Evening guys. Looking for a fairly foolproof way to change/flush my coolant on my 85 Cutty with 3.8 V6. I have seen several different ways. What do you all prefer and is there a way to do it without a evac/refill system? Thanks!
CUTLASS Best way to flush/change coolant?
- Thread starter RICKDIZZLE
- Start date
Warm up engine to circulate the water, drain completely from lower petcock, close petcock, stick open hose as far as it will go in thru the fill inlet, refill and restart motor. Do it about twice depending on how dirty the coolant looks. No need to disconnect hoses. I have installed a petcock at one of the block threaded plugs so that it drains from the block too.
No block will drain completely unless you open the block drains. And no block drain will open without a dose of C4. For a really foolproof drain you need to get them open, chase the threads, and replace the plug with a liberal dose of anti-seize thread dope. I have searched in vain for a stainless steel replacement drain plug. That would be the best option if it existed. Once the drains are open, then you can open the radiator drain, open a radiator hose, and flush from above with a garden hose. If the coolant is rusty/cruddy, then treat with a cleaner and flush until clean. I have seen systems so cruddy that it took a dose of Cascade dish washing detergent to get it clean. You fill with clean water, dose it, run it for several hours, drain, and flush several times. The down side to that is that the Cascade will find ALL leaks, especially in the radiator. And it will often eat the water pump. But on a really fugly dirty system, that should be replaced anyway.
I THINK they're 1/4"-18 NPT threads. Here's a stainless plug with a magnet on it. Supposed to be for oil galleries or whatever, but I believe it's the same size as coolant drain plugs, IIRC. I may not be recalling correctly, so if that's the case, then never mind. 🙂
I thought they were 1/8" pipe threads. At least my Pontiac engines are. Or I could be totally wrong. EDIT: Yes, old Pontiacs use 1/8" npt, other are 1/4". And they do sell stainless steel plugs. These are 304 stainless, so probably marine grade. I should have known that.................................................................................................................
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I used brass pipe plugs for the block when I put my engine together. They match the brass core plugs.
Here's how I've always flushed mine:
Drain existing coolant and leave petcock open. Take off the upper hose at the radiator and angle it off to the side so it can flow (don't drench anything electronic). Stick an open garden hose (no nozzle) in the Rad Cap hole and turn it on full. The petcock won't be able to keep up with the hose and the rad will slowly fill. Once this happens, turn the car on and let it run. Eventually it will get up to temp and the thermo will open and start flushing the contents of the block. Let the cycle run a few times until nothing but clear water comes out the upper rad hose. Cut the engine off, turn the hose off and remove, leave the top hose off, let the rad drain. Close the petcock and fill with premixed antifreeze high enough to see but not get close to the upper hose opening. Run the engine again and let the thermo cycle until you just start seeing a steady stream of the coolant. Turn the engine off, reattach the upper hose and fill all the way. With the engine up to temp it wont take long to purge the rest.
Hutch
Here's how I've always flushed mine:
Drain existing coolant and leave petcock open. Take off the upper hose at the radiator and angle it off to the side so it can flow (don't drench anything electronic). Stick an open garden hose (no nozzle) in the Rad Cap hole and turn it on full. The petcock won't be able to keep up with the hose and the rad will slowly fill. Once this happens, turn the car on and let it run. Eventually it will get up to temp and the thermo will open and start flushing the contents of the block. Let the cycle run a few times until nothing but clear water comes out the upper rad hose. Cut the engine off, turn the hose off and remove, leave the top hose off, let the rad drain. Close the petcock and fill with premixed antifreeze high enough to see but not get close to the upper hose opening. Run the engine again and let the thermo cycle until you just start seeing a steady stream of the coolant. Turn the engine off, reattach the upper hose and fill all the way. With the engine up to temp it wont take long to purge the rest.
Hutch
Thank you. Makes perfect sense. How many gallons of premix you think are good to grab?
2 Gal usually does the trick, but I usually get 3 in case of spillage loss. It also doesn't hurt to have some spare on hand.
Hutch
Someone smarter than me pointed out that if you are not going to mix your full strength coolant with distilled water, than you just may as well get the pre-mix. That way you don't get tap water in your system to cause issues.
There is no easy way to do this if you want to be thorough.
Drain, fill with water, run until hot enough to open thermostat, cool, drain. Repeat until draining is clear. It will either become clear after 4 or 5 times or it's really dirty.
Then I would repeat this twice but fill with distilled water.
Then a final drain. Now look up the cooling system capacity. If it's 16L. You NEED to add 8L of coolant to be a 50/50 mix. If you can not get 8L in, undo a heater hose or something near the rear to let water out or pour it in the reservoir.
If you get 8L in, top off with distilled. You might need a couple heat cycles to allow air out, coolant in.
This is only my procedure for my own cars. Zero chance a shop will spend this much time with a flush and fill.
Drain, fill with water, run until hot enough to open thermostat, cool, drain. Repeat until draining is clear. It will either become clear after 4 or 5 times or it's really dirty.
Then I would repeat this twice but fill with distilled water.
Then a final drain. Now look up the cooling system capacity. If it's 16L. You NEED to add 8L of coolant to be a 50/50 mix. If you can not get 8L in, undo a heater hose or something near the rear to let water out or pour it in the reservoir.
If you get 8L in, top off with distilled. You might need a couple heat cycles to allow air out, coolant in.
This is only my procedure for my own cars. Zero chance a shop will spend this much time with a flush and fill.
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