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So I paid more attention to water temps today. Drove around in ambient temps of ~67-71F..

Driving around town water temps fluctuated from ~88-94C
On the highway ~86-89C
Waiting in a long line for In-N-Out Burger drive-thru ~92-98C
When driving around town and on highway, the coolant temps should not be dropping into the mid to high 80's centigrade (unless you were driving it really hard).

Try unplugging the tstat electrical connector and repeating similar drives. If the temps fluctuate down to the 80s again, then the tstat may be soft failing mechanically. If the temps stay between 92 to 98, then the low temps may be an electrical issue with the tstat or possibly even a bad temp sensor causing the dme to overcool the engine.

Still a good idea to do a smoke test, btw.
 

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03 325xi Wagon 5AT
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Discussion Starter #63
When driving around town and on highway, the coolant temps should not be dropping into the mid to high 80's centigrade (unless you were driving it really hard).

Try unplugging the tstat electrical connector and repeating similar drives. If the temps fluctuate down to the 80s again, then the tstat may be soft failing mechanically. If the temps stay between 92 to 98, then the low temps may be an electrical issue with the tstat or possibly even a bad temp sensor causing the dme to overcool the engine.

Still a good idea to do a smoke test, btw.
Drive around with this unplugged?
909083

909084
 

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That’s the connector.

yours is 3 years newer than my 323iT but your electrical wires look much newer and greater shape.
 

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Drive around with this unplugged?
Yup, that is the one. Make sure to zip tie it away from the fan. That connector powers a heating element the DME uses to open the tstat earlier than it would otherwise. These t-stats are rated for 97C temperature, and will start to open a little before 97C. When the DME activates the heating element, this makes the t-stat hotter than it otherwise would be and causes it to open at lower temps than it would on a purely mechanical basis alone.

So by unplugging the connector, you remove the DME's ability to 'control' the t-stat opening and are thus able to observe just the mechanical function of the t-stat spring & wax element. On its own, a good tstat should keep temps at 97/8C at idle, while cruising on the highway temps might get down around 92/3C or so. When the tstat mechanically soft fails it often is stays open at lower temps than it should and runs the engine cold. The engine should also reach 92 to 96C within a few minutes of driving, if it takes forever to warm up (while driving) then there is an issue.

As an fyi, here is what happens when temp sensors go bad, or are left unplugged, and cause the DME to intentionally overcool the engine:


and from post #622 by maxbobo onward:
 

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Discussion Starter #66
That’s the connector.

yours is 3 years newer than my 323iT but your electrical wires look much newer and greater shape.
Yeah, things look pretty well cared for under the hood. Makes me want to care for it all the more!

Yup, that is the one. Make sure to zip tie it away from the fan. That connector powers a heating element the DME uses to open the tstat earlier than it would otherwise. These t-stats are rated for 97C temperature, and will start to open a little before 97C. When the DME activates the heating element, this makes the t-stat hotter than it otherwise would be and causes it to open at lower temps than it would on a purely mechanical basis alone.

So by unplugging the connector, you remove the DME's ability to 'control' the t-stat opening and are thus able to observe just the mechanical function of the t-stat spring & wax element. On its own, a good tstat should keep temps at 97/8C at idle, while cruising on the highway temps might get down around 92/3C or so. When the tstat mechanically soft fails it often is stays open at lower temps than it should and runs the engine cold. The engine should also reach 92 to 96C within a few minutes of driving, if it takes forever to warm up (while driving) then there is an issue.

As an fyi, here is what happens when temp sensors go bad, or are left unplugged, and cause the DME to intentionally overcool the engine:


and from post #622 by maxbobo onward:
Thanks, great info! I'll try this out tomorrow.

Was in there today changing out spark plugs and noticed a tiny amount of coolant drip again on the driver's side. Looked like it was coming out of some hose below the expansion tank. I'll use this pic I found in another thread to show where I believe it's leaking from..

