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  1. #1
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    Member No: 29176 aingalls is an unknown quantity at this point aingalls's Avatar
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    The Temperature Gauge Puzzle

    While I have consulted this forum many, many times over the years to help solve problems with my 97 528i - this time the solution is not coming to me as easily. I thought I might post for help...

    PROBLEM: Temperature gauge goes to mid point after warming up as it should, but after I drive for a while I experience the following:

    - Gauge slowly moves up. Sometimes to 3/4 and then back down. Sometimes to red and then back down.
    - Running the heater on full @ 90 degrees produces warm air and then cold. Seems to cycle between the two extremes.
    - Rear air vent produces cold air only.
    - May or may not have a slight coolant smell in cabin.
    - Periodic filling of the coolant to the "cold" line (when it is cold) will, over time, reduce to 2 to 3 inches of coolant in reservior (never empty though).

    BACKGROUND:

    - Replaced thermostat last summer.
    - Followed Jim Cash's bleed procedure to the letter.

    SOLUTIONS BEING CONSIDERED:

    - Aux coolant pump
    - Yet another thermostat (this time with a 1/16" inch vent hole drilled near the top).
    - Cabin temperature sensor (but why the smell?)
    - Final Stage Resistor unit (??)

    Any insight you may have on this problem is greatly appreciated.

    Thanks,
    Tony I


  2. #2
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    Member No: 92682 Filehorse will become famous soon enough Filehorse's Avatar
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    Yes | No

    How often are you "periodically" adding coolant? >

    That info coupled with your suspicions of a "coolant smell" in the cabin suggests a leak in the system. With leaks come the likelihood of air getting into the system and air can cause the symptoms you are experiencing. A sticking thermostat will also cause the same symptoms so don't fall in love with the fact that you replaced the t-stat only a year ago - it could still be faulty.

    As far as an approach to solving the problem, I'd start with bleeding the system to ensure all the air is gone. Jim Cash has many excellent write-ups describing in detail how to bleed the straight 6 engine. The next step would be to pressure test the cooling system looking for the leak. The upper and lower radiator hose connections (both ends) are always suspects as the sealing O-rings get brittle with age. The good news is that neither of these initial approaches require the outlay of $$$ for parts although you may have to rely on a good BMW tech to handle the pressure test.

    One thing for sure, you need to run this problem to ground ASAP. The 6-hole engines are notoriously susceptible to short-term overheating damage in the form of damaged cylinder heads. No matter what the cause, it'll be a lot less than dealing with a damaged head.

    Let us know what you find out.


    Filehorse
    Knoxville, TN
    BMWCCA #407627

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  3. #3
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    Yes | No

    Repost of above reply

    That info coupled with your suspicions of a "coolant smell" in the cabin suggests a leak in the system. With leaks come the likelihood of air getting into the system and air can cause the symptoms you are experiencing. A sticking thermostat will also cause the same symptoms so don't fall in love with the fact that you replaced the t-stat only a year ago - it could still be faulty.

    As far as an approach to solving the problem, I'd start with bleeding the system to ensure all the air is gone. Jim Cash has many excellent write-ups describing in detail how to bleed the straight 6 engine. The next step would be to pressure test the cooling system looking for the leak. The upper and lower radiator hose connections (both ends) are always suspects as the sealing O-rings get brittle with age. The good news is that neither of these initial approaches require the outlay of $$$ for parts although you may have to rely on a good BMW tech to handle the pressure test.

    One thing for sure, you need to run this problem to ground ASAP. The 6-hole engines are notoriously susceptible to short-term overheating damage in the form of damaged cylinder heads. No matter what the cause, it'll be a lot less than dealing with a damaged head.

    Let us know what you find out.


    Filehorse
    Knoxville, TN
    BMWCCA #407627

    2002 525i Steptronic Sport/Premium | Build Date: 05/02
    81,000 Ultimate Driving miles
    Xenons
    Style 81s | Bridgestone Potenza RE960 AS
    Titanium Gray | Gray Leather
    35% LLumar ATR LLumaStar tint
    Valentine 1 | Hardwired
    Steering wheel position memory w/Alzheimers
    "Lifetime" ATF replaced at 40,000; Switched to Valvoline MaxLife @ the 80,000 mile service
    "LIfetime" Final Drive gear oil replaced at 81,000; Redline 75W-90 GL-5
    StopTech SportStop slotted rotors w/Axxis Deluxe Advanced pads
    StopTech SS Braided Brake Lines

    2001 E46 325i (Jet Black) Forced Retirement 6/28/09

    2001 E46 325i (Orient Blue) Forced Retirement 10/09

    1989 E30 325i (Alpine White) Retired

  4. #4
    Eurodavid
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    +1...

