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VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old February 9th, 2019, 13:00   #1
BenM
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TDI(s): 2002 Jetta
Unhappy Heat varying wildly with RPM, mechanic says air

I'm hoping someone can help I had some maintenance done and since then I've had heating problems.


I had a timing belt/pump replacement about six weeks ago, and didn't drive the car very far after that for a few weeks, when I did take a longer drive the heat was iffy but it was cold out, but then the overflow started puking.


I put a known good thermostat I replaced when the plastic housing cracked and bled the system. Heat came back, engine warmed up fine (180-190), it puked again on the test drive after overheating. I took it back to the shop because I suspected the water pump.


They power flushed it and said it was good. It's a place about 40 miles away that I used to have good luck with, but on the way back about half way the heat started varying again and continued the whole way home.


I get little to no heat at low RPM, from idle to abut 1,500 it's pretty cold, but as soon as I start out and get the RPMs up the heat comes back, but not hot like it used to be. After warming up over 180 on the way home and holding for a while when the heat stopped working properly it would stay at 160-175. I have a scangauge hooked up.


Even revving in the driveway heat is tied to RPM. I put cardboard down in front of the radiator and it didn't overheat again but it didn't quite hit 180 and heat output stayed the same. When not lugging up hills it holds at 165 pretty well now.


My thermostat hose is lukewarm and my head hose is very hot, is that the correct flow direction? It seems backward to me but most of my experience is on GM and AMC/Jeep. Thanks.
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Old February 9th, 2019, 17:26   #2
STDOUBT
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I'm finding the sequence of problems in your post a bit confusing.
Towards the end you mention "overheating".
What symptoms did this all start with? Overheating? or intermittent heat from the blowers?
I had a timing belt/pump replacement about six weeks ago
What pump? Water pump? OK, what brand of pump? Did the mechanic also change out all the rollers and the tensioner for the new belt? If not, your mechanic shouldn't be working on TDIs.
the overflow started puking.
^Can you describe this better?

I recommend a high-temp thermostat like a stant 45379 which will let your motor get plenty hot before allowing full flow through the radiator.
When your mechanic says "air" is the problem does he mean air in the coolant system? The ALH coolant tract should "burp" itself if you get it up to temp. Leaving the cap off the overflow jug while running, and checking for return from the topmost line into it, is a good tell.

Where is your coolant level in the ball after running?
Have you checked for residual pressure by opening the ball after sitting overnight? If the ball remains pressurized once cold, your head gasket is failed.

If your car is only getting up to 180F after 40 miles, the thermostat is the first culprit.
Also power-flushing these is not recommended.
I tend to suspect your water pump is dodgy.
EDIT: for the record, what color is your coolant?
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Last edited by STDOUBT; February 9th, 2019 at 17:29.
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Old February 9th, 2019, 19:32   #3
Nero Morg
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As an addition, check your heater core for a buildup of scale, or any other foreign debris. My wife's car did something similar to where the heat only worked until you revved it up. Turns out the inlet port of the heater core had a broken piece of the inlet pipe wedged sideways in it.

Also, make sure your pump is pumping correctly. At operating temps (or as close as you can get it) the small line that goes to the top of the coolant ball should have a constant flow of coolant into the ball. You can see it by opening the cap.
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Old February 10th, 2019, 13:52   #4
BenM
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Quote:
Originally Posted by STDOUBT View Post
I'm finding the sequence of problems in your post a bit confusing.
Towards the end you mention "overheating".
What symptoms did this all start with? Overheating? or intermittent heat from the blowers?
I had a timing belt/pump replacement about six weeks ago
What pump? Water pump? OK, what brand of pump? Did the mechanic also change out all the rollers and the tensioner for the new belt? If not, your mechanic shouldn't be working on TDIs.
I needed the timing belt replaced for regular maintenance at the 70,000 interval. They replace the pump, tensioner, etc. when they do it. No idea on the brand.

Quote:
the overflow started puking.
^Can you describe this better?
I stopped the car and turned it off. Coolant was dripping down from the fender and when I popped the hood it was coming out of the overflow in the plastic reservoir.

Quote:
I recommend a high-temp thermostat like a stant 45379 which will let your motor get plenty hot before allowing full flow through the radiator.
When your mechanic says "air" is the problem does he mean air in the coolant system? The ALH coolant tract should "burp" itself if you get it up to temp. Leaving the cap off the overflow jug while running, and checking for return from the topmost line into it, is a good tell.
He specifically referred to air trapped in the heater core.


I've always burped it by warming it up with the cap off and keeping topped off while squeezing the radiator hoses.
Quote:


Where is your coolant level in the ball after running?
Have you checked for residual pressure by opening the ball after sitting overnight? If the ball remains pressurized once cold, your head gasket is failed.

The coolant level after the flush is now at about 2/3 of the ball, when I open it after cooling off for a few minutes there's no pressure.

