Cooling System 101

Forza91 · Apr 21, 2012

Does the temp guage in the cluster correlate to the reading that the ecu gets fromt the CTS or thermostat? I know it seems like a really stupid question, but i'm trying to troubleshoot a CEL that I got recently (P0128). The diagnostics computer said it could be due to wrong coolant levels or a bad CTS. I've check the level and recently replaced the CTS with a green OEM one and the CEL has gone away (for now), but for the most part my temp gauge still sits at that first tick mark. Could the thermostat be burning out or does the temp gauge need recalibration?

A_Shifter · Apr 21, 2012

Forza91 said:
Does the temp guage in the cluster correlate to the reading that the ecu gets fromt the CTS or thermostat? I know it seems like a really stupid question, but i'm trying to troubleshoot a CEL that I got recently (P0128). The diagnostics computer said it could be due to wrong coolant levels or a bad CTS. I've check the level and recently replaced the CTS with a green OEM one and the CEL has gone away (for now), but for the most part my temp gauge still sits at that first tick mark. Could the thermostat be burning out or does the temp gauge need recalibration?

I ran a search but ran out of time this morning - I think there's a thread somewhere here about that gauge basically being a glorified idiot light.
Also read about attempts to get it to read actual temp, but as I recall it was either waaaay too much of a PITA or it hadn't been figured out yet.
Anybody else?

jayb79 · Apr 22, 2012

requires vagtacho or something similar to edit the hex code. but it can be done, was easier 4 me to put scangauge on steering column.

je · May 24, 2012

Is this true? The bolts that hold the coolant flange to the block are M7, and NOT M6.. or even M8? M7? Who came up with this?

I dropped one of the 2 bolts and it's lost, I think somewhere around the block, but I can't get to it. The local dealer is closed (under construction) and other dealers are closed for the day - and Partsource, Canadian Tire, and Home Depot don't have a bolt that will fit.

M7 x 1.00? Seriously?

TonyJetta · May 24, 2012

Did you try a hardware store?

Tony

je · May 24, 2012

I tried Partsource, Canadian Tire, and Home Depot. They didn't have a bolt that fit, only M6 and M8. Home Depot has a thread fit jig, where I found the M7 to fit, but they don't sell that size. These places have an aisle full of hard-to-find fasteners, not this size though.

TonyJetta · May 25, 2012

I don't know what hardware stores are in Canada. In the US, smaller hardware stores like Ace or True Value have a more varied inventory of hardware than the big-box stores like Lowes and Home Depot.

Tony

je · May 26, 2012

TBH, I don't see any hardware stores any place near since the big box stores came in. Home Hardware, the only one in the area, doesn't have this stuff either.

In case anyone should need it, here's a thread with the same issue. I should try motorcycle or cycing shops, I guess.
Seriously, VW? M7 bolt?

I found the bolt - I went to another dealer today that I emailed asking for this (the look on this guy's face when I asked for the part he didn't answer my email about - same as the look from the second dealer I went to to ask...), and they said that while they don't have that, there are 2 dealers nearby who do.. and they are... the second dealer I came from who didn have it (they had 4), and the first dealer I originally went to (they had 2). So I went to the first one to 'order' it (since maybe their stock quantity is wrong) and the parts guy said (this time I brought the other one) .. oh, a water pump bolt? I have that.. then went and got it.. and it cost $1.86 with tax. I must have spent ten times that in gas running around the city looking. Thanks also to Perjad from Precision Tuning who first told me that it's the same as the water pump bolt, so it was easier to ask for (but it's the same part in the computer.. )...

flee · May 26, 2012

je said:
I think somewhere around the block, but I can't get to it.

You'll always have a spare...

dunerking · Jun 21, 2012

Does anyone know if I can top off my coolant with Pentosin pentofrost SF? Just noticed my level was at min,and low level lite popped on. Thanks TDI club.

TonyJetta · Jun 21, 2012

For that little amount, you can fill with distilled water and be fine.

