yes i have a 96 blazer 4.3 and having this problem of brown sludge... could this sludge cause a p0118 coolant sensor code to come up ive replace both sensors and thermostat, my blazer runs around 220-235 degrees after the switch but used to read 190-210 before the switch... (of course the replacements where covered in this sludge prob. making the reading off)like i said this sludge seems to be in everything especially the radiator... there is a sticker that says to use dexcool but i believe the owner before put regular antifreeze into it making it sludge up like this. i have no leaks or missing coolant just these codes which i believe are from this sludge any suggestion would be awesome

 

wow.. long posts to catch up on.. as a Mechanic in a small garage I have ran into the brown sludge before.. it would seem most of my experience is from people mixing the dex-cool with the old Green antifreeze. I havent seen it deteriorate anything, but it does slime up the system. it is a mess to clean out as well. we always just go with the mfg ... if it has dex cool in it, replace it with dex cool. if it is green, put the green back in it. flushing a system is a great thing and if you follow regular maint schedules that is rare and very great of you. most people get in a car, put gas in it, once in a while remember to change the oil cuz they are clueless where the dipstick is or how to use it. Cant tell you how many times i have seen no oil on the stick, cant see coolant at all in the overflow tank or even in the radiator or didnt know they need to check the transmission oil.. or more importantly change the trans fluid. I guess all i'm saying is, avoid the sludge, if it is low, put what is came with in it.. if you are unsure if it is dex cool or the green stuff, then ask a mechanic. it really isnt that hard to find out what is in the radiator.. just pouring something in it isnt always a smart thing.. any rate that is my 2 cents worth.

 

That is probably why you have a brown sludge in your system. When you switch from Dexcool to green coolant, you have to make sure your cooling system has been purged of all traces of Dexcool before you put the green coolant in. Dexcool and conventional green coolant don't play well together. When they mix they have a chemical reaction that produces the brown sludge you are experiencing in your vehicle.

 

I replaced the Dexcool in my 99 Blazer (80K miles) about 6 months after getting it in 2006 because the intake manifold gaskets were leaking. Replaced hoses and water pump too

I put Prestone green stuff in 2006 (80K miles)

Since then I replaced heater core at 110K miles and cracked radiator at 120K miles

I now have 130K plus miles and the green antifreeze is disappearing somewhere. yes I replaced the cap

I guess you could say I have mixed results with the Dexcool............

To be completely honest my 1998 Corvette (111000 miles) had the engine rebuilt 24K miles ago and I am going to keep the new Dexcool in it. I flushed it about 3K miles ago and put in new Dexcool when I changed the radiator.

The original owner of the Vette had the engine rebuilt at 86K miles because the water pump went out and cracked the block or head which was fixed, $4000 according to him for parts and machining and was rebuilt by his pal a Certified Viper mechanic from Dodge dealer so I am not concerned about it. I only put about 4-6K miles a year on it

Kinda funny (but not really) thing is my radiator in the Blazer cracked in the exact same place as the one in the Vette, right above the inlet hose on driver side. Luckily both were fairly cheap at Napa so I got low price for them at Autozone where I know the manager

 

i recently flushed out the coolong system of a '04 mercury sable, had the most awful brown crap in it. what i beileve happend was that the owner (who had prevoiusly had a g.m. product) topped off the coolant in this car with coolant they already had on hand, yep, dex-cool. the combination of green antifreeze & dex-cool is a bad thing, took 4 times of filling with water, letting it get to operating temp then draining to get it all out. ive heard of other cases where the mix of the 2 different coolants completely sludged up into a "gel". personally i prefer the "green" stuff, its not nearly as expensive and i pay attention to level and condition. my wife's '97 S-blazer had been changed over to "green" long before i got it, my old '92 chevy 3/4 ton had dex-cool in it and i left it be for the 5 years & 75,000 miles that i owned it. i didnt have a problem with it. but it is a bit of a pain to have to keep 2 different kinds of coolant on hand. at least with the blazer already having the green stuff, i dont have to keep a jug of antifreeze just for it, i can use the same stuff i run in the ranger. i beilive proper upkeep is the main thing, and never mix orange with green. the '97 S-blazer now has 187,000 miles on it. not sure how many on which coolant. i did put a radiator in it last spring, but thats irrelavant, the plastic tank had developed a small crack on the drivers side, after nearly 200,000 miles worth of thermal cycling, im not surprized it was failing. i did replace it with a full alluminum radiator.

 

My blazer still got the dex-cool and I have not had any problems in the 3 years I owned so far, My venture was already switched to green antifreeze before I got it