One often neglected task on many cars is the maintenance of the cooling system. In general, it’s recommended that you flush and clean out your cooling system once every 36 months, or approximately every three years. I like to perform this task on my own cars about once a year, or if I let it slip, once every two years. The reason for this is that old, exhausted coolant can actually cause irreversible damage to your engine components: We here at Pelican found this out firsthand when the head gasket on our '93 BMW 325is was replaced. The previous owner didn't look like he had changed the fluid once in the past ten years. As a result, there were many parts of the engine that were corroded and showing severe signs of wear.
A properly maintained cooling system must have a few things in order: adequate supply of coolant, a radiator that acts as a heat exchanger with the outside air, a fan or air flow source, a water pump to keep the coolant circulating, and a thermostat to regulate the engine at its optimum operating temperature. The coolant must also have the correct mixture and chemical compounds to promote heat transfer, protect against freezing, and also inhibit corrosion. To keep your MINI operating correctly, it's important to check the level, strength, and overall condition of the coolant on a regular basis. You also need to change the coolant before it degrades to the point where it doesn't perform its job adequately.
A fact that I keep hearing kicked around revolves around the reported findings of the U.S. Department of Transportation, which states that cooling system failures are the leading cause of mechanical breakdowns on the highway. Not exactly surprising, since proper cooling maintenance is one of the most neglected areas of most cars.
Electrolysis - One failure mode associated with dirty coolant is known as electrolysis. Electrolysis occurs when stray electrical current routes itself through the engine coolant. The electricity is attempting to find the shortest path, and impurities in the coolant often generate a path of least resistance that the electricity travels across. The source of this stray electricity is often from electrical engine accessories that have not been properly grounded. A missing engine or transmission ground strap can also cause the coolant to become electrified. Sometimes the path of least resistance becomes a radiator, a heater hose, or even the heater core. These components are often well grounded, and offer a ground path from the engine to the chassis by means of the semi-conductive path of the coolant.
Electrolysis can destroy your engine quickly. Although it's semi-normal to have very small amounts of voltage potential in your coolant system, values greater than about a tenth of a volt can start reactions between the coolant and the metal in your engine. In particular, electrolysis affects primarily aluminum engine components, resulting in pitting and scarring of the aluminum surface. This eating away of the metal can cause coolant system leaks, and in particular, radiator leaks around aluminum welds. Cast-iron components are also vulnerable, but typically the aluminum metal parts fail first.
How can you test for electrolysis? Other than actually seeing visible signs of erosion, you can perform a current flow test. Connect the negative terminal of a voltmeter to the chassis ground. Test for adequate continuity by touching another point on the chassis - the resistance should be near to zero. With the engine cold and running, submerge the positive probe into the coolant tank, making sure that the probe does not touch any metal parts. The voltage should be less than .10 volts. If not, methodically turn off or unplug each electrical accessory until the reading reads below .10 volts. Have an assistant switch accessories (like the A/C compressor, heater blower, etc.) while you measure the voltage.
If an accessory doesn't have an on/off switch, test it by temporarily running a ground from the housing of the accessory to the chassis. Ground each component and check the voltmeter. If the wire restores a missing ground connection to the accessory, then you've found a component with a faulty ground.
During this test, be sure to check the starter. Not only will a poorly grounded starter struggle to turn over the engine, it will also zap away tremendous amounts of metal in your cooling system components. Watch the meter carefully when starting the engine. Any voltage spike will indicate a faulty ground connection.
Coolant System Additives - Many people are rightly skeptical of coolant system additives - there are a lot of myths in the automotive industry. Luckily, the coolant system additives are in the category of good practice, for reasons I'll explain here. It all begins with chemistry. Like today's modern oils, many of today's modern coolants incorporate some of the chemicals that help cooling and increase heat flow around your cooling system components. As more and more automotive components are made out of aluminum, and radiators become smaller, the use of these additives becomes more advantageous.
Aftermarket coolant system additives are known as surfactants. What is a surfactant? A surfactant or surface active agent, is a molecule that has a water-loving end (hydrophilic and water fearing end (hydrophobic). Localized boiling of coolant in the cylinder head can create large shock waves that can wreck havoc on your engine, particularly on aluminum components. Without going into too much boring detail, these surfactants also help to reduce the amount of air in the cooling system, and also control the amount of foam within the system.