909086


I wonder if this is where it decided to give out after I overfilled the tank all those times. Shop said they didn't find any leaks from cooling system pressure test though...
 

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Yeah, things look pretty well cared for under the hood. Makes me want to care for it all the more!



Thanks, great info! I'll try this out tomorrow.

Was in there today changing out spark plugs and noticed a tiny amount of coolant drip again on the driver's side. Looked like it was coming out of some hose below the expansion tank. I'll use this pic I found in another thread to show where I believe it's leaking from..

View attachment 909086

I wonder if this is where it decided to give out after I overfilled the tank all those times. Shop said they didn't find any leaks from cooling system pressure test though...

My shop said they didn’t find a leak in mine either, so it’s probably a small or intermittent leak that isn’t all the obvious. If you can’t find it cold with a pressure test, try looking when it’s hot.
If the cap couldn’t vent enough pressure/fluid quickly enough it could have taken the next easiest path, which could be something like the o-ring on the hose connector you pointed out. Try wiggling it to see if it drips? Maybe it’s just a worn oring, those small hoses are usually pretty inexpensive


On the topic of OE/OEM/Genuine parts, here is the link to the article on FCP, it’s well worth the read.
I can’t begin to stress the importance of using genuine parts in cases like sensors, electrical/electronic parts, gaskets, and how using cheap parts is NOT worth it!
For genuine parts, check Tischer (www.getbmwparts.com)


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Stick doesn't work correctly anymore, I have to go by coolant level from top of filler neck now (5.5 inches).

I just bought the car, drove it around for a couple weeks, never checked coolant levels.. then went on this road trip which is when I overheated. No idea if it was over filled previously.

Cap felt not very tight when I opened it for the first time after overheat. Might have just been that.
so you do'nt know if it worked or not?
 

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Discussion Starter #72 (Edited)
Do this to know if head gasket bad or not: cold morning check and fill the level to the top limiter. close cap drive 20 miles. Check next cold morning if level dropped. If yes, remove spark plugs and look carefully for any sign of wetness on the tips.
Checked coolant level cold yesterday (approx middle to upper limit), then drove ~20 miles in ~65-73F weather.

Just checked coolant levels cold again today. Can't say I notice a definitive drop in coolant level despite even a tiny coolant leak somewhere.. MAYBE a very small perceivable drop in level.

Also changed spark plugs yesterday before the drive. This is what the old ones look like for what it's worth (don't know if it shows anything related to the overheat)

909139
 

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Hi everyone! I'm new to this forum and just acquired my first E46 (03 325xi wagon automatic) which I'm pretty stoked on..

Bought it a few weeks ago with ~192k miles on the odo. Car is quite clean, engine bay really clean with no leaks, hoses and plastics look new. Was apparently mechanic owned for a bit and alot of the cooling system has been replaced. I see records for new expansion tank, cap, fan clutch, and coolant level sensor at ~160k in March 2016. Radiator, thermostat, and auxiliary fan switch replaced at 170k in December 2016. I haven't been able to confirm whether water pump has been replaced recently.

Anyway, a week ago I took the car on a 3 hour road trip to Yosemite area from Bay Area where I live. I had to drive through some 100F degree weather and the car was fine through most of it until the last bit of the trip going through some twisty uphill.. I noticed the the water temp red light on! I can't recall how deep in the red the needle was or how long the red light was on for before I shut the engine off and pulled over immediately (probably within ~5sec, 10 sec MAX). I imagine the light couldn't have been on that long since I frequently look at my dash. I don't recall if the low coolant light came on. I opened the hood to find that it appeared to have puked out all it's coolant from the expansion tank cap.