Tony

dunerking · Jun 21, 2012

Thanks Tony.
Do you know if I can use the Pentosin in the future? I'm not sure what is currently in it. I'm hoping its the VW G12 blend.

dunerking · Jun 21, 2012

Thanks Tony.
BTW,I like your fleet! I also have a 05 Dodge CTD,with our 04 Jetta TDI. The wife would like a 2010 Jetta Sport Wagon TDI. I've been searching around for the correct color and options,but haven't found the exact One.

TonyJetta · Jun 22, 2012

dunerking said:
Do you know if I can use the Pentosin in the future? I'm not sure what is currently in it. I'm hoping its the VW G12 blend.

If you are not certain of what coolant is in it, I would not mix it.

For the cost, it might be worth it to flush the unknown coolant out of the engine and fill wiht either the Pentosin or VW G12.

dunerking said:
Thanks Tony.
BTW,I like your fleet! I also have a 05 Dodge CTD,with our 04 Jetta TDI. The wife would like a 2010 Jetta Sport Wagon TDI. I've been searching around for the correct color and options,but haven't found the exact One.

Thanks for the kind words.

Yea, I think you are best of waiting to get what you want. You and your wife will be happer in the long run.

Tony

Rual817 · Aug 1, 2012

Forza91 said:
Does the temp guage in the cluster correlate to the reading that the ecu gets fromt the CTS or thermostat? I know it seems like a really stupid question, but i'm trying to troubleshoot a CEL that I got recently (P0128). The diagnostics computer said it could be due to wrong coolant levels or a bad CTS. I've check the level and recently replaced the CTS with a green OEM one and the CEL has gone away (for now), but for the most part my temp gauge still sits at that first tick mark. Could the thermostat be burning out or does the temp gauge need recalibration?

I had the same thing on my '00 last yr. Replaced the Thermostat and it started registering 190. Before it would NEVER get past 2nd line. True about being an idiot light. My SGII registers 185-210 and temp gauge never leaves 190 once engine is warmed up.

libbybapa · May 20, 2013

I've been working on an ALH conversion into a '91 vanagon and so investigating the flow path of the stock ALH cooling system and the engine itself. One change that I like from the older style cooling system is that the bypass is internal to the block itself. In that regard, I was wondering if someone could elaborate on where the bypass circuit draws it's coolant from and what path it takes to the port behind the thermostat?

Powder Hound · May 20, 2013

Check post #20 in this very thread. I don't know what else someone could provide that is not in that document, except possibly red and blue colored paths with directional arrows.

libbybapa · May 20, 2013

I read the entire thread and looked closely at all of the diagrams. Post 20 is just a quote of post 2 with thanks added. While all of that is excellent information, none of it addresses the question I am asking which is really just idle curiosity. I am not talking about any of the coolant pipes or hoses external to the long block. I have not yet pulled apart an ALH engine to examine the coolant channels in the block and head. I assume the bypass channel travels up to the top of the water jacket in the head but was wondering if someone could confirm the route it takes.

2001BeetleNM · Jul 10, 2021

Does anyone know the name of the hose that goes from the coolant flange to the oil cooler. In the first diagram above it's the hose that goes from #9 to #18. This coolant hose is not numbered. I need to replace mine and am trying to find a part number.

bajaONE · Mar 8, 2022

Can someone point me to the part numbers of the o-ring from the components on that was the second one of the second post ". Cooling System Components " number 8 o-ring. Cannot find it on rockauto and need one. or two. It was expanded out, so had to cut it and use gasket maker and would like to get the proper labeled o-ring that is not close to an "o".

Powder Hound · Mar 10, 2022

Coolant Flange for Cylinder Head O-Ring (A4)(B5.5)

For Volkswagen Jetta, Golf and New Beetle TDI on the A4 chassis with the ALH or BEW. O-Ring Seal between 3-way cooling flange that attaches to the back of the cylinder head over the transmission. T...

www.idparts.com

OEM Number: 037121688

You are welcome.

