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Dec. 15, 2008 12:20 p.m. PeterAK Dork

Just had the radiator, water pump, belts and hoses done on the '97 328i. Yesterday the low coolant message was on (less than 100 miles since the cooling system overhaul) and I had to add a few cups of coolant to get it up to the full line. Drove 10 miles to work this morning. Got in the car to go grab lunch, same low coolant message comes on. Check it, and it's low again.

Crap. Now I'm worried that the wife let it overheat before the cooling service and killed the head gasket.

Any chance that it is just working air bubbles out of the system? I talked to the mechanic and he said they use a process that sucks all the air out of the system and he is concerned it's a HG.

I'm going on a five hour road trip in a few hours. Think I'm going to take the other car to be on the safe side, it's freakin' cold out and getting stranded and/or doing more damage to the Bimmer would suck.

Thoughts? Mechanic suggested a leak down test to check the HG.

I'm sick of this (and I am lusting over the 2005 Legacy GT wagons I keep coming across with five speeds). Anybody want a Bimmer?
Dec. 15, 2008 12:46 p.m. ansonivan New Reader

It's possible that the system still had a little air in it. Drive the thing some more (obviously not on the road trip) and see how it goes before spending the money on a leak down test.
Dec. 15, 2008 12:58 p.m. bludroptop Dork

Was it losing coolant BEFORE you had the service done?

These are pretty easy to bleed if you know how and have a little patience. I'd first try topping the coolant using the bleeder valve and following the procedure. Absent any other signs of trouble (froth in the oil or excessive smoke), I'd be optimistic that it just needs a burp.

Certainly can't hurt to try that before paying for the leakdown test.
Dec. 15, 2008 1:00 p.m. Ian F Reader

I'd be tempted to agree with the above, except since the mechanic actually knew to use a vacuum fill system (don't have to, but it does make it a hell of a lot faster to fill), I'd say a leak test is in your future.

Fill it again. Make sure the dash heater control is open (the temp knob by the center vents) and drive it locally while watching the temp guage like a hawk.

Personally, I'd only run BMW coolant and distilled water as well.
Dec. 15, 2008 1:19 p.m. John Brown SuperDork

Ian F wrote: ... only run BMW coolant and distilled water as well.

PLUS ELEVENTY FORKING BILLION.

Your car has very little use for the conditioners in city water, the salt in softened water or the metal in country tap water.
Dec. 15, 2008 1:21 p.m. PeterAK Dork

Thanks gang. Wasn't losing colant before, well until the radiator cracked... I had them use BMW coolant and distilled water in it for the service so should be good to go there.

The dash heater control was set to cold when I last got in the car, but it is now set to hot. How would that impact things?

I'm off to trade cars with the wife for my road trip... Going to drive the car in town for the rest of the week and keep an eye on the temp guage.
Dec. 15, 2008 1:26 p.m. Ian F Reader

PeterAK wrote: The dash heater control was set to cold when I last got in the car, but it is now set to hot. How would that impact things?

It controls a coolant valve to the heater. If it's set to cold, any air in the heater system won't get out, but at the same time, will compress enough so that the system won't develope the pressure to operate properly - result: overheating.

I know this from experience... fortunately, I was only driving around the block to test the system, so I was able to get home before it went critical. After bleeding the system again with the valve open (on full hot), the car was fine. I did this work without a vacuum set-up. Not difficult, just slower.
Dec. 19, 2008 5:41 p.m. bam2002 New Reader

If it was overheated I hope its only a head gasket,

I have seen a few used cars that "needed a head gasket" turn out to be a cracked head. you have a 50-50 shot..

Or is it leaking inside the car. If you have the heater on, can you smell the antifreeze?
Dec. 21, 2008 10:59 p.m. fornetti14 New Reader

My M50 E36 had some air trapped for a while too. It stopped after the first few times I drove it. I believe there is a small bleed screw near the top of the radiator cap (sorry it's been 5 years since I had that car).
Dec. 21, 2008 11:06 p.m. RussellH New Reader

Make sure the coolant's not leaking. It usually leaks from the small tube going from the recovery tank to the radiator. Also, bleed it yourself. Open the plastic bleed screw at the top of the radiator, set the heater to full heat and start the car up, run it at a faster idle so the coolant starts bubbling out of the bleed screw. Do this until you see no air bubbles. Close the bleed screw, fill the recovery tank bottle, tighten the cap well and you're done.
Dec. 22, 2008 11:38 a.m. miatame2 New Reader

E36s and similar era 740s are notoriously difficult to bleed fully, and I have personal experience with three E36s that like to make coolant disappear. For whatever reason they are very finicky when it gets cold (more so than on any other car I've seen). The coolant just seems to vanish. So far like clock work every fall I've needed to add distilled to my mom's and wife's car on the first really cold day.

I'd just keep filling it with distilled (or better yet, a mix) to the "cold" line when the message pops up, but keep an eye out for coolant drips on the driveway and crusties in the engine bay. My bet is that it isn't anything serious.