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Thread: e34 535i sudden overheating

  1. #1
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    Default e34 535i sudden overheating

    Hello!

    About a month ago i was passing some traffic on highway and suddenly hear a beep, check the display and it says the engine is too hot, i stop asap and sure enough its spilling coolant out of the overflow pipe from the pressuretank. I fill her up with water and no more problems.
    So week before the last week i got the coolant changed. And day before yesterday it suddenly overheated again, this time i have coolant with me so i fill the tank and its ok untill this morning when it did it again
    And when i took off the pressuretank cap, the hose that lets coolant to it was kind of spittin the coolant, like it was mixed with air (it made growly sounds too).

    The overheating is very very sudden, like in few seconds it goes from dead center to just before the red, or atleast it seems like that to me, i keep my eye on the meters constatly.

    Common sense tells that air in the system causes the problem and i will bleed it but can there be anything else, like faulty thermostat or maybe it sucks in air from somewhere? I just want to be sure that it wont happen again, head/gasket are just way too costly to experiment with.

    Coolant does not seem to have oil in it, the oil does not seem to have coolant in it, she wont smoke with when its warm and dry outside and the large radiator hose has pressure in it put you can still squeeze it, when the engine is warm and running.

    PS When i bleed the system can the pressuretank cap be open when engine is running so i can fill it/check coolant level on the fly?

    Thanks for reading!

    Toomas

  2. #2
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    I am not 100% sure, but does the 3.5l engine have the same water pump as the m50 2.5l ?

    I had a similar experience and it was due to the water pump. The impellor is plastic and is a push fit onto the drive spigot. I found that when the engine got hot, the joint expanded slightly and started to slip, leading to the engine hitting the red zone. On stopping and cooling down, the plastic contracts back onto the spigot and all is well, until the next time.

    Not sure if this is the case with the 3.5 engine but it would give the symptoms you are having.

    HTH.

  3. #3
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    Thanks for the reply.
    While the M30 has different water pump (atleast according to realoem.com) it is a possibility since supposedly the previous owner changed the pump few months ago.


    Toomas

  4. #4
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    Quote Originally Posted by Toomas
    Thanks for the reply.
    While the M30 has different water pump (atleast according to realoem.com) it is a possibility since supposedly the previous owner changed the pump few months ago. Toomas
    Sounds like a pressure block, how many ks and has the engine ever had the head gasket replaced? Usually the old 6 will spit out the side or mix coolant and oil- having a failed gasket cause compression inside the cooling system is much rarer- though others here would know about this better than me. I'd suggest a careful bleed.

    But there's no info in your profile so its very hard to be specific...

    1. Are you using the right coolant? ie the real BMW-branded Blue stuff? This is a MUST as you may know.

    2. only use distilled water and premix it- a min of 33% coolant or more is required, so you require at least 4x1.5L bottles from BMW to get it done

    3. Bleeding can be tough, but I believe the car will self bleed too if you can get most of it out in the beginning. Easiest way is to drill a 1/8" hole in the thermostat plate (at the top of it) so that you can bleed the head of the air trapped inside it without having to wait for the engine to heat up enough to open the thermostat so the air can actually make it out of the head and to the bleeder.

    If you have no hole in the thermostat, it will have a small air-lock behind it, and since air transmits heat slower than water, the spring on the stat can take some time to reach the same temp as the coolant so your head can be pretty hot before the bloody thing opens. This is why the drill-hole in stat flange is a good idea. Without it you just have to hold your nerve and feel for the upper hose to heat up indicating that the thermostat has opened and the coolant is flowing into the top of the radiator.

    After that, you can bleed the air out by opening the bleed screw (before this not much will come out) which will now hiss and spit shitloads of steam until maybe 1/2 a litre of steam has escaped. Then you are back to a clear coolant stream and you can close the bleeder and fill the expanison tank back to the high mark with premixed coolant once the system has lost some pressure.

    If you are anal like me you will then then drive around a bit, pop the hood a few times (having done a few hills) and check the last bubbles are gone without taking the expansion tank cap off- you are only doing small bleeds at the bleeder to remove the last bubbles, so the expansino tank will barely be dropping at all. This is proabbly way ove rthe top as I said as many say the engines slef bleed after a bit.

    That's my procedure, it is easier than a piss in the pub when you can imagine the air bubble lock inside and how it is affected by the thermostat- and what affects its operation.