Quote:




If your car is only getting up to 180F after 40 miles, the thermostat is the first culprit.
Also power-flushing these is not recommended.
I tend to suspect your water pump is dodgy.
EDIT: for the record, what color is your coolant?
They refilled it with an "all makes" coolant. I am unable to tell green or orange but it's in that range.
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Old February 10th, 2019, 14:04   #5
BenM
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Quote:
Originally Posted by Nero Morg View Post
As an addition, check your heater core for a buildup of scale, or any other foreign debris. My wife's car did something similar to where the heat only worked until you revved it up. Turns out the inlet port of the heater core had a broken piece of the inlet pipe wedged sideways in it.

Also, make sure your pump is pumping correctly. At operating temps (or as close as you can get it) the small line that goes to the top of the coolant ball should have a constant flow of coolant into the ball. You can see it by opening the cap.

I'll try to check the to/from lines of the heater core next drive. I saw the trickle last time but I'm not seeing it every time. I have pulled the hose off to watch for it before the flush but need to take another drive.


There's some confusing diagrams out there but I'm pretty sure that the coolant flows Head -> Radiator -> Thermostat -> Pump instead of the more familiar to me idea of having the thermostat in the head at the hot side it's in the pump on the cool side. It's not something that's reversed flow with the Pump -> Thermostat -> Radiator -> Head? Therefore the top hose being hot and the bottom being cool or warm is correct?


I ask because I've seen it done several ways on vehicles I've owned and I want to make sure it's pumping and not just cooling via water convection.
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Old February 10th, 2019, 14:18   #6
Nero Morg
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I'm pretty sure it goes pump, thermostat, head/block until the thermostat opens, then it goes pump, radiator, head/block
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Old February 10th, 2019, 14:24   #7
BenM
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Quote:
Originally Posted by STDOUBT View Post
If your car is only getting up to 180F after 40 miles, the thermostat is the first culprit.
EDIT: for the record, what color is your coolant?

On the drive home it went to just above 170F, then I went up a long hill in 5th and got it to 200F. After the long drift back downhill it was back down around 175, then continued for a little while until the heat started fading in and out when it held between 160 and 175 but usually just above 165.


When the engine dropped to idle the heat would fade out and revving it would bring it right back.


After coming home I put some cardboard in front and ran it up a couple of hills where I had managed to overheat it before the flush and it didn't overheat. I was thinking that something happened to the thermostat on that run home but it's still pretty solid at holding the new temperature so I'm unsure if it will affect the heat. I know on my old Jeeps that a worn thermostat just got "weak" like that and wouldn't hold the hotter temperature in cold weather causing low cabin heat but it didn't have nearly the effect at idle unless the pump itself had a terrible gap between the impeller and the housing but I just don't have the experience working on this engine (it's really been quite reliable) or any diesel.
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Old February 10th, 2019, 15:47   #8
BenM
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Ok, sorry to reply all at once, I had to work today. I took the car out for a test run afterward.



Down a 35mph hill about 1 mile. I started the Jetta, moved my Jeep, drove down the hill. It's windy so I was on and off the pedal. It quickly got to 100F and started producing some good heat on recirc. I turned at the light, heat stayed pretty good waiting.



About 1.5 Miles of 55mph highway. The car reached 135F and struggled to move past. Then I reached several stop lights. They were too short and I couldn't feel the heat drop very much. Switched heat to outside air due to fog starting on windows.



I stopped at the bottom of a 2 mile hill that can just be run in 5th. The top hose was hot, the bottom cold. The heater inlet hot, the outlet just warm. I drove up and down a small hill then tackled the big one.


2 Mile Hill. I reached approx. 162F at the top, 45-50MPH in 5th. Good heat the whole way. I turned around at the light and went back down in neutral at 45-55mph. I stopped at the bottom, the heat had all but gone by then. The hoses were same as before.


2 Mile Hill, Run 2. I hit 185F by the top. Good heat. Both heater hoses hot. Top radiator hose hot, bottom a touch of heat. At the bottom heat gone again. I retraced my way home, 165-175F, mediocre heat at lights, better on highway, good going back up the steep hill in 3rd and 4th, hit 182F.


Driveway. Heat good pulling in, All hoses hot except lower radiator hose warm on top side, cold on bottom side. After ~5 min almost no heat, worse than the bottom of the hill.


Videos of before and after for the tiny ball hose: https://imgur.com/gallery/98tEapr
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Old February 10th, 2019, 17:37   #9
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Your engine will warm-up more (get hotter) going up hill.. And, going down hill, without pushing on the accelerator (coasting in gear), the engine will cool down because the Injection Pump shuts-off fueling coasting in gear with foot off accelerator <<< known fact.

