Shaking vibrating radiator fan... When AC is switched on

[RUM4MO]

That would be purely guess work on my part if I said yes or no, remote diagnosing most issues is not the way to go.

These AC compressors are quite robustly bolted to the engine block so why/how could a small rotating mass inside that cause a remote radiator and fan assembly to shake around a lot, even if it was terminally faulty, something strange going on with that car, is it even shaking around this morning before the temperature gets hot?

[Olly66]

My thoughts exactly! The car runs beautifully 99% of the time even with the AC on. BUT on the +30 degree days we had recently, with the AC on, and the recycle air button off, there is a strong vibration and loud rumble..... That's it in a nutshell.

[Ricmondo]

Not a Lib Dem Brexit comment but...Airlocks?

I’ve had the same symptoms on a very different very much older and much bigger engined car in very hot weather, air in the cooling system caused cavitation up stream of the water pump, that manifested itself as vibration and a rumble.

Purging the air in the system cured the problem.

I think it is unlikely to be your problem but if all else fails it is something to consider as a last resort.

Best of luck.

[RUM4MO]

In all these VW Group cars and other marques, you tend to find that there is a constant return of a small amount of coolant to the reservoir tank, this is meant to ensure purging of any collected air. Remember this is said to only happen when in hot weather, the AC is switched on to presumably cool the cabin down.

One thing though, there was a poster on one of these VW Group motoring forums who said that his/her car only lost coolant if the chiller was switched on, I don't think that that problem was ever talked about again though!

[Ricmondo]

True.

In the instance I cited the car originally had a thermo-syphon cooling system, a water pump had been added in the 1930s, it also had a complex system of externally piped water galleries to cool the seven litre four cylinder engine so a very different proposition to a Polo.

Fans of the TV programme Chasing Classic Cars may recall that simple airlocks caused the Indianapolis Novi that Wayne was shaking down to overheat and eject coolant.

Moving on to more modern times I have experienced troublesome airlocks producing all manner of problems, they generally arose in the cabin heating system after coolant had been changed or topped up but migrated into the main cooling system. A worn water pump, a slipping drive belt or a partially blocked radiator can also produce cavitation.

I doubt that the problems being discussed are airlock or cavitation related but as Sherlock Holmes sagely declared once all the likely suspects have been eliminated you have to turn to the unlikely.

[Olly66]

Maybe not so unlikely. Not sure if you saw my small addition where I said there is a knocking noise from behind the glove box....a few knocks and then it stops. Maybe the recharge caused an airlock? How would I clear it?
TIA

[RUM4MO]

I'd be sticking with that knocking noise being a duff flap motor hunting.

Ricmondo, CCC, yes it seems to be filling up my PVR these days, wife can't stand it but I kind of like these sorts of progs as it is really only his working life's journal with no BS added in to pad it out.

Edit:- I've had an airlock in a late 2009 Ibiza 1.4 16V, all that was happening was that the cabin heater was being denied regular hot water, it would get hot initially and then stop getting hot water. I later discovered that it was an issue for that engine type, I had replaced the engine coolant temperature sensor as it had given out a couple of duff values which were enough to log a fault code, but as I could not be sure that the old sealing ring had come out with the sensor, I took far too long to swop sensors over, that meant that too much coolant escaped - so when I swopped over the sensor and replaced the missing coolant, I introduced a pocket of air into the system, with that engine type, the correct procedure if replacing the coolant DIY style is:- remove the engine coolant temperature sensor > fill the system with premixed coolant until bubble free coolant is coming out of the mounting point for the engine coolant temperature > while continuing to fill the system with coolant, refit the engine coolant temperature sensor. Doing that solved that air lock issue.

Being a SEAT, there was no temperature gauge so I could not monitor the coolant temperature!

[Ricmondo]

I can’t remember which car it was but one in the 50s,60s had a note in the handbook that translated as ensure the car is parked facing up hill when refilling coolant.

I always make sure I stand on one leg when pouring in the anti freeze just in case.