Arguments for 20W-50:
* High Temperatures: 20W-50 is a heavier oil, offering better protection at high temperatures. If you frequently tow heavy loads, drive in extremely hot climates, or your engine is prone to overheating, 20W-50 might offer better protection against wear than a lighter weight oil. Older engines, especially those with higher mileage, can benefit from the added protection.
* Leak Prevention: In older engines with worn seals and gaskets, the thicker 20W-50 may help reduce leaks by providing a better seal.
Arguments against 20W-50:
* Increased Engine Strain: A heavier oil increases the engine's work in pumping the oil. This can lead to slightly reduced fuel economy and increased wear on the oil pump in some cases. A 1990 Wrangler likely has a somewhat simpler engine, and this might be more pronounced.
* Cold Weather Starting: The "20" in 20W-50 refers to its cold-weather viscosity. While it will flow better than a straight 50-weight oil, it might be difficult to start in very cold temperatures compared to a lighter weight oil like 10W-30 or 5W-30.
* Modern Engine Design: Modern engines are designed for lighter weight oils. While a 1990 Wrangler is not strictly modern, using an oil much thicker than recommended could still cause issues.
What you should do:
1. Check your owner's manual: The most important resource is your Jeep's owner's manual. It will specify the recommended oil viscosity and weight. This should be your primary guide.
2. Consider your climate and driving conditions: If you live in a hot climate or frequently tow heavy loads, a slightly thicker oil might be acceptable *if* the owner's manual allows it or suggests a range.
3. Consult a mechanic: A knowledgeable mechanic familiar with older Jeeps can offer specific advice based on your Wrangler's condition and your driving habits.
In short, without knowing your specific climate, driving conditions, and the overall condition of your engine, it's impossible to say definitively whether 20W-50 is good or bad. Always prioritize the recommendations in your owner's manual. Using the wrong oil viscosity can cause damage to your engine.