So I wait maybe 10-15min for it to cool down and opened the cap which seemed to be not that tight.. added some distilled water; probably almost 1 gallon? Started the engine up with the cap open and it felt normal but the temp started to rise shortly after and it overflowed out the tank a lot so I turned it off. I remembered I have to bleed it so I looked up some youtube videos and added the rest of the distilled water and a bunch of coolant with the bleed screw open, left the heater on to get coolant through the heater core for a few minutes. It started right up again, felt normal.. let air bubbles bleed out the screw for a bit, tightened up the screw, capped off the reservoir, let it run a few more minutes.. temp gauge held steady the whole time. Drove another 10 miles to our campsite with the heater blasting and everything seemed alright. Made it back home the next day next day through the same 100F degree weather, 3 hour trip, no problems. Temp gauge held steady, engine sounded and felt normal. No visible steam coming out the pipes, no visible leaks in the engine bay..

It's been about a week since then and I've checked my coolant levels cold a few times and it's been well below minimum according to the coolant level indicator stick each time. Only had to add a couple splashes to get it between min/max though. I don't know how accurate that thing is.. and I still see no leaks. I'm bringing it into the shop to get it checked out in a couple days. I'm thinking cooling system pressure test, compression test, and leak down test. Are there any other things I should be aware of? Water pump damage from being run dry, etc?

This post ended up a bit more long winded than anticipated but I want to give some good background info. Hopefully it was just a case of someone not quite tightening the reservoir cap enough and a reminder to check the basics first. Your help is greatly appreciated, thank you!

Also, I've attached some pics of my cold coolant levels from this past week and how much I fill it to get it between min/max on the indicator. I've been driving the car regularly between checking. View attachment 908758 View attachment 908759 View attachment 908760 View attachment 908761
I struggled with this issue for a few months too.1. I found my newly installed water pump after 28000km had failed the seals were leaking so i put in another water pump but this didnt fix it ........found another issue. The radiator was cracked.Its common to crack near the filler cap .Its weak and thin plastic so every time you losen and tighten the filler cap it weakens that plastic and eventually it cracks. I spotted a thin hairline crack after getting a tip from YOUTUBE guy. The other item is the expansion tank which bursts at the seam. Happened to me too. Your water dropping issue sounds like my hairline crack in the radiator. Overheats and loses water.I replaced the radiator and water level does not drop anymore and no overheating. If you have overheating at idle or stop start traffic then its your EFAN thats stopped working. I installed a manual switch to activate my fan in traffic and no overheating since. I have a thermostat issue too because my car doesnt get to operating temp quickly as it should. Good luck! Be careful of crappy parts tooo from China...buy cheap Buy TWICE!
 

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I struggled with this issue for a few months too.1. I found my newly installed water pump after 28000km had failed the seals were leaking so i put in another water pump but this didnt fix it ........found another issue. The radiator was cracked.Its common to crack near the filler cap .Its weak and thin plastic so every time you losen and tighten the filler cap it weakens that plastic and eventually it cracks. I spotted a thin hairline crack after getting a tip from YOUTUBE guy. The other item is the expansion tank which bursts at the seam. Happened to me too. Your water dropping issue sounds like my hairline crack in the radiator. Overheats and loses water.I replaced the radiator and water level does not drop anymore and no overheating. If you have overheating at idle or stop start traffic then its your EFAN thats stopped working. I installed a manual switch to activate my fan in traffic and no overheating since. I have a thermostat issue too because my car doesnt get to operating temp quickly as it should. Good luck! Be careful of crappy parts tooo from China...buy cheap Buy TWICE!
I too have countless stories of trying to save some money and buying cheaper parts, even store brand parts, wheels bearings bad from the start, another wheel bearing lasting about 15k miles. Replacing one part to find out that other parts were bad or almost ready to fail and doing another fix to that related part.
I’ve become a very strong advocate for using genuine or OE parts only, and in many cases, like the e46 cooling system, to do a complete overhaul of the whole system. It may cost more upfront but you are already in there and doing a few extra parts is only a small bit more time as compared to doing one part then shortly after tearing it all back apart to replace the part you already had off or had access to.
Fcp has a lot of good overhaul kits with genuine and Oe parts that work great in this case. As with out e46, I found not one leak but three potential failed parts where I am super glad I went with an overhaul kit


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