A 12V Primer & Resources...

Collapse
This is a sticky topic.
X
X
 
  • Time
  • Show
Clear All
new posts
  • Lago Blue
    S2Forum Maniac
    • Jul 2009
    • 843
    • Country: Canada

    #1

    A 12V Primer & Resources...

    ...For newer owners of that particular V6 engine.

    Because this topic may not become worthy of its' own forum section, perhaps this may be of help. This is meant as a single place to simply list links to tech articles which may be of specific interest to V6 owners. To keep it from becoming too lengthy, perhaps we can proceed as follows.

    a) Rather than a place where entire posts reside, it may work best if just a series of short descriptive titles, perhaps include the reason it is useful if not obvious, accompanied by links to content;

    b) Below are some suggestions, links to some obvious sites (sadly, some perhaps now best just for data mining), and of specific articles on this forum and others. Questions, comment, discussions and your foot-noted grand opus on crankcase ventilation can perhaps best continue to be posted elsewhere. So to repeat, don't post your questions here, do browse through the articles though, and comb the forum archives using the search and and advanced search functions first, then if you still have a question, post it at 'Today's Posts'; &

    c) Because "12v" also often is meant as 12 volts, forum searching can be even more tedious, the intent here is this will help to more easily link back into the archives. Certainly, as we all tend to stick to our own silos, it may also be helpful to list articles from elsewhere. Please add your suggestions as to what you found of utility, or that you think others may find informative.


    12v.org

    12v Discussion at Audiworld.com

    12v V6 Board at Quattroworld.com

    1.) Perhaps required reading...

    2.) What you may often find...

    3.) With a 12V, what's reasonably possible...

    4.) Code 2411 (EGR system ) Re-visited...

    5.) Tour through a near stock 12v intake system...
    Last edited by Lago Blue; 23 March 2021, 21:27.
  • Lago Blue
    S2Forum Maniac
    • Jul 2009
    • 843
    • Country: Canada

    #2
    6.) 12v V6 Engine Cooling System Info
    ​​​​​​​​​​​​ Audi 12v V6 Cooling System schematic Screen Shot 2025-12-09 at 9.26.53 PM.png
    The diagram above doesn't detail the particular plumbing directly around t-stat, which may cause some confusion. The t-stat is constructed as a bar-bell shaped shuttle valve that controls two openings simultaneously, the rad bypass and the rad return to the pump.
    I think the system's cycle works like this:
    - From cold, the spring in the t-stat holds the rad return to the pump path closed, and the rad bypass path to the pump open;
    - At first, warmed coolant from the heads returns to the pump via the bypass, and by the heater return;
    - This way available heat is sent to the cabin and windscreen soonest;
    - Warming coolant in the bypass runs over the wax pellet in the t-stat on the way to the pump, the wax expands, overcomes the spring pressure and gradually closes the bypass as it also opens the rad return;
    - Flow to the rad now also goes to the oil heater / cooler behind the oil filter which serves to moderate oil temp;
    - During engine ops the t-stat is throttling coolant flow to try to keep the temp on the design target;
    - At engine shut-down the t-stat spring overcomes the cooling wax pellet and closes the rad return path, and opens the bypass again.

    Unlike earlier Audi's, from1993 there is no valve to control coolant flow through the heater core.

    Photos of the 12v t-stat:
    12v V6 T-stat front side Screen Shot 2025-12-10 at 1.10.07 AM.png​ image_92833.png ​​

    1st photo shows the front side (as in this side faces the front of the car). The 'tickle valve' vent hole (small raised tubular detail seen nearest camera at about the 4 o'clock position in the photo) is set at 12 o'clock on installation, it helps the system bleed air and fill with coolant during re-fill. The smaller disc on end of the back side (2nd photo) is what will close the rad bypass.

    - A t-stat can stick at either end of its travel or in-between if jammed with debris. Besides over or under cooling, this may exhibit by preventing system re-fill.
    - It is good practice to test a t-stat before installation that it opens at the marked temperature.
    - The t-stat can be changed out without disturbing the timing belt.

