Ok guys, need some advice, popped the radiator cap off my 02 Blazer LS, 4.3 vortec engine and the top of the radiator was, not saying it was full but all around the cap was this greasy looking junk, since I've only owned it about 2 months, I do not know what antifreeze the PO used in the engine, but this can't be doing the engine any good, runs excellent but was in the process of changing the thermostat to a 195 deg. as the temp gage only goes up to the first tick mark pass the first large mark and I know it can't be reaching operating temp. Will this temp cause a MPG problem, the upper console is registering 19.6 MPG, is this the most I can expect from it?

 

If its rusty looking its the dexcool antifreeze gm uses. I flushed mine out and used the green stuff.

 

Do a search for Dex-Cool. It's been a PITA for a lot of people.

 

We are not going into a "DexCool vs..." thread.

Do a complete coolant system drain and flush, fill with the coolant of your choice and install a new radiator cap.

 

Lock it!

 

 

What color is the "greasy looking junk"?

If it is white (ish) it is oil and you have a bigger problem.