Volkswagen Passat Forum banner
1 - 20 of 29 Posts

·
Registered
Joined
·
3,286 Posts
Discussion Starter · #1 ·
Turned on the heat on the first chilly morning and it's barely warm. I'm figuring it's either a clog or airlocked. If I flush it, what's better, water or air? The only thing that concerns me about using air is that I might damage the heater core and from what I can tell, it seems that the core can't be replaced without pulling the dash. Regardless of what I use, should I flush in the opposite direction of flow?
 

·
Registered
Joined
·
28,326 Posts
Reverse flush with water. Check that the temp guage is reading 190, if not, the thermostat may be stuck open. If it overheats on the highway, the water pump impeller is slipping on the shaft.
 

·
Registered
Joined
·
3,286 Posts
Discussion Starter · #3 ·
Reverse flush with water. Check that the temp guage is reading 190, if not, the thermostat may be stuck open. If it overheats on the highway, the water pump impeller is slipping on the shaft.

Thanks. I'll use water. The stat should be okay as it's fairly new and the temp runs normal. I changed it as well as the pump when I did the TB. It had the new style bronze(?) impellor.
 

·
Registered
Joined
·
28,326 Posts
You might have an air pocket, but the flush would not hurt. Just bleed the system at the hose to eliminate any air when you are done.
 

·
Registered
Joined
·
715 Posts
I'm glad this thread came up. The dealership told me that I need to replace my heater core. I noticed last year that my heater was blowing cooler and cooler. At one point it was blowing cold air. When the winter was getting ready to end it starting blowing warmer if I set the temp to 79 or 80 degrees. Do you guys think that I need to replace the heater core or should I just have the system flushed. If the core was bad wouldn't it blow cold air all the time. I need help with this because the winter is around the corner.

Thanks
Dwight
 

·
Registered
Joined
·
28,326 Posts
I'm glad this thread came up. The dealership told me that I need to replace my heater core. I noticed last year that my heater was blowing cooler and cooler. At one point it was blowing cold air. When the winter was getting ready to end it starting blowing warmer if I set the temp to 79 or 80 degrees. Do you guys think that I need to replace the heater core or should I just have the system flushed. If the core was bad wouldn't it blow cold air all the time. I need help with this because the winter is around the corner.

Thanks
Dwight
If the core was bad it would leak. If it is clogged, it may get warm and cool off as you drive. You probably have a problem in the Climatronic instead of the core.
 

·
Registered
Joined
·
12 Posts
My core is probably gunged up abit as my heater only blows warm.
Hae tried many ways to clean including domestic radiator sludge remover.
 

·
Registered
Joined
·
28,326 Posts
The best way is to remove the heater hoses and run a garden hose to the heater. I don't know which is intake on the heater though.
 

·
Registered
Joined
·
3,286 Posts
Discussion Starter · #10 ·
Just flushed the core and it stayed clean for one minute. I removed the reservoir and a two teaspoon blob of what looked just like mud came out. It must be collecting in all the low velocity areas (throttle body, reservoir, and heater core).

I could do a rinse and fill, but I don't think it will help. I remember there used to be kits where you tee in a garden hose to do a continuous flush. This worked fine on my 64 chevelle with an iron block and heads, but would this be ok on an engine with aluminum heads? I'm thinking not.
 

·
Registered
Joined
·
3,286 Posts
Discussion Starter · #11 ·
Okay, now I'm a bit worried. I disconnected both the inlet and outlet with the engine running fully hot. There is barely any flow at idle. When the idle is brought up there is plenty of flow, even when the inlet is connected to the core. I had to bleed it with the engine running at 2000 rpm.

The pump and stat are fairly new and the engine holds the temp steady (dash guage, not vag-com). Is this normal? Anything I should check?

Engine is an ATQ.
 

·
Registered
Joined
·
28,326 Posts
I never checked flow rates at idle. It should flow more at 2000 rpm. How is the heat working now?
 

·
Registered
Joined
·
3,286 Posts
Discussion Starter · #13 ·
I must have a ton of crap in the system. The issue comes and goes. I think the previous owner used G11. When I did the TB I couldn't get a good drain as I didn't have a John Holmes 5mm hex bit.
 

·
Registered
Joined
·
3,286 Posts
Discussion Starter · #14 ·
OK, this thing is killing me. I bled it and reclamped it with Oetiker clamps. Tonight- no heat.

I'm thinking the problem might be in the dash. What physically happens when the heat knob is turned? Does it move a coolant diverter valve, or does it move a flapper in the heater box?

PS- Winter has finally arrived here, so I have to get this done.
 

·
Registered
Joined
·
3,286 Posts
Discussion Starter · #16 ·
Besides a trained mouse with a helmet-cam, is there a way to check the flapper connection without taking the entire dash apart?
 

·
Registered
Joined
·
2,249 Posts
nm...
 

·
Registered
Joined
·
67 Posts
I have the same problem - very little heat at idle. I have flushed and flushed the heater core and what goes in comes out at the same rate. I have bled the air out through the weep hole until it ran with coolant flowing for a while. Not long ago I flushed the system, but I have never found any significant bits of trash or sludge in the system. No doubt it has had the wrong coolant at some point because the tank is stained brown inside.

The flow out of the heater core at idle is very weak - I don't think there is a heater control valve on these cars ('02 V6 here), but if there was I was suspect it wasn't opening properly. I have searched and searched and it always goes back to a plugged heater core, but mine doesn't seem to be restricted at all.

Stumped!
 

·
Registered
Joined
·
23 Posts
My passat has started this cold heat business last month. I was hoping it was a diverter valve or heater control. Whats the best way to flush the heater core?
 

·
Registered
Joined
·
17 Posts
Same problem here. Thank God for heated seats! It's supposed to get really cold here so last night I finally brought the car in the shop, pulled the cowl cover, clamped the two heater hoses with clamping pliers, pulled the hoses off the core and flushed the core out with the water hose. Not much flow through the core at first, then flow increased and back flushed the other direction. On the way home lots of heat...first time when it was cold out that I was able to turn it off "HI".
 
1 - 20 of 29 Posts
Top