Hot or Cold

[benjam_in]

having a bit of trouble with my heating at the mo when the water gets hot so the needle is pointing straight up when i turn the heating on i get cold air but when its a little cooler i get hot air again! any ideas??

[Paulio]

Alright mate,
   
                 have got a very similar prob myself at the mo and have had a few suggestions. i was told that it may well be the heater matrix which has packed up or that it could just be a blocked matrix. it can become blocked when changing or topping up the coolant. what you can do is take the cap off of the expansion tank and leave the engine running with it off to allow it to boil and expell any trapped air that might be blocking the matrix. Out of curiosity what year is your car mate?

[benjam_in]

1988 will give that a go see what happens

[tobz.]

If your car is getting too hot you may be building up excessive pressure in the cooling system and that's when the heater matrix bypass valve will cut in. These valves were fitted as a recall on mk2's in the 1990's basically it stops your heater matrix exploding and scalding your feet. As the temp drops again the pressure lowers and the valve will allow coolant to flow through the matrix once more.

As for why your temp is getting that hot it could be a number of things, change your coolant and ensure you have the right mix of antifreeze, is your rad fan working?, has the head gasket gone?, is there a slight blokage in the system somewhere?

Tobz

[rubjonny]

The normal operating temperature is in the middle on the gauge so that sounds OK.

The bypass valves do go wrong, first thing I would do is remove them and replace with straight through piping, then see how it goes.  If you get heat again you know the valves were at fault and can consider getting a new set if you feel uncomfortable with them removed.