In general, there are three main reasons why using these additives is beneficial to your cooling system. Firstly, they reduce harmful cavitations and foaming that may occur when your water pump is kicking out fluid at a rapid pace. This reduced foaming helps to prevent damage to aluminum surfaces. Secondly, the use of these additives aid in the transmission of heat from the coolant to the radiating surfaces within the radiator. Even if your car runs very cool, these additives add an extra level of protection in case a thermostat or similar component fails. Thirdly, the additives contain corrosion inhibitors. Most cars on the road have cooling systems that do not contain the ideal 50/50 water / antifreeze ratio that the antifreeze manufacturers design for. The additives help to minimize potential corrosion by maintaining adequate pH levels. Even if your antifreeze already contains surfactant additives, the use of these additional additives is typically beneficial because most cars are shortchanged on the 50/50 coolant/water mix.
In general, the benefits of additives like Water Wetter are:
Reduces corrosion due to rust, and electrolysis
Increases the 'wetting ability' of water and improves heat transfer, thus reducing cylinder head temperatures
Cleans and lubricates coolant system seals like those found in the water pump
Reduces the formation of foam and cavitations which can cause corrosion
Reduces the effects of 'hard water' in the cooling system
In general, the addition of these additives is cheap, and it's a proven benefit too - no snake oil here. Using the additives on a perfectly maintained car can also provide a significant margin of error in case something goes wrong.
It's important to keep your cooling system at the correct pH as well. Water has a pH of 7 and is considered neutral. Battery acid is highly corrosive and has a pH of about 2-3, whereas baking soda is very alkaline, and has a pH of about 10-11. In general, you want to make sure that your coolant has a pH greater than seven. Any pH less than that will result in an acidic mixture, which will start to corrode your engine. The corrosion inhibitors in additives and antifreeze are added specifically to keep the pH above 7. A properly mixed 50/50 split between water and antifreeze will yield a pH of about 8-9. Over time, the glycol (one of the main components of antifreeze) will break down and degrade, creating acidic compounds. The alkaline corrosion inhibitors must be adequate enough to neutralize these acidic byproducts over the life of the coolant. Minerals in the water, heat, dissolved oxygen, and other factors gradually deplete the coolant of its corrosion inhibitors. Once gone, the mixture will become acidic, and will begin to eat away at your engine.
Cooling System Maintenance: Checking the Level - It's very important to check your coolant level regularly, as this will help detect leaks that can siphon off coolant and cause overheating in your engine. You should regularly check the coolant level in the
coolant expansion tank, making sure that it is within the prescribed High/Low marks. These marks are printed on the side of the tank. The tank is slightly transparent, and you can see through it slightly to see the current coolant level.
Your MINI will lose a little bit of coolant here and there over time due to evaporation from the reservoir. However, a significant loss of coolant over a very short period of time almost certainly signifies a leak in the system. Sometimes a leak can be seen when you park the car overnight. Often the coolant leaks out and then evaporates while you're driving, leaving no tell-tale mark of coolant on the pavement. If you suspect a coolant leak, visually inspect all of the hoses, the water pump, the reservoir, and the radiator for seepage or the 'weeping' of coolant out of seams and gaskets. Check the seal on the radiator cap. Check that the radiator cap is fastened securely. If you suspect a leak that you cannot see, a pressure test from a professional mechanic can verify the integrity of your system.
If you can't find any visible leaks and the system appears to hold pressure, then check to make sure that the cap is good, and is rated for the proper pressure. Verify that the cap you have for your MINI is the proper one for your engine.
If the system does not hold pressure, and you're still at a loss where coolant might be disappearing to, then you might want to start looking in the oil. A faulty head gasket will often cause coolant to leak into the oil. If you remove your oil cap and find a yellow murky substance, then you probably have a faulty head gasket. The oil level may be elevated and you will be able to see droplets of coolant inside the oil filler hole. If coolant is leaking past the gasket into a combustion chamber, you will see steam exiting out of the tailpipe, and the spark plugs will foul easily. In addition, the exhaust will be contaminated with the silicate corrosion inhibitors found in the coolant, and your oxygen sensor will be destroyed - plan on replacing it if you have experienced this problem.
Checking Coolant Strength & Condition - You should periodically test the strength and condition of your coolant to assure that you have achieved the optimum balance for your MINI. This is just as important for protection against heat as it is for protection against freezing. An imbalance between water and antifreeze levels will change the boiling point and/or freezing point of the mixture. A 50/50 mixture of water and ethylene glycol (EG) antifreeze will provide protection against boiling up to approximately 255° F (with a 15 psi radiator cap). This mixture will protect against freezing to a chilly -34° F. On the other hand, a similar 50/50 mixture of propylene glycol (PG) antifreeze and water will give you protection from -26° F to about 257° F.