    The stock t-stat is 87℃, so the coolant temp gauge will read about there. The 1st photo below indicates normal operating range, the 2nd (although for a UrS C4 by UrS4boy) has a bit more info:
    Audi 12v Coolant Temp Gauge normal range Screen Shot 2025-12-10 at 3.08.50 PM.png Audi C4 UrS Coolant Temp Gauge w: info Screen Shot 2025-12-10 at 2.22.58 PM.png

    Thie doc below runs through the drain, flush and refill procedure (from the old NatWhite site):
    the NatWhite Audi 12v coolant drain, flush & fill procedureScreen Shot 2025-12-14 at 3.38.07 PM.png

    Some bleed and fill notes:
    - The factory bleed valves (on the heater return hose and by the G62) are both old and fragile. They may be seized. - Rather than risk breaking the heater bleed, it would be safer to partially pull the hose off the heater core pipe upstream of the bleed where it comes through the firewall.
    - Luckily, my bleeder beside the G62 was not seized, I used anti-seize compound on re-installing that screw.
    - If found seized perhaps you can remove the G62 instead to effect bleeding?
    -
    - A 1993 90 12v CSq w/ an AAH has coolant capacity is 11 Ltrs. / 11.6 US qts. / 9.7 Imp. qts., less if you don't drain the block.
    - Have a new block drain O-ring ready.
    - The engine block drain may not yield anything till you pick through the debris lodged above it. Wear goggles.
    -
    - Take some A/F mix with you and go for a short drive or two.

    This drawing from the Bentley, and this photo by Grillage will help you find the engine block coolant drain plug.
    Audi 12v Eng Blk Coolant Drain Plug Location drwg. from Bentley Manual Screen Shot 2025-12-14 at 1.04.59 PM.png Audi 12v Eng. Block Coolant Drain Plug Location photo Screen Shot 2025-12-14 at 1.22.37 PM.png

    The coolant drain plug (NLA) N 904 520 02 (takes an 8mm Allen tipped socket) and O-ring N 904 520 02 (Viton, size: 11mm ID 17mm OD 3mm thickness):
    Audi 12v Eng Block Coolant Drain plug and O-ring Screen Shot 2025-12-15 at 3.53.07 PM.png

    The engine coolant temp. sensor (ECT) G62 is a Negative Temperature Coefficient (NTC) sensor that is used by the ECM as a connection factor for the following:

    * Cold start enrichment
    * Connection to injection and igntion timimg for cold engine
    * Idle speed control
    * Deceleration fuel shut-off

    The ECT sensor also is used to activate certain systems at a predetermined temperature such as O2 sensor control, knock control, and exhaust gas recriculation. (From the Audi Engine Management Systems Program Manual). P/N is 026 906 161.

    Checking G62 sensor:
    http://Engine Coolant Temperature (E...nsor, checking

    F76 is an electronic thermal switch that connects to the temp gauge, the coolant level warning switch, and the ECM. P/N is 034 919 369C.

    F76 Tech Bullitn re 3-wire:
    Audi 12v V6 Tech Bulletin re ECT F76 new 3-wire Screen Shot 2025-12-10 at 1.03.50 PM.png​​​​​​​

    This post explains the design intent of the12v V6 coolant temp gauge operation and some of its behaviour (It may also apply to the all the other 80 and 90 series cars.):
    https://www.audiworld.com/forums/12v.../#post22431325

    How coolant temp can be displayed via the (GM made) digital climate control:
    https://www.audiworld.com/forums/12v.../#post22417602

    What may happen if your 12v engine does not warm the coolant sufficiently soon enough:
    https://www.audiworld.com/forums/12v.../#post22431302

    A couple of posts in this thread explain how either of two separate defects in the instrument cluster can give you a misbehaving coolant temp gauge:
    https://www.s2forum.com/forum/techni...339-mfts/page2

    Why the big plastic engine under-tray is considered part of the cooling system:
    https://www.audiworld.com/forums/12v.../#post22449164
    Last edited by Lago Blue; 16 December 2025, 18:55.

    Comment

    Working...