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      10-30-2012, 02:00 PM   #1
goldguilexx
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cooling problems

So i have had an issue with my cooling sytem for about over a month now. Ive replaced my water pump, the thermostat, the sensors, the upper and lower hose and the expansion tank. the only thing left to replace is the radiator and the fan. The mechanics ive taken them to both say they are fine and dont need replacing but at this point im just going by the process of elimination.
The car will be running normal temp (temp needle pointing straight up at 12 o clock) and then after the car has warmed up for say 20 minutes or so the needles starts to go to the right (towards the red) when idle on a stop light or something. The fix was to rev the engine to about 2k rpms and make the coolant flow due to lack of circulation as it seems and problem fixed till the next light. then the process would start all over.
A week ago one of the mechanics replaced a aux fan switch and the issue went away for a week end and sure enough it started back up. I made sure the radiator had enough coolant/water in it and that does not seem to be the issue.
Now the reving up to 2k trick does not work so i open up the bleed valve and let the steam air come out. Upper hose is hot and the expansion tank is as cool as a cucumber. Other than that issue the car has always run perfect, no other issues.
Last thing, air always seems to be inside the system, so im assuming an air pocket is trapped inside and wont budge out maybe.

Anyone have similar issues?


2004 bmw z4 3.0i roadster 100k+ miles automatic, out of warranty

Last edited by goldguilexx; 10-31-2012 at 04:10 PM.
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      10-30-2012, 06:13 PM   #2
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Hi Gold,

First thing that popped into my head was a bad thermostat- but as you already changed that, it appears unlikely( unless someone put in a wrongly rated on, or installed it incorrectly?).
Have you tried turning on your heater on full blast to see if that air is hot? (You can also use this trick as an emergency measure to help cool the car- the heater core uses the engine coolant to heat you up, and this also cools the car at the same time. Obviously this won't be very comfy in CA, but a small amount of sweat would probably be better than a blown head gasket!)

Other thoughts: bad radiator cap/clog somewhere in the radiator/system/ air stuck in system / bad fan/clutch/relay?

The radiator cap is a $5 device that opens up and closes at the proper pressure (~15psi iirc) to make sure that the superheated coolant can expand and go to the expansion tank. When the pressure drops (ie coolant cools), the cap allows the coolant to get sucked back into the radiator. Does the spring and the valve cap look ok? The fact that you have a cool coolant tank is an interesting clue. Does it look overfilled/empty?

Air in system- this can cause a bunch of issues. Easy fix though. When your mechanics replaced those hoses, they should have already done this, but they may also have not. The basic idea is to remove the radiator cap [on a cool car!], fill it up with coolant and turn on the engine. The water pump will pump the coolant around and the radiator will "burp" out any air in the system. You will then refill the coolant, and try it once more if you are paranoid (After the car has cooled). Be careful if you do try this, and be sure to keep an eye on the temp gauge.

Have you also physically made sure that your fan(s) are powering up?



I'm sure some others will come along with some other suggestions soon. Good luck!
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      10-30-2012, 07:36 PM   #3
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There is a bleeder screw on the expansion tank.
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      10-30-2012, 07:50 PM   #4
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Thank you for the helpful hints gas can. I tried the ac trick but it stopped working last night. only cold air comes out (heater or not) and does not cool the car. The cap will be replaced this week (need to make a pit stop at a local dealership for it). As for the radiator yes, its possible it could be clogged or even that the thermostat was faulty.
The fan and aux switch are fine.
The caps spring looks tight but otherwise fine. I think ill burp the car myself tonight and see if it helps any.
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      10-30-2012, 07:51 PM   #5
goldguilexx
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and yes shipkiller, i tried the bleeder screw on the expansion tank as well. as i open it it lets out a nice amount of steam. this helps greatly with cooling the car.
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      10-30-2012, 08:05 PM   #6
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I am going to ask the dumb question so do not take umbridge.

Since you used the bleeder screw and had steam coming out, did you add coolant afterward? I ask this because I have seen individuals NOT do this.

When I had to replace the hoses on my Roadster, I had to bleed the system several times before I had a nice stream (without air) coming out of the bleeder screw.
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      10-30-2012, 08:38 PM   #7
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lol, yes, i did add coolant to the radiator after undoing the cap. Looks like the coolant just stays at the same level (its not much that i add)
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      10-31-2012, 06:37 PM   #8
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Hi Gold,

This really does sound like you have some air stuck somewhere in the system. Sometimes getting the air out can be a true pain, but not doing so causes a bunch of issues which causes dealers/mechanics to replace parts at random hoping the problem goes away. I suggest truly bleeding the system several times to be safe. I dont have much experience with bmws specifically so I don't know about the relief valve mentioned above, but you may want to try to bleed it the old fashioned way to just to be safe (removing cap, turning car on, and adding coolant as car burps out air).

Also, anyway you could check the thermostat to ensure that it's working properly? Easy way to test it- pull it out- get some boiling hot water- drop the thermostat in to the water. If it's working properly, you will physically see it open. Needless to say, you don't want to reuse whatever container used for food/drinking again (antifreeze causes blindness )

When you do find out what's causing it, please let us know so that we can learn for the future!