If you increase the concentration of antifreeze in your coolant, you will raise the effective boiling point, and lower the freezing point. While this may seem beneficial on the surface, having a antifreeze content of greater than 65-70% will significantly reduce the ability of the coolant to transmit and transfer heat. This increases the chances of overheating. As with most things in life, it's a good thing to maintain a healthy balance.
Beware - you cannot accurately determine the condition of your coolant simply by looking at it. The chemical composition and concentrations in the coolant are very important - if the chemistry is off, then your coolant may be harming your engine.
As mentioned previously, it is important to keep the coolant fresh. The main ingredient in antifreeze, ethylene glycol, typically accounts for 95% of antifreeze by weight. It does not typically wear out, but the corrosion inhibitors that comprise the remaining 5% typically do degrade and wear out over time. Keeping the coolant fresh is especially important with engines that have both aluminum heads and cast iron blocks.
I recommend that the coolant be changed at least every two years, or every 25,000 miles. I'm not a huge fan of long-life antifreeze - if these longer-life fluids are mixed with conventional antifreeze (a very easy mistake to make), the corrosion inhibitors react and reduce the effective protection of the long-life fluid. If you do have this long-life fluid installed in your car, only add the same type of anti-freeze to the car. Don't mix and match regular and long-life fluid.
Unfortunately, it's tough to determine if your long-life coolant has been mixed or topped off with ordinary antifreeze. Although some coolants are dyed a separate color (like Dex-Cool in GM vehicles), when mixed with standard antifreeze, it typically isn't enough to overpower the bright green color. In general, unless you know the entire service history of your MINI, it's a wise idea to err on the side of caution, and use a shorter service interval for changing your coolant.
Okay, so how do you check the coolant in your system? I recommend using little chemical strip tests that measure how much reserve alkalinity is left within the coolant. The test strip changes color when immersed in the coolant. You can then compare the final color change to a reference chart in order to determine the condition of the coolant. Obviously, if the coolant tests poorly or is borderline, you should plan on replacing your coolant very soon.
An additional note - EG and PG antifreeze have differing specific gravities, so make sure that you use the correct type of test strip when testing your coolant. Otherwise, you may end up with false readings.
Changing the Coolant in Your MINI - Okay, so I've convinced you that your coolant needs changing. The good news is that it's relatively easy on the MINI. Begin by getting a large drip pan to place underneath your car. The MINI Cooper S holds 6 liters or roughly 1.5 gallons of coolant so make sure that whatever container you use is capable of holding all of that coolant.
With your MINI cold, elevate it on jack stands (See our project on jacking up your car for more info). I’ve found that removing the front bumper cover and extending the radiator out to the service position makes it a bit easier to access the lower radiator hose.
Once the bumper cover and carriers are removed, locate the two plastic retaining pins at the top of the radiator on each side. Use a screwdriver to pry out the center pin, then remove the outer pin (See Figure 1). These pins secure the radiator to the mounting frame, but will also allow you to gain a little more free room by rocking the radiator back and forth.
In front of the radiator is the A/C condenser. This is secured to the front of the radiator by two 10mm bolts on both the left and right sides (See Figure 2 and Figure 3 ). Loosen but do not remove the bolts. Now look at the front of the intercooler. You will see that the top radiator hose is held to the front with an 8mm bolt. Remove the bolt and let the hose hang freely (See Figure 4).
The front panel of the car has two mounting holes in which BMW specifies the use of two special rods to allow the frame to slide on. However, these rods cost over $100 each and is a special order part. Instead, you can use two M8 x 100 bolts with two fender washers (See Figure 5).
Thread the bolts into the holes and look up on the front driver’s frame rail. Remove the 10mm bolt that holds both the A/C port and the bracket containing the wiring harness for the radiator fans. Remove the bracket and disconnect the harness (See Figure 6). Remove the two 10mm nuts holding the A/C condenser and carefully lay it down off to the side of the radiator frame. Now slide the whole radiator frame over the two bolts until it stops (See Figure 7).
At this point, set up a drain pan or some other collector directly under the lower radiator hose where it attaches to the radiator at the bottom. Take the cap off the coolant expansion tank and remove the hose clamp on the lower radiator hose. The hose may be stuck on the neck of the radiator, so you may have to use a screwdriver to carefully walk the hose off the neck. Keep in mind that as soon as the hose is free, coolant will start flowing out (See Figure 8 and Figure 9 ). Now let the coolant drain. This may take several minutes.
BEWARE: I have found it nearly impossible to empty the coolant without having it spill on myself. Don't wear any decent clothes, and make sure that you are wearing safety glasses when working underneath the car. The coolant will empty out much like water comes out of a shower - it will spray all over, and will be difficult to catch 100% into your pan. Have plenty of paper towels on hand to clean up the spilled coolant.
