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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 09-28-2008, 02:55 AM   #1
userml1653
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Overheating issues

To start off this is the second time I've replaced my expansion tank in 8 months. It has cracked twice. After I replaced the second time which was about 10 days ago yesterday was the second time it overheated. As soon as I saw the temperature rise a little I turned on the heater. I left it on for about a minute and temperature was back to normal. I was stuck in traffic, so I drove it for another 20 min and it was fine. It seams that I have to tip off the coolant every week. The first mechanic I took it to said I might have to replace my thermostat. The second one said its probably the radiator clogged. I want to try to keep the cost as low as possible. Therefore I don't want to spend money on any unnecessary costs. Any input would be appreciated. Thank you
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Old 09-29-2008, 02:14 PM   #2
userml1653
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anyone?
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Old 09-29-2008, 02:20 PM   #3
mjw
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how many miles has your car done? As your car is 7 years old, probably not unreasonable to assume that it's the tstat - they stick which leads to overheating. Not expensive part - in the UK around 50 from dealer + half an hour's labour for fitting. Unlikely to be a clogged rad - unless rad / system quick fix sealer has been used (e.g. rad weld) to cure a leak previously (this can block the pipes etc)
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Old 09-29-2008, 03:26 PM   #4
justvisiting
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My question is why is your expansion tank popping? I know they pop with overflow of coolant leads to increased pressure enough to pop it. But if you are constantly adding coolant that suggests you have a leak.. either at the waterpump, or being burnt off in the engine ( you'd be able to smell this out the exhaust).

My thought is actually the coolant may not have been flushed properly when you replaced the expansion tanks, with air still in the system, it bubbles up and expands as its heated, then when you open up the system, there seems to be a decrease in coolant in the tank. Then it repeats again as there is probably still more air.
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Old 09-29-2008, 10:15 PM   #5
userml1653
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That's what I thought. I figured there is air in the system and that's why it's causing the expansion tank to burst as well. Anyhow what should my next step be?
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Old 09-30-2008, 10:54 AM   #6
justvisiting
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well if the coolant is new, and it was flushed previously: i believe there are 2 different protocols
1 is to open up the blue bleed screw, without the coolant cap on and allow the engine to run for 10 minutes allowing any air to escape from the system.
The second is to turn the fan and heat on high, and open the bleed screw allowing air. I did both at the same time.

If it were me, I would just replace all the coolant again to be thorough. www.bmw325i.net has a good DIY.
just remember to retighten the bleed screw before you go back out for a drive.
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Old 09-30-2008, 01:55 PM   #7
userml1653
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When I filled the coolant that was the procedure i followed. I left the bleed screw with the heater on max while i filled the coolant. If I leave the engine running with the cap off and screw open, won't it splash all over the place?
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Old 09-30-2008, 03:35 PM   #8
justvisiting
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it does when you rev it, but with the engine just circulating, the air should just be bubbling out, Maybe a little splash. Hopefully someone else can give some input as I havn't done in a couple of years since I replaced my waterpump. It's very important to make sure that its completely and thoroughly bled though. which is why I like to have the engine going to make sure all the coolant can be circulated.
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Old 09-30-2008, 06:56 PM   #9
userml1653
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I'll try that out. Hopefully it'll fix it. Thanks for you help
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Old 10-06-2008, 10:12 PM   #10
userml1653
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I wasn't able to fix it. I ended up taking it to a shop. The radiator is leaking and the fan isn't turning on. So I have to replace both. It's costing me $625. Hopefully I won't have anymore problems. But thanks for everyone's help.
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