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Thermostat Change A8 BFM

  #1  
Old 12-04-2010, 01:22 AM
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Location: Orange County
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Default Thermostat Change A8 BFM

How long does it take change the thermostat on the A8 2004 BFM engine. Any special equipment needed?

Reading the forums sounds like have a thermostat issue. Here are some pictures of the temp. It goes up and down like a yo-yo. No coolant loss at all, once very nearly hit the red zone, but backed off. Strange?

I have had the car overheat 6 months ago when I had a hole in the expansion tank. So I have seen the steam and pouring out the red overheating sign flashing in the dash.

But the needle going from 1/2 to 3/4 back to 1/2 way, has me going crazy, any idea where it's supposed to stay under normal operating conditions? (the flash did not fire in one the pics)
 
Attached Thumbnails Thermostat Change A8 BFM-heat1.jpg   Thermostat Change A8 BFM-heat2.jpg   Thermostat Change A8 BFM-heat3.jpg   Thermostat Change A8 BFM-heat4.jpg  
  #2  
Old 12-04-2010, 01:22 PM
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Thermos are notorious on the A8s for failing and R/R a thermo is 3/4 the way to a new timing belt - if you are close to belt change time, bite the bullet and do the entire job.

But, if you had a coolant leak in the past and have had the bouncing temp since, I would suspect a pocket of air in your coolant system, reference your Bentley manual to bleed the air out of the system (you do have one, dont you? )
 
  #3  
Old 12-04-2010, 05:26 PM
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Yep , the thermo is buried on the front of the engine, behind the timing belt on earlier engines and I assume similar on yours. Changing does generally require all the special tools used for the belt change, since it has to come out of the way to get to it.

A really inconsistent needle can also be a bad coolant temp sensor.
If you have a bad thermostat and temp goes back down, it should do it for a logical reason...higher rpms and/or heavy heater use will temporarily send the temp down some (high heat, high fan speed is agreat emergency cooldown method...common used used by racers as an extra radiator). But if the temp needle drops back for no apparent reason, it may be the sensor...or, in rare cases, an intermittently sticking thermostat... possible but not likely...they usually stay stuck open or closed.

And yes, A8's are notorious for thermostat failures...mine was on it's 3rd before 100K miles.
 

Last edited by silverd2; 12-04-2010 at 05:30 PM.
  #4  
Old 12-05-2010, 11:21 PM
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Location: Orange County
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I checked the Bentley manual, and bleed the air out of the cooling system, not a huge amount, but made a big difference on temp needle, staying around the half way mark now. Easy fix I hope. I shall monitor for the next week.

I have ordered the TB and thermostat, any idea where I can buy the special tools for this change, at least I will have all the bits to do the TB job, in the future.
 
  #5  
Old 12-06-2010, 11:40 AM
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Join Date: Jun 2010
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First, blauparts.com rents the tools BUT with a catch...you have to buy the entire belt kit from them first and another catch to that: their kits tend to be "overkill", include a lot of parts that many people don't change (myself included): cam seals, crank seal, all rollers, tensioners, water pump, etc ( I DO recommend water pump, while you're in there).

I buy most special tools from Ebay...actually discount tool companies that use Ebay for sales (like Zdmark, El Paso Tools, etc) with very good results at great prices. Take the tool numbers out of Bentley and punch those into Ebay, Google or whatever and you'll find suppliers. Full price for exact factory tool is outrageous and unnecessary.
 

Last edited by silverd2; 12-07-2010 at 06:05 PM.
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