[Tin Injun Tom]

My brother just emailed, had a puddle of coolant under the cab of his '96 Siera this morning. Dropped off his truck to have it checked out.
He's been adding the Prestone yellow stuff (for the last six months) that's supposed to be OK to mix with the Dex-Cool. Last couple of days, he's been hearing gurgling noises coming from the heater core area. After searching the net today, he said he found numerous horror stories about Dex-Cool and the 4.3L on the internet.

He wonders if he did harm to the cooling system by adding the "yellow stuff" to the OEM orange coolant.
And how much labor would be involved if the heater core has to be replaced. Truck has A/C

Thanks,
Tom

[engineer]

if he has been adding coolant for the last several months, there was already a leak that should have been fixed, now the leak is more apparent, so when he gets the heater core fixed, he should replace all the coolant with the same type. no mixing.

[Larry P]

Noise in the heater core could be that its was just low on coolant. It would gurgle on accell or under load a little. Dosent matter he mixed the coolant. The T Blazers had the biggest sludge problem with the 4.3 and dexcool. Did he find out the core is the leak or was it the intake gasket running down the back of the engine. Either job is no big deal. And like engineer said just flush it out and stay with the same coolant brand and it will be fine.

[speedshopmike]

agree with engineer; no mixing!

[speedshopmike]

dexcool sludge is caused by air in the system.

[Tin Injun Tom]

Thanks for the tips.
It was discovered to be the intake gasket that was leaking. Typical for the 4.3.
The truck has 118K so it's not unexpected. I would think if he heard swishing/gurgling from the heater core (when he revved the engine), it would indicate good circulation. That tells me there shouldn't be a sludge problem. Going to have the whole system flushed, new thermastat, etc.

He hadn't added a great deal of antifreeze, since last summer. Just bought one gallon, and used it to keep the overflow jug full.

[Region Warrior]

Dont know about the yellow stuff, but mixing the older GM green coolant and the new Dexcool is fine.
Just need to go by the early coolant change intervals.

[69lm69gp]

My understanding, from when Dexcool first came out, is that once you mix Dexcool and ethylene glycol (green) coolant is that testing for the freeze protection is no longer valid.

[Larry P]

Once the dexcool is mixed it goes to the shorter change interval as Region Warrior said, we use a recyled coolant at the dealership and all brands and colors get mixed ,then filtered and some wynns produts are added to it. And the freeze protecion is fine for -35 F ,you just have to flush at 30k. If you flush dexcool at 30k and even refill with dexcool it usuall wont sludge.

[stimpy]

my 96 had no sludge in it when I drain and changed At 95K and I drained it from the bottom of the block . but I also kept it topped off with dex and DI water too .