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Re: no heat 2002 passat
If you want to back wash just reverse the hoses on the outside where they connect to the heater core. if that don't work look on each hose and see if one of them has a device that has a vacuum line running to it . If there is this is a water shut off thats activated when the air con is on. temporarly you can just put a coupling in where the device comes out
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Chances are it is indeed the heater core as even a spent heater unit will blow hot air off the engine when the ambient temps are hot . When the temps drop, the heat from the engine block is not enough to heat the cab properly. Have you tried the old cardboard in front of the radiator trick? Speaking of semi's,ever notice they cover their radiators in the winter? That's because it helps get their block temps up a little higher and assists with heating as well. It's not much help but do the buyer a favour and let them know beforehand. Have a good one. :)
Do you live in an extremely cold region? If so, those folks usually have a problem with heater in winter time. With a fully warmed up engine, how hot does it get in degrees F? Are the heater hoses hot?
Sounds like a flow flap or vacuum control head issue. The system uses 1 blower motor and one fan resistor. Both systems are intergrated to produce a BLENDED temperature. This means that to raise A/C temps originating at say 20 degrees to come out of the ducts at 45 degrees for cooling you need airflow through the heater core WHILE the A/C is on. This is done with a blender flap. Hot air that is potentially matching the water thermostat (165 degrees) is expelled to blend with the 20 degree air to raise the discharge temperature to 45 degrees and up. In winter, the A/C is engaged by design to keep the compressor lubed with oil. Usually this happens in Defroster mode, but through either Design or defect, may occur in heat position. Now some of the Digital Climate control units have a Diagnostic sequence you can activate with certain button pushing combinations. Research Your Model, Year and then Climate Control Diagnostics on the internet. The sequence is something Dealers know about. This Diagnostics would identify a malfunctioning Flap valve actuator. I recommend people to visit a Salvage yard which allows you to dismantle a car yourself and see how the car is built. Hope this helps and makes sense to you.
P0507 Higher idle speed than expected partially stuck open thermostat engine running colder than normal raises idle speed. Small vacuum leak raises idle speed. sticking throttle cable holding throttle plate open. P0741 Torque Converter Clutch system stuck off : Code conditions : No engine or transaxle system codes set, engine run time over 5 seconds , Throttle Fluid pressure switch not indicating Park/Neutral,TCC commanded On @ max duty cycle, throttle angle over 8% Trans fluid Temp input 68-248f Degrees not in fuel cut off, trans gear ratio indicates 2nd, 3rd, 4th gear delivered torque 32-150 ft lbs, the PCM detected a TCC slip value that was over the torque limits . most likely cause is bad tcc solenoid or torque converter itself. Trans shop can diagnose and repair
stat is like 8 bucks,labor should not be more than 40 (at my shop) worried the heater core may be the problem tho. That is a very costly job.Try this,put a "winter front " on the car,piece of cardboard in front of the rad. I am assuming this car has no temp. gauge,so the winter front will make the water temp go way up,if the heater works after like 5 miles of driving ,cool, the stat is bad,if the heater still doesn't work the heater core is bad. The whole dashboard has to come out for the heater core ,yuk Don't drive more than like 20 miles with the radiator covered,just to be safe,
If your temperature gauge and actual engine temp are normal and coolant level is full, you don't need a thermostat.(normal run temp is from 200 to 210 degrees. Likely your problem is a blend door not moving properly. Unfortunately, most controls on your heater box are inaccessible and the entire box needs to be removed (big job, get a manual or have a shop do the work)
your radiator could be getting stopped up. also water pump could be weak. during summer though you have electric fans that should be working. need to check. you can purchase some stuff called water wetter by redline racing oil that will drop water temp 20 degrees which is substantial when a thermostat is usually 180 to 190 and boiling is 212.
Previa heaters are usually ultra-reliable.
So, regarding your question, the only reason for the temp gauge to drop down with the heater on is the thermostat is sticking open, or you have a lower than recommended thermostat installed. The factory thermostat is a 192 degree F/89 degrees C stat. Down your way, a lot of the parts places vend the "summer" thermostats, and I suspect that this is your problem.
Look to see what the temp degrees that are printed on the stat. Should be 192 F or 89 C. The "summer" stats are 185 F/ 85 C. Also, make sure that your stat has a small "wiggle valve", some aftermarket stats do not have this. Very important. Install the stat with the "wiggle valve" pointing straight up/12 o'clock...
Regarding your trans dropping out od OD, this is because the coolant temp is dropping below 172 degrees F. This is the threshold for the OD to engage. Below 172/no OD engagement.