Heating blowing hot/cold at different speeds

[pumapuma001]

Hi
I've had ongoing heating issues with my 1.7 Puma, the heater would blow hot and cold randomly and recently I noticed the engine overheating after travelling 20 miles or more.

After researching about it, I decided to change the HCV and this sorted the overheating. However the heater still blows hot and cold. If I drive 40mph or under, the heater will blow hot air constantly. If I drive over 40 mph it will turn cold.

I've checked around the oil cap for any white residue and have not seen any so I'm guessing the head gasket is fine.

Anyone had the same issue or has anyone got any ideas what could be wrong?

Thanks
Jeff

 

[pumapuma001]

Should have added - before changing the HCV it would blow hot and cold regardless of what setting I had it on.

Since changing the valve, it will blow cold on cold / hot on hot, but the strange part is when I hit 40mph it comes out cold...

 

[quest63]

Did you change it for a genuine Ford HCV? cheap ebay ones are frowned upon as unreliable

 

[pumapuma001]

I was an ebay one and seemed to have done something as the car doesn't overheat anymore. The heating issue has always been there even before changing the HCV though. If I got a genuine Ford HCV and it didn't fix the issue, what else could it be?

 

[quest63]

If it isn't the HCV, heater problems are then usually caused by the heater control panel with the switches on.

I just want to make sure though that the lack of hot air at certain times isnt just the fan stopping blowing rather than say the HCV misbehaving or water not reaching the HCV due to an airblock in the system. Are you sure the fan is still blowing when t goes cold?

Where does your temperature guage needle usually sit at?

 

[pumapuma001]

The fans are working as I was experimenting on my way into work this morning and have tried it on high and low. The same thing happens. The temp gauge sits at normal all the time (in the middle).
Not sure if there's an airblock in the system though. When I replaced the HCV I drained the system and started afresh with new coolant, pumping it through making sure it was circulating ok etc. After a few days I had noticed the water dropped below the min so I topped it up and its been fine ever since.

 

[martyc]

A couple of things spring to mind... Thermostat, is this working properly? At increased speeds the airflow is greater, increasing the cooling effect thru the rad. If its over cooling because the stat isn't closing when temp drops this 'could' cause the coolant temp to drop. The other thought is water pump. If it isn't circulating the water properly the coolant flow through the matrix wouldn't be constant and may cause fluctuations in heater output. These could be far out and are not puma specific but I have had both these faults on other cars in the past (ironically, both fords, one of which ended in engine failure) so thought they could be worth mentioning

 

[Ginger Tom]

I understand what your saying Marty but with both situations I would expect the temp gauge to fluctuate.

The water pump situation would generally show itself when in traffic due to the lack of air flow through the radiator, had that on me mums tt pile of crap.

The stuck open thermostat would generally show itself on a long journey with the improve air flow, whereas the stuck closed would show itself again when in traffic and from start up.

I accept that these are generalisations.