So I just picked up a used 2006 R53 today with 86k miles on the clock. After driving it around for a couple hours, I went to park & heard a gurgling/boiling sound coming from the expansion tank, then smelled hot coolant & saw a trail on the ground. I've read that these tanks tend to fail quite often, as do the caps. As far as I could tell, the coolant seemed to be coming from the cap. However, being a former Subaru owner, the first thing I thought was.....head gasket. Are these cars at all prone to HG failure? What would be the best way to check my coolant system to see what's going on?

 

You MIGHT have a bubble of air in the cooling system....
Headgaskets are OK if the car is not overheated and the coolant is kept fresh...factory flush is 4 years...
Two bleed valves...one by the top of the radiator hose, the other hidden by the thermostat....
Overflowing can happen from a bad cap...new one comes with tank...

 

Caps cost around $20 from the dealer if you want to give that a quick try.

 

Hold on before you buy a new cap. First, the previous owner might have topped off the coolant before they sold it to you, and it's slightly overfilled, causing it to puke out of the cap. Second, with a flashlight, check in the expansion tank. Be careful opening it after driving the car: it's under pressure, and nobody likes the boiling money shot. Do you see any smoke in the head space of the expansion tank? Do you see chocolate milk shakey type substance? No? Good. Third, Check the dipstick for the same chocolatey substance. No? Good. You're fine. Fourth, Be sure that the tank isn't leaking from the seam in the middle: dry it off well with a towel, and run the car and see if there's moisture at the seam. If that all checks out, you can consider buying a cap, but wait, I forgot: is your check engine light on?

 

What Helix said and then if all checks out ok, find out when/if the coolant was flushed; if not or unsure, have it done. Head gasket problems are not too common for the R53s.
Greg

 

Great advice from Helix.

The coolant tanks on these are prone to failure, but I'm not sure if they actually changed anything on the new ones. The tank on my 05 was replaced at about 17K because it was leaking at the seam. Now with 40K it's still fine. I think the thermostat seal also prone to failure and is supposed to be a simple repair.

 

If my tank goes again I'm getting an aftermarket aluminum tank and never have the problem again. 225k miles I only had one tank fail.

 

+1
If you keep them filled to the FULL line...about the seam, they seem to last a long time...
I bet overfilling is what causes them to fail sooner....the old idea that full is good, so a bit "extra" must be better!!

 

To further put your mind at ease, get ahold of a coolant pressure tester with a screw-on adapter (or use a MOTIVE brake bleeder), install it on the expansion tank and pump it up to 20 psi on the gauge. It should hold steady pressure. If not, it's going somewhere: head gasket, bad hose or clamp, bad expansion tank.

 

To make you feel better mine also leaks, sometimes ill see it in the snow, sometimes it barely
Even seeps. I have air in the system and my tank is leaking slightly at the middle seam, gonna swap it all out soon. I wouldn't worry about it too much every bmw I've come across had cooling system issues.

 

Most likely just the coolant level. The same thing will happen no matter the expansion tank, ask me how I know...

 

Thanks for all the replies. I picked up a new cap from the dealer today just to be on the safe side, though after driving it around all day today it didn't erupt once. So, it was probably over-filled....