Have a 1999 Blazer LT and the water pump went out so we took it out to get it fixed at a shop. Also had it supposedly radiator flush and a new catalytic converter installed. It came back ran fine in town but drive 20 minutes on highway into another town slowed down and overheated and sounded like boiling. Took it back to shop they let it run for almost an hour never overheated.

Came back home drove out of town another day and did same thing. Gave up on shop so decided to put in new thermostat and check out myself with a friend. They put the green antifreeze in it? Changed thermostat and then no heat. Bled the air out and then a heater hose blew out. replaced both heater hoses and let it run about 30 minutes or so and bled air out again never overheated. Drove down hiway to test it out ran fine came back to town to drop off friend and started overheating again
Turned on heater and it cooled down some but by the time got home, about 3 blocks it was making boiling sound again.

Changed oil and checked for signs of bad head gasket but no sludge or anything. Runs fine but you cant drive it anywhere without overheating.

Should we flush it and put dexcool back in? Never had issue before this.

 

New water pump?

I'd put a Prestone-type tee fitting on heater hose and flush out with a garden hose. *A F T E R* running a heavy duty flush for a day or two.

 

Have you`ve checked the thermostat lately?If this is original part,chances are it failed like most gm parts do.Plus what about the water pump?Is this original that you know of..If so change that out too.Most of the time when GM/Chevy water pump goes out, it tends to leak out of the hole that`s located underneath the pulley.Or the main bearing will have a awful noise you couldn`t ignore.It also depends on what brand pump you used.Stay away from china made crappy parts from auto zone.Even though they say"Lifetime warranty" it`s still crap.I`ll give you an example what I`m talking about.I used to own a 1981 Chevy malibu that I had for 25yrs.I had to change out the water pump,because it was leaking out the hole I mentioned earlier.I was younger back in those days..Not knowing any better about auto zone parts,so I bought a cheap water pump from them.Did all the work myself.After I installed the water pump everything checked out o.k. No leaks or noises. 2 months later water pump failed again, it sprung a leak.So I had start the process all over again.Went back to auto zone, they replaced the water pump for free.I had to spend more money on radiator fluid,because I never use used radiator fluid.Installed the new pump,good to go.So now 6 months later the water pump failed again.That`s when I relized you get what you pay for.I was pissed,went back to autozone had them credit my credit card.A friend of mine told me about "Summit Racing.com" so I bought a "Edelbrock" aluminium water pump from summit.This water pump lasted 15 yrs. before I had to replace it again.So the rule of them in my book.."You get what you pay for" Never buy cheap made in china parts from auto zone, unless you can`t afford something that cost more.Napa sells some great parts too.

 

One place to look, especially if you are driving highway that has long hill's or mountain that you are climbing. Check out your fan clutch. I my self am not a fan of dexcool. I like to use the all makes all models yellow/green antifreeze. But that is also my opinion.

 

I had a camaro once that did exactly that . It turned out to be a rad that was fairly plugged.

 

I tend to agree with Strangerock. A quick old school test is to put your hand on the radiator (engine off) after driving a while and see if it's cool on the bottom and hot on top. My 99 did the same thing until I replaced the radiator. I see no mention of actual temps. How bad is it overheating? You mentioned that They put in the green stuff..is that after a full flush? Mixing the two types creates a brown sludge.

 

Sounds like you could have a blockage. I would recommend removing your thermostat and running with out and put some flush in it and drive it for a couple of days. Once you do that flush it with water, and it wouldn't be a bad idea to flush your heater core either. Then fill it with regular 50/50 green coolant and see if that helps.

 

OK so been busy as so to add to the blazer problem our big ol Sheppard mix started having bad seizures 2 in one day and we had to take Him to an emergency vet and my girlfriend had to have two wisdom teeth pulled.....

The shop put in the new water pump, flushed it, ànd put in the green antifreeze within the last few weeks. We replaced the thermostat a couple weeks ago and the heater core hoses right before I posted this thread. I only assume they being a shop fully flushed it before putting in the green antifreeze.

There are no hills or mountains this is the boring flat lands of Indiana.

Guess I'll try the radiator hand test , depending on results followed by another flush and maybe a clutch fan if not too expensive as the dog and dentist set us back quite a bundle. Hopefully it doesn't need a new radiator as it could destroy our budget this month!

 

If it is the fan clutch, I have a fan and clutch you can have if you want to pay shipping. It is just taking up space in storage.

 

Just a thought. I put a new waterpump on a car a long time ago and as soon as the car was warm enough it would start to overheat. It turned out that the new waterpump the impeller expanded enough to start slipping around the shaft thus disabling the waterpump. Had several mechanic friends tell me I was crazy, but replaced it with another one and everything was fine. With all the companies out there, including the manufacturer, a bad part is a common problem. So before you spend a lot of money doing other things you might want to check the waterpump again.