# Jetta MK4 - Heater not getting hot



## .:mr.black:. (Apr 1, 2008)

If anyone can help I bought a 2001 Jetta this summer and now that the weather is getting colder I'm realizing my heater isn't working. I drive the car for 20-25 minutes and the air coming out is lukewarm at best. My heater gauge reads about 3/8's of the way (not quite 190 degrees) after driving for 20 min.

I did replace the timing belt and water pump in the summer as well as the coolant with new bottles of G12. 

If anyone has any advice it would be appreciated.

Thanks

Also, apologies if I posted in the wrong forum but I didn't see any other relevant place.


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## xxsur3shotxx (Sep 24, 2009)

.:mr.black:. said:


> If anyone can help I bought a 2001 Jetta this summer and now that the weather is getting colder I'm realizing my heater isn't working. I drive the car for 20-25 minutes and the air coming out is lukewarm at best. My heater gauge reads about 3/8's of the way (not quite 190 degrees) after driving for 20 min.
> 
> I did replace the timing belt and water pump in the summer as well as the coolant with new bottles of G12.
> 
> ...


1.) Did you burp the system? It's likely you still have some air in the system, preventing you from getting heat.
2.) If you are 100% confident that there is no air in the system, and the car is not reaching operating temperature, the thermostat is likely stuck open.


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## HavokRuels (Jan 9, 2011)

xxsur3shotxx said:


> 2.) If you are 100% confident that there is no air in the system, and the car is not reaching operating temperature, the thermostat is likely stuck open.


:thumbup:


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## BassNotes (Mar 16, 2005)

Check to see if both heater hoses get hot.

If not, then you have a coolant flow problem (including the possibility of a thermostat malfunction).

If they do, then the problem would probably be that the ventilation air is not flowing through the heater core properly, but around it.


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## .:mr.black:. (Apr 1, 2008)

I'm pretty sure I "burped" the system. I ran the car and kept topping off the coolant as it went down. I checked it again this morning and it won't seem to go down anymore.

If I leave my heat off and run the car for about 10 -15 min I can get it up to operating temp. - 190 degrees. I drove home again from work this morning and for some reason it seems like its warmer than before?

I checked the hoses going into and out from my heater core and both are hot. 

I'll run it this weekend and see if it gets any better. I have some heat but its definitely not getting Hot. Just warm/lukewarm.

Also my fan is working on all 4 settings. I did get some of that black foam crap that came out of my dash if that means anything?

Thanks for the replies.


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## BassNotes (Mar 16, 2005)

Probably a problem with the blend door (or its control mechanism).


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## MaRkIe-MaRk (Oct 28, 2011)

i have the same problem with my gti, heater just gets a little warm i have yet to figure out what the deal is lemme know if you ever get it solved!


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## Jayj (Jul 1, 2011)

that foam you referred to is off the blend door. If you turn it over to a/c you'll mostlikely find it to be lack luster as well. The heater box will need to be removed/replaced. I have seen people re-cover the door though.


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## fastinradford (Aug 3, 2010)

god its just the thermostat, lol


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## .:mr.black:. (Apr 1, 2008)

Ok so I replaced the thermostat, not as difficult as i thought it would be, and now I have a little more heat. When the car gets up to 190 (about 10 min) I get warm air coming from the vent. Its definitely warmer than before but it does not get hot.

In the summer I did have the A/C going and that also was cool but not really that cold. 

How do I repair/replace the blend door? Does that involve removing the dash?

Thanks


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## Jayj (Jul 1, 2011)

center console and dash need to be removed. Heater core and evaporator core need to be disconnected. If I remember correctly, the box is held in place by 4 10 mm bolts through the firewall.


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## flood514 (Jun 3, 2011)

I had the same problem with my 98 passat. One day after replacing the CTS and plastic POS that houses it, heat was back full. Not sure if the car looks at the coolant temp before letting it through the core or what but it may be worth a try.


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## Affixer (Mar 20, 2011)

I'm having similar issues, how do you burp the system?


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## radlynx (Jan 4, 2007)

drive it on a windy road with steep hill. fan in full blast and heater in full blast. :laugh:



Affixer said:


> I'm having similar issues, how do you burp the system?


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## toby lawrence (Dec 12, 2011)

If the engine itself isn't getting to temp... it's most likely a bad thermostat that is stuck open. The coolant is always flowing so it's being cooled as it warms up instead of normal operation where it warms up and the thermostat creeps open to let it be partially cooled and stay at the operating temperature.

Drain coolant from radiator, take off lower thermostat housing, replace, put back on thermostat housing, do typical coolant refill procedure (refill, burp w/ heater on full blast, refill, repeat as necessary) and you should be good to go. :thumbup:


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## Chulicious (Jun 11, 2016)

I was able to do this repair on a 2003 MK4 Jetta 1.8T. Here is a video that should help if someone is still a bit confused. I could not find one like this. Took my under 4 hours + trip to Home Depot. 

https://youtu.be/bxPMzzLmEuM


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