Rusted Cooling System Diagnosis
 

So I had the thermostat fail one morning when the temp was about 2 degrees. Long story short, the cooling system has been rusted since I bought the '95 Blazer. I've flushed it with regular water and CLR. The system has been drained and rinsed and replaced antifreeze with universal green.
Intake manifold gaskets were replaced a while back and it now has a new thermostat.
I believe a leaking radiator cap was allowing the coolant out instead of pressurizing the system to raise the boiling point. However I'm not sure if this is the cause of the rusty system since the beginning. The radiator cap has not been replaced since I purchased the vehicle.
After I get it going again I am going to proceed with testing for an acidic system using Ph strips.
I will also be looking into electrolisys as a cause as well by looking for a grounding problem. So far I have tested between the intake manifold and battery ground with no voltage or resistance difference. I have not tested between the block and the battery though. When checking voltage, fluctuating voltage between .2 and 1Vdc between battery ground and the coolant overflow tank. This was measured with the bad radiator cap installed.
Unless the cold was getting to me, I could swear there was a surging idle that corresponded with the rise/fall in voltage measured at the overflow tank. It's an interesting idea that may also solve my idle problems as well.

Does anyone know where all the engine grounds are located so I could check them all in case one is missing? What about a path for voltage from the transmission by means of the cooler lines?

problem might be when u switched from dex-cool to green coolant that will cause problems from what iv read. only grounds are the ones running from the neg battery terminal to the block and another to the frame

OMG! (as the young people say) an electrolysis problem would cause a clearer condition in your coolant and a crust around the metal parts.
Surging is a vacuum problem. Check all your vac lines and egr. There is a hard plastic line that hits on the drivers side from the purge valve to the egr that always cracks. Tape it up if its cracked.

I didn't switch from Dex-Cool that I know of but I have been flushing flakes of brown powder out of the system repeatedly. I'll start with the radiator cap and see what happens. Regardless it's waiting until spring to get a good cleaning. Assuming it stays around that long. I'm getting pretty tired of working on it every couple months.

you said you switch to "universal green" thats not dex-cool. dex-cool is orange in color and shouldn't be mixed or switched with the green type

GM started with Dexcool in 1996. Your 1995 should have green, (ethylene glycol), unless it has a sticker stating that Dexcool needs to be used. Some of the very late production 1995's may have used Dexcool. Rule of thumb on 95, green ;)

As for electrolisys: With one DVOM probe on battery negative, and the other probe in the coolant in the radiator, maximum allowable is .3VDC

There are several grounds on the rear of each cylinder head.

TZFBird is the truck running ok, other then the idle problem. Capt says max.3VDC but that's with perfect test conditions, real accurate DVOM and guaranteed hard 99.99 contact's. IMO 1/2 a volte DC will not cause your motor to surge or bad idle.
95's coolant will show signs of rust contamination, we got Fe not Al.
I still say look for vac leak.


Chuck, you were correct, asked the wife, not doing it right....but no answer on what's wrong. Go figure?

Besides all the problems a TPS can cause it runs fine. I do agree that .5V will not affect something but that .5V has to come from somewhere. There could always be a 5V wire that is shorting and pulling down the source voltage by grounding through the cooling system. Just speculation at this point though.

Electrolisys is caused by a poor ground, usually the negative cable from the battery to the block. If it is grounded properly, and the cable is good, voltage will be less than .3VDC.