no hot air till i drive

[1992julian 10]

hello, my 1.8 16v wont blow out any hot air till i drive it why would be doing this? i jsut changed the thermostat, could it be the water pump? thanks in advance if any one can help

[VW_OwneR_85 1]

I guess it could be water pump , my thought towards that would be its lost some fins so its not circulating coolant very well on idle, and when you drive it at 2k + revs it then has enough oommphh to circulate the coolant around , you can see how well the pump is circulating by the small coolant return hose at the top of the expansion tank, you should have something comming out on idle and the more you rev it the more it will flow,

[swiftkid 1]

What do you mean 'until you drive it'? As in when you stop at traffic lights it is not blowing hot air or as in you leave it on idle from start and won't blow air until you drive it?

 

If you have recently done thermostat it might be an airlock or as VW_Owner (sorry don't know your name) says the fins might be bust on the water pump, it wouldn't be the first time I've seen it happen thats for sure.

[1992julian 10]

when i first start the car it just wont blow hot air for as long as i wait but as soon i drive it comes out warm and stays that way, just needs to be driven before any hot air will come out

[16VG60 1]

From cold, before you start the engine is your coolant level correct in the reservoir? If not the first item to loose circulation is the heater matrix. However once driven the coolant would be pumped into it and of course once heated the loss of water to it when idled get thereafter would not be so much noticed. Do you have one of those nasty diverted valves fitted that were part of a recall to prevent the old type heater matrix from grenading? These valves are often ok to start with but after a few years cause significant coolant flow issues like that which you are experiencing. If you do have one of these fitted, then my advice would be to remove it and your matrix and fit the later matrix without the bypass valve. Otherwise as others have said, an airlock is another favourite in these situations, but however, once cleared it should not re-occur with every engine start. Worn pump is a possibility, but would be very unusual. I hope this helps to resolve this annoying fault.