    Tony,

    I own a 1996 e39 528i (euro spec), and completely understand your frustration. But follow exactly what Filehorse laid out: there is no other cause for what you are experiencing other than the facts of either air is getting in the system somehow (possibly upon expansion of cooling components and the contraction when cooling, or worse, a head gasket leak doing the same thing) and/or a thermostat that is not working properly (take the old one out, and test it, doing the pan on stove method, with a thermometer in it).

    I know you don't want to hear this (especially at this time of the year, winter), but that is what you are facing. If you are willing to try it (I did it), Craig in Canada turned me onto some stuff that you can pour in your coolant (it's actually one of the few things good for the system), and one of its properties is that it is fluorescent. You then drive your car as normal, then one evening when it is dark, sign a black light around the engine & cooling system looking for leaks. The product is called RM-22 or RL-22, or something like that, I'll look for my stuff and post back what it exactly is called (unless Craig sees this and tells ya).

    Eurodavid

    P.S. Also, as an all around precaution, get a new rad cap, and I don't care if the old one seems perfectly fine (doesn't hurt to have a backup). Get a new one, as I can't tell you how many times I've heard of air getting back in an old cooling system (or even a completely redone one) where it was found to the old cap not working properly.


  5. #5
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    Re: The Temperature Gauge Puzzle

    Much thanks to Filehorse and Eurodavid for the feedback. Sounds like I'll probably end up:

    (1) Rebleeding and rebleeding again, and/or
    (2) New thermostat (can change with my eyes closed by now), and/or
    (3) I really like the idea about the flourescent dye and black light to spot leaks.

    Thanks again, Tony I

  6. #6
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    Yes | No

    +2, however I would rule out the t-stat because (m

    you should still get heat before the t-stat opens (providing you have a full system). No heat from the cabin heater is almost a 100% sign of air in the cooling system. A bad HVAC controller can keep the water control valves closed but you said you do get some heat, so that's not it.
    You need to find the leak and fix it. If you can't spot any dried coolant you need to have a pressure test done to find it.
    Hope it isn't the head gasket.
    When you refill your cooling system add coolant thru the bleed screw hole in the t-stat housing first. That will shorten the time it takes to get all of the air out.

  7. #7
    jimcash
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    Re: The Temperature Gauge Puzzle

    Of all the 4 items you are considering for solutions the only one that "might" be possible for your symptons would be the thermostat.

    BUT - if you are having to add coolant then you have a leak. And that is letting air in the system and that is why you are getting temperature fluctations.

    Because of the smell I would start to suspect a hose up near the firewall - one to the heater?

    Get this puppy pressure tested - by someone who really knows how to find a "iffy" leak in a BMW system. And don't accept a "no leak found".


    And remember the 6's need to have the front end raised to get the air to go to the front for bleeding.

    Do NOT fool with this - especially when it has been going into the red - otherwise you will be doing this bleed process all over again - right after they install the replacement engine.

    Cheers
    Jim Cash

  8. #8
    Curtis001
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    Re: Check your fan clutch

    If your fan clutch is no longer operational, as mine was once, it will cause the car to run hotter....yet you may not realize it immediately. When running too hot, the fluid will expand and pressurize your system in excess of what it should be, and you can wind up losing small amounts of coolant over time as a result. Mine was pressurizing and pushing it past all the hose connections. Eventually, probably due to higher temps and pressure, my coolant overflow tank gave out and BOOM. There goes the top end.

    While I agree with some of the other things to look at, my FIRST look would be the fan clutch! That blew my engine.

  9. #9
    Craig in Canada
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    IMO "cold" from heater rules this out (m)

    It's ALWAYS a good thing to check though...


  10. #10
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    +1 Re: Check your fan clutch

    think of the basics first and the fan clutch does the job of moving the air via the main fan when the car is not moving

    - the Aux fan is just an expensive appendage in my mind, unless the cluster had a tell-tail light to tell you it was on due to the over-temperature sensor, but it doesn't

    The new BMWs all have electric main fans now, but some still without the temp gauge in the cluster - warranties are good but expensive. I supposed if you cooked a new engine they'd find some excuse in the service booklet to hit you up for the cost of a new motor


    a short-circuiting temperature sensor resistor could also cause the temperature gauge to increase, on a M52 engine when you disconnect (open-circuit) the temp gauge goes to cold.

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