Results 1 to 5 of 5

Thread: low pressure coolant expansion tank cap

  1. #1
    Join Date
    Apr 2016
    Location
    Mariposa, CA
    Posts
    13
    My Cars
    2004 BMW Z4 3.0

    low pressure coolant expansion tank cap

    So I'm looking thru the various parts catalogs to find a new cowl cover for my 2004 Z4 and off to the side I read about cooling system problems caused by the factory cap being rated at 2 bar (~30psi) combined with ageing plastic tanks. Now G.A.S. is making a replacement cap rated at 1.2 bar (~17psi) and claiming perfectly good cooling system performance with less stress on the other components. Interesting. Anyone out there had experience with the reduced pressure caps---good or bad? I will see temps over 100F around here so I'm being cautious plus their cap is $35, but I guess that isn't an outrage if it saves a motor, right? Pondering in Mariposa.

  2. #2
    Join Date
    Jun 2007
    Location
    Seneca, SC
    Posts
    364
    My Cars
    2007 750i BMW; 2003 Z4 3.0 BMW; 2002 Lexus LS430;
    It came with a 2 bar rated cap for a reason.

  3. #3
    Join Date
    Dec 2013
    Location
    Chicagoland area
    Posts
    4,372
    My Cars
    EXOTICS
    Performing a cooling system refresh is recommended for ageing plastic tanks, hoses and all cooling components,
    why attempt to extend the life of failing brittle parts? Preventing failure by replacing old worn out parts is smarter!

  4. #4
    Join Date
    Jan 2008
    Location
    Arida Zona
    Posts
    30,108
    My Cars
    z3
    First off, the cap does NOT set the system pressure. System pressure is set by the fill level and the temperature the engine runs at. A properly operating cooling system will not be running at 2 bar

    Secondly, there are already many OEM BMW caps at 1.2 bar if you wanted to go that route. I'm not sure what GAS is selling, but BMW already makes 1.2 bar caps for other models

    Thirdly, you should not run a lower pressure cap on your car as it may allow venting of cooling in some circumstances which could cause coolant loss. M54's regulate their temperature quite effectively but will sometime see occasional spikes in temperature. A lower pressure cap may allow some coolant to burp out during these temperature spikes. In extreme circumstances, if enough coolant is burped out the engine will run hot due to low coolant, causing a chain reaction where because it is running hotter the cooling system pressures are higher, so it will burp even more cooling, causing it to run even lower on coolant.

    There is really no reason to change out the stock radiator cap. Do NOT overfill your stock cooling system and you will be fine. Open your expansion tank when cold and check the red level indicator. If it is ALL THE WAY at the top, remove coolant until you see it go down. Then re-top off juts to the proper fill level. It is very common these systems are overfilled during the bleeding process and that causes them to run at too high of a pressure which can crack expansion tanks and cause other issues. Low coolant is not a good thing obviously, but being overfilled with coolant is a bad thing as well.

  5. #5
    Join Date
    Apr 2016
    Location
    Mariposa, CA
    Posts
    13
    My Cars
    2004 BMW Z4 3.0
    I get it, thanks for info. I'll be checking the coolant level closely in the future. For the moment, all is well. 8-)) hp

Similar Threads

  1. Running the engine with the coolant expansion tank cap off.
    By silverm3bmw in forum 1991 - 1999 (E36)
    Replies: 40
    Last Post: 11-23-2011, 05:18 PM
  2. Coolant Expansion Tank Cap - Pressure rating
    By Tnarkowicz in forum 1976 - 1989 (E24)
    Replies: 3
    Last Post: 09-01-2011, 10:49 PM
  3. WTB - Coolant expansion tank cap
    By Wgoins88 in forum 1983 - 1991 (E30)
    Replies: 10
    Last Post: 10-22-2006, 08:40 PM
  4. Replace? coolant expansion tank, cap, bleeder screw...
    By old skool in forum 1991 - 1999 (E36)
    Replies: 7
    Last Post: 03-24-2005, 08:56 AM
  5. E36 coolant expansion tank & cap
    By nat325i in forum BMW Parts For Sale
    Replies: 0
    Last Post: 01-18-2004, 05:51 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •