In this tech
article I will go over the steps involved with flushing out the cooling
system on the BMW E36 3 Series models from 1992-99. Keep in mind that this
article is specific to the E36, however the procedures and principles here
apply to nearly every water-cooled car on the road. (So if you own an
air-cooled car, you are in the wrong place.)
why should you flush the cooling system? Basically, to ensure that all the
small passages and ports inside your vehicleís engine are clear of things
like rust or corrosion. In some case, I have seen dirt and tar in there as
well. When you flush out the system, it removes all this corrosion, and
keeps coolant flowing freely through the engine. If the corrosion gets too
bad, it can cause all sorts of problems from overheating, to blown head
gaskets and even cracked engine blocks.
torn down a lot of engines before and seen some really interesting things.
In most cases, the corrosion was minimal and would easily be removed during
a good flush. On the most extreme was my friendís Triumph TR-7 (quite
possibly the worst car ever made) The corrosion had grown so bad, that
nearly all the cooling passages to the head were completely clogged, causing
the head to overheat and warp. (As to why the engineers put an aluminum head
on a cast iron block is still beyond meÖ)
While you most likely wonít have a failure as extreme as my
friendís TR-7, this is a good example of a worst-case scenario.
what causes the corrosion in there? The most common is failure to put any
coolant/anti-freeze in there. You probably know this story, driving to Vegas
or some other ridiculously hot area. The car starts to overheat, so you pull
into a gas station and add water without adding the correct amount of
coolant too. And what happens to metal when you leave it immersed in water
for too long? The nemesis of all Gearheads worldwide, RUST! When you add
coolant to water, it acts as a protectant for the metal. And this rust
doesnít just stay still in the engine, it circulates all over, getting
caught in cooling passages clogging, up the radiator, until eventually you
have a nice iron oxide fortified smoothie running through your engine. Other
culprits include leaks or rips in cooling hoses, faulty water pumps or even
leaking head gaskets. One other thing to keep in mind is that whenever
possible, use distilled water to fill up your radiator. Distilled water is
water that has been boiled and re-condensed to remove any minerals or
calcitants. (BAD STUFF Ė CAUSES RUST)
with these words out of the way, letís begin.
With the engine cool, begin by crawling under your car and remove the
plastic panel that covers the radiator. There are two 10mm screws on the
side that hold the panel on and 2 8mm screws at the front. Once you remove
the 8mm screws, you will be able to pull the brake ducts off. Unhook the
electrical connection on the driverís side brake duct and remove the
a hold of some empty coffee cans, buckets or any other large container. We
will need these to catch the overflow from the radiator. Now locate the
drain plug on the bottom of the radiator. You should be able to remove this
with a flathead screwdriver. Keep in mind to wear goggles when you are under
there. You donít want this stuff spilling into your eyes while you are
under the car.
let the radiator drain completely. It may help to remove the coolant
overflow cap. This will help release the vacuum inside the system and allow
more coolant to flow out. Once the radiator is completely drained, we can
move on the draining the engine block. Look under the exhaust manifold on
the passenger side, you will see a 19mm screw. Move the drain tray under the
screw and remove it. Now the block will drain out completely.
Keep a hand on the drain tray to move it as the coolant drains out.
For the next step, itís a good idea to have a particularly large
drain tray. Something along the lines of a childrenís wading pool might
suffice. (I highly recommend that everyone out there try to be at least
somewhat ecologically conscious) Stick
a garden hose in the coolant overflow tank and turn it on. Now watch the
water draining out the bottom of the engine. You will want to let the hose
run until the water running out is clear. Basically, when the water is
clear, you have flushed out the system. Dispose all the old coolant in a
safe way. Obviously, donít let your kids swim in it or let animals drink
back under the car and re-install the 19mm plug on the engine block and
close the radiator drain plug. Itís a good idea to use a new rubber
sealing ring every time you do this. It will help prevent against any
we need to re-fill the system. The first step is to locate the coolant
bleeder screw on top of the thermostat housing. This small screw is used to
let any air in the cooling system bleed out.
Use a 8mm open-end wrench to get it open.
you will want to determine the correct water to coolant mixture for your
car. This varies from climate to climate, so be sure to check your ownerís
manual. I usually pour a gallon of coolant in the coolant reservoir then
pour in a gallon of water. Once you have this small amount of coolant in the
motor, start the car; turn the heater vents to full on, and let it warm up
to operating temperature. This will let the thermostat open and allow the
coolant to circulate throughout the engine. Once warmed up, top up the
coolant reservoir tank as needed.
look at the bleeder screw. Because
of physics, air will naturally go to the highest point possible. In this
case, the bleeder screw. With the screw open, you will see bubbles pouring
out the side. Keep watching the screw until you see a steady stream of
coolant coming out. Once you see this, all the air has been bled out and you
can close the bleeder screw.
Lastly, re-install the
brake ducts and lower plastic cover, and thatís it, youíre done!
Well, there you have it - it's
really not too difficult at all. If you would like
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