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      10-31-2012, 07:26 PM   #9
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thanks for the advise gas can! I just spoke to a shop just minutes ago, he says he found a crack in the head. He stated he performed a leak test and saw loss of pressure near cylinder 4 and 5 (in between) and a head job would set me back 1800K! Not sure if to trust it or not so im going to get another opinion. Ill keep this posted as it progresses.

and yes, antifreeze can cause blindness but also is said to taste very sweet, weird. lol!
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      10-31-2012, 09:23 PM   #10
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Oh man I'm sorry to hear that. I would definitely get a second or third opinion though.

Also, have you checked your engine oil? See any frothy/milky oil? If the head cracked, there might be a coolant leak into the engine oil system- usually you will see this on the dipstick. And also possibly from your tailpipe.

I wonder if this was a result of the engine overheating though. Heads cracking these days is quite rare....usually the head gasket will pop before the head itself. I know that fords used to be notorious for this a while back...

Lets hope that initial pressure reading was just a fluke!
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      11-01-2012, 04:07 PM   #11
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Yeah, it was not a good feeling hearing that. But im getting a second opinion done just for good measure. I dont want my beloved Z to turn into a money pit type of deal.

I did check the dip stick and tail pipe and they seem clear of any odd colors or smells.
I however heard that aluminum heads have this issue and was actually more common than rare.

So i will be scheduling up another appointment at a trusted but expensive shop and have them confirm the readings and take it from there. Fingers crossed that I do not need a new head or a new engine!
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      11-02-2012, 12:04 PM   #12
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random note: Since Wednesday no overheating issues what so ever. Only thing done was a leak test (unknown with what or how) and I replaced the radiator cap as I read it could be a stupid fix. Weird. Im still going to get the thing looked over regardless and do a full check. Just thought it was worth mentioning.
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      11-03-2012, 07:56 PM   #13
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the cap.... it did nothing. Overheated again last night. My baby's going in for a head job or new engine at worst this Monday. Sigh................

Once she is all opened up and we know for sure what the issue is ill post about it again.
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      11-03-2012, 09:21 PM   #14
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air in the cooling system

The syptoms described sound like air in the cooling system to me.

The BMW service info has a specific procedure for filling/bleeding the cooling system on your car. I would follow that procedure (exactly) before you do anything else.

Oh yea, I don't care if it has been "done" already. Start over and do it again (exactly) per the manual.
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      11-03-2012, 10:02 PM   #15
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No harm in doing it again. By chance do you know where I can find the info? A link perhaps? All the links I find end come up for other BMW's.
Any help would be greatly appreciated.
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      11-03-2012, 10:13 PM   #16
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http://tis.spaghetticoder.org/s/view.pl?1/06/06/86

I found this. Is this what you are referring to? I see so any methods its a bit daunting. I even saw a post about a turkey baster or something.
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      11-04-2012, 08:55 AM   #17
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Hi Gold,

Sorry to hear it wasn't the cap, but the fact that this is intermittent really does make me think that it's still air in the system. That bleeding procedure seems arduous, but if it solves the problem, by all means try it!

I also found this thread from this forum that might also give you some pointers : http://www.zpost.com/forums/showthread.php?t=538686

The bottom part has some info specific to bleeding - this may be a useful supplement for the procedure you found.

Pelican parts also has a faq on this stuff at http://www.pelicanparts.com/bmw/tech...lant-Flush.htm

It's more geared towards the e36, but the info maybe helpful in filling some gaps if you try this out.

This the time I miss the old iron heads- aluminium may be lighter, but those iron heads could take more of a beating before warping/cracking/exploding. Hopefully your block is still ok and this is all caused by a rogue bubble!

Good luck!
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      11-07-2012, 01:14 AM   #18
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Tried the air bleeding thing again. No more bubbles came out and plenty of coolant inside. Still only cold air comes out on max heat and air on full. Car runs fine and 15 or 20 min into the drive if I'm not on the accelareator the temp starts to rise. Gotta rev to 2k and needle goes back to normal operating temps. Sigh.....
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      11-07-2012, 06:56 AM   #19
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Cold air on max heat is a big indicator that you still have a large air bubble in the system.
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      11-07-2012, 11:05 AM   #20
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Hmmm..... Either I'm doing it wrong or maybe it's a clog in the radiator.
I followed the blessing procedure to a T. Such a headache!
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      11-07-2012, 03:18 PM   #21
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I've had problems with air bubbles in this engine on my other cars. When I bleed the system it always helps to:

1. Make sure the front end is raised well above the rear so that the air bubbles can come out through the bleed screw. This is important when filling and bleeding the system.
2. Squeeze the lower hose while the engine is running and the heater is on max hot to help force any air though the system

If all else fails, I would drain the system (including the engine block) and start the bleed process over again. It is very important to add coolant very slowly into the expansion tank to minimize the potential pockets of air that get into the system.

Good luck and let us know if this takes care of it. It sure sounds like an air pocket to me as well.
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      11-07-2012, 08:01 PM   #22
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havent tried draining all the coolent yet so maybe its a good last ditch effort before I take it to the shop and start opening things up. I did a flush not too long ago (say 6 months or so) for just maintenance sake as my car had hit 100k miles. Ill try that this weekend.
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