BMW is known for good handling and that German performance every enthusiast drools over. From the 2002 to the iconic 3 Series and beyond, BMW is one of those cars that gets attention and praise from everyone.
Whether it’s the raced-out kid revving his car like a jackass at every light, or the established dad who likes to drive it like he stole it every now and then, BMW checks all the boxes.
Lately, however, BMW has gone a little south when it comes to reliability.
Like anything good, there are usually a few quirks or two, especially when corporate gets involved to raise the bottom line.
From way too many models, to plastic parts, leaks, and bad turbos – it’s a BEEMA thing!
In this article, let’s talk about some of the common cooling system issues BMWs face and where the company needs to get back to their roots (in my opinion).
From coolant leaks to oil consumption. Where is BMW heading? Here are some of the things your BMW wishes its parents did better.
what’s with all the damn plastic!
“I was driving along and smoke started billowing out from under the hood!”
I’ve heard this more than once from customers with that glazed-over look of distress on their face. The common issue found is a split coolant hose or fitting that has had enough of the German beatings of hot and cold expansion and contraction.
Although BMW isn’t the only bad guy here in a car world of plastic parts, their plastic seems to be just one step above recycled milk jugs. From expansion tank failure to split upper flanges at the engine block, the problem is real.
Common areas where BMW’s leak coolant
The truth is back in the day of BMW the cooling systems had way fewer problems and leaks. They used aluminum for many components that are now milk jugs. Although it would corrode a bit after a while, it didn’t leak nearly as much as today’s plastic spaceships.
Here’s a few places your BMW may water your driveway from.
Expansion tank: These plastic tanks are under extreme stress from the constant heat cycles of regular operation. The E46 3 Series was great for splitting the side of these tanks like a tight pair of pants at the prom.
Upper bypass hose: This beauty is found on the newer E90 3 Series and beyond. It connects to the expansion tank and runs over to the upper hose nipple. Each end has rubber and/or a quick connect.
The issue lies in between where the straw BMW got for cheap from a McDonald’s tag sale is located. These things split without warning, especially if they are disturbed while you are doing another repair. This is such an issue I recommend replacing this as part of maintenance every 15-20K or so.
I’ve been bit before
I did some work on a 3 Series for a used car dealer I’m friends with and someone I do a lot of work for. I installed some odds and ends and a new radiator because it was leaking at the seams.
The mistake I made?
I didn’t replace this hose. In an attempt to save my buddy some casino money, I skipped the hose because it wasn’t leaking and looked OK.
I wrapped it up and put my coolant system pressure tester on it overnight, no leaks. Road tested it and wrote the bill up like a boss. These were the days before I owned the big shop, I was moonlighting, my wife followed me to drop it off, and we were done.
A few hours later I get a picture of a BMW throwing up all over my buddy’s parking lot. The hose I avoided because it wasn’t leaking blew.
Lesson learned and I felt like quite the dumbass for a while, that’s what happens with these things.
What else leaks on these?
Water pumps: The newer BMWs 2006 and up or so use electric water pumps. These are cool in the sense they can control and regulate coolant flow much better. They tend to last around 70-80k miles, but I’ve seen a few badass ones go longer.
These do leak, usually at the rear seam, but where these really shine is when they stop functioning and set “speed deviation codes.” This is basically when the ECU is screaming at the water pump to get spinning like a stressed dad on a family vacation. The engine is running hot, and the computer knows it, but the electric pump isn’t working.
In their infinite wisdom, BMW also decided the coolant temp gauge wasn’t cool anymore. Nope, it’s much better to leave the driver completely in the dark until the engine is hotter than the surface of the sun.
Radiators: In all fairness, this is a problem across the board for most cars. The plastic radiator tanks tend to leak where the aluminum section connects. The two sections are pressed together, and it can leak, especially when the weather gets cold.
One of the worst
Ready for a good one? The E65 – E66 745i has a coolant pipe that runs from the back of the mechanical water pump to the rear of the engine through the valley under the intake manifold. These leak, and the fix is a massive job requiring removal of things that should be left to the factory that built it.
This is so bad there is actually a kit which allows you to replace this pipe using an expandable pipe. You still need to remove the intake, but at least all of the front covers and such stay on.
When this leaks, you will see coolant running down the transmission bell housing area, along with a healthy bill to sort it out.
E46 3 series heater hose pipes: These pipes run from behind the oil filter housing area to the rear heater hose connections. There are two; think E46 3 series with the M54 engine.
You will see coolant crusting back from the crank pulley as it runs down the forward portion of the block on the driver’s side. Replacing these requires removal of the intake.
Rear crossover plate, M62B44 engine: This V-8 was actually a decent engine. Over time, it tends to leak a lot, but it does seem to hold together. Some of these were even used in Range Rovers for a while.
These are great for a phone call from your mechanic. “There’s coolant leaking out at the transmission bell housing area.”
These leak in two spots: one is under the intake manifold. There is a valley plate that looks like a big rectangle bolted down under there. Worst is the plate at the rear of the engine; it conveniently requires the transmission to be removed to get to it.
Here’s where you will get bit if you’re not careful: you replace the plate and a leak still shows up from the rear plate you can’t see. I’ve had to pull the trigger on each scenario, and it’s not easy. The last thing anyone in my business wants to do is sell a repair that is expensive, just to call the customer and say, “So there is another leak.”
What about the newer BMW’s ?
Of course, the plastic is still being used, so what’s up with the newer engines? Has the bleeding stopped?
NOPE, a few common leaks we see now are from the coolant lines to the turbo on the N20 4-cylinder engines. There are lines that feed the turbo coolant for cooling; the issue is this is right next to the exhaust, which puts a lot of temperature stress on these hoses and O-rings.
Mainly, the O-rings fail, and you can get away with just replacing those; however, I have seen more recently the entire rubber hose failing. I suggest doing it all using factory BMW parts only if you want to be done with it (at least until next time).
Another fun gremlin is on the newer 6 cylinders; these are in the 7-series and beyond but will surely let the coolant out at one point or another.
The upper radiator hose runs into the abyss, guess where: under the intake manifold.
There is a plastic flange that the hose connects to. This flange is bolted right up to the engine block. These leak, as well as the cooling housing underneath it.
Is it all bad?
I have to be honest here, I used to be a hardcore BMW fan. Lately, however, I feel like BMW needs to get back on track with reliability and part quality, especially with cooling system components. The plastic they use is susceptible to degradation from constant heat cycles and overdue coolant flushes.
It’s not really a question of “if”—it’s “when” you will have a cooling system issue. With that said, I’m definitely not bashing BMW here; they still make one hell of a car. Most car manufacturers today are just as guilty of using cheap plastic parts.
BMW would definitely do better in the reliability department if they went back to metal components like they used in the past. Until then, keep an eye on your coolant level and get those hoses checked regularly.
