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No hot air even when hot

2K views 15 replies 8 participants last post by  unsavoury 
#1 ·
So today I overheated and instantly leaned for the hot air, I didn't get any, all I got was cool and refreshing air..


I know the engine was hot though as the temp was in the red and steam was coming out the back.



What the devil is causing this then?
 
#2 ·
An air lock or a blocked heater matrix.

Try bleeding the system first from all THREE points.
 
#4 ·
It can be hard to eliminate airlocks.

Did you overheat after a nice run at fairly high rpm, then slowed down coming off a slip road to a junction/roundabout/lights etc and the coolant boiled?

That's the usual way an airlock manifests. If you are going fast, the water pump keeps it moving - the pump pressure goes up with the square of the rpm, so it comes down fast at low rpm. You then get the airlock resting maybe in the water pump and no coolant flows.

Bleed it again. Try setting the heater matrix to hot when you do it.
 
#10 ·
You'd better find where it is going then!

It could be leaks in the coolant pipes, radiator, of the coolant reservoir filler cap. Or it could be head gasket failure.

Two litres is a lot. If it is going into a cylinder the spark plug should look different to the others.
If it's going into the sump your oil should look like coffee. Plus, you should be seeing mayo on the end of the dipstick.

It need not be HGF though. Radiators fail with fine pinhole leaks. The underbody coolant pipes rust out after about 10 years - you can see them with a torch if you look from underneath the sills. The inlet manifold gasket can go. Coolant may be dripping onto the ground, have you examined the ground after parking up?

You need to do some detective work.
 
#12 ·
When I bought the car last month I arrive home in a cloud of steam, I didn't see the temp dial though. I was told on here it was probably the coolant cap as they fail.

I didn't get one but kept meaning to and in the time since buying it have hardly used it. In that time it's been serviced and the guy showed me evidence of a previous coolant leak but couldn't find one now. I asked about the three bleed points and he said he knows there are two at the front and one at the back.

When I drove it Sunday I over heated on the way to where I was going and on the way back so by Monday the expansion tank was pretty empty from all the lost steam.


My plan is to replace the cap and ( now I have bought the right size socket) bleed the heater point.
 
#14 ·
My best guess from all that you have said is that, when the coolant was changed, the heater bleed was not done. This would lead to considerable air entrainment in the heater circuit. On heating the trapped air will expand rapidly blowing the coolant out, probably through the filler cap. Hopefully, that is what has happened and no other connections have blown.
The heater bleed screw must be opened to expel the trapped air, be careful because these can clog up with gunge over time. It is best to remove the screw completely to ensure that it and the housing is clear and water is flowing through.
Whether you get yourself the correct socket or leave it with someone else to do is up to you but this needs sorting as a matter of urgency before the other, well known, consequences of overheating raise their ugly heads.
Best to invest in a new filler cap too.

Best of luck with it all

Mike
 
#15 ·
Bear in mind, even if there is no coolant patch on the ground, it is possible to (a) get a 'drying' leak, where the car leaks small amounts when hot and basically evaporates the leaked coolant from a hot surface and (b) you can get a pinhole leak in for instance the radiator, where you get a very fine jet of coolant coming out when it's under pressure, that might just spray so fine that there won't be a visible damp patch and in any case it stops very soon after the engine is cooled off.

I'm not saying this is what you've got, but it's as well to keep an open mind about the possibilities if the coolant loss persists.
 
#16 ·
Bled the heater point now, didn't seem to get air bubbles though there was a gap before I got liquid so I guess that's it. I'll pop the new cap on when it gets here tomorrow, test the heater and if it works well assume my overheating should be ok.


Actually I'll drive round the estate for half an hour and try and see if it does, that way I'm only up the road if it goes nuclear
 
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