I have an 05 VW Passat TDI and I'm not getting much heat in the cab. Just wondering if anyone here can shed some light on what I could look for myself. Had it to the dealer, they said they'd fixed it and took some of my money but it still doesn't heat.

Can you control cold to hot with a good amount of change?Is the blend door sticking?Is the 2 hoses to the heater core the same temp? Sign the heater core is plugged up.

Yes there is a good change from hot to cold, just the hot isn't very hot. So I'm thinking the blend door is ok. I'll check the hoses.

Engine temperature? A stuck open thermostat will not have heat to bring into the cab. If there is one good warm hose, then blend door or ?? Can you drop the blower motor & check for heater core obstruction with leaves or mouse nest?

Engine warms right up so I'd be surprised if it's a thermostat but... And there is good velocity of air coming out the vents.

Did you search on the VW forum? http://forums.tdiclub.com/ This is by far the best forum as far as technical info goes I have ever seen on the web, tons of info and lots of help. I go here whenever I need VW help on my 03 TDI. I have never been let down yet.

iThanks for the added info. A heater is a heater is a heater... the components are all similar & none of it rocket science. Let's try to eliminate the easy stuff before taking things apart. If the engine warms up properly then the coolant has enough heat. The vents blow air so the suction & bird case (I mean "dizzy mouse cage") are not likely problems. Locate the heater hoses under the hood... can you put your hand on them? After warmed up, is one hotter than the other? Is there a control valve in the hose like some vehicles? If there is a control valve, does it move when you change the controls? If nothing external can be found... then likely the blend door.

Thanks, I went there and got some good help. Now I have excellent heat when driving or when the car is parked but idling at or above 1200 rpm. Any time rpm drop below 1200 I can feel a drop in temp, even tho my SGII shows no drop in coolant temp.

Did you search on the VW forum? http://forums.tdiclub.com/ This is by far the best forum as far as technical info goes I have ever seen on the web, tons of info and lots of help. I go here whenever I need VW help on my 03 TDI. I have never been let down yet.

I would look at the Temp control on the heater hose, it is perhaps not functioning properly. It could be Vacuum controled or cable or even electric, just not sure. But since you lose heat when idleing, it would point to either, low vacuum, or electrical current not allowing the valve to stay open. Could also possible be a stuck thermostat, or clogged passages in the heater core or Radiator or both. Also when was the last time your Coolant was changed? If your PH is off it may have caused an issue the impeller on the water pump to erode so that it is not moving enough water at idle, or other internal damage.Could also be heater fan not getting enough current at idle, or one of the air intakes is blocked with leaves or similar.In any event if it works at speed but not at idle, it has to be close to something I mentioned. No heat= no/low coolant flow or low air flow over the core.

Thanks George. I did a pretty thorough heater core flush and that improved the problem immensely. Not totally happy with it yet so I might look into your ideas.

Has to be something simple. Good luck.

I'd question the water pump.. Mk4s (factory WP) used a composite impeller. Most aftermarket units (i.e. from www.germanautoparts.com) have the steel impellers. The composite one are known to separate from the shaft and not spin at full bore, often eventually crumbling to bits and then you've got bigger problems. when was the last WP/tbelt swap?

I bought this: http://www.ross-tech.com/***-com/index.html a few years ago for our Passat. Cost about $120 after an upgrade and it is amazing how much info it will give you. I think I paid around $50 for the basic software and the interface on ebay and another $70 from ross-tech for the upgrade. I scan it sometimes just to see what is going on and there is usually a soft code for some kind of heat/ac issue. Blend door fault if I remember right.

Indeed, the ***-COM is an indispensable tool for VW owners.

I'd question the water pump.. Mk4s (factory WP) used a composite impeller. Most aftermarket units (i.e. from www.germanautoparts.com) have the steel impellers. The composite one are known to separate from the shaft and not spin at full bore, often eventually crumbling to bits and then you've got bigger problems. when was the last WP/tbelt swap?

I think it's coming due shortly. When I bought the car last August I checked into that and it had been done at the correct time. I will sure check into it.