Coolant flow is out the head just below the Vacuum Pump through a coolant flange and one stainless steel small pipe. From there, coolant flows to a number of places... Coolant flows to the EGR Cooler/Warmer, on to the Heater Core and back to a Black Steel pipe that goes under the IP to the Water Pump housing (cast in the block). Coolant also flows to the Oil Cooler and then back to the Black Steel pipe. And, coolant flows from the Stainless Steel pipe to the Expansion Tank (round thingy) then out the bottom to the Black Steel pipe ......<<<<< all of those flows never stop when the engine is running (cold or hot)......... That coolant flows across the T-stat causing it to open ever so slightly when hot enough... it does not just pop open. T-stat operation is a slow opening and closing process.

Now, once the T-stat opens coolant flows in the top of the rad (hot on top, cold on bottom) from the Coolant Flange on the end of the head and out the bottom through the long hose to the black plastic coolant flange at the T-stat. The bottom hose can be cold while the top hose is hot...... it's all about the slow opening of the T-stat and the extremely good cooling effect of the Radiator..

That system is excellent when it comes to self-burping and getting rid of air. I've never seen one get "air-locked." I believe that to be BS..... even with the huge cooling system in my Van with the ALH, burping has never been a problem.
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Old February 10th, 2019, 17:38   #10
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I don't like how the flow is inconsistent. I also don't like how the coolant looks green. Hopefully you didn't get coolants mixed up and have gelling in the system now. When you pulled your thermostat, did you check the water pump impeller? With it snowing it shouldn't be overheating. Drove mine today and it held at 180 no problem in the snow...
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Old February 10th, 2019, 18:04   #11
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They refilled it with an "all makes" coolant. I am unable to tell green or orange but it's in that range.

I'm hoping someone else will chime in, but I'm 99% confident they put the wrong coolant in. If they did, you're looking at an early demise of all the aluminum in your cooling system. Your car wants G12 (pink) or G13 (purple-ish). Remedy would be to run the system from cold, and let it idle while you flush (un-pressurized) with distilled water -keeping the overflow half-full- until it comes out clear. Turn it off, add 3 liters of distilled H2O, then add 3 liters of G12.
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Old February 10th, 2019, 18:14   #12
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One more thing, get yourself a mechanic who knows TDIs

Fishers, Chris Car Tunes
10441 South Crooked Creek Rd
Huntingdon, PA 16652
(814) 643-3332

RocketChip - Jeff Robertson
Red Lion, PA
http://www.rocketchip.com/
"JSRMonster"

Marquette Automotive
360 W Fox Rd
Sunbury PA 17801
(570) 286-4240
Dennis Marquette- "Metal Man" - Also has a parts business
mavwp@ptd.net
http://www.metalmanparts.com

Kevin & Robert's Automotive
3846 Columbia Ave
Mountville, PA 17554
(717) 285.3738

D R Auto
Paradise, PA
(717) 687-6867

F&P Auto
Route 819
Hunker, Pa 15639
(724) 925-6456 Fred Petrella

Woodlawn Foreign Car Service Inc
454 W Woodlawn St, Philadelphia, PA
(215) 843-5939

David Brubaker (Davidbru)

Green Road, Inc (Saturnhacker)
906 Old Fern Hill Road
Unit 5
West Chester, PA 19380
610 344-2182

Mair's Continental Motors
1455 Friedensburg Road
Reading, Pa. 19606
610-779-3555
www.mairscontinentalmotors.com

Automotive Consulting Services
GotEuroCorrado on tdiclub.com
Roman Goldin
21 North York Road, Unit 3b
Hatboro, PA 19040
(267) 317 8229

German Diesel Motorwerks
8085 PA-104
Mount Pleasant Mills, PA 17853
Phone: (570) 539-8333
Fax: (570) 539-8334
Email: info@germandiesel.net
Web: www.germandiesel.net
EIN: 452346543
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Old February 11th, 2019, 07:00   #13
BenM
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Quote:
Originally Posted by STDOUBT View Post
They refilled it with an "all makes" coolant. I am unable to tell green or orange but it's in that range.

I'm hoping someone else will chime in, but I'm 99% confident they put the wrong coolant in. If they did, you're looking at an early demise of all the aluminum in your cooling system. Your car wants G12 (pink) or G13 (purple-ish). Remedy would be to run the system from cold, and let it idle while you flush (un-pressurized) with distilled water -keeping the overflow half-full- until it comes out clear. Turn it off, add 3 liters of distilled H2O, then add 3 liters of G12.
Thanks.

I've always used G12/G13. I have some Hella brand G12, it looks orange to me, and I'll refill as soon as I get this resolved. I'm trying to walk lightly with them but I called this morning after driving into work because it's still happening and it's over freezing now. It caught once and stayed hot at idle for a little while but by the time I got to the parking garage and turned it off the heat had gone; it feels like a little bit of a slip-stick.
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Old February 11th, 2019, 07:01   #14
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One more thing, get yourself a mechanic who knows TDIs
I think this is the last time I'm going to this place, thanks, I'll keep them in mind for the future.
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Old February 11th, 2019, 11:44   #15
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While you have the coolant out, you should pull the thermostat to really drain a lot of it out of the block. While it's off inspect your water pump impeller.
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