from Goss’ Garage by Pat Goss
Should I? Shouldn’t I? It’s the eternal automotive question. Unfortunately, without the right answer you may be headed down a repair highway full of potholes.
Classic example: “My owner’s manual requires a valve adjustment every fifteen thousand miles, but my mechanic says that unless they’re noisy I shouldn’t waste my money. Should I, or shouldn’t I?”
This mechanic needs a fresh nappie and transport back to mechanic’s pre-school! Actually, owner’s manuals never require unnecessary maintenance they only suggest the absolute minimum necessary for a car to deliver about 100,000 miles. But in today’s world does the extra cost of using a car for only 100,000 miles make sense? Fewer miles driven means higher cost per mile and who can afford more expense, rather than less, these days?
For average vehicle life follow your owners’s manual but for maximum life and lower overall cost, use an aftermarket service schedule. Within reason more preventive maintenance means longer vehicle life while less means shorter life and more problems. Also things aren’t always what they seem.
Anyone, including technicians, who think they know more than the engineers who designed the car, is sadly mistaken. Designing an automobile and determining the minimum necessary maintenance requires thousands of people and awesome computing power. So if you accept the word of anyone who thinks they’re smarter than all those engineers and computers you need to find the zip code for La-La Land because you’re a candidate.
Even if some maintenance seems unnecessary and although we may never know the why, there is a reason for every service. Second guessing thousands of engineers is risky at best and financially ruinous at its extreme. In our valve adjustment example, the claim that no noise means no problem is completely wrong. On engines that require valve adjustment total silence usually leads to future damage.
Engines use intake valves to control the flow of fuel and air into each cylinder and exhaust valves to control exiting hot exhaust gasses. Valves are pushed open (flow turned on) by a camshaft and closed (flow turned off) by springs. During use, intake valves collect carbon deposits, which move them away from surrounding metal when closed. This creates excess space between the valves and the parts that push them open. Excess space allows the parts to slap against one another and a tap, tap tapping noise is born!
But how can a too quiet engine be bad? Exhaust valves are subjected to extremely high temperature which causes a loss of space rather than excess space. The loss of space between parts is the result of extreme heat that melts away tiny amounts of exhaust valve metal. The loss of metal makes them recede into the surrounding metal which reduces space between moving parts and simultaneously reduces noise.
The problem is that some space between the valves and the parts that push the valves open is necessary so exhaust valves can firmly touch the surrounding metal when they’re closed. Firm metal to metal contact is needed to dissipate heat which cools the exhaust valves. Without adjustment to maintain adequate space between parts, the valves can’t make firm contact, don’t dissipate heat properly and eventually the valves melt. It’s known as burnt valves and the repair bill is scary-expensive!
But this is not about valve adjustments per se, it is about never doing less than your owner’s manual suggests. More maintenance makes all cars last longer but less can kill them or painfully dent your credit line.
© Copyright 2/24/2009 Pat Goss. All Rights Reserved.