My 740IL is over heating I have a thermosate Question - BMW Forum - BimmerWerkz.com
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#1 (permalink) Old 03-12-2009, 09:20 PM
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My 740IL is over heating I have a thermosate Question

Hello,
I just got a BMW 740il. It drives great, but it is overheating.
I first noticed water leaking at the neck of the expansion tank. It turned out the small tube was cracked so I replaced the expansion tank. I figured this was the problem.

It wasn't. The car did the samething. After about a half mile of driving the temp needle goes a little past halfway and water/coolant starts to come out of the expansion tank cap!

I took out the thermostate and put it in boiling water and nothing happend.
Is the termostate on these car electric?...should the thermostate have opend when I put it in the boiling water?

Any ideas? Thank You, Les Marietta GA
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#2 (permalink) Old 03-12-2009, 09:27 PM
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Quote:
Originally Posted by LesG View Post
Hello,
I just got a BMW 740il. It drives great, but it is overheating.
I first noticed water leaking at the neck of the expansion tank. It turned out the small tube was cracked so I replaced the expansion tank. I figured this was the problem.

It wasn't. The car did the samething. After about a half mile of driving the temp needle goes a little past halfway and water/coolant starts to come out of the expansion tank cap!

I took out the thermostate and put it in boiling water and nothing happend.
Is the termostate on these car electric?...should the thermostate have opend when I put it in the boiling water?

Any ideas? Thank You, Les Marietta GA
Yes....you just tested your t-stat & it failed.....it is suppose to open.....

next time to check the t-stat, just warm up engine & feel the upper & lower radiator hoses, they should feel about same temp. the t-stat is open & coolant is circulating......if one hose is hotter than the other then t-stat is not opening, engine will overheat..

replace your t-stat

johnny,

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#3 (permalink) Old 03-12-2009, 09:36 PM
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Radiator/Waterpump/Thermostat done!

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#4 (permalink) Old 03-12-2009, 09:39 PM
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Thank You

Thank You Very Much! Les
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#5 (permalink) Old 03-13-2009, 09:17 PM
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Still Overheating! I replaced the T STAT and just removed the Water Pump and

Hello,

I replaced the t-stat and the car is STILL overheating. I bleed the system as Johnny said to in another thread. and it is still overheating.

I just got the water pump out and it looks fine. It is a BMW PUMP with metal impellars and they look fine. The pump turns fine with no looseness.

If the impellars are in good shape and the pump turns freely with no looseness should I spend the money to replace it?....what could be wrong with it?

NO hoses seem to be clogged and I flushed the radiator and it seemed to flow fine.

What should I do?

Could it be the heater core clogged? I hate even say it, but could the headgasket have failed?

Thank for all the help! Les Marietta GA
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#6 (permalink) Old 03-14-2009, 08:11 AM
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I would say its the Viscous coupling gone/going, which in turn is'nt cooling the radiator down.

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#7 (permalink) Old 04-07-2009, 10:57 PM
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Did you solve your heating problem? If not, it could be your radiator. I had a heating problem with an auto years ago. Someone suggested that I check my radiator by first running the engine until it reaches normal temperature. Then very carefully touch the radiator all over. Don't hold your hand on the radiator because it's hot. If you find a cold area or areas, that indicates that your radiator is partially clogged. Replace it. I hope this helps.
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