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PostPosted: Sun Nov 08, 2009 10:28 am 
Retired Gearhead
Retired Gearhead
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Joined: Mon May 19, 2008 12:35 pm
Posts: 3989
Location: Ames, Iowa
Year and Trim: 98 Caravan is the daily driver 215K
Here is a method to reverse flush the engine, radiator and heater core separately. 95 SLE is described, others similar.

Disclaimer: Working on automobiles can result in damage to property, personal injury, or death. The author is not responsible for any losses incurred as a result of the use of this information. Persons using this information do so at their own risk.


Pressures: Your cooling system is designed to operate at pressures less than 20 psi. Most city water systems are pressurized to 80 or 90 psi. It is possible to damage the heater core, the radiator or internal engine gaskets by exceeding the design pressure. Make sure as you flush each component that a path remains open to the atmosphere, and that you only hold the flushing hose nozzle in place with your hand so that you can prevent or release the buildup of pressure as you flush. Do not clamp the garden hose to any engine hoses.

Initial Drain: Drain coolant from the radiator and part of the engine by undoing the splash shield and the lower radiator hose. Loosen the radiator cap to provide a vent. Catch and contain the first flushes from each component when the concentration of coolant is high. Don't leave puddles of coolant on the ground. Dogs and other animals can ingest the sweet tasting stuff and die from it. Check with your local municipality for proper methods of disposal of used coolant.

Engine: Remove the thermostat, then install the top radiator hose and thermostat hose fitting back on the engine with the radiator end of the top hose disconnected. Remove the lower radiator hose from the radiator. Wrap a rag around a garden hose nozzle and flush the engine through the top radiator hose until the water from the lower radiator hose runs clear.

Heater core: Remove the hoses from the tensioner assembly and flush through the bottom hose until the water from the top hose runs clear.

Radiator: Remove the top and bottom radiator hoses from the thermostat housing and the water pump. Wrap a rag around the hose nozzle and flush through the bottom radiator hose until the water from the top hose runs clear.

System: Run engine briefly and repeatedly to stir up sediment: Install a flushing tee (available at Wal-Mart) in the top heater hose by disconnecting the hose from the top fitting and using a spare piece of hose to connect to the tensioner assembly. Reconnect all but the top radiator hose at the thermostat. Fill the system with water at the thermostat opening, and then the radiator. Install a drilled thermostat. With the radiator cap removed, flush through the flushing tee, periodically starting the engine and allowing it to run for only 7-8 seconds at a time. Flushing must be done on a cold engine and the engine must not be allowed to get warm. Cold flushing water will crack hot engine castings. Depending on how cruddy the engine is, it may take 5 or 10 engine "mixes" until the water runs clear after the engine is run.

Filling: Remove the lower radiator hose from the radiator to drain the water from the radiator and partially from the engine. Remove the flushing tee and both heater hoses from the tensioner assembly and blow the water out of the heater core and hoses by mouth or by gentle air pressure. Reconnect the lower radiator hose. Hold the ends of the heater hoses at the same level and pour straight "mixes with any color" coolant in one hose until it begins to run out the other. Reconnect the heater hoses. Fill the engine at the thermostat opening, and then the radiator using straight coolant using the procedure described here. Considering the water remaining in the engine, that should give you at least a 50/50 mix. After cleaning it, fill the expansion tank with 50/50 mix. The system holds about 13 quarts, so you will need to add 6.5 quarts of pure coolant to get a 50/50 mix.

Bring engine to operating temperature and bleed air from screw on thermostat top radiator hose fitting. Air trapped in the heater core or engine may work its way to the radiator or expansion tank after a few operating cycles. Check the coolant level in the radiator and the expansion tank with the engine cold for a few days after flushing. The coolant in the radiator should be all the way to the top - if not, add 50/50 mix to fill the radiator. Likewise keep the expansion tank filled to the appropriate mark. The coolant level should stabilize within a few days.

Thanks to the Gearheads and Administrative Staff for review and helpful comments.


1998 3.8 Dodge Caravan 214K
2000 3.3 Dodge Caravan 175K
1949 Plymouth Special Deluxe 4-dr sedan 25K (needs some work!)

Last edited by bill buttermore on Sun Nov 08, 2009 10:29 am, edited 1 time in total.

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