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Why does my beloved car rattle on the highway?

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Dear Tom and Ray:


I write to you concerning our beloved Cumulus, a 1977 white Buick LaSabre. We call it Cumulus because it rides like a cloud. It has 147,000 miles, and we are beginning to hear things we don't like. When we take longer trips on the highway we develop large amounts of valve rattle. After about an hour of highway driving, the valves sound as though they are about to come out through the hood. When this happens, we pull over to check the oil level and coolant level. Both are fine, but when we start up again the temp light is on. What do we have to do to keep the car running for another 50,000 miles?
Charlie

TOM: What you're calling "valve rattle" could either be pinging or the lifters making noise due to low oil pressure. Either way, it's probably related to a temperature problem. Even though you say you check the coolant level and it's fine, I'll bet you're checking the level in the overflow container--which has the FULL/ADD lines on it. The problem is that if you do have a hole in your cooling system, there would be no suction to draw coolant in from the overflow reservoir when the engine cools. In other words, the overflow container could read "full" when the system is actually low or empty.

RAY: Severe overheating could cause serious pinging. A little bit of pinging isn't all that bad. In fact, GM used to euphemistically refer to pinging as "the sound of economy." A lot of pinging, however, is the sound of engine destruction, and if you hear it every time you accelerate, that's too much.

TOM: Overheating could also cause the oil to thin out, and even though your oil level may be OK, your oil PRESSURE could be low--you might even need a new oil pump. If that were the case, the first things to be deprived of oil would be your lifters. Either way, Charlie, you better get this fixed if you want to go another 50K in Cumulus. If you choose not to fix it, we suggest you invest in a much more powerful radio with lots of speakers. That will drown out this noise and allow you to play a nice funeral dirge as you drive this thing into the ground.
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