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2004 Volkswagen Passat Gl Engine 4 Cyl.1.8L "runs cold"

1. Changed out thermostat thought it was stuck open ( new one same problem). At idle Kinds worms up to @ 130 F. With a/c on a hot day gets up to 190 f. so good gauge works, never runs hot or over 190. 2. On a cold day worms up to @ 110 f. at idle; BUT! when you start driving temperature drops down to ? BOTTOM MARK on gauge. Stop at idle for 5 to 10 min and temp comes up to @ 130f. And heater starts to get kinda warn again. Heater never gets real Hot even when on Hot day with 190 F. water temp but does get REAL WARM BUT NOT REAL HOT LIKE IT SHOULD. It's like it has a thermostat temp BYPASS for NEED of warm Heater air. Heater Core circulates all the time the same. ( I did do a flush out on H/C seemed like a good flow with just gravity flow pleasure only). Put a water plastic drinking water bottle on and squeezed it and it squirts out ok bough direction.

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Heater core is not working.

Posted on Jan 15, 2013

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Posted on Jan 02, 2017

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SOURCE: 89 Gas F 150 Completely flushed engine,rad and

yes, the radiator cap may not be holding pressure. that may be your problem, also make sure all air is out of system.

Posted on Dec 22, 2010

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SOURCE: heater slow to warm up 2000 528i

Have your thermostat checked, sound like it is not working when cold.

Posted on Nov 13, 2012

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The heat in my Volkswagen passat 2002 only gets warm while driving. when sitting it blows out cold air. what is wrong with my heat

Sounds like either low anti freeze, thermostat is not working or your heater core is leaking. Is there any anti freeze leaking under the car? You water pump could be bad if there is fluid on the ground below.

Jan 28, 2015 | Volkswagen Cars & Trucks

1 Answer

Heaters running cold at 90 degrees

If the engine is running at a normal temperature I would suspect the thermostat.
Normally from a cold start the coolant should only circulate through the bypass hose, the heater matrix, and back through the engine, As the engine warms up and the thermostat begins to open the coolant is directed through the main radiator - at this point you will be able to feel the upper and lower radiator hoses warming up.
If the thermostat is faulty and permanently open you will be able to feel the upper and lower radiator hoses warming up very soon after starting the engine and at the same time as you feel the heater hoses begin to warm. This causes most of the heat to be radiated away and so the heater will never warm up.
Unfortunately the thermostat is hidden underneath the water pump on a passat and requires the cooling system to be drained before it can be changed. It may also require the power steering pump to be removed to get access to the thermostat cover.

Feb 01, 2014 | 2001 Volkswagen Passat

1 Answer


Heed of antifreeze coolant temperature!!!
First time you might check the thermostat operating.
The thermostat location for VW Passat 4Motion 1.9 TDI - AJM engine, is on back of the alternator at the bottom side of the bracket.
IMPORTANT: It is NOT necessary to replace the alternator if you want to change the thermostat !!!
Thermostat checking:
1. Cold engine. Start up the engine and watch of the water temp indicator. After first value 60 Celsius Degree you still warm up the engine until the lifter (pointer) reach 80 C deg. (second mark after 60 C deg.). At this time you let engine running at idle speed and check with your hand the thermostat plastic housing and hose temperature in bottom left side of the engine. Heed of alternator driving belt and ventilator fan !!!
2. If the thermostat is good the hose must be cold until the water temp indicator reach almost 90 C deg.
3. The thermostat opening temperature is 87 C deg.
4. If the hose is already warm the thermostat is out of order.

Thermostat location, Part number: 044121113, in german - "Kuehlregle" (Price around $25):

Important note: Always replace the thermostat seal, position 7 in the above picture.

Please do rate my response. Thanks!

Jan 05, 2011 | 2000 Volkswagen Passat 4Motion

1 Answer

04 Vw passat 4 Cyl.the heater do not work good is not hot

Please see my tip at . These are generic instructions. If you get stuck or need specific instructions for your car, please get back to me with model, year and engine info.

Oct 20, 2010 | 2004 Volkswagen Passat

1 Answer

I have a 2004 V6 Volkswagen Passat with 110,000 miles on it and it has suddenly began to idle a little rough. Any thoughts?

Could be a lot of things. A sensor, bad gas, clogged fuel filter, spark plugs, plug wires, camshaft position sensor, etc.. Check engine light on?? If so, have the the code scanned to find out the fault code. Go to your mechanic, or local auto parts superstore...most do it for free banking on you will buy the part from them.

Apr 02, 2010 | 2004 Volkswagen Passat

2 Answers

Heater Only Producing Warm Air

I had the same problem and remedied it by disconnecting the heater core at the firewall (you have to remove the plastic shield by the windshield to access) and filling the core with radiator flush. I let it sit for 4-5 hours and then flushed the core with water from my garden hose. To make the connection, I cut a rubber washing machine supply hose, which fit inside the tubes to the heater core.

Once flushed, I added "Water Wetter" to remove any air bubbles from the system. heat now works great.

BTW - both the dealer and and independent said I needed to replace the heater core, at a cost of $1500. Glad I tried this first! Good luck!

Jan 31, 2009 | 2001 Volkswagen Passat

1 Answer

Heater cystem

Heater Core is blown so now it's not producing Hot air just cold! Same thing happened in my 96 Jeep. You have to replace the heater core.

Jan 08, 2009 | 2004 Volkswagen Passat

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