The Case of the Vanishing Coolant

Tom M. asks: My daughter has a 2001 Oldsmobile Aurora. The low coolant light is constantly coming on and we are refilling the antifreeze tank. The problem is that there is never a puddle on the ground or any signs of a leak. The car has not overheated that we know of. What is going on? Missing antifreeze, or coolant, is actually a very common mystery. Many of us who have had the benefit of driving older cars have had the coolant exit the sys­tem from overheating while we drive along. That usually goes something like this: “What is with the weird mist on the windshield? What is that sweet smell? Is there a candy factory near here? Thar she blows!”

Seeing the coolant go out of the hood in a white plume is actually good in one way. At least you know what happened. Many times missing coolant seems to go … nowhere. No puddle under the car, no Yellowstone impression on the expressway during a heat wave. So where did it all go? How do you figure out what is wrong? There are some things to look for, but first, let’s go through the coolant system step by step. First off, coolant is simply a mixture of water and a liquid that will not freeze during winter, such as a type of glycol. It also has additives that help keep the in­sides of the engine and cooling system from corroding. The cooling system has two main functions in a typical car: managing the temperature of the engine and pro­viding heat into the passenger compartment. Almost all modern cars have liquid-cooled engines. The liquid is circulated throughout the engine to keep all the parts warm, but not too hot.

Once the coolant is warmed up by the heat of the engine combustion, the tem­perature is maintained at the best operating temperature for the engine by passing through a radiator. Coolant flows through small tubes in the radiator that have metal fins attached. Air from the outside of the car blows over the fins as you drive along and draws the heat out of the coolant. (This is also how your home heat sys­tem works if you have “forced hot water” heating.) When your car idles and there is no air being forced into the front of the car, there is a fan that pulls air into the engine compartment and through the radiator. The next part is called the water pump — which should be called a coolant pump, right? This is a simple little metal disc about the size of a silver dollar called an impeller. It is inside a housing that has a small shaft that spins the disc, creating a pumping action. The impeller is driven off of the car’s timing belt or accessory belt. It pumps the coolant in a loop through the system. This little devil is very inexpensive. However, when it goes bad it is pricy to fixon most cars because it is buried inside the deepest recesses of the engine compartment. That is why it is often replaced when the car’s timing belt is replaced. The thermostat is next. This is a simple device with metal parts that open and close as the coolant heats up. The job of the thermostat is to keep coolant out of the radiator and in the engine block until it warms up. Once the coolant is heated up, the thermostat allows the coolant to go through the rest of the system and thus be maintained at a stable temperature. It is basically a valve that works automatically. A bad thermostat can cause a car to have no heat, or to get too hot and “overheat.” Thermostats are inexpensive and easy to access. The problem is that if the car over­heats, the car engine can suffer other damage.

The last part of the system is the reservoir. In old cars there was just the radia­tor and a cap that had a built-in spring. If the system heated up and the pressure grew, the cap would allow a bit of coolant or steam out, protecting the system from bursting someplace. Today almost all cars have what is called the “overflow tank.” It is a bit of a misnomer. The tank actually allows the warm fluid to expand and fillup in the tank, and then cool and be pulled back into the radiator. If you look at this plastic tank you will see that there are two marks showing the level when hot and also when cold. This is the place you check the fluid level and add fluid.

So if the coolant is missing and there is no steam or puddle, where did it go? I went to Joseph Wolf, owner of Auto Clinic on Pond Street in Norfolk, and ran the question past him. His reply was that if the car is a V6 start by having the mechanic check the intake manifold gasket. He tells me “The 3.1-liter V6 cars have had trou­ble

there.” Joseph went on to point out that when the coolant leaks there, it hits the warm engine block and evaporates.

He also suggested the following if that is not the problem: — Check the carpet for signs of wetness under the dash where the driver and passenger’s feet go. The coolant could be coming from the heating loop that warms the passenger area. It might be dripping down onto the floor. — Pull the oil dipstick and look at it. See any whitish gray stuff? One of the places coolant can go is into the engine’s oil passages. At some points they are sepa­rated by gaskets. The coolant often shows up as a whitish liquid in the oil when this is happening. It is a bad thing. None of these are really do-it-yourself jobs to fix, so if the coolant is going away without a trace, your best bet is to see a mechanic to have the system pressure tested. By the way, have you ever noticed there are two radiators in most cars? If you know why, please send me an email message, to john@columnshift.com. The answer is part of next week’s column.