Cooling System Problem - 04 Impala

I have a 2004 Chevy Impala 3.4L V6. It seems that after driving at freeway speeds for about 20 minutes, the engine "overheats" and goes into it's sputtering "protection mode". This had been happening during my commute to work at just about the same point every day, right when I get off the freeway. Lately, however, it seems be be happening earlier.

The funny thing is this: The temp gauge will stay in the middle during the entire trip, then rise extremely rapidly (a couple seconds) to the highest level when this happens. Sometimes during the ride the gauge will rise rapidly (not reaching the hot stage) and then rapidly return back to the mid-point. Coolant levels are good, both fans are running, and the temperature of the coolant seems to be ok (not boiling or anything) when I park the car after this condition.

The problem happened again the other night just as I was arriving home from work. I noticed that after I turned off the car (with the gauge pegged at hot) there was a constant clicking sound coming from the engine compartment. I opened the hood and the sound seemed to be coming from the area underneath the coolant recovery tank. I placed a finger on the tank and could feel it vibrate lightly with each click.

Occasionally I smell what I believe to be the odor of burning coolant during and after driving, although the timing of this doesn't match up with the temp gauge issue.

Also, with the weather getting colder I have just started using the heat in my car. It only heats while I am accelerating. The air from the vents is ice cold when idling. I think this may be related.

I'd love to be able to fix this problem myself if I can, but I need an accurate disgnosis first. Money is a little short these days.

Please help! Thanks!

Sounds like there is air in the system. If the coolant level is not low than I would almost suspect head gaskets as the source of the air. Not uncommon for them to fail on a 3.4. You can have a shop "sniff" the coolant with an exhaust analyzer to see if there are hydrocarbons in the coolant. There should be little to none! I would suspect you would see over 500ppm.

Thanks for the reply! Without having a shop sample the exhaust, is there another way to investigate if this is the problem? Also, is a head gasket easy or complex to replace if that's the problem? Thanks!

There not terribly complicated. If you have ever done an intake gasket you where 3/4's of the way there.