What causes the trans fluid to be black and thin when hot becomes stuck in second gear on a 1991 dodge Dakota 6-cylinder?

Black and thin transmission fluid in a hot 1991 Dodge Dakota 6-cylinder that's stuck in second gear strongly suggests severe internal transmission damage. The black color indicates burnt fluid, a result of excessive heat generated by friction from failing components. The thin consistency means the fluid has lost its viscosity, further exacerbating the problem. Being stuck in second gear points to specific internal failures.

Here are the likely culprits:

* Worn Clutch Packs: The clutch packs are responsible for engaging the different gears. Severe wear or damage to these packs leads to slippage (causing the thin, black fluid) and inability to engage higher gears properly (stuck in second).

* Low Fluid Level: While less likely to cause the *black* color, consistently low fluid level will drastically increase heat and wear, eventually resulting in burnt fluid and gear problems. It's crucial to check your fluid level (when the transmission is cool) to rule this out.

* Failed Valve Body: The valve body controls the flow of fluid to engage different gears. A malfunctioning valve body can restrict fluid flow, preventing proper gear shifts and contributing to overheating and fluid breakdown.

* Broken or Worn Internal Components: This is a broad category encompassing many possibilities like worn synchronizers, broken shafts, or damaged planetary gears. These internal mechanical failures generate extreme heat and friction, leading to the symptoms you're seeing.

* Torque Converter Problems: While less directly related to being stuck in second, a failing torque converter can cause excessive heat and contribute to the fluid degradation and overall transmission problems.

Important Note: It's highly unlikely you'll be able to fix this yourself. The damage is likely extensive and requires professional diagnosis and likely a major rebuild or even a transmission replacement. Attempting repairs yourself without the proper tools, knowledge, and experience could lead to further damage.

What to do:

1. Don't drive the truck: Continuing to drive it will cause further damage and could be dangerous.

2. Have it towed to a reputable transmission shop: They can perform a proper diagnosis and provide an accurate estimate for repair or replacement.

3. Prepare for a significant repair cost: Transmission rebuilds or replacements are expensive.

The black, thin fluid is a clear indication of serious internal problems. Ignoring it will only worsen the situation and increase the cost of repair.