Question: What are the pros and cons of using cans of pressurized sealant to repair tire punctures?--J.M.
Answer: Among some professional tire experts, the sealants have a poor reputation, but they can be very useful to have in an emergency.
The most obvious drawback is the mistaken idea that they can provide a permanent repair to a punctured tire. The sealants work by forming an airtight membrane over small holes in the tire.
The fact that you have a hole in your tire, however, indicates that the tire has been damaged. Sealing the hole with glop just disguises, but does not repair, the damage. In some cases that won't be a hazard, but there are plenty of instances when the cord body of the tire can be seriously damaged and you would not know it.
Another obvious negative is that tires can deteriorate over years of storage in a trunk, and they can lose their pressure. So, just when you need it, the sealant might not work.
Now, if you are willing to accept the idea that you are not going to use the sealants as a long-term repair and that they might not work on a big hole, I think they're a great thing to have in the trunk.
A lot of people wouldn't think of changing a tire on a freeway shoulder. Nowadays, being stuck on a freeway can be a dangerous situation. A can of sealant might just get you to a service garage where a permanent repair can be made.
A permanent repair should not be a simple rubber plug that is inserted from the outside of the tire, the way most service stations want to repair tires. A plug/patch should be applied to the inside of the tire. It's important to get the tire off the rim of the wheel, and make sure a broken portion of a nail or other foreign object isn't inside.
Incidentally, there are many different brands of sealants. I prefer the ones with a hose and threaded fitting that screws into the wheel stem. The type with a nipple that you simply push up against the wheel stem are difficult to use. I have seen them leak pressure and squirt sealant outside the tire.
Q: My 1978 GMC pickup with a 350 engine has a problem with engine temperature. It used to heat up fine, but now it only comes up to 150 degrees. I put a new 195-degree thermostat in it, flushed the cooling system and put new antifreeze in. I would surely appreciate any advice you could give me.--H.E.
A: It sounds as if you did all the right things, so either you have a foul-up in your heater hoses, your instruments are wrong or your pickup is defying the laws of physics.
If you have recently done some engine work that involved changing the heater hoses, possibly you switched the route of the hoses to permit the coolant to bypass the thermostat.
Another possibility is that you are taking a temperature reading when the engine hasn't fully heated or when it suddenly depressurizes, which can quickly drop the temperature near the radiator cap.
An equal mixture of water and antifreeze should provide overheating protection to 262 degrees at the 14-pounds-per-square-inch pressure in your engine. The warning light is programmed to come on at about 260 degrees.
Ralph Vartabedian cannot answer mail personally but will respond in this column to automotive questions of general interest. Do not telephone. Write to Your Wheels, You section, The Times, Times Mirror Square, Los Angeles 90053.