With all of the coolant removed from the system, use a funnel and place it into plastic containers. One gallon spring water or milk containers make excellent storage containers for used coolant. Don't pour the coolant down the drain, instead take it to a recycling station. A note about coolant - it is highly toxic and dangerous to pets and small children. Used coolant should be packaged up right away. Less-than-intelligent animals seem to like the smell and taste of coolant, and will be attracted to it. Package it up and seal it off, otherwise you may find kitty dead in the garage one day - no joking. Rinse and dilute any contaminated areas with water.
Using a large funnel in the expansion tank, slowly fill the car with new coolant. Use a 50/50 mixture of antifreeze and distilled water. Do not use tap water or spring water, as these have impurities that will contaminate your system. Distilled or ionized water is 100% H20, and does not contain any minerals, additives, or impurities. Fill the system very slowly, as it will take a bit of time for the coolant to get to all points in the system.
When the system is full of coolant, you will need to bleed air out of it. The procedure for bleeding these cars seems somewhat sloppy and not too slick. With the bleed screw loosened, fill the expansion tank until fluid begins coming out of the bleed screw. Now start the engine and let it warm up, keeping an eye on the coolant level. It will likely drop as the thermostat opens. Turn the heater on to full blast. This will allow the coolant to enter the heater core of the car.
Continue filling until there are no more bubbles coming out. This, of course will mean that plenty of coolant will spill all over your radiator, and down onto the ground. Have a catch pan ready to capture this coolant spill. When no more bubbles exit out of the bleed screw, tighten the screw.
Now, run the engine until it reaches its operating temperature. Turn off the engine and let it cool down. Then, top off the coolant in the expansion tank to the appropriate level, if necessary.
R50 Cooper: There are a few differences in the coolant fill procedure for the R50 Cooper. Unlike the supercharged cars, the coolant is added to the car at the thermostat neck on the engine. Before you start to fill the engine, loosen the vent screw in the plastic coupler piece coming from the lower radiator hose as well as the vent screw in the distribution pipe on the rear of the thermostat housing. Also turn the ignition of the car on (don’t start it just yet) and set the heater controls to the maximum level with the fan on low. This will open the lines going to the heater core inside the car.
Because of the position of the thermostat under the filler neck, adding coolant to the R50 can be a little difficult. What will help considerably is a filling kit that works off gravity. This kit (Lisle 24610) allows you to attach a large reservoir to the filler neck using a series of adapters. Once attached, pour the coolant into the reservoir and let gravity do the rest. You’ll want to fill the engine until you start to see coolant coming out of both vent screws. Once you see this, close both of the screws. Keep filling the reservoir until it no longer drain into the filler neck. Now remove the reservoir and close the vent screws.
With the vent screws closed, continue to fill the engine until the coolant level reaches the inner ring of the filler neck. Now put the pressure cap back on the filler neck and fill the overflow tank on the rear bulkhead to the MAX mark. Now start the engine and let it idle. You’ll want to keep an eye of the coolant level at the overflow tank. Top off the coolant in the tank until the car fully warms up and the coolant level drops.
Draining the coolant on the R55/R56/R57 MINI requires removing one of the lower radiator hoses as there is no drain plug. Remove the cap on the coolant expansion tank. You’ll need to remove the front splash shield on the underside of the engine compartment and disconnect the hose clamp holding the lower radiator hose to the radiator. Make sure that you have a container large enough to hold at least 5 gallons of coolant. Once all the coolant has been drained, re-attach the hose to the radiator. Now set the heater to its maximum setting and fill the coolant reservoir with the engine running.
To drain any remaining
coolant from the system (R50/R53), from underneath the car,
there is a 14mm drain plug (green arrow) located at the rear face
base of the cylinder block adjacent to the starter
underneath the exhaust manifold heat shield (if looking down at the engine).
I'm sure one question you're about to ask is "what type of coolant should I use?" BMW has issued a 1991 technical bulletin, 17-01-88-(1743), which details problems with what is known as silicate gel precipitation in engines. This is the 'green goo' (yes, it actually says that in the BMW Tech bulletin - gotta love those German translators) that results as a consequence of an antifreeze over-concentration in the coolant, combined with hard water, and the phosphates commonly used in many antifreezes. BMW factory antifreeze has been formulated to prevent this problem of silicate drop-out without any coolant performance loss. This antifreeze contains no nitrites and no phosphates. The part number for a one gallon container is 82-14-0-031-133, and it costs about $15-$20 per gallon from PelicanParts.com. Although I am always eager to find alternatives to expensive BMW factory products, I would stick with the factory coolant for now.