2003 325i Overheating Confusion

[325ibadwords]

Ive seen some posts similar to my question, but of course our vehicle has to add an extra layer of flare so hoping to find some advice and direction on possible causes and repair.... and even possibly recommendations on the best place to buy these parts without having to sell a kid....
I won’t go into detail on how we got suckered into buying a 2003 BMW 325i for our daughter with “absolutely nothing wrong with it” - that also overheated 5-10min after we bought it and driving it home. Granted, I will say we test drove it and left it running for a good 30 minutes before jumping into the sucker hole & it was fine.
Ill start with, the car overheated while driving. After an extremely long drive home and draining out the local water companies, we got it home. Looked it over & found the coolant reservoir busted and radiator fan not working. I researched and found that the BMW made horrible decisions on creating a plastic @#*!? cooling system - which we immediately did the cooling system overhaul. That worked great.... for 3 months.
My daughter said she heard a sizzle/pressure release type sound the other night after leaving work, but the dork didnt think it was anything to worry about since the sound stopped - then the car overheated the next day. We had her pull over & we towed the car home. We found that the coolant reservoir tank that we just replaced, had the side blown out... (not sure if it matters, but this may be a good time to say that I bought the cooling overhaul kit off of eBay for $160 and radiator fan for $60) There didnt appear to be any leaks other than the Grand Canyon in the side of the reservoir tank so I got a different one that at least looks to be better quality (Behr?) But now the car is overheating when she’s stopped at a red light or slow moving in traffic& She said she doesnt see any signs of leaking on the driveway. I told her to check the coolant tank when the engine is cold & she said the tank was almost empty which we were afraid meant something along the lines of a cracked head, but she said she filled it up with water and it did fine until she got into traffic. Pulled over to let it cool, a good Samaritan stopped to help her & when he got the cap off to put coolant in - they saw it was almost full with coolant 🤔🧐
She’s an 18year old just learning the lemon ropes, but this is a new one for me. I’m finally getting to look at it tomorrow and going to see if the radiator fan is working or if it was just a POS part that’s quit working too.
My question is,
1. Does it sound right for the coolant reservoir to be almost empty but then coolant magically appear once it’s heated up and moving?
2. Other than the obvious of listening to see if the radiator kicks on, is there anything else that can cause overheating when slow or stopped?
3. My husband did bleed the coolant after he replaced the reservoir, but if it didnt completely get all of the air out, at this point- can I still try to bleed it out or is it better to just flush all of the coolant out and do it all over agin?
4. If a radiator fan quits working, will it cause the coolant reservoir blow out the side? Can something else cause that? Or is that just the high performance engine vs a crappy plastic part?
I come to this forum because it has really cut out a lot of trial and error with other issues we have come across and it has actually saved us a lot of time and money. I truly am grateful for any help/ideas that anyone has to offer. I would even be grateful for just sharing a favorite place you order your parts from.
Again, thank you for your time and I appreciate your knowledge!

[RGBaker]

1. Coolant moves to and from the reservoir tank, so not impossible it looks low and later full -- but the process for filling and burping the system can't be ignored. You must make sure your system is full. And you must use BMW-approved coolant (or you'll regret it later).
2. The fan 'kicks in' so clearly look for that but the thermostat opens and closes (at least is should) out of sight. If it's sticking, slow or partial you'll have issues.
3. You can bleed and fill without doing it from full empty -- but you absolutely must do it right. Air pockets will cause issues, as will low levels.
4. 'Quits working' as in blocked? Or do you mean 'fan quits'? Anyway, overheating creates too much pressure, which in turn puts too much strain on coolant tanks, hoses and radiator seams. A fifteen year old car -- all of those things can fail. And once you're overheated, the pressure can cause other things to fail -- often not the cause, but the result of overheating.

Sounds like you need to replace the reservoir (again). If your fan works, and you've checked it in operation to confirm fuses & sensors are OK the fan may be fine. The water pump is a weak point, and a collapsed impeller causes all sorts of issues but is hard to spot without removing the pump. While you're this deep, replace the thermostat and the radiator hoses just because. Have the radiator pressure tested -- if it fails, replace that. Fill with approved coolant and bleed properly.

The bad news is the cooling system is the weak point in this model. And once you've got problems, it's hard to find a single point of failure -- it may well be multiple ones. The good news is the list of parts (and the quality replacements) is available, often sold in packages that frame the problem you're chasing.

Note: if any of the overheat episodes have been severe enough to damage block/heads/gaskets all bets are off. But the absence of steam in the exhaust, coolant in the oil & oil in the coolant are all good signs!

[MarcoZandrini]

Installing aftermarket cooling system parts is strictly verboten!! Go to www.realoem.com and enter the last 7 characters of the car’s vehicle identification number. Hit enter and bookmark the page. Scroll down to the engine and get the part numbers for the water pump, thermostat, upper and lower radiator hoses. Then go to radiator and get the part numbers for the expansion tank, cap and mounting bracket. Lastly, as I bet the car has an automatic transmission, staying in the radiator section, scroll down to automatic transmission cooling, get the part number for the automatic transmission fluid cooler. The cooler (heat exchanger) will break when you remove it.
Next, go to FCPEuro and buy the parts. Now, FCPEuro will list 4 separate parts for each part number:
- BMW branded (most expensive)
- part made by the manufacturer that made the part for BMW (OE) (less expensive)
- part made by a supplier to BMW, but didn’t make this part for BMW (OEM) (even cheaper)
- aftermarket (don’t bother)

Buy OE or OEM parts. All parts sold by FCPEuro have a lifetime warranty!

Your situation is the perfect example as why a pre-purchase inspection performed by a reputable indie shop that specializes in bimmers is critical.

[jclausen]

Agree with the pre purchase the best money one can spend and the stock coolant system works just fine when it is mantained correctly

[E39 Newbie]

1. Does it sound right for the coolant reservoir to be almost empty but then coolant magically appear once it’s heated up and moving?
2. Other than the obvious of listening to see if the radiator kicks on, is there anything else that can cause overheating when slow or stopped?
3. My husband did bleed the coolant after he replaced the reservoir, but if it didnt completely get all of the air out, at this point- can I still try to bleed it out or is it better to just flush all of the coolant out and do it all over agin?
4. If a radiator fan quits working, will it cause the coolant reservoir blow out the side? Can something else cause that? Or is that just the high performance engine vs a crappy plastic part?
I come to this forum because it has really cut out a lot of trial and error with other issues we have come across and it has actually saved us a lot of time and money. I truly am grateful for any help/ideas that anyone has to offer. I would even be grateful for just sharing a favorite place you order your parts from.
Again, thank you for your time and I appreciate your knowledge!

1. Yes. The reservoir, unlike older cars, is a pressurized, integral, part of the cooling system. When the water heats up it expands, and the reservoir looks full. But that's the least of your worries.

2. Yes, just offhand, a partially clogged radiator, a partially stuck thermostat, an inefficient/failing water pump. Or worse.

3. I'd probably flush it again, but not until I did other diagnosis first.

4. The reservoir can blow out because of age, or a crappy part, or worse. It's pressurized. Too much can cause it to fail.

Which brings me to my point. Why would there be too much pressure (potentially)? A failing head gasket will cause all of these problems. Before throwing more money at this, do a compression test and make sure your head gasket is intact. If it is, I would proceed to rehab the cooling system. I would just assume that everything the seller told you was BS. Replace the radiator, or have it professionally flushed and pressure tested. The water pump and thermostat housing are pretty easy to change once the radiator is out, so you may as well do those, too. But first, check the head gasket.