![\"Cooling](\"https:\/\/plymouthgtx.net\/blog\/wp-content\/uploads\/2026\/06\/cooling-system-maintenance-for-plymouth-gtx-2.jpg\" "\\"Cooling")
<\/figure>\n\n\n\n\n\nAttach a garden hose to the \u201cT\u201d fitting and run water through the system until it runs clear. Be sure to flush the heater core by opening the inlet and outlet valves; a brief burst of water will remove any sediment that settled there. After the water runs clean, close the drain valve, reinstall the heater hose, and refill the system with a fresh 50\u201150 premix. Finally, bleed any trapped air by running the engine with the radiator cap off until the thermostat opens and the coolant circulates freely.<\/p>\n\n\n\n
Selecting the Proper Coolant for Mopar Engines<\/h2>\n\n\n\n
The original GTX specification called for a silicate\u2011free coolant, but many modern premixes contain silicates to protect aluminum radiators. Because the GTX\u2019s radiator is made of copper\u2011brass, a silicate\u2011free formula is still the safest choice. Look for a product labeled \u201cMopar approved\u201d or \u201cOEM style\u201d that contains organic acid technology (OAT) or hybrid organic acid technology (HOAT) without silicates.<\/p>\n\n\n\n
Mix the coolant with distilled water at a 1:1 ratio unless your local climate demands a different balance. In colder regions, a 60\u201140 mix (coolant to water) will lower the freezing point, while in hot desert areas a 40\u201160 mix can improve heat transfer. Always verify the mixture with a refractometer; the ideal reading for a 50\u201150 mix is about 34\u202f\u00b0Brix, which corresponds to a boiling point near 265\u202f\u00b0F.<\/p>\n\n\n\n
Maintaining the Thermostat, Water Pump, and Fan Assembly<\/h2>\n\n\n\n
The thermostat controls when coolant flows to the radiator. A stuck\u2011closed thermostat will cause the engine to overheat, while a stuck\u2011open unit can lead to low operating temperature and higher fuel consumption. To test the thermostat, remove it from the engine, place it in a pot of water, and heat the water gradually. The thermostat should begin to open around 180\u202f\u00b0F. If it opens too early or never opens, replace it with a new unit that matches the original part number.<\/p>\n\n\n\n
The water pump on a GTX is a cast\u2011iron impeller driven by the serpentine belt. Listen for a whining sound that changes with engine speed; a change in pitch often signals bearing wear. When replacing the pump, use a new gasket and torque the bolts to the manufacturer\u2019s specification, usually about 20\u202flb\u2011ft. The fan clutch should be inspected for free rotation when the engine is off; resistance can indicate worn bearings that will affect cooling under load.<\/p>\n\n\n\n
Leak Detection and Pressure Testing the System<\/h2>\n\n\n\n
After a flush and component replacement, a pressure test will reveal hidden leaks. Attach a radiator pressure tester to the filler neck, pump it up to the pressure rating printed on the radiator cap (typically 15\u202fpsi), and watch for any drop in pressure over a few minutes. If the pressure holds, the system is sealed; if it drops, inspect the radiator seams, hose connections, and the water pump housing for small cracks or corrosion.<\/p>\n\n\n\n Pay special attention to the heater core connections. A slow leak there can manifest as a damp floorboard inside the cabin. Use a flashlight and a piece of white paper to spot tiny drips. Tightening the hose clamps or replacing a cracked core will prevent coolant loss that can later damage the engine\u2019s internal seals.<\/p>\n\n\n\n During winter, keep the GTX\u2019s coolant topped up and consider adding a small amount of antifreeze concentrate to protect against accidental freezing. In summer, schedule a coolant check after every 2,000 miles of highway driving, because the high load on the engine can accelerate corrosion. Never open the radiator cap when the engine is hot; the pressure can cause boiling coolant to spray and cause severe burns.<\/p>\n\n\n\n A frequent misstep among classic car owners is mixing different coolant brands or types. The resulting chemical reaction can create sludge that clogs the radiator and heater core. Stick to a single brand and perform a full flush whenever you switch formulas. Also, avoid using tap water for the premix; minerals in tap water can precipitate inside the cooling passages and create deposits that reduce heat transfer efficiency.<\/p>\n","protected":false},"excerpt":{"rendered":" The Plymouth GTX is a classic muscle car that rewards careful stewardship, and a well\u2011tuned cooling system is one of the most visible signs of that care. When the engine runs at the right temperature, power is smooth, fuel consumption stays reasonable, and the risk of costly overheating damage drops dramatically. This guide walks you […]<\/p>\n","protected":false},"author":1,"featured_media":481,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-484","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog"],"yoast_head":"\n![\"Cooling](\"https:\/\/plymouthgtx.net\/blog\/wp-content\/uploads\/2026\/06\/cooling-system-maintenance-for-plymouth-gtx-3.jpg\" "\\"Cooling")
<\/figure>\n\n\n\n\n\nSeasonal Care Tips and Common Mistakes to Avoid<\/h2>\n\n\n\n