Question: I have a Chevrolet Nova with 1987 and a 1. 6-liter engine. Does this car need to adjust the valve regularly? I got conflicting advice from the mechanic. --C. E. M. A: Obviously, one of your mechanisms is making up the answer. Your Nova has so-called solid valve lifts that need to be adjusted regularly. Precise Service intervals should be listed in the user manual, but the typical maintenance intervals for valve adjustment are 15,000 miles. There are two types of lifts in the car. - Solid and hydraulic. Until the last few years, most cars have hydraulic lifts. These are small cylinders filled with liquid, which form the connection between the Cam and the push rod or the valve rod. The hydraulic lift is automatically adjusted to maintain small or zero tolerances. The solid lift has a adjusting screw for keeping a few parts of the inch gap. Away from the reason of the hydraulic system, the hydraulic system provides the advantage of maintenance For free, in terms of rpm, it runs faster than the new engine. The hydraulic lift can be pumped at high speed and prevent the valve from being completely closed. A solid lifter on a typical small engine that can be very high RPM without floating or preventing the valve from floating. Q: I am the original owner of 1974 Corvette. After 10 years, all four brake calipers need to be replaced. The owner\'s manual suggests using the Dot 3 brake fluid, but I would like to switch to the new silicon fluid instead. Is there a problem with compatibility between the two fluids? --S. L. S. A: If you decide to change the brake fluid, you will either have A big trouble or will spend A lot of money. The Silicon brake fluid, better known as Dot 5, is completely incompatible with Dot 3 or Dot 4, which is the other two widely used brake fluids. The main difference between all these fluids is their reaction to water. The Dot 3 and 4 tend to absorb water easily, and when the brake system is heated under intensive use, the brake fluid will boil, creating a steam bag and then causing the sponge brake action. Dot 3 has 350- Degrees dry boiling point, which means that if it does not contain water, it will not boil until it reaches 350 degrees. The dry boiling point of Dot 4 is 475 degrees. However, the boiling point can drop to 275 degrees or less when water is absorbed into these liquids. The silicon fluid is not a problem because it does not absorb water. Another major advantage is that water scarcity helps to prevent corrosion of brake components such as master cylinders, calipers and wheel cylinders. The problem for you is that switching fluid requires you to replace each rubber seal, clean the system with solvent, and blow out the system with air. So, you actually need to overhaul the entire hydraulic system, which is a big expense that you can\'t guarantee from the advantages you get from the silicon fluid. Q: My car is overheating and I found that the problem is that the thermostat is faulty. Can you tell me the main use of the thermostat? --C. B. A: The thermostat regulates the flow of coolant from the engine to the radiator, and the coolant cools in the radiator. When the engine coolant reaches anywhere from 160 to 195 degrees, the thermostat opens. The engine will overheat if it gets stuck. If stuck, the engine will not be able to reach the proper operating temperature. Vartabedian can\'t reply to the email in person, but will try to answer questions about cars that are of interest to everyone in this column. Don\'t call. Write to your wheel, Times Square, Los Angeles, California. 90053.