Help/pointers on flushing 91 cooling system
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Joined: Mar 2017
Posts: 52
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Help/pointers on flushing 91 cooling system
So, Im just not sure what the best way to flush out the radiator is. The cap is separate, back near the firewall. And Ill get underneath to see where the drain plug is for the radiator..unless someone can tell me?. But with the cap being not directly attached to the radiator, whats the order of operations for this procedure? Im surprised there arent any helpful videos on YouTube either. Theres some for the LT cars, and for the earlier models with the cap on the radiator. But the ones like mine arent helping me much. Any suggestions much appreciated.
Race Director
Joined: Jul 2004
Posts: 12,681
Likes: 329
From: Scottsdale Arizona
I just had a look at the service manual (94). It looks like you open the petcock, remove the rad cap on the surge tank and then remove the thermostat as well as the knock sensors. Once it’s drained, you reinstall everything except the thermostat and refill with clean water. Run until warm. Drain and repeat until clean. Pretty tedious.
Instructor
Joined: Feb 2023
Posts: 155
Likes: 172
From: Louisville, Kentucky
What color is the coolant that's in it? If it's still yellow or green and just smells like anti-freeze, you don't need to flush. Just drain it and refill.
If it's brown and smells bad, then I'll grant you a flush might help.
Regardless of vehicle, the easiest way is to undo the upper and lower radiator hoses and flush it with the garden hose. Force the water in the top opening, catch it in a pan at the bottom. Flush it until the water comes out clear.
Then rig something up to connect the garden hose to the heater hose lines and flush the heater core. You can sort of flush the block out without pulling the thermostat. Just force the water in the radiator hose that doesn't go through the thermostat. Fill it up, let it drain. Repeat until it runs clean.
Then button it all back up and fill it with distilled water and coolant. Follow the normal bleeding procedure, and off you go.
You'll need a lot of containers to capture the discharge. You'll probably run 10 gallons through everything before it's clean.
I don't like the "flush" kits that have you cut a heater or radiator line and insert a fitting with a hose attachment in it. They're usually made of really cheap plastic that cracks and fails pretty quickly.
If it's brown and smells bad, then I'll grant you a flush might help.
Regardless of vehicle, the easiest way is to undo the upper and lower radiator hoses and flush it with the garden hose. Force the water in the top opening, catch it in a pan at the bottom. Flush it until the water comes out clear.
Then rig something up to connect the garden hose to the heater hose lines and flush the heater core. You can sort of flush the block out without pulling the thermostat. Just force the water in the radiator hose that doesn't go through the thermostat. Fill it up, let it drain. Repeat until it runs clean.
Then button it all back up and fill it with distilled water and coolant. Follow the normal bleeding procedure, and off you go.
You'll need a lot of containers to capture the discharge. You'll probably run 10 gallons through everything before it's clean.
I don't like the "flush" kits that have you cut a heater or radiator line and insert a fitting with a hose attachment in it. They're usually made of really cheap plastic that cracks and fails pretty quickly.
