My -96 Audi A4 1.6l motor ADP. Heater does not blow hot. The engine is a normal hot or even too warm. Water does not circulate in the system correctly? The thermostat works correctly in my view, although the lower radiator does not heat up. Thermal sensors have been replaced, water pump has been renewed, Visco is renovated, upgraded radiator, belts have been replaced. I think that the warm air from the heater cell stateroom, guiding the flap does not open. I do not know if any even exist. Water flowing into the cell heater is hot. I would like the heater exploded view of channeling and control flaps. I do not understand the heater operation buttons features. Some of the linkages move the buttons, some do not? Audi Dealer did not know how to fix a defect, they will renew only cooler. Is it possible that the heater cells may be blocked, yes I have flushed it. Regards, Mika (not Hakkinen)

the way any motor vehicles interior heater works is by allowing water from the engines cooling system to circulate through a mush smaller radiator located behind the dashboard and the fan blows air through the radiator allowing the warm water to heat the air so when you select warm or cold via the interior controls a valve fitted in line of the water pipes that is linking the engine bay radiator to the interior one allows water to flow which makes me believe that valve is not functioning

In normal circumstances the heater wouldn't begin blowing warm air until the vehicle has travelled 5 miles - call it 5 minutes. That's because the thermostat only begins to open at around that mileage/time and allows coolant to circulate around the engine. Before that - there just isn't any warm coolant in the heater matrix.

After 10 miles/10 minutes of normal driving the engine will be at its correct operating temperature and the coolant will be hotter - as will the circulating coolant in the heater matrix. That's when the heater blows the hottest air.

If you're sure that the heater has lost efficiency it may be due to air being trapped in the heater matrix/coolant system, or a blockage caused by limescale/engine corrosion within the heater matrix itself.

To remove any trapped air, set the heater to maximum, remove the radiator cap/coolant bottle cap and let the engine tick over for 10 minutes.

If the heater matrix is blocked/partially blocked, drain the coolant system, refill with plain water, set the heater control to open .. and let the engine tick over for 10 minutes. Drain it again.

Refill again with plain water and add a can of 'radiator flush'. Follow the instructions on the can of 'radiator flush'.

Drain again and refill with coolant/water.

If the heater is still inefficient then the only option is to replace it - and that's not an easy job.

If the temp gauge is now more stable, the problem is in your heater system, not the engine cooling system.

After the engine has reached normal operating temperature, feel both heater hoses going into the firewall. Are both hot? If both are hot, it's probably the door or doors in the heater case not operating from the selector knob on the dash. If only one hose is hot, the coolant is not circulating through the heater core. Look for a water valve in the hoses that is shut. If no valve, crack open the cold line to see if you can start circulation through the core. If neither hose is hot, pull off the inlet to the heater core (it may come from the cylinder head area) and run the engine and check stream flow. It won't spurt out like a garden hose, it should flow out in a smooth even stream, maybe just enough pressure to push a steady stream. If no flow comes out, coolant is low, or there is a circulation problem in the engine, like a kinked hose, a weak water pump...
Does the radiator cap hold pressure in the cooling system?

Are both heater hoses hot when the heater is on? Look for the water control valve to see if it's letting water into the heater core. The core could be plugged too.

The next possibility, if you haven't already thiught of it, is as simple as making sure there is enough water/antifreeze solution in your radiator. If the level is too low, your hoses will get hot, but there will not be enought water to circulate into your heater core.

check the level of antifreeze', or it may be that your thermostat is sticking.

sounds like the thermostat is not functioning correctly? either that or not in at all? thus making the water which would normally warm up quickly, warm up extremely slowly and on really cold days not at all? with a 2.6 engine your car shoudl warm up in record time?

My 2005 Nissan Sentra 1.8s with 55,000 mi. blows cold air from the heater. Coolant not circulating in engine. Lower hose stays cool to touch. Both heater hoses cold. Changed thermostat - didn't fix it. Coolant not leaking or dirty. None in oil - no oil in radiator. Changed worn water pump belt - pump spins freely with no noise or resistance. Cooling fans come on after warm-up. Temperature gauge stays in normal range then jumps to hot and back again. Coolant good to 10 below - didn't freeze here yet. No other problems or repairs to car. Afraid to drive and make worse. Help!

My 2002 Audi A4 doesn't produce the hot air, It's an Auto computer control temperature system. I took my car to the local mechanic (gas station), he said that the water pump and the timing belt need to be replaced.

The heating system normally produces by the engine, then normally the "thermostat' is causing the issue, but the temperature gauge doesn't indicate the overheat.

Any idea what's cause this problem?