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FCP Euro Service Kits

FCP Euro Kits

antifreeze puddle

It may seem obvious that a coolant leak shouldn't go long without being diagnosed. The chance of over-heating, having to buy top-up coolant, and the spots on your driveway are just a few reasons. But the reality is that coolant leaks are not only messy but can cause damage to parts in the engine bay if left unattended.

Antifreeze can cause premature failure of parts it comes into contact with - serpentine belts, pulleys, and electrical components. Basically, if it wasn't designed to come into contact with antifreeze, antifreeze will have adverse effects on it. When a coolant leak is neglected it dries into a white residue that can be washed away with a mild water based detergent (simple green).

Today's antifreeze is made by mixing distilled water and an alcohol-based agent, either Ethylene Glycol or Propylene Glycol. Ethylene Glycol is a very toxic chemical, while Propylene Glycol is considerably less toxic. When you let these chemicals wash over your pulleys and belts or plastic housings and connectors and let dry, it will begin to degrade and corrode the part. A lot of the time it dries out belts causing them to crack. If a substantial amount of coolant is leaked it can find its way to the idler and tensioner pulleys and soak the bearings. When this happens, the coolant washes away the grease in the pulley bearing and causes the pulley to fail.

One pulley failed after another

About a month before I bought my current E36 M3 its main cooling fan self-destructed sending shrapnel into the radiator, upper and lower hoses, and slicing the accessory belt. As you can imagine, this sent coolant all over the front portion of the engine bay. The previous owner had the car taken in and got a full cooling system overhaul, along with accessory belt. Thankfully I didn't have to pay for any of that.  A few weeks after I purchased the car, the idler pulley started squealing, so I replaced it. Another week goes by and the upper tensioner pulley started squealing, so I replaced it. And another week goes by and the lower tensioner pulley started squealing. After replacing the final pulley I noticed that all the old pulleys were covered in dried coolant, along with their mounting hardware. Now, don't get me wrong, I'd much rather replace a few pulleys than have to replace the whole cooling system. But, the life of the pulleys definitely could have been prolonged if proper cleaning had taken place.

Cleaning after a coolant leak

Before taking your car to a shop to get it steam cleaned, take a look and see if you can do it yourself and save yourself a few bucks.  If you have a messy engine bay - whether it be from dirt, dust, coolant, or oil - all you really need is a pack of clean shop towels, a water based cleaner (Simple Green), a hose, and a mild degreaser that is safe for the engine bay. CRC makes a great engine degreaser, as well as GUNK, available at most auto-parts stores.

  • To start off I recommend you cover any exposed electrical items. I cover my alternator with a clean towel, then cover the towel with aluminium foil. I also cover the MAF with aluminium foil. I have seen people hose off their engine bays without covering the alternator without adverse effects, but I'd rather not take chances.
  • After my alternator and MAF are covered I spray engine degreaser over my valve cover, intake manifold, throttle body, vanos unit, radiator covers, and I give the front of the engine a good spray. Engine degreaser is safe on plastics, rubbers, and metals, so it is safe to spray on your belts and pulleys.
  • Let the cleaner sit for 10 minutes and then gently spray it off with a hose. Be sure not to use high pressure on any electrical connectors.
  • Inspect the areas that you were most concerned about. (Areas where coolant or oil had leaked) If more attention is needed, spray some simple green on the area and rub the grime away with a clean rag.

When the engine bay is clean to your satisfaction, it is important to let it sit for a few hours so the water can evaporate completely. I like to let my car sit overnight just to be sure. When your engine bay is completely dry remove any aluminium foil and rags that may be covering components.

It can be a little nerve racking spraying your engine with water; it's a very counterintuitive thing to do. Just work slowly, and be sure not to directly spray any electrical connectors. Components in the engine compartment are designed to withstand adverse weather, just make sure you let them dry properly and everything will be fine.

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Written by :
Tony Robinett

Tony lives in Spokane, Washington and is a 3-D Design Engineer, machinist, and welder. When he’s not at work he is designing and fabricating parts for his M3, and other BMWs alike.


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