2010 Jetta Heat Blowing Lukewarm

2010vwjetta · Jan 4, 2018

The heat on my 2010 TDI Jetta seems to not be blowing as hot as it should be recently. I haven't measured the air coming out yet but with the car fully warmed up after driving for almost an hour the air coming out feels only slightly warm to the hand. The air flow seems fine and cabin air filter was replaced recently. Temperature mixing door seems to be functioning properly as well.

The only things I can think of are a partially clogged heater core (unlikely in my head given the age of the vehicle and coolant) or if they have one the heater hose valve is not opening fully. That leads me to my main question, does the MK5 Jetta even have a valve on the heater hoses to stop the flow of coolant when off of heat? And if so, where is it located? I know it was much more common in older vehicles without air conditioning but I have seen newer cars with them depending on the design of the climate control system. Thanks for any help!

pdq import repair · Jan 4, 2018

There is no valve on coolant flow through the core, they us a blend door for temp and the core gets full flow all the time.
Not uncommon for cores to plug over time due to what I consider a crappy design. Mine did on my 09. Seems back in those years they were fooling around with different coolants too as the 09s especially have problems and the coolant looks bad prematurely. Mine had original factory coolant all it's life and it was not due for change by VW's schedule but it was just ugly stuff.
Heater core can be done without pulling the dash. You can easily check it by pulling off the underdash cover on the drivers side and the cover over the heater core and feel the heat, or lack of, on both sides of the core at the hoses.

2010vwjetta · Jan 4, 2018

pdq import repair said:
There is no valve on coolant flow through the core, they us a blend door for temp and the core gets full flow all the time.
Not uncommon for cores to plug over time due to what I consider a crappy design. Mine did on my 09. Seems back in those years they were fooling around with different coolants too as the 09s especially have problems and the coolant looks bad prematurely. Mine had original factory coolant all it's life and it was not due for change by VW's schedule but it was just ugly stuff.
Heater core can be done without pulling the dash. You can easily check it by pulling off the underdash cover on the drivers side and the cover over the heater core and feel the heat, or lack of, on both sides of the core at the hoses.

Awesome that gives me a place to start. The car has the original coolant in it as its supposed to be 10 year coolant correct? I am guessing it needs to be changed sooner.

narongc73 · Jan 4, 2018

how's changing the coolant going to help you any? flush or get a new heater core.

meerschm · Jan 4, 2018

also give the coolant in the expansion bottle under the hood a look.

if it is a brownish-orange color, that is not a good sign.

2010vwjetta · Jan 4, 2018

narongc73 said:
how's changing the coolant going to help you any? flush or get a new heater core.

I meant more as the coolant isn't actually going to last 10 years, and needs to be changed sooner. Obviously if the core is plugged up I would change that first and flush/change the coolant at the same time.

meerschm said:
also give the coolant in the expansion bottle under the hood a look.

if it is a brownish-orange color, that is not a good sign.

I'll have to take a look.

dandywriter · Jan 4, 2018

You lose a lot of coolant when you change the timing belt, replacing the water pump. Have you changed your timing belt yet? If not, it is a convenient time to do the coolant work.

2010vwjetta · Jan 4, 2018

dandywriter said:
You lose a lot of coolant when you change the timing belt, replacing the water pump. Have you changed your timing belt yet? If not, it is a convenient time to do the coolant work.

Conveniently I have a timing belt kit in the mail that should be here tomorrow.

meerschm · Jan 4, 2018

If you suspect any stuff in the system, pick up a couple lengths of hose and one of those coolant flush kits.

http://www.myturbodiesel.com/gallery/photos/1303/

there are two smaller diameter heater hose circuits, you want to flush out both with city water pressure, (not too high, so make sure an outlet like the radiator hose or coolant resevoir cap is open)

folks have found quite a bit of crap in the system.

pdq import repair · Jan 5, 2018

The heater core design is the problem. It is not a single tube that snakes it way through the core and back out, but rather a design that dumps coolant into a common area and it then flows through the tubes and back out. The design failure is that both hoses enter at the top of the core. Any solids in the coolant can precipitate out and settle into the lower tubes and eventually just fill the core with debris. It is extremely hard to flush out because of that too. If they had used the single tube design, or merely put the outlet tube on the bottom it would self clean in a way, or be flushable.

We have limited luck with flushing. I flushed my own car several times before finally replacing the core. I tried all manner of chemicals and techniques using my car as the guinea pig, none worked well. Even after replacing the core I tried to clear it out by soaking it overnight and flushing back and forth, letting it dry and shaking out debris seemed to work best, though that is not practical in the car. I went from 2 tubes open to full flow eventually but it took a lot of determination and struggle.

If the core is plugged, the only real cure is replacement and careful monitoring of coolant condition and maybe a regular yearly flush through the core.

meerschm · Jan 5, 2018

if you have a wet/dry shopvac,

consider using it to suck coolant out of hoses.

this can save some mess. (but then you have to clean the shopvac)

2010vwjetta · Jan 6, 2018

pdq import repair said:
The heater core design is the problem. It is not a single tube that snakes it way through the core and back out, but rather a design that dumps coolant into a common area and it then flows through the tubes and back out. The design failure is that both hoses enter at the top of the core. Any solids in the coolant can precipitate out and settle into the lower tubes and eventually just fill the core with debris. It is extremely hard to flush out because of that too. If they had used the single tube design, or merely put the outlet tube on the bottom it would self clean in a way, or be flushable.

We have limited luck with flushing. I flushed my own car several times before finally replacing the core. I tried all manner of chemicals and techniques using my car as the guinea pig, none worked well. Even after replacing the core I tried to clear it out by soaking it overnight and flushing back and forth, letting it dry and shaking out debris seemed to work best, though that is not practical in the car. I went from 2 tubes open to full flow eventually but it took a lot of determination and struggle.

If the core is plugged, the only real cure is replacement and careful monitoring of coolant condition and maybe a regular yearly flush through the core.

I am going to go straight to replacing the core, and flush the rest of the system.

meerschm said:
if you have a wet/dry shopvac,

consider using it to suck coolant out of hoses.

this can save some mess. (but then you have to clean the shopvac)

Actually have an old shop vac that would be perfect for that.

Any recommendations for a heater core? I usually buy parts from rock auto but their selection is limited to a Spectra Premium and Nissens.

meerschm · Jan 7, 2018

vwpartscenter.net

dealer who sells online at a discount

https://www.vwpartscenter.net/auto-...vac-cat/evaporator-and-heater-components-scat

2010vwjetta · Jan 7, 2018

Thanks!

pdq import repair · Jan 8, 2018

If you are going to do the heater core, also get the heater tube gasket and clamp set. # 12 in the above picture.

Before just replacing blindly, I would confirm temps going in and out of the core. it is easy to do, just remove the underdash cover and the heater core is visible on the heater housing. remove the plastic cover over it and you should be able to feel temp differences. Mine was quite obvious.

narongc73 · Jan 8, 2018

Agreed. Mine is still good at 247k.

2010vwjetta · Jan 8, 2018

pdq import repair said:
If you are going to do the heater core, also get the heater tube gasket and clamp set. # 12 in the above picture.

Before just replacing blindly, I would confirm temps going in and out of the core. it is easy to do, just remove the underdash cover and the heater core is visible on the heater housing. remove the plastic cover over it and you should be able to feel temp differences. Mine was quite obvious.

I ordered the core and that gasket/clamp set tonight. I will check the temps but I am quite suspect that it is indeed the problem as the coolant in the reservoir doesn't look too good. Kind of brownish orange like a previous poster said.

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