Obs Coolant Flush & Thermostat Replace

nubuilder · February 8, 2010

Well, I finally figured out how to drain the radiator. I used the pet-cock on the driver's side of the radiator. To get to it, I had to remove 10 bolts under the driver's side inner fender that bolt it to the frame and hold down the ECM. Then I pried the inner fender 2.5 inches away from the frame rail so I could get my hand up to turn the pet-cock. The pet-cock on mine was white. I could barely see it by looking down from above. The pet-cock turns less that a quarter turn before it stops. Don't be overly alarmed by this. It takes a little more pressure to get it open. Once you get it broke loose, it only takes a little more than half a turn to open it. The pet-cock does not come out of the radiator. It acts like a spicket and only lets the coolant out at a controlled rate. The upside to this is that it doesn't piss completely all over the place but the downside is that you can't get the big chunks of rust/contaminants out. I jacked up the passenger side of the truck about 2-3 inches; just enough to tilt the truck.

MAKE SURE TO WATCH YOUR GAUGE DURING THIS PROCESS.

I drained the original fluid, poured 1.5 gallons of distilled water in, drained, poured in another 1.5 gallons, drained. During this process, I ran the truck no more than 15 minutes each time. Then I poured in 2.5 gallons and one container of Prestone SuperFlush. I drove the truck around the block a couple of times and then let it idle for another 10 minutes; so probably 20-25 minutes; and then drained it. I then poured 1 gallon in two more times and drained. Finally I filled it up. I started with 2.25 gallons of Prestone DEX-COOL straight mix. The radiator was looking a little full. I mixed .25 gallons of coolant with .75 gallons of distilled water. I poured the mix so that I filled up the overflow tank between the HOT and COLD mark.

I'm just going to let the engine take care of sucking in what it needs. I'll regularly check it for a week to make sure all the levels are OK.

As far as the thermostat goes, it was super easy to remove. All you have to do is remove the 2 bolts that hold it on. The most difficult part is getting the old thermostat out of the intake manifold. Mine was sealed in there pretty good. I just put a flat screwdriver under the top thingy (you'll know when you see it) and pulled up. The thermostat popped out pretty suddenly and in a jerking motion. It turned out that I didn't damage the old thermostat at all. Now just put the new thermostat in and torque the bolts down to 20 ft lbs.

Side note

This whole process took me a very long time. The coolant capacity of the 1998 5.7L with A/C is supposed to be 20qts (5gal). Through my entire flushing process with all I added to the system, I ended up getting 7 gallons out. Don't count on all my inputs being correct. I also only got in close to 3 gallons. I'm hoping the engine sucks more down. All I can say is I must have been really, really, really low. Repetitive draining and circulating water is the only way to get everything out that you can.

For 1996-98 models, the manual says to only use DEX-COOL antifreeze. I think this is suppose to have something to do with the radiator being ??aluminum?? in these models. Apparently ethylene-glycol is corrosive when it comes in contact with aluminum. Whatever. I guess it's better to be safe then sorry.

Anyways, hope this helps someone. Any questions, feel free to post them. Good luck.