Drive it forever : Get under dash, chase leaks

Dear Mike: I have a 1998 Pontiac Grand Prix GT 3.8-liter V-6 with 140,000 miles. The car runs quite well, but no matter what setting the climate control is on — automatic, split zone, upper dash, lower dash, combo — the vast majority of the air comes out of the windshield vents and driver and passenger foot-well vents.

I have noticed this problem on other vehicles I have owned as they approach and surpass 100,000 miles. Are the vacuum hoses in the system losing their seals or developing cracks?

A: I think your diagnosis is at least partially accurate. Your problem may be a single rubber vacuum fitting that’s split open, or it could be dozens of similar parts slowly failing because the rubber has gotten hard and no longer has the compliance to grip the vacuum lines.

Many HVAC systems use manifold vacuums to operate simple diaphragm activators that, in turn, open and shut blend-air doors. When the rubber and plastic parts get old and start to crack and leak, the system becomes less responsive. Compound this with blend-air door hinges and linkages that become stiff and downright recalcitrant, as well as disintegrating foam rubber seals, and you’ve got trouble.

So, sorry to say, you’ve got to get under the dash and start chasing leaks.

Dear Mike: I own a 1999 Mercury Sable that has the very annoying feature of self-locking doors. This feature is so irritating to me that I have strongly considered selling the car. I’m wondering if there is any way that I can disable the self-locking doors myself.

— S.C.

A: This is one of my own pet peeves. I’m always trying to open a door that has locked itself and having to go back around to the other side, or dig in my pocket for the key fob.

Some vehicles can be reprogrammed to stop this, but on others it’s hard-wired in. Ask the dealer. Your other option is to pull the fuse for the central locking system and go with manual locks.

Dear Mike: We own a 2002 Pontiac Montana minivan with an OEM six-disc in-dash CD changer. Just last week the CD changer stopped working. The radio still works but it no longer makes any of those mechanical noises it would make when it switched discs.

Is this a typical problem with six-disc changers? Are there any remedies? — M.P.

A: I’ve lost an assortment of CDs in car CD changers that went belly up while I was driving. I avoid using them because they’re so unreliable.

Dear Mike: Do you know how long a hybrid car battery is expected to last and what the replacement cost would be? No one I know seems to have the answer and I have not received any replies from other automobile writers.

Is the information a big secret or is it possible that no one really knows, including the car manufacturers? — C.H.

A: I can’t give you any insight into this. If the car companies really know, they’re not saying. I suspect they really don’t know. But those battery packs are going to be a substantial burden to replace when they fail. And they will fail, eventually.

I’m recommending leasing for hybrids so you’re not stuck with a dead car and a huge battery-replacement bill.

Dear Mike: I purchased a 1986 Ford F250 truck that has dual fuel tanks. The rear tank quit working last week.

I checked to make sure I still had fuel in it. What do I need to check next?

— D.B.

A: There are two things to check. The transfer valve may have failed or the fuel pump for the second tank may not be working. The pump is inside the tank, and may be tough to access. Check for voltage at the pump’s electrical connection.

Dear Mike: Now that we have switched from MTBE to 10 percent ethanol in our gasoline here in Massachusetts, do I still need to use “drygas” additive to remove water condensate in the winter? Ethanol is hydrophilic, but will it eliminate the water in the gas tank and lines?

— P.P., Ashland, Mass.

A: No, you do not need to use drygas additive. The ethanol will eliminate the water in the gas tank and lines.

Q: I have been hearing that adding a fuel vaporizer to your car can increase the gas mileage by 20 percent to 50 percent. If this is true why do car manufacturers not install them in their cars?

A: Because it’s not true.