Changing coolant
Burning Brakes
Joined: Jun 2016
Posts: 761
Likes: 66
From: Fitzwilliam New Hampshire
You should do a complete coolant flush that involves removing the knock sensors and flushing the block. No need to use dexcool, reg old school green glycol is what belongs in the system, don't chance mixing the 2 types if you don't get all the original out, like some still in heater core, that's a no-no. Why would you change from what's recommended? Also if you use straight anti freeze, not premix, best to mix with distilled water, not tap water for a 50/50 mix.
Last edited by A Peter C4; May 14, 2017 at 08:42 PM.
Heel & Toe
Joined: May 2012
Posts: 15
Likes: 1
From: Scottsdale Arizona
My '88 Owners Manual calls for using Ethylene glycol which is the conventional green coolant rather than the GM DexCool coolant. I took my car to the local Chevy dealer who topped off my coolant with the DexCool stuff and it turned my cooling system into a grey oily solution that was most difficult to flush out. I am now back to the conventional ethylene glycol coolant and the car's oil temperature seems to be more consistent than previously noticed. So, I suggest you use whatever is in the owners manual.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
No real reason to "upgrade" to DexCool. DexCool does allow for not needing to do a coolant flush for 5 years but the regular ethylene glycol coolant is usually changed every two years but it works well and will cost less.
The biggest difficulty in going with DexCool is having to make sure you completely flush all traces of the green coolant. The two coolants don't play well together when mixed. You could get a nasty brown liquid that can cause blockages in the system.
As mentioned, use distilled water when mixing the green coolant. You can find distilled water at any grocery store for something like a buck per gallon. And buy the concentrate version of the green coolant. It's available in a 50/50 mix, but it's more expensive than the concentrate.
The flush/refill procedure in the FSM calls for draining the old coolant and fill with water. Start the engine and let it get to operating temp. Then drain and refill two more times. At that point you can refill with new coolant. It's a good idea to remove the knock sensors from the block which will insure that all of the old coolant is drained. It's also a good time to replace the upper and lower radiator hoses at the same time.
And don't let any coolant drain down over the OptiSpark. Bad (expensive
) things will happen. 
The biggest difficulty in going with DexCool is having to make sure you completely flush all traces of the green coolant. The two coolants don't play well together when mixed. You could get a nasty brown liquid that can cause blockages in the system.
As mentioned, use distilled water when mixing the green coolant. You can find distilled water at any grocery store for something like a buck per gallon. And buy the concentrate version of the green coolant. It's available in a 50/50 mix, but it's more expensive than the concentrate.
The flush/refill procedure in the FSM calls for draining the old coolant and fill with water. Start the engine and let it get to operating temp. Then drain and refill two more times. At that point you can refill with new coolant. It's a good idea to remove the knock sensors from the block which will insure that all of the old coolant is drained. It's also a good time to replace the upper and lower radiator hoses at the same time.
And don't let any coolant drain down over the OptiSpark. Bad (expensive
) things will happen.
