So I changed my coolant today. Couldn't find those drain plugs on the block, so I said screw that and just drained the radiator, took a garden hose and flushed it out. I also cleaned out the overflow tank (I followed the Haynes manual), which meant I had to take the battery out as well.

I also put a new thermostat in (whoever designed where the thermo housing is on the 3.4 needs to die an extremely slow death). I couldn't get to the driver side screw, so I actually took off the throttle body. I just put in a new stock replacement thermo.

Filled up the radiator and overflow tank with fluid (I wasn't sure of how much....I just put 1 gallon in) and drove around.

Now the problems: My car overheats big time now...on the highway, it stays at 190-220, with rapid fluctuation between that area (maybe I didn't put enough fluid in).

the BIG one: everytime I hit the brakes, the whole car dims. The radio shuts off or dims big time when I hit the high beams, and the needle falls deep in the yellow before bouncing back out with the AC on...WTF is going on???

**sigh** When I try to fix things, it seems like more things break

 

Not sure about the V-6.... Are there air-bleeder screw????

Check the battery connections... Are you reading 13.8-14.2 volts at the battery at idle??

 

You probably have loose battery / electrical connections... you might also be losing your alternator too... Try filling up with more coolant before taking everything apart again, if all else fails I believe I'd blame the thermo... but are your fans kicking in?

 

OK, I seemed to have fixed the electrical issue...I cleaned the battery terminals and they seem OK. I'll drive around tonight to see how the headlights are.

The radiator: I filled it up to the top,, started , and watched for bubbles. They came out....but the level of coolant never went down (this is all w/ the cap off). The temp hit 210, and then fluid started to jump up and overflow, so I shut the car off (big mistake)...coolant shoot almost a foot up from the radiator like a geizer

So I took a break, let it cool, and filled up the radiator again with coolant to the top, started it, and waited for bubbles. This time, there were more bubbles and the coolant level dropped because the thermo must've opened so I filled up the whole radiator with fluid, waited a bit again, and put the cap on, then put the rest in the resovior. Drove the car around and the temp stays normal.

I guess I fixed it. But what temp do the fans turn on? Mine seem to turn on pretty late. And how do I know all the air is out? Should I repeat this whole thing again? What happens if I overfill?

And there is no bleeder screw on a 3.4

 

Low fans kick in around alittle before the first quarter, Hi fan kicks in alittle before the halfway point (IF it even makes it that far) for me... Check your sending unit... it's located on the driverside right into the block... if it's bad your gauge will be off... On my dad's Z28 this sending unit was bad and kept telling us that the car was overheating (alittle before the 4th quarter) when it was REALLY not even HALFWAY that hot!!!... The way we found out was when a mechanic read the actuall temperature while it was idle...The temperature read about 190 when the actual gauge was ready to redline and we were wandering why the fans never kicked in!!! your FANS will kick in at the right temperature, and if the Hi fans have to kick in at a high temperature, you'll get a check gauges light... have you got that yet? Basicly the fans come on at the right time and only your gauge will be off.

When it says your car is overheating, how does it feel or drive? is it real sluggish? is steam emitting from it?... If coolant is circulating through it I doubt if its really that hot... check that sending unit, there's a good chance that your car's running just fine and just your GAUGE is off by 80 degree's... (thats what it was on the Z28... until we changed that sending unit)

The gauge will flucuate like crazy too, explaining your flucuations at highway speeds.

If this IS the problem, then your car is not overheating and the fans are coming on at just the right time, the GAUGE is just telling you it's 80 degrees hotter than it really is... This could have easily have been done when you hosed water in it perhaps.

If you replace it, go with the GM part because they hold up longer and give more accurate readings to the gauge.

Btw... when you add coolant... turn the car ON first... THEN pour coolant... you don't see the true coolant level until your car is on... (just WHATEVER you do, under NO CIRCUMSTANCES open it while it's HOT!!! My dad gained 3rd degree burns and had his hand eaten up for doing that...)