- Buyer's Guide
It is hurricane season along the Gulf Coast and I am presently down to one car. In the event of evacuation, coastal residents desire more than one personal vehicle to carry out precious items such as pictures, clothes and records. For this reason, I wanted to purchase a used pickup truck as a second vehicle for temporary duty.
My father gave me his 1982 Chevy S10 pickup with only 59,000 miles on the odometer. For the second time this year, the crankshaft broke, and I parked it. (Like most mechanics, I repair my own vehicles only after taking care of customers’ cars first.)
I thought I had the perfect solution: buy another S10 with reasonable mileage; this one a 1997 model. The only apparent problem was a broken air conditioner. I planned to fix the A/C, drive it for 8 to 10 months, then sell it for what I paid for it. After checking the dipstick on the transmission, I found more repairs to be made; slightly burned oil with little chalky black bits clinging to the stick. These were pieces of burned seals. Upon closer inspection, I saw a replaced water pump and lower hose. This was evidence that the truck had overheated, and the transmission fluid was burned. In less than two months, the transmission was going to fail. With these looming repairs, I decided not to buy this truck.
In a discussion about repairing transmissions, how do whales, government legislation and Hernando Cortez come up in conversation?
Transmission repairs fall into two categories, simple fluid exchange service or catastrophic repairs. Simple fluid exchanges are recommended in service manuals usually ranging from intervals of 30,000 to 100,000 miles. Service intervals of 100,000 miles suggest that there is not much strain for the modern automatic transmission fluid (ATF) to do its job.
The 100,000-mile interval used to be the norm in the 1950s and 1960s. What caused the shortened recommended interval? The Endangered Species Act of 1973.
Thirty to forty years ago, we had the perfect ingredients for long transmission life: low heat demand and a ready supply of whale oil. Most of the cars in junkyards arrived with functioning transmissions. We did not have the heat demands on the motors we have today. In previous columns, I’ve written of the increase of thermostat temperatures - and that the transmission oil used typically was almost perfect. Mechanics never changed the fluid until fixing a leaking gasket or seal. Worn out and failed transmissions were rare. There were not as many franchised transmission shops back then.
The trouble was, thousands of sperm whales were killed every year to acquire the almost 29 million pounds of whale oil used in ATF. Sperm whale oil is an almost pure ester, not really an oil at all. So the Endangered Species Act of 1973 was brought about partly by automatic transmissions.
At the same time, along with the reduced harvest of sperm whale, the automatic transmission industry was burdened with the demands of front-wheel drive engines and the increased restrictions on emissions. Many devices were added to motors to accomplish this, which increased the overall temperatures of the motors. Parts of these more restrictive goals were reached by elevating the coolant temperature thermostat, and transmission temperatures were increased even higher.
The new formulations for ATF worked fine and lasted for as long as 100,000 miles for temperatures below 175°F. However, I don’t know a single car made since 1980 that has a thermostat below 185°F. Most are 192°F to 195°F, and often even 10 degrees higher. Most manufacturers route the transmission fluid through a cooler built in the bottom or downstream side of a cross-flow radiator. Essentially, the transmission fluid is cooled by the water in the radiator that itself is near the boiling point at one atmosphere, 212°F.
The radiator cooling fans in front-wheel drive cars are set to engage only when the water temperature exceeds 200°F to 210°F. So what effect does that have on the ATF life? The Arrhenius rule (which deals with chemical reactivity) suggests that for every 18-degree Fahrenheit increase in oil temperature, the lubricant lifecycle is reduced by half. If the oil temperature is 200°F (vs. 182°F) then 50,000 miles is the expected life of the fluid. Many vehicles are above 200°F and need to be serviced at 50,000 miles or perhaps even 25,000.
First and foremost, an automatic transmission is fluid coupling with selective gears. Imagine two fans facing one another. One fan is powered, and pushes air across the other fan, which in turn powers the other fan. In the automatic transmission, a similar configuration exists for the torque converter. The fluid pushed by one plate moves across the other plate, which in turn drives the gears via a fluid coupling. This part of the transmission holds 70 percent of the AFT fluid. As long as conditions remain cool, a good nonfoaming, noncorrosive, moderate viscosity fluid will work. But they generally are not cool, and sperm whale oil (really an ester), is no longer available. So what are we going to use?
Spanish explorer Hernando Cortez was introduced to a medicinal skin oil and lubricant that the Aztecs used called Jojoba. It is almost the chemical duplicate of spermaceti, the oil from the head of the sperm whale. Both are esters, not (hydrocarbon) oils. Esters occur when an acid is reacted with an alcohol. Esters have strong atomic bonds and do not oxidize easily, They do however handle heat well. Rapeseed or canola oil is also in this category and is used in some transmission additives.
Now, sperm whales are no longer in danger of being harvested for their oil, because a substitute has been found. Environmentally friendly oils have been produced that can do the old job with the old parameters. Emission laws force us to operate at higher temperatures, however, heating the ATF beyond its ability to endure for more than 50,000 miles. So what to do?
The automotive tip for the month is this: If you ever break a hose, lose a water pump, or overheat your car in any fashion, change the burned ATF. Transmission repairs are seldom less than $1,500.
The tip for the decade, indeed the life of your car, is this: Put a transmission cooler on your vehicle, mounted outside the radiator loop. Put it next to the oil cooler.