ZPOST
BMW Garage BMW Meets Register Search Today's Posts Mark Forums Read


Go Back   ZPOST > BMW Z4 Roadster and Coupe > General BMW Z4 Forum
  TireRack

SUPPORT ZPOST BY DOING YOUR TIRERACK SHOPPING FROM THIS BANNER, THANKS!
Post Reply
 
Thread Tools Search this Thread
      06-13-2017, 10:06 PM   #1
t0pless
Private
20
Rep
52
Posts

Drives: 2003 Z4 3.0
Join Date: Oct 2013
Location: United States

iTrader: (0)

Calling all Coolant System Experts

Hey everyone,

My car started overheating in the humid 95F+ southern Illinois weather today. My P2 gauge (and hidden OBD coolant gauge) showed temps blast past 120C and the dash gauge ticked quickly towards red. I shut down my engine, let it cool, and limped it back to school.

All within the last 10,000 Miles I have replaced:

Thermostat
Water Pump
Upper and lower rad hoses
Expansion Tank w/ Cap
Coolant Flush (BMW fluid mixed with Distilled water 50%)


A couple of things that I noticed:

-I am overheating both at idle and at speed. At one point I was going 60mph on a downhill with no throttle input but still had steadily rising temperatures.

-THERE IS NO COOLANT LEAK. Removing the cap showed coolant at full level. The system is definitely pressurized as opening the cap released a large hissing noise. This was checked several times. There is also coolant flow through the top fill port so the water pump is definitely working, and there are no abnormal noises.

-There is proper heat exchange at the heater core. Blasting the heat helped slow down the temperature increase and at no point did the vent air become cold.

-Oil level is correct and there were no signs of coolant in the oil. No loss of power or issues starting the car.

-The system is properly bled.

Concerns and suspicions I have:

-The lower radiator hose was cool to the touch. The radiator was not super hot, but I was not able to touch it for very long.

-The radiator fan does not kick in unless if I turn on AC. If I turn on the AC, the fan kicks up on command with no issues or noises. With the AC off, the fan will turn off regardless of the engine temperature (the fan did not stay on after overheating which it is also supposed to do). With the AC on my engine still overheats both at idle and at speed.

-The engine temperature did not decrease under WOT. (The electronically controlled thermostat is supposed to open under WOT rapidly changing engine temp.)

With this in mind, I have a feeling it's either my thermostat or a blocked passageway in the radiator. Since I'm at school, tools are not readily accessible. I have friends in the area that do, but I'd like to get an idea what to check before I start wrenching on their driveway.
Appreciate 0
      06-14-2017, 07:57 AM   #2
gas-can
Second Lieutenant
25
Rep
204
Posts

Drives: 2006 3.0i Roadster
Join Date: Oct 2012
Location: USA

iTrader: (0)

The first thing coming to my mind is a bad thermostat. They are supposed to fail-open, but I've seen the opposite. If that happens, the cooling system basically ignores the radiator and operates in a closed loop. Radiator may be warm-cold (at least at top), while engine is cooking. Turning on the heat usually blows very hot air and may cool the engine down a bit since that circuit is usually on the engine side. If the sensors for the fans are in the radiator, fan may not come on (unless AC is turned on).

I think your t-stat is both electronic and mechanical. If you have a code reader, it might give you some hints.

That said, are you absolutely sure you bled the system properly? I don't know the specifics of the M54 but the N52 has a very specific bleeding method that has to be followed - I'd imagine its predecessor would be similar. Sometimes air can get stuck in different places and give you all kinds of hell.

I don't think I have to tell you that it's not smart to drive the car anywhere (even limping) until this is fixed, especially since your engine is made of aluminium.

good luck,
-gc
Appreciate 0
      06-24-2017, 05:20 PM   #3
NO_RETURN
Private
NO_RETURN's Avatar
United_States
5
Rep
72
Posts

Drives: 328i M Sport MELBOURNE RED
Join Date: Dec 2014
Location: Arizona

iTrader: (0)

Not to jump to the worst case scenario but have you checked the oil for coolant contamination or oil in the coolant? Just looking at the dipstick is not always going to show it. Also any steam in the exhaust? You said it overheated.... multiple times?... you may have a compromised the head gasket... not a death sentence but a very costly repair. If it is the head gasket stop driving it, you will eventually blow the entire engine.

Hopefully it's just like something with the thermostat or sender. Did you or the shop that installed it use RTV silicone on the Tstat or water pump. The tolerances are very tight and it may have gummed it up. Also the temp sensor / sender should have been replaced too.

However Don't forget to Check the heater hoses as well. I bought a $350+ cooling system rebuild kit for my sons 323 and the one hose not included was the lower heater hose. A day after installing the kit, we found the leak in the heater pipe that connects to the bottom of the tank.

Hope it's something simple... good luck!
__________________
2014 328i M Sport Melbourne Red
2012 X5 35i
2004 Z4 30i
2001 323i
2008 Wrangler Unlimited Rubicon

Last edited by NO_RETURN; 06-24-2017 at 05:27 PM..
Appreciate 0
      06-25-2017, 05:43 AM   #4
Vanne
Down Under!!
Vanne's Avatar
United Arab Emirates
1593
Rep
4,293
Posts

Drives: 2007 Z4MC
Join Date: Mar 2013
Location: Dubai

iTrader: (4)

the bottom rad hose being cool to touch that is an issue, and that's either the Thermostat or you've got as massive airpocket down there.. That's where id start.
__________________
2007 EuroSpec Z4///MC - Building/Developing Z4 GT3
Powered by
Appreciate 0
      06-25-2017, 12:53 PM   #5
dc_wright
Captain
dc_wright's Avatar
249
Rep
758
Posts

Drives: 2006 Z43.0si Roadster
Join Date: Oct 2014
Location: Orlando, FL

iTrader: (0)

The cool to the touch lower hose is a sign of no flow through the radiator. Could be either the thermostat isn't opening, or you've had a water pump failure. If you've driven it for some time since the last cooling system work without any issues, and now it's started the overheating then not likely to be an air pocket.
Did the new water pump have a metal or plastic/composite impeller? The plastic impeller water pumps have long been a weak spot in the BMW cooling system. BMW changed to a composite impeller which is much higher glass fill than the original, but even they have a shorter life than the metal impellers. The failure mode is the impeller cracks where it's molded onto the shaft, comes loose, and stops pumping.
__________________
Top Down 365
Appreciate 0
Post Reply

Bookmarks

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -5. The time now is 12:54 PM.




zpost
Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
1Addicts.com, BIMMERPOST.com, E90Post.com, F30Post.com, M3Post.com, ZPost.com, 5Post.com, 6Post.com, 7Post.com, XBimmers.com logo and trademark are properties of BIMMERPOST