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New here and probably a bit late for a reply, but if it helps. I've had my 2015 3.0TDi (241bhp) for nearly 8 weeks now and with predominantly short trips (1-5miles each way) and a couple of slightly longer ones on dual carriageways I've averaged 36.6mpg. Coming from a 2008 Mondeo 2.5t that would average about 18mpg on the same runs I'm over the moon with it.

Just signed up looking forward to getting involved . my name is Paul. I have a 2013 Q5 3.0 TDI S Line, my son has the 2008 Q5 3.0 TDI Quattro SE. Live in Boston I own a Ross Tech VCDS , just like my golfing all the gear and no idea. but willing to learn. 68 year old and a memory like a sieve 🙂 so be nice to pensioners please 🙂

Chris. I have looked again at the videos at full screen which has made things clearer. All I would add is: 1/ The knocking is unrelated to the lack of coolant circulation. The knock may be within the engine, or connected with the alternator pulley or bearing, or an engine mount, or the exhaust hitting something. I really can not be any more specific. 2/ The oil ring on the underside of the bonnet indicates the engine has been run without the filler cap at some point. Whether it blew out in the crash (which seems very unlikely) or was not secured after the last oil top up I can not say, but pressure in the crankcase would blow oil spray out of the filler pipe without it. 3/ The lack of coolant flow is likely to be an air lock as mentioned earlier, particularly if it was OK before the crash. However if you want to test the system for blockages you need to drain the radiator, disconnect the hoses, and run water through it from a garden hose. The radiator should easily cope with as much water flow as you can give. You could also do this test on the engine block if you remove the thermostat first. (Test the thermostat while it is out by putting it in boiling water.) Do the same to the heater matrix, though of course the flow will be lower.

Had my new (to me) Q5 for a couple of months now and thought I'd sign up having found forums very useful with my previous cars. 2015 Q5 Mk1 facelift with a 3.0TDi S-Line Plus..... Still learning lots as this is my first Audi after spending the last 9 years with a Mk4 Ford Mondeo 2.5t, but I have managed to make a few modifications to her already including - OBDEleven module so I've activated Drive Select with additional modes, fog/cornering lights and gauge sweep. Interior LED light swap. Carplay unit from AliExpress so I can have Android Auto again. Front and Reversing camera's which link into the above unit. Rear armrest from a Q7 so I could get the integrated cup holders, was surprised it was a direct swap. Retrofitted footwell lights front and rear. Retrofitted the active door warning lights and puddle lights. Nice set of alloy pedal covers that match the Mrs' Skoda Enyaq's. RamAir airfilter. Botslab G980H front and rear dashcam from Amazon. And an adjustable dipstick as I'm stuck in my ways 😁

I can't answer your questions Chris as I have not done the job myself. Neverthless you ought to investigate further as that knock indicates something is wrong. It may be unrelated to the cooling system, such as a broken engine mount for instance. No I could not see any oily mark. The videos were too small and jerky for these old eyes to follow so I just listened with my eyes shut. I did hear you talking about an air lock. That is a real possibility on these cooling systems, and can be a devil to remove. Squeezing the hoses sometimes helps, other times you may need to apply vacuum to expand the air until it reaches the reservoir.

It's satisfying to the job yourself but sometimes you need the big guns of a professional, whether they be impact wrenches or a lift.

Thanks for the videos Chris. The moving images are confusing, but at one point I did hear the knocking you mentioned above the normal diesel rattle. I think you will need to remove the radiator to get to the bottom of this and ensure that the fan is not hitting it. Check that its mounting points have not been bent out of position. You may even have to renew the radiator because too many of the fins appear to have been flattened to allow decent air flow. Note that the AC radiator will be immediately behind the engine radiator. There may also be a gearbox oil cooler there as well. Both will need to be disconnected.

Chris. Please clarify how much damage there is to the radiator. At one point you mentioned minor damage; elsewhere you mentioned it was caved in and had lost all its coolant. The ticking noise could be the fan contacting damaged radiator fins. I assume "the lid of the overflow tank"which you left off, is the pressure cap of the expansion tank. To run without it will allow the coolant to boil away because the system can not develope the necessary pressure.