I have a 2004 Audi A4 and am having coolant system issues. I seem to be forever bleeding the system as air keeps getting stuck in the heater matrix (so we have no heat) and more recently the temp gauge seems to be going up past normal for a bit and then goes back again. Also,the computer has started randomly saying it is low on coolant. I am assume both these symptoms are because air happens to have got to the sensors.
There are 2 bleed points on it
a hole in one of the hoses which goes to the heater matrix
a nut on a metal water pipe on top of the engine which you undo a bit which lets air out.
Based on my central heating experience ( :) ) I have brought the engine up to temp and then with the engine off (in case it sucks in air when bleeding) I loosen the nut on top of the engine and let the air/ water and air mix come out until it is water only. I then do the same for the heater matrix.
Only other thing to say is that it seems to be losing water (needs topping up in the header tank) about once a week.
I can understand there may well be a leak somewhere but don't understand why it keeps getting air in the system.
Sorry replying to my own post have now woken up properly :) . In my situation, there is always plenty of water in the expansion tank so any water escaping should be topped up by that.
Blimey, this reminds me of my dads old Austin from the 1950s, I guess some things never change in cars. That was a pinn hole leak in the heater somewhere, but in those days you could simply change such bits. Brian
That is one possibility. Another is that in fact the thermostat or water pump is not working correctly so a pressurised valve is blowing off. And coolant is being lost because of localised overheating and boiling and steam
If it were me, i'd strip the entire cooling system, remove the rad, reverse flush it, test it for blockages , test it for leaks by pumping it full of air, check the water pump and replace it and or its drive belts if necessary replace any suspect hoses and the thernmostat as well if it is sticking.
You need to sort the leak first. Some small ones - like say a weep from the water pump gland - can be hard to see, as it evaporates off. This is where a pressure test with dye added to the coolant can help - a leak will leave a mark. Of course the leak could be internal to the engine and costly to fix - but hopefully not and just something simple.
Once the leak is fixed and the system bled, it shouldn't nee doing again.
If it's not externally leaking it can be head gasket failure or cracked cylinder head/block
Bubbles of exhaust gas force water out of overflow. Run engine with radiator cap off and see if there are exhaust gas bubbles coming out. Only do this when engine is cold.
Check oil filler cap does not have brown sludge adhering. (indicates water is getting into oil)
I guess the point I semi-made is that those things you linked to cost a lot and would achieve little. OP already knows there's a leak. I'd start by trying the cheap easy approach, a bottle of leak seal. Sometimes it does. If not, you've got another job to do.
I got mine from Ebay a few years ago. Direct from the far east maker so much cheaper than the same thing with a Sealey label on it. Very nice quality too.
But you can't safely poke around a running engine looking for a leak. Where a pressure tester comes in handy. Also useful when re-filling an engine cold. Allows you to bleed it more easily.
No they cost a lot as a one off private purchase because they are the tools required for the correct diagnosis. Coolant sniffing takes all of five minutes and should quickly eliminate most cases of combustion chamber to coolant system head gasket failures, a pressure test with fluorescein dye in the coolant taking half an hour should locate or eliminate most if not all hose, radiator, heater matrix and water pump gland issues. A performance test from cold to determine thermostat operation is a ten minute from cold start job. Hot coolant can leave mineral deposits but hose runs are frequently impossible to fully inspect, water pumps buried behind the timing belt in an enclosed housing can leak without showing any obvious signs of failure.
You could even have issues with coolant being topped up with just antifreeze, so the concentration goes high and the specific heat capacity of the coolant is reduced, with not enough heat rejection a blowoff of coolant in heavy traffic is possible.
Replacing the likes of a thermostat or water pump 'on spec' can cost 500 quid or more on some cars as it can also require cambelt removal which might entail diesel pump retiming costing 500 quid or more. Same with radiator removal, that often requires bumper removal and a front frame moving to the service position. Ever tried to disconnect a radiator hose on a modern vehicle? No traditional hose clips, no traditional hoses even but integrated clamping to semi rigid aluminium and rubber coolant lines. A bit of road salt trapped in the wrong place and removal means replacement not only of the radiator but the coolant lines as well. Call it 1k or more with labour to fix a problem you haven't even properly diagnosed.
That is why proper diagnostic techniques while the car is still fully assembled are required. Disturb as little as possible, identify the issue and fix what really is faulty.
Leak seal IS always a bodge, the kind of thing that is done because the so called mechanic hasn't got a clue. Yes you might get away with it but do it on some engines and you disguise the real issues leading to much higher repair bills later on. The K series in the Lotus Elise is a case in point, piss about with leak seal and you WILL terminally damage the engine, almost everything but the ancillaries terminally f***ed. Whereas replacing the head gasket, replacing the locating dowels and fitting the later modified thermostat arrangement will 'fix' cooling issues almost certainly forever.
Time you checked again. Our relatively extensive petrol fuelled 'fleet' dates from the 1950's to the present day and all but two require bleeding when replacing the coolant. The exceptions being one dating from 1960, the other from 1972.
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