Q: My husband and I have a four-cylinder 2006 Chevy Malibu with 137,000 miles on it. Since the fall of 2012, the car has been leaking coolant. It's not leaking to the ground and it's not leaking into the engine — oil is clean. Five shops including a Chevy dealership looked at the car but have been unable to find a leak. They've done their pressure tests but the car passes and they can't tell where the leak is located. One or two mechanics suggested the head gasket as a potential culprit. Six months ago we added a sealant product to the radiator that seemed to resolve the issue temporarily, but after a few months the cooling system was clogged and the car was starting to overheat. Within the past couple of weeks the car has started to hemorrhage coolant. In the last couple of days we've gone through a gallon of coolant. We need to figure out the real issue and fix it. We would greatly appreciate any advice or suggestions you may have for us!
A: At this point, you've got a big problem. Sample the coolant with a coolant test strip for the presence of hydrocarbons — anything more than a trace would indicate that combustion gases are getting into the coolant. The most likely causes for this are a failed head gasket, cracked head or cylinder.
A second test can be done in one of two ways. With the engine cold, remove the coolant pressure cap and start the engine. If coolant bubbles up and out of the reservoir, combustion pressure is entering the cooling system. The more involved test involves removing spark plugs and installing an air fitting adapter in order to introduce air pressure into the cylinders one at a time. Seeing or hearing bubbling in the coolant confirms this type of failure.
Check for a leaking heater core, although this might produce a hot coolant odor in the cabin. Make sure to check the transmission fluid as well. If the cooling chamber in the radiator for transmission fluid is leaking, the two fluids can mix to some degree, and since there's pressure in the cooling system, coolant can be forced into the transmission.
Q: When I brought my 2013 Subaru Outback in for an oil change, the dealer suggested a 15,000-mile checkup that involves changing fluids, filters, etc. at a cost of $450. Even the service person suggested waiting until 30,000 miles. Are those expensive "checkups" really necessary? I realize the need for changing fluids and filters, but it seems that such services every 15,000 or 30,000 miles are a bit too often. How often should one get those expensive checkups?
A: Looking in my ALLDATA automotive database at Subaru's recommended maintenance under normal driving conditions, I find the following; oil/filter/tire rotation every 7,500 miles, and replace the cabin filter at 15,000-mile intervals. Subaru recommends including engine air filter and brake fluid changes at 30,000-mile services. All other components of Subaru's recommend services are "inspections" like fluid levels, brakes, CV-joint boots and the like, many of which you could do yourself.
Unless there's a warranty eligibility issue, I'd stick to the basics and do as much as possible yourself.
Q: The transmission in my 1997 Volkswagen Jetta is beginning to slip and I don't know how to add fluid because there is no dipstick. Any suggestions?
A: That's because this transmission is effectively sealed and the fluid must be checked or changed through a rather involved process best done at the dealership or professional shop.