Hi guys! I'm new to the forum, so my lack of knowledge in the blazer world is going to be scary to say the least. I'm working on my mom's 99 blazer. Itsthe 4.3 auto with 175k on it. All original... Just your normal tune up stuff is all that has been done.
It has been running very rough lately, like its missing. She paid a mechanic to change the plugs, wires, and cap a few months back. It is now doing the same thing again. She asked me to look at it and when I picked it up, I noticed it was running a little bit hotter than normal (about 3/4 on the gauge) It is not leaking fluid onto the ground. I dont see any antifreezein the oil and the exhaust is normal. Im wondering where Im losing fluid, and if its related to the engine running rough? Maybe an intake manifold gasket? Any information is appreciated.

 

You can get a product that will test the coolant for byproducts of combustion. This will let you know if you have a head gasket problem. You can pull the plugs (watch out for #3 it can be "fun") and check for signs of coolant (crystal clean plug).

Is the coolant level actually dropping? A failing thermostat or a weak radiator cap (both quick, easy, and cheap things to replace) could cause a high running temperature. I would start there and do an engine/radiator/heater-core flush to get the coolant replaced and any gunk out. While you are at it, clean the radiator of any debris that it may have collected over the years.

As far as the running rough, do you think it is attributed to the higher operating temperature? I would remove and clean the throttle body (remove the IAC valve and thoroughly clean the passage), remove the MAF sensor and give that a good cleaning with MAF specific cleaner, and remove the EGR valve and give that a thorough cleaning. All of these items can affect the operation of the motor.

Also, check the spark plug wires where the attach to the distributor cap to make sure that they are not pushed off of the towers. If air gets trapped inside them, the pressure from the air expanding when heated can push the plug wires off. I like to take a small screw driver and put it into the boot while I push it on. This allows the air to escape.

Hope this helps! If you need more information about any of the things I listed, run a search on those keywords as they have been discussed in other threads.

Good luck!!