Recently, my Heater has been blowing Warm and then Cold, even though the dial is set on Hot.

I drained the water last Autumn and re-filled.

The Heater used to throw out real Hot air ... it's gradually got colder.

I know that outside air has been cold and I don't do many miles in one go - anything else would give the strange symtoms?

Blockage/partial blockage in Heater matrix?

 

First stop for me would be fitting a new waterpump. Sounds as if yours is on it's last legs. Possible seperation of the impeller housing from the driving shaft.

 

Surely it would overheat?

Waterpump driven by cambelt, yes?

I need to do the Cambelt this spring in any case - may do the pump at the same time?

 

I was half asleep when I wrote that... Sorry.

If doing cambelt I would do water pump at same time. Not entirely certain if it is cambelt driven (mainly up on VWs) but should be easy found out. I believe it is on the 'accessory' belt (auxillaries). Past experience says if it hasn't been changed then change it, I've not once met a 5 series beemer with heating issues that was not a knackered pump. I generally find with most vehicles that heating issues are down to either a leaky radiator or knackered pump. Doesn't necessarily result in overheating during a journey but it will eventually when it worsens. Used to be able to drive BMWs for miles and miles before the temp gauge began to break by centre.

Other than that is your passenger footwell wet at all?

 

sure you haven't just got an air block mate!

 

My my99 turbo started to do this a year or so ago, it turned out to be a dodgy thermostat. swapped that out and it's been perfect ever since.

 

Some 'proper' bleeding could solve the issue...

 

Worth a try like cheep enough to replace before of going to the extremes of changing the waterpump!

 

Thanks for the inputs.

I hadn't thought of thermostat .... the Radiator is original (now 10 years old) .... as an aside, last summer I had an overheating problem with my MX5 (turned out to be a silted up Rad!) although overheating isn't an issue in this case.

 

sounds like an air block mate.

 

Cheers for the replies ....

 

Check the coolant level first of all, if you replaced the coolant last year, it is highly likely you didn't get all the air out. It can't be the water pump with what your describing.

 

Have you checked to see what your cocklink is telling you?

 

Done that ..... where's my water gone?

It's never needed topping up at all, ever .. in 10 years!

Guess I didn't get all the air out as you say?

Topped up now with 50/50 - it took about 2/3rds Litre ... It holds 7, so not much of a loss, enough to create an airlock though?

 

It takes about a litre (roughly the contents of the header tank) before you get enough air in the top of the coolant system to cause inconsistent flow through the system. It can be very hard to fill the coolant system without trapping air, the easiest way is to take the robber coolant hose off the header tank that comes from the turbo, and use a funnel to fill the engine through the turbo, this allows water to go to both sides of the thermostat. Once you start seeing coolant well up in the bottom of the header tank, put the pipe back on and top up the header tank, job done.

Paul

 

Thanks Paul .... I appreciate your tip

 

could well be the stat, worst case could be headgasket!

 

^^^ agreed. My last car (non scoob) started blowing hot and cold and loosing a little coolant. The temp level would alternate between hot and cold as the stat would open and close but the car still ran so I reasoned the head was still ok. A trip to the local garage confirmed it was the head gasket, it was slowly leaking coolant into the engine (hence steam out of the exhaust) and was pressurising the coolant system pushing water into the cylinder bore and combustion gasses into the coolant system.

It could just be a big air lock but if you are loosing coolant in a car that has never needed any previously then I would be thinking head gasket.

 

Get Katy Perry on the case........

 

Yeh every time i hear my heater doesn't work, no matter what vehicle, 9 times out of ten it turns out to be the head gasket. but yours could be the 1 out of 10 with a bit of luck!!

 

For me, it's the heavy loss of coolant that I find worrying! It's either being consumed internally, or there's so much pressure in the system, that the cap must opening and ejecting serious amounts!..... This normally would mean HG failure, unfortunately.

SSU, can't you use full boost just round the block from where you live... park up... let engine cool for 10min... carefully remove pressure cap... stick nose in... does it reek of pungent combustion gasses?!!!