Cheers,

PH

bajaONE · Mar 10, 2022

Powder Hound said:
Coolant Flange for Cylinder Head O-Ring (A4)(B5.5)

For Volkswagen Jetta, Golf and New Beetle TDI on the A4 chassis with the ALH or BEW. O-Ring Seal between 3-way cooling flange that attaches to the back of the cylinder head over the transmission. T...

www.idparts.com

OEM Number: 037121688
You are welcome.
Cheers,

PH

thanks and just ordered one for each Jetta, only one needs it but might as well have one ready for the other jetta . Have a friend from CO flying down in 9 days so works perfect. Also needed a new windshield washer pump. thanks again.

fmr55555 · Sep 26, 2022

Turbo Steve said:
TDI Cooling System Schematic

1 - Expansion tank
2 - Intake manifold
3 - EGR cooler
4 - Connector
5 - Heater core
6 - Coolant center line
7 - ATF cooler (Vehicles with automatic transmission)
8 - Coolant hose, upper
9 - Coolant hose, lower
10 - Radiator
11 - Oil cooler
12 - Coolant pump/coolant thermostat
13 - Cylinder head/cylinder block

Cooling System Components

1 - Connector
2 - Coolant hose, upper
3 - To heater core
4 - From heater core
5 - To connector in coolant hose, upper
6 - Engine Coolant Temperature (ECT) Sensor (G62) Blue in color
7 - Bracket
8 - O-ring
9 - Connector (Always replace)
10 - Bolt: 10 Nm (7 ft lb)
11 - Coolant line
12 - To radiator, upper part
13 - O-ring (Always replace)
14 - To expansion tank, lower part
15 - Bolt - 15 Nm (11 ft lb)
16 - From radiator, lower part
17 - Coolant thermostat
18 - Oil cooler
19 - Coolant or Water-pump
20 - Cooler For EGR
21 - To expansion tank, upper

Radiator Fan Diagrams

1 - Radiator
2 - O-ring (Always replace)
3 - Coolant hose, upper
4 - Connector
5 - Retaining clip
6 - A/C Cut-out Thermal Switch -F163-
7 - From connector on cylinder head
8 - From connector on cylinder head/connector
9 - From ATF cooler (Only for vehicles with automatic transmission)
10 - Electrical connector / Color: black
11 - Cap: Test pressure 1.4 to 1.6 bar
12 - Bolt: tighten to 10 Nm (7 ft lb)
13 - Coolant expansion tank
14 - From connector to radiator for EGR/connector
15 - To cylinder head
16 - Fan shroud
17 - Right coolant fan -V35-
18 - Fan bracket
19 - Retaining clip
20 - Coolant fan -V7-
21 - Bracket
22 - Coolant hose, lower
23 - Electrical connector / Black, 3-pin connector
24 - Coolant Fan Control (FC) Thermal Switch -F18-
* Stage 1. 0N: 92 to 97 C
* Stage 1. OFF: 84 to 91 C
* Stage 2. ON: 99 to 105 C
* Stage 2. OFF: 91 to 98 C
25 - Bracket

ALH Coolant Water-pump

1. Idler Pully Bolt
2. Idler Pully
3. Pump Housing Bolt
4. Coolant Water-pump
5. O-ring seal

Thermostat 195*F.

1. Mounting Bolt
2. Flange
3. O-ring
4. Thermostat

FYI - For draining G-12 coolant out of the cooling system, open the cooling system drain thumb screw (pictured below).

I have a 2005 TDI wagon with BEW engine. There is a coolant leak; fluid found on driveway beneath passenger side of front bumper, near right front tire. Seems like it is an external leak. I plan to do a pressure test to pinpoint exact location of leak. I found the diagrams, etc. for ALH engine and wonder how different this is from BEW. If it is possible to pass along similar info for BEW it would be great. Have not yet gotten pressure tester but looking around for best buy on universal type available here in Vancouver BC Canada area. So far found the following from Princess auto for about $100 Canadian.

https://www.princessauto.com/en/radiator-pump-pressure-leak-tester-kit/product/PA0008597668

I assume that it clamps to expansion tank. Any suggestions for better/more economical testers and diagnostic tips are much appreciated.

Thanks,
Richard

jayb79 · Sep 26, 2022

It's most likely the metal clamp holding the plastic tank end to the core has rotted and allowed the leak under pressure. You should be able to see it if you look close enough from under the car. A new aftermarket radiator is probably cheaper than the tester.

Cooling System 101

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