Finding the Right Temp
Q: What's the normal operating temperature range of a Ford automatic transmission with overdrive? I don't have a stock application and don't run cooler lines to a heat exchanger in the radiator, because my vehicle is a modernized 1955 Willys Wagon with a modified 1986 Mustang 302 High-Output engine with electronic fuel injection. This powers a modified Ford transmission. It uses a large transmission cooler with a thermostatically controlled electric fan. The cooler is mounted under the frame near the rear axle because there's zero space up front due to the large radiator and air-conditioning condenser. At freeway speeds the temperature climbs to around 220-230 degrees, but cools to around 200 as soon as I slow down on an offramp. All the sources I've been in contact with only suggest "as cool as possible" or something close to the engine coolant temperature.
A: You're going to get a lot of different answers depending on whom you ask. Part of the reason is the variability among different model vehicles, transmissions, and driving conditions--plus, until recently, the rarity of factory-installed transmission temperature gauges on non-commercial applications. The service manual for a late-model Ford Super Duty pickup with an automatic transmission states normal operating transmission temperature to be 150 to 170 degrees F. Of course, these temperatures will amplify with speed and load due to the increase in friction. So the "cooler the better" theory seems to hold true in real-world applications. Aftermarket oil-cooler manufacturers use a graph depicting the decrease in transmission lifespan as average transmission-fluid temperatures increase. A significant drop in transmission longevity begins at temperatures above 175 degrees F, and a heat-induced chemical breakdown of the fluid at about 240. I wouldn't attempt to guess what the lowest temperature you can achieve on your tricked-out Willys might be, but reaching 230 on the highway without a cargo or trailer load appears to be on the high side. Perhaps the fan on the transmission cooler can be activated at a lower temperature by changing or adjusting the temperature switch. Or the fan may already be running full time to no avail due to the insufficient capacity of the cooling system. Mounting it to the frame at the rear axle isn't an ideal location for airflow.
Breaking the Trans Code
Q: The transmission in my 2004 Sport Trac 4x4 is beginning to shift hard and sometimes jumps when it finally shifts at around 3000 rpm. Eventually, the overdrive turns off automatically and the indicator light flashes, telling me the overdrive has been turned off. When I turn the engine off and restart it, overdrive's back on. I may not have any more problems for a day or so, but it's occurring about twice a week now.
A: This should be a straightforward job for a competent technician, but a handful for anyone else. The overdrive-off switch at the end of the shift lever has a simple function. If you don't touch it, the transmission shifts normally from first through fourth gear (overdrive). Once the switch is depressed, the O/D off indicator lights up on the instrument panel and the transmission only shifts from first through third gear. This eliminates O/D to enhance driveability while towing, taking a steep downgrade, or driving in poor traction conditions. The technical terms are "transmission control switch" and "transmission control indicator lamp," and both are linked to the powertrain control module. In your case, the indicator light is flashing, as opposed to continuously lit, which indicates a failure in the transmission's electronic pressure control circuit, or a monitored sensor. This particular fault appears to be intermittent. When the problem does occur, the PCM stores a trouble code in system memory, and then puts the transmission in a fixed "limp-home" mode. That's a default late hard shift pattern. Once the ignition is cycled (turned off and on again), the system goes back to normal operation until the failure repeats itself. It's going to require a system scan tool to read the transmission trouble codes and incoming data.