Symptoms
Overheating on hills or in traffic, coolant loss, or a cracked pressurized plastic coolant bottle. Comanche Club members suggest replacing the plastic bottle with an aluminum one, or converting the 1987–90 Renix closed system to the later open layout.
The fix, step by step
- Start cheap: test the cap, thermostat, fan clutch and electric fan, and clean the temperature-sender contacts.
- Pressure-test for leaks.
- Replace a cracked bottle and tired hoses, and the water pump if it weeps.
- If you convert a Renix truck to the open system, follow a documented write-up, such as Cruiser54's on Comanche Club, and bleed the system fully afterward.
Tools & part numbers
- Cooling-system pressure tester
- fan-clutch wrench
- drain pan
- funnel kit
Where to buy the parts
Crown 52027984 coolant bottle and cap, 1991–2001 XJ & MJQuadratec ↗Amazon ↗
Crown coolant bottle cap, XJ & MJQuadratec ↗Amazon ↗
Comanche water pump and cooling catalogRockAuto ↗
Hunting a used or discontinued part? Search eBay Motors for Jeep Comanche MJ parts →
Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.