Coolant expansion tank for e70 4.8
 

Hey guys,

So I just picked up a new expansion tank. I have done some research on replacing the tank and that seems easy enough. Lately I have driven it a couple of times and had to use the crappy prestone green coolant to not leak too much coolant. I do have two one gallon containers of the bmw blue coolant but will that be enough if I have to drain the coolant and flush it out? Also is their a radiator drain plug or do I just need to pull the lowest hose and drain that way? I haven't found much in the way of being able to flush the coolant on this engine, seen one for the n55 but that doesn't help me as it's setup quite differently.

Any help is appreciated!

Blake

As for draining, there's a radiator drain plug, and a drain plug on the block. Be forewarned: the drain plug on the block is not easy to get to, and poses quite a challenge to remove and replace the drain plug. You may choose not to drain the block.

IIRC the 4.8 takes about 10L of coolant total, so 2x4L jugs of the BMW coolant, when mixed 50/50 with distilled water, is more than enough.

Gotcha, do you know which side the drain plug is on for the radiator and what it looks like? Also when flushing, should I fill the system with distilled water and run it for a tad, drain again and then replace with 50/50 mixture? Gonna go buy a crap ton of distilled here in a bit.

Radiator drain plug is very obvious - it is blue plastic. If memory serves, it is on the left (driver's) side of the radiator.

There's several equally-good ways of draining and refilling the coolant to approximate a "flush". If you are draining only the rad and filling with distilled water, you might not know for sure what ratio of coolant to water you're left with. I've always just filled with 50/50, even if I intended to drain and fill again soon. Actually, the failed radiator hose last summer took care of a complete and proper drain for me :rolleyes:

Also, the radiator drain plug is plastic and very fragile. Be careful not to overtighten it. Better yet, replace it.

Rather than draining the whole system with the plugs, you might consider getting one of the vacuum drain kits. There are inexpensive Chicom kits that do a great job. They will suck the system dry, (using shop air as power), and when the whole system is at a vacuum, it will introduce the new fluid, which avoids air pockets. Granted, for BMWs this is not essential to fill without air pockets as with some VW/Audi vehicles which MUST have this or an Air Lift vacuum fill, but it's damn convenient. These kits also include a pressure tester.

Owning a few older BMWs, coolant changes are not too uncommon for me, so having a vacuum fill kit really saves a lot of hassle. The radiator drain plugs are VERY fragile, and if you work on BMWs long enough, you're bound to break one once in a while. Not to mention it seals with an o-ring, so you really should replace that o-ring, (or the plug that comes with a new o-ring,) if it's removed. While Snap-on and others make these kits, those are megabucks. The better kits DO use metal coolant system adapters, but for occasional use, the plastic ones work fine. Cheap enough to make this a MUST for your BMW. This is the kit I use:

https://www.amazon.com/Goplus-Radiat...ressure+tester

If you look on Amazon, there are a few vendors selling basically the same Chicom kit at a wide variety of prices with several different names. It really does look like they all come out of the same factory, so I'd go for the $79 version.

So with this vacuum kit, you just suck out all the coolant and pour new coolant in?

Just like one of the oil extractors?

Yes, you suck out all the coolant, but you don't "pour" the new coolant in. There's a valve on the device that gets switched, then instead of sucking the coolant out and sending down a hose, (to a jug to get recycled), there's a different hose that you place directly in a jug of new coolant, (mixed 50/50 with distilled water.) As you switch the valve, the vacuum created in your cooling system sucks the coolant from the jug into the system. (The vacuum created by the pressure from your shop-air is no longer a factor once you switch the valve.) Anyway, this may sound complicated, but it works well and is easy to do.

By the way, the kit includes adapters from most cars, including our BMWs. The only one I ever had problems with is the one for Porsche; I could never get that one to seal right on my Cayenne S, (exchanged for my X5), so I had to buy an AST metal adapter for that car. It had very fine threads compared to the BMWs. I think the adapter cost as much as the whole kit. Never had a problem with the BMWs though.