaining sealant residue from the bottom of the block then rebuilt it and filled with deionised water and antifreeze.

Changed oil, oil filter, air filter, new glow plugs, new injector seals, new copper injector washers, cleaned oil cooler, flushed all hoses, flushed the new radiator, cleaned out the thermostat housing, removed and cleaned the heater matrix with wet and dry vacuum, I have replaced everything I possibly could.

It’s now all back together with the new down pipe, I deleted the EGR valve and blanked everything off, the amount of carbon buildup in the inlet was ridiculous, I had to scrape it out and used a lot of carb cleaner to get it clean. It was a mission but car is back together and temperature is finally as it should be. Thank you for your advice, much appreciated!

[Nino]

You are very welcome, I am glad you got it sorted.

[Snoopy]

Lot of work, Fingers crossed for you.