Our 1989 Cutlass Ciera goes about 15 miles and then will act like it shift down the engine dies After 5 minutes you can go again It runs in park when put drive?

The symptoms you describe with your 1989 Cutlass Ciera – running for about 15 miles, then seemingly downshifting before dying, restarting after 5 minutes, and running fine in Park but not Drive – strongly suggest a problem related to heat and/or the transmission. Here's a breakdown of likely culprits:

* Transmission Fluid Overheating: This is the most probable cause. After 15 miles, the transmission fluid might be overheating. When it cools down (the 5-minute wait), it's able to function again. Look for signs of leaking transmission fluid under the car. Low fluid levels or fluid that's dark brown or smells burnt are strong indicators of a problem.

* Transmission Cooler Failure: The transmission cooler (often located in front of the radiator) may be clogged or failing, preventing adequate cooling of the transmission fluid.

* Transmission Internal Problems: More serious internal problems within the transmission, like worn clutches or a failing torque converter, could also cause overheating and intermittent failure. This is more likely if the fluid looks bad.

* Neutral Safety Switch: While less likely given your description (it runs in Park), a faulty neutral safety switch could prevent the car from starting or running in gear. However, if it's intermittent and heat-related, it could be a contributing factor.

What to do:

1. Check the Transmission Fluid: This is the most crucial first step. Locate the transmission dipstick (usually near the engine, often marked with a transmission symbol), check the fluid level, and examine its condition. If it's low, dark, or burnt-smelling, you likely have a significant transmission problem.

2. Inspect the Transmission Cooler: Carefully examine the transmission cooler lines and the cooler itself for leaks, damage, or blockage.

3. Consider the Temperature: Is this happening more often on hot days or after prolonged periods of driving? This would further point towards a heat-related issue.

4. Get it Diagnosed: Take your Cutlass Ciera to a qualified mechanic specializing in older vehicles. They can perform a proper diagnosis, including checking the transmission fluid, inspecting the cooler, and potentially performing more advanced diagnostics to pinpoint the exact cause.

Important Note: Continuing to drive the car with a potentially overheating transmission could cause significant and costly damage. It's best to limit driving until the problem is diagnosed and repaired.