Overheating Problem?

J

jamosborne

New member
My first post and i have what seems to be a slightly bizarre problem with my 2003 3.0 Z4 which i would appreciate some help with!! When the car has been running for around an hour the coolant temp gauge starts to climb anywhere up to around 3/4 then will drop back down to the level it should be at. It will continue to do this randomly but never goes above 3/4s and the red light never comes on at all. It doesn't matter what kind of driving it is either does it whether in town or on a motorway journey. Car hasn't lost any coolant at all, oil is all ok i'm just a little stumped as to what it could be. My local dealer as always has not been very helpful apart from wanting to charge me a small fortune to diagnose a fault they say they have never really seen. Has anyone else had any similar issues or have any ideas what the problem might be? I have had an airlock in the system suggested but the coolant system has been bled and that hasn't made any difference at all. Thanks for any help!
 
Has your fuel economy gone south also? I would have a guess at either a sticking thermostat or a bad coolant temperature sensor. Both are cheap parts but the former quite hard to replace i believe.
 
Dealers tend to rely on fault codes first and can struggle with basic principles :headbang: I assume they checked for any fault codes?
  • Basics to eliminate first should include,
    Check coolant levels are correct and all tanks, caps, bleed screws, housings, rad's and hoses are sound, any sign of leak stains round these can be due to tiny amounts of coolant leaking when pressure and heat rise and immediately evaporate, air is drawn in during cooling replacing the coolant level to normal.
    Air locks in the system can cause your symptoms, the air bleeding process is a bit of a fiddle on BMW and symptoms will return if you have leaks.
    Temperature sensors (there will be several) can cause a range of problems from gauge reading incorrectly, late or non-activation of fans and all sorts of running problems.
    Water pump, either function which is relatively uncommon or more likely internal/external seal breakdown which can again cause micro-leaks and can be difficult to detect.
    Electric fans not running correctly, usually due to poor sender/power connections, or can be fan seizing which is a known fault on some BMWs.
    Thermostat is possible but yours are not classic symptoms which tend to be either cold running or total overheat.

Hope you get it sorted as it only takes one full-on overheat to cause real damage.
 
Thanks for the feedback. It didn't show up any fault codes think i will just have to bite the bullet and take it in to get sorted. Found a good local independent specialist would rather take it there my local main dealer is pathetic i wouldn't trust them to find what the problem is!! Will get it booked in tomorrow.
 
I have a 2005 Z4, i took it in for a smog check last week and after he was finished the test (which it passed with flying colors, way below minimums) there was a "puff" of vapor and then the coolant started pouping out the bottom. He shut the car down so it didn't overheat and then i founf the problem, the coolant tank had a 5 inch crack down the side. I replaced the tank and topped off the coolant, started the car and it ran fine. After about 25 minutes of running the gauge went all the way over to red, so I shut it down let it cool and repalced the thermostat assembly. Same thing after 25 minutes of running the gage went all the way to the red. Now with all that being said has anyone had the same problem and what was the fix. Also can anyone tell me were i can get a repair manual for this car? I appriciate any help, summer is here and its time to go topless. lol
 
Hi David, firstly welcome to the forum! :thumbsup:

Are you sure that when you topped the car off with coolant you squeezed all the radiator hoses to help feed out all the air bubbles that may have entered into the system?

When the temperature rises above nominal, does the radiator fan switch on? How quickly does it rise, make sure it doesn't hit red again as it will cause head-gasket failure!

Repair manuals for the Z4 maybe difficult to find, and you haven't told us which engine you have, but the ubiquitous 3 and 5 series BMW's should have repair manuals and share the Z4's engines. There is also the BMW TIS (workshop manual for dealerships) which some people may have *cough*. If you want anything specific, it wont hurt to ask :wink:
 
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