    For those that have not pulled the thermostat out before it might be hard to conceptualise, but it's good to get all this sorted cos all these cars need the coolant changed (even at stealer price it is cheap insurance against the problems many face unnecessarily) the moment one buys one, and a new thermostat is a steal for $15 too. I do a decent radiator, heater core and block flush too- just to check for any of the (all too common) signs of neglect. The M30 water pumps is dirt cheap, so if in any doubt change that too, all your belts (for a quieter ride), then there is the PS and tranny fluid, usually the PO has done the engine oil at least- but check and some nice synthetic to help guarantee the diff'll last you out- I'd almost always get a set of dogbones too.. that's my little list of the usual suspects for a new e34... Nick
    Last edited by genphreak; 06-26-2006 at 03:09 AM.

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  5. #5
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    The clock reads around 350k km (~220k miles) and i dont know if the gasket has been replaced but atleast from visual inspection it does not bleed.
    It was also checked by the local dealer few weeks ago and they didnt say anything about the headgasket.
    And i use random pre-mixed (-36* c) blue (or are they green?) coolants.

    I think i will try to bleed it tonight and take her to an expert tomorrow, i just have to be 100% sure it wont happen again.
    /me cant afford to rebuild the head

  6. #6
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    Random premixed? I don't know if you really mean generic or some brand called random, but either way it is not OE coolant... and probably indicates poor servicing prior. Change it with a by the book, complete system flush: Every bit you leave in there will clog and corrode components in the engine after it reaches iits use by date. Avoid a new radiator, stuck heater valves, leaking heater core (coolant spilling out into the cockpit- pleugh!), head gasket replacement by flushing everything well with tap water (as i said remove radiator) and directly flush the block and the heater core with a hose- then fill with nice fresh coolant that you know won't harm the car. Use the right mix of it- and mix it prior to putting it in this way you know you have the desired ratio. I run 33% as it never goes below freezing here in Oz. Other aplces 50% or more can be prerequisite. Just check your handbook. Have you a Bently manual? It is very very helpful if you haven't work on these cars before, they have special ways of doing things that can make for expensive or a tough time learning... Nick

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  7. #7
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    Regrdless if you follow my bleed procudure with an 8mm spanner you will be able to work out if it is an air block or a gasket leak. Then you'll know what is on the cards. I've done the head gasket, it is hard work but can be done in a weekend if you have a good book to follow and all your homework done (and the right, new parts all ready for the job). You don't even have to remove the intake manifold but you will need to replace the O2 sensor.

    The head should be sent off to a shop for a clean, test and vavle reset, new valve guides and stem seals (at least) should be put in. You might need a new cam and rockers too. As well as Don Gale's banjo bolts (search the forum for these). All stuff best left to them so with that in the middle it can take you 2 weekends to complete. Nice to have a break in the middle so you have time to clean things up properly.

    It's also the best ever time to replace all your coolant hoses, thermostat, timing chain guide, water pump etc. I'd replace the cam sproket and if you possilbly can plump for a new oil pump drive and main timing chain/crank sprocket too- the job gets bigger cos that means pulling the oil pan, but after that the engine is ready for another 300,000 easy and you don't ahve to go in again if you do it right. On an M30 it isn't hard if you pay ti a little repect during the job and don't rush anything. Read the procedure twice before doing everything- you need to know what you might have missed- and can't go back to do again once its all together again without serious consequences... Let us know how it goes with the bleed proceudure- and good luck! Nick
    Last edited by genphreak; 06-26-2006 at 03:54 AM.

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  8. #8
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    Yes i meant generic coolant that you buy from gas station for example, everyone uses it. And its allready mixed to the point that it can whitstand -36*C and yes it can drop this low here, even lower on rare occasions

  9. #9
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    Quote Originally Posted by Toomas
    Yes i meant generic coolant that you buy from gas station for example, everyone uses it. And its allready mixed to the point that it can whitstand -36*C and yes it can drop this low here, even lower on rare occasions
    Yikes, sounds like an acid cocktail going down. If its been like this more than a year, you could well be up for a new head given the age of the motor. 'tis bleed and see time Toomas. Welcome to the forum btw! Nick

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  10. #10
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    There was nothing to bleed, i filled it untill the coolant started to flow out of the bleeding screw. Then let her run untill the temp cauge was in middle and when i opened the screw coolant started to spill out, no bubbles or anything and it was a rather clean flow untill it hit the fan :S

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