Question about 1996 Audi A6
I cooked it & have had the head skimmed re fitted & now the water system pressureised very quickly but the heater in the car was blowing cold even though it was set to hot do you think the thermostat is stuck & is it on the back of the head ? Thanks
Hi there, this could be a faulty thermostat but typically, these issues are caused by air locks in the heating system when the car cooling system is drained to take the head off.
The water pump may be working which is fine but there may be some big air bubbles in the pipes that carry the water from the engine to the heater matrix.
Have you tried without starting the car, taking off the water filler cap, not the coolant refill cap but the radiatpr cap. Not sure if this cap is actually on the radiator on the Audi or if there is one locatd closer to the thermostate housing, but once the cap is off top up the water to just below the neck and then squeeze the water hoses around the radiator to try and push water into the cooling system. You need to to squeeze quickly and with both hands to try and force water around the system and then slowly let the hose expand in your hands. Watch for bubbles coming out of the filler so that you can top up the water level again as it goes down. There will be a lot of bubbles if its really air locked and you may have to spend some time doing this. Keep toping up the water level though and once you can't seem to get any more bubbles out. Then if you can close the system again - i.e. put the radiator cap on and go for a ride. if possible find a steep incline where you can point the car up a steep incline and get the engine really reving to push the water round the system.
Go home - wait for the engine to cool and if the heater has not started to work on that trip, once the engine is cool, repeat the process with the hose squeezing to see if you can get more bubbles out, followed by toping up and so on.
If that really makes no improvement the worrys would be that your right that the thermostat could be bad although you should notice that with the temperature gauge moving up pretty rapidly and the car getting over hot if the thermostat is stuck shut. If its stuck open then it wouldn't stop the heater working it would just be slow to warm up.
It could also be the heater valve on the hot/cold switch where teh valve is not opening, and a last ditch issue would be that the water pump is not working.
My advise would be try and clear the air lock first. Also if you have a manual for the car (haynes manual), they normally talk to the correct way to refill the heating system to prevent the air locks. Some times there are venting points on the block that can be unscrewed to bleed the air out but for that you need the manual.
I hope that will at least help some - best wishes.
Posted on Aug 29, 2008
Thermostat is permanently closed because it broke apart and blocked the passage. Change thermostat and check if the IN and OUT hoses are connected to the heater correctly. it looks like there is non-return valve which does not allow water to flow into the heater.
Posted on May 17, 2009
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Posted on Jan 02, 2017
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The thermostat on most internal combustion
engines controls the flow of coolant to the radiator and this is fed into the
top tank of the radiator.
The bottom hose is normally at the inlet to the
Vehicles with AC will have two radiators, and even
some, a third for transmission or oil cooling but the largest of them will be
the one handling engine cooling.
Locate the topmost hose of the radiator and
simply follow it back toward the engine and it is normally connected to a
dome-like fitting, under which you will find the thermostat.
If you are experiencing overheating though, it
may not be a failed thermostat; this can be caused by a radiator blocked with
debris, an internally collapsed hose and worst case, a failing head-gasket. The
latter can fail in several places and overheating is often caused by the
failure of it between coolant channels and one or more of the cylinders. This
allows passage of hot combustion gases directly into the coolant flow.
Check the following: the overflow bottle for traces of oil contamination and possible odor of exhaust fumes, the oil dipstick for a milky deposit and when the engine is running, the overflow bottle for bubbles.
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