How to make your heater hotter
There are a number of things you can do to make the most of them and this advice applies to all of the cars no matter what engine you have.
The first is to clear out all of the pipes. Corrosion and blocking of the pipes that lead to the heater and inside the heater itself is very common. I'll come on to how to do this in a moment
The second is to make sure your thermostat is working correctly, on the motorway or a fast road after 10 miles or so the gauge should sit at around the middle. If it falls to about 1/4 or even lower then it may be that your thermostat is stuck open
Thirdly and this applies particularly to the diesel, when your headgasket fails your heater often ceases to give you any heat (and indeed this may be the first thing you notice as they don't fail spectacularly unlike other engines/cars).
As a basic introduction I'll explain a little about how the heater works.
The coolant has two circuits it may travel around. The first is the heater circuit.
Water is pumped by the water pump through the engine to the thermostat housing where it then travels through some piping into the car behind the dash into a mini radiator with a fan in it which then blows air through it so producing warm air in the car. Then the cooler water is then returned back to the engine where it is again heated up. This process repeats itself continuously when the engine runs. As the diesel engine doesn't produce much heat it can take a while for any noticable heat to be produced in the cabin. Indeed if the heater fan is left on and the engine left to idle forever the car will likely never reach its proper operating temperature.
The second circuit is the main cooling circuit. When the water in the engine reaches a certain temperature (89°C for diesels I think and 82-86°C for the petrol varients), the thermostat opens (which is basically a valve). This then diverts hot engine coolant through the main radiator on the front of the car where it is cooled by air rushing in, when you are moving, or by a cooling fan when you are stationary and then it returns to the engine to be re-heated. The thermostat opens and closes as necessary to keep the engine at its designed operating temperature.
Meanwhile the heater circuit is still operating happily providing hot water to the heater radiator hidden behind the dash.
Now for the corrosion problem.
Antifreeze contains additives to slow/stop corrosion of parts of the cooling system such as radiators pipes etc etc. However these additives are used up over time and so unless the antifreeze is replaced at the correct intervals (usually 2 years for ethylene glycol based antifreeze) then significant corrosion of the cooling system can occur. This gives rise to possible leaks and more often rusty sediment that collects in pipes and radiators blocking them up.
There are various chemical coolant flushes that can help remove some of this rust build up but there are a few steps that I'd do first.
First remove all of the rubber coolant hoses on the car and flush and clean each one out in turn to remove rust buildup. Sometimes the buildup is so bad that the pipes actually feel like they crunch and crack when you squeeze the rubber as the insides are so full of rust. After you've done this then get your hose and flush the radiator through (in both directions if possible) as this will remove more sediment from it. Then repeat by flushing the engine block in the same way. On diesels remove the metal coolant pipe that runs along the back of the inlet manifold and check that it is clear (it probably won't be). If needed poke it out with a screwdriver/wire etc. (my one was so corroded that it actually had started to collapse and leak so I made a new one rather than pay the 60 odd quid that rover wanted). Then replace the metal coolant pipe. Then it is time to turn out attention to the heater behind the dash. When you removed the rubber hoses you'll have removed two from the back of the engine bay which leads to the heater matrix(radiator) behind the dashboard. These matrix's/radiators are very prone to collecting sediment so carefully remove any you can see with a bit of wire from the pipes. Then apply your hose to them turned up high to try and flush the crud out of the system. Then apply the hose to the other pipe and repeat several times until the water runs clear and free from rusty bits floating in it. This can take some time depending on the build up. Sometimes the buildup is so bad that you actually have to remove the radiator from behind the dash and manually clean all of the pipes to remove blockages but hopefull that isn't the case. After you've done all of this then re-fit all of the pipes and refill with plain water and if you feel the buildup of rust is heavy, some radiator flushing treatment. Then follow the instructions on the bottle (apart from it takes a diesels much longer to warm up than many of the bottle suggest. I'd suggest taking a diesel for a 30 mile run on a motorway to get it up to temperature as it'll never reach its operating temperature if it is only left to idle. Then whilst the water is still hot but the engine is off (Caution is needed here), undo the bottom radiator hose clip and remove the hose so releasing all of the very hot water from the engine. The chances are it'll be very rust coloured again. Then leave the engine for half an hour or so too cool down before filling and emptying the cooling system with fresh water a couple of times until it runs out clear. Then refit all of the hoses and fill with the correct mixture of antifreeze (33%-50% antifreeze normally). Don't ever put cold water into a hot engine as you risk cracking the cylinder block/head which will necessitate a new one or an expensive repair. Another tip here is to stick a label or write the date on the expansion tank so you'll remember when you last changed the antifreeze.
Then restart and check for leaks and hopefully your heater performance will have improved. If not some alternative solutions are:
On petrol models - Fit a higher temperature thermostat
On diesel models - Fit a thermostat without a "jiggle pin".
All models - Occasionally swap the top and bottom heater hoses over (easier on the petrol models than the diesel ones) where they pass through the bulkhead to behind the dash can help keep a heater radiator crud free and help unblock them too. (If you are quick you can do this without loosing too much coolant.
If these fail to help then I'm afraid you'll have to remove the dash and the heater matrix(radiator) and either renew it or attempt to unblock it manually.
I hope some of this mammouth post helps and if anything needs clarifying/explaining then please let me know
Last edited by Beaker; 26th February 2005 at 21:29.