I have a horrible smell coming out of the vents of my '09 Corvette whenever I use the air conditioning or heater. The smell seems to get better after I drive the car for awhile (or maybe I just get immune to the odor). My daughter Samantha was home for a few weeks in the summer. She asked me to take her car to the service station to fill it up with gas, and I noticed the same smell coming from her air conditioning. She drives an '07 Chevy Cobalt. Is it just me, or is there a problem with the A/C systems on GM products?
Via the Internet
You're correct: GM has received a lot of complaints about musty odors coming from the heating, ventilation, and air-conditioning (HVAC) systems of its newer vehicles at start-up, especially in hot, humid climates.
It's possible that the odor is the result of microbial growth on the evaporator core.When you turn on the blower-motor fan, the microbial growth releases a musty odor into the passenger compartment. This condition could be caused by condensation build-up on the evaporator core. This condensation can't evaporate naturally in high-humidity conditions. Other potential sources of the odor include a stopped-up HVAC drain tube, which can also cause microbial growth.
Remember: if there's any way for water to enter the vehicle and get into the carpet, that could also cause a musty odor to develop. Some of the culprits here include a leaking heater core, torn weather stripping, or a poorly sealed window.
If you determine the carpet isn't wet, and the HVAC tube isn't stopped up, the odor is most likely caused by microbes on the evaporator core. Fortunately there's a technical service bulletin (TSB # 99-01-39-004C) covering a repair procedure for this problem. It covers all '93-10 GM passenger cars and trucks.
The repair procedure includes the following:
•Diagnostics to confirm that the A/C drain tube is not restricted
•Visual inspection-and, if necessary, replacement-of the cabin air filter
•Applying a cooling-coil coating to the evaporator-core surfaces
•If needed, installation of an Electronic Evaporator Dryer Module Kit (PN 12497910 or A/C Delco 15-5876)
This repair is a time-consuming and complicated job, so it's recommended that you have it done by a GM-certified technician. If you decide to attempt this operation yourself, be sure to get a copy of the TSB and follow the step-by-step procedure. Here's to the sweet smell of success.
Oil-Change Intervals Revisited
I've had more feedback on this topic than any other I've written about. It seems there are a lot of conflicting opinions on when to change the oil in your Corvette, most of them having to do with the onboard engine-oil-life monitoring system and the durability of synthetic oils.
Since 1990, Corvettes have been equipped with an oil-life-monitoring computer that records the number of engine starts and revolutions, coolant and oil temperatures, and other data to help determine when the oil should be changed. Once the computer has determined that the oil's life has been exhausted, it will illuminate a "Change Oil" light in the instrument-panel cluster (IPC). The system can't, however, analyze the oil-it can only make an educated guess at its condition by measuring trends in engine operation.
On newer Corvettes, the "Change Oil" lamp will typically illuminate at between 3,000 and 10,000 miles after the previous oil change. In cases of severe duty, it may come on before 3,000, but it will never come on at more than 10,000, which is the maximum oil-change interval allowed by GM for the LS engine. (Remember: This monitoring system must be reset after each oil change.)
Keep in mind that in addition to lubricating an engine's moving parts, motor oils are designed to carry combustion by-products away from the pistons and cylinders. Oil is formulated to collect and deal with dirt and dust that enter the engine through the intake, and condensation that forms when the engine heats up and then cools off. It must also handle any coolant or fuel that may get in the crankcase, as well as any acids that may form from the reaction between water and other contaminants.
When trying to determining the rate at which contamination and additive depletion occur, it's important to consider climate, driving conditions, fuel injection or carburetion adjustments, and the general mechanical condition of the engine. In a perfect, climate-controlled world, with ideal driving conditions and a meticulously tuned car, most newer Corvettes could go 7,500 to 10,000 miles between oil changes. But in the world in which most of us live, I think a 3,000-to-3,500-mile interval is prudent. Remember: changing your oil more often than needed will not hurt an engine, and an oil-related engine failure will cost you a lot more than five quarts of synthetic and a filter.
If you do choose an oil-change interval of 10,000 miles, remember that while the Delco PF 44 oil filter uses an excellent "Duragard" synthetic filter media, it is of a rather small capacity. For this reason, it is recommended that you change the filter every 3,000 to 3,500 miles.
I have an '00 Corvette, and it seems like it's using about a half a quart of oil between changes. There's no evidence of an oil leak on the garage floor. I even took the car to my local dealer to find out if my engine had an internal problem and was burning oil. It charged me $90 and told me It couldn't find a problem. (That dealer went out of business about two weeks after it worked on my car.) Was it just giving me a quick line to get rid of me, or is it normal for a Corvette to use some oil?
Via the Internet
All engines-including those used in Corvettes-require oil to lubricate and protect internal moving parts such as cylinder walls, pistons, and rings from wear. When the piston moves up and down on the cylinder wall, it leaves a thin film of oil. During the power stroke, a part of this oil layer is consumed in the combustion process. As a result, some oil consumption should be considered normal in any engine. (The accepted rate of oil consumption for Corvettes from '90 to '09 is approximately one quart every 2,000 miles.)
We recently received a question about a show car that was never driven more than a few miles at a time. This car would actually show the oil level to be over-full, even when the correct amount of oil was in the crankcase. This phenomenon can be caused by fuel and condensation generated during cold engine operation, and the engine's inability to generate enough heat to evaporate these contaminates.
Rest assured that if there's no oil on the floor, your Corvette is not leaking. Just keep an eye on that oil level and be sure it stays topped off.
I own an '08 Corvette, and the convertible top is separating near the windshield. Is this a common problem on these models, and is there a way to fix it permanently?
Via the Internet
Fortunately, there is a Customer Satisfaction Campaign (Bulletin # 08312) that addresses your problem. It seems that fabric on the convertible top can begin to separate from its retaining bracket near the windshield at vehicle speeds of approximately 100 mph or faster. (Don't worry; we won't tell.)
The repair includes the installation of a new retainer bracket and covers the following models:
•'08 Corvettes from VIN 85117774 through 86135284
•'09 Corvettes from VIN 95100002 through 95112678
Contact your dealer and confirm that your Vette is covered by the campaign. The program will be in effect until May 31, 2010.
Hope this helps, Ralph, and watch out for radar.
Got a question for our Tech Corner expert? Just jot it down on a paper towel or a lightly soiled shop rag and send it to us at VETTE Magazine, Attn: Tech Corner, 9036 Brittany Way, Tampa, FL 33619. Alternatively, you can submit your question via the Web, by emailing it to us at firstname.lastname@example.org. Be sure to put "Tech Corner" in the subject line.