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7 Series - E38 (1995 - 2001)

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  #1  
Old 11-08-2012, 02:42 PM
Jojolove Jojolove is offline
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1998 740il Overheating

I have a 1998 BMW 740il that continues to overheat, I have replaced the thermostat, waterpump, radiatar, heater control valve and it still over heats. Got a compression test done and a combustion leak test done and it came back fine. Took it to the dealer and they flushed the system still overheating. What else could be done?
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Last edited by Jojolove; 11-08-2012 at 03:18 PM.
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  #2  
Old 11-08-2012, 04:28 PM
Jojolove Jojolove is offline
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FYI- I am new to this site. Just want some expertise.
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  #3  
Old 11-09-2012, 07:09 PM
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BigBoy740il BigBoy740il is online now
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Welcome Jolo,

You mentioned that you changed the major coolant system parts but did not mention the overflow bottle, thermo fan clutch or bleed screw. I would change those and bleed the system again.
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Last edited by BigBoy740il; 11-09-2012 at 07:11 PM.
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  #4  
Old 11-09-2012, 07:40 PM
Jojolove Jojolove is offline
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Thank you so much for your response!! What is the overflow bottle? Meaning if I ordered the part what do I ask for?
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  #5  
Old 12-01-2012, 10:43 PM
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BigBoy740il BigBoy740il is online now
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The correct term is the coolant reservoir. It's located on the left side of the radiator, next to air filter box. It is a common failure item and prone to splitting and leaking. The bleed screw gets brittle are sometimes cracks off. A failure of both the reservoir or the bleed screw allows air into the cooling system, preventing it from flowing properly. The thermo fan clutch couples and activates the engine fan. Without this action, the engine gets hot and the engine fan never kicks it. To test it simply start the car. With the engine cold, you should be able to stop the fan blades with a rolled up news paper. Same test with engine hot, should shred the news paper. Replace fan clutch if it fails either test.
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Last edited by BigBoy740il; 12-01-2012 at 10:53 PM.
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  #6  
Old 12-01-2012, 10:46 PM
SFbay SFbay is offline
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Are you sure it was vented properly??? Heater blows hot when idling?? It can be a real btch to vent it.
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  #7  
Old 12-01-2012, 11:02 PM
Jojolove Jojolove is offline
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@bigboy740iL change the fan clutch. But not the reservoir or bleed screw. The mechanic who was working on my car didn't want to change those things after I complained about throwing parts at my car. I took it to another mechanic and he said my car was never diagnosed properly. I waiting for him to get back to me.
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  #8  
Old 12-01-2012, 11:03 PM
Jojolove Jojolove is offline
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What does vented mean?
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  #9  
Old 12-02-2012, 12:24 PM
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bluebee bluebee is offline
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I think they're talking about bleeding.

If you're overheating, you first:
a) check if air is blowing over the radiator (i.e., fan)
b) check if water is circulating (i.e., waterpump, thermostat, leaks)
c) check if air is circulating instead of water (i.e., bleeding)

Since overheating is the number one problem in these engines, there is more information than you can possibly imagine on your specific problem.

If it's a simple overheat, these set of links (from the E39 bestlinks) should help:
- What to look for when your KTMP (1) or coolant temperature gauge indicates overheating (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) & what to look for in a perfectly normal E39 cooling system (1) & a picture of every failed part in the cooling system (1) & various techniques to properly bleed (1) (2) (3) & refill (1) & drain (1) (2) & flush (1) & what coolant to use (1) & what parts to replace (1) (2) & how to retrofit brass bleeder screws (1) (2) & what special tools to make or buy (1) & how to tell how old your cooling system is (1) (2) & how to test the cooling system auxiliary electrical fan (1) (2) (3) (4) & a DIY for replacing the auxilliary fan (1) (2) (3) & the infamous fuse 75 (1) & the aux fan relay (1) & how to diagnose lack of HVAC/IHKA heater core heat with cooling system (auxiliary pump) at idle (1) & a Behr radiator and Behr/Heat expansion tank autopsy (1) (2) & request for another Behr surge tank autopsy (1) & why new made-in-China Behr/Hella expansion tanks are DOA (1) & E39 Fan shroud removal DIY (Besian) (M54) & some of the better cooling system DIYs (cn90 1997-1998 M54TU) (cn90 V8) (aioros '99-03 M54) (Ågent99 '01 530i) (pelican 3-series) (bluebee M54B25) & tricks to replace the fan clutch nut (1) & lower-hose thermoswitch o-ring (1) & to non-destructively remove the heater hoses (1) or radiator nipple (1) or expansion tank nipple (1) (2) or Oetiker clamp (1) or misplaced thermostat wiring loom (1) or broken bleeder screw (1) & modifying the cooling system pressure cap (1), or using propanol-based zero-pressure fluids like NPG+ (1) (2) (3) (4) (5) or all-aluminum cooling system parts by Zionsville (1) (2) (3) aluminum radiators & what happens if you drive one mile too far with an overheated BMW cooling system (1).

If it already overheated, causing damage, these will help:
- Summary advice to provide users who suspect a major engine repair due to overheating (1) (2) (3) (4) & how to test an engine for a blown head gasket, cracked heads, a warped block, stripped head bolt threads, cam seizures, contaminated bearings, coolant hydrolock, or piston, ring, or valve damage (1) (2) & what are the major factors in deciding whether to rebuild the engine, replace the engine, or sell the car (1) & a DIY for replacing the I6 M54 head gasket (1) (2) & replacing the V8 M62TU head gasket (1) & why these engines are so prone to heat-related damage in the first place (1) & welding the crack between cylinder #3 and the water jacket on the exhaust side (1) & what engine swaps are most recommended (1) (2) (3) & where to obtain a new or rebuilt head (1) replacement short block or long block (1) (2) & how to lift & remove the engine (1) & the most recent real-world results from the last 50 people faced with similar blown engine problems from which this advice came from (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) (40) (41) (42) (43) (44) (45) (46) (47) (48) (49) (50)
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Please read the suggested threads, where the best always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need
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  #10  
Old 12-16-2012, 09:30 AM
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BigBoy740il BigBoy740il is online now
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@Jojolove. Did your New indy diagnose your cooling problem?
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  #11  
Old 12-16-2012, 09:46 AM
Jojolove Jojolove is offline
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Not officially, still waiting. He told me the first guy didn't diagnose my car properly. He said he was just throwing parts at it. Hopefully I know something by tomorrow.
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  #12  
Old 12-21-2012, 09:58 PM
SFbay SFbay is offline
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Quote:
Originally Posted by Jojolove View Post
Not officially, still waiting. He told me the first guy didn't diagnose my car properly. He said he was just throwing parts at it. Hopefully I know something by tomorrow.
2 options:
Air pocket
Head gasket
Try to vent it and make sure lower hose is hot and aux fan is spinning
Most likely heater core has air pocket or it could be leaky.
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