2000 Echo Overheating / Engine Knock

[geezer1]

2000 Echo with 250,000 miles. I change the oil myself but other than that I leave it for the dealer or a shop to work on.

Last summer, on a hot August day with the AC on, the red overheat light actually came on. Pulled off, let it cool down, turned off the AC, drove home with no problems. Never happened again. Still ... in the warmer months it feels and smells like the engine is overheating after long, "fast" highway drives or driving up to the mountains. And after getting the engine good and darned hot, if I press hard on the accelerator the engine knocks like crazy. If I press gently, no knock. Also, no knocking at all during the cold winter months.

I suspect - but I don't really know - that the engine knock is being caused by the engine getting too hot. Mass airflow sensor has been replaced recently as have spark plugs. I buy brand-name gas and run mid-grade fuel instead of regular. Catalytic converter, muffler, and O2 sensors replaced about 60,000 miles ago.

Took it to the dealer. Dealer couldn't detect knock but wanted to replace almost the entire cooling system, saying the water pump leaks, yada, yada. However, coolant level in overflow tank isn't dropping at all and no puddles on the garage floor.

I'm starting to get weary of spending money on this car but I do like it and it's great for my long-distance commute. I'm now thinking I should do some work on it myself and need to determine in what order I attack this problem. My first thought was to replace the thermostat. If that doesn't work, what next? EGR valve? Any suggestions?

Also, since I don't (until now) work on my car I'll need some guidance. Let's start with the thermostat. Easy-to-undestand instructions would be nice. Any takers?

[soloecho2]

Does the Rad fan run when the AC is selected on ?? Do you have any friends with a Scan gauge so that you can see the actual Water temp. Watch the temp at idle if it starts rising above 180 (does the fan come on) increase RPMs does the temp drop then it may be the water pump. Just a WAG to stat with.

[jambo101]

At 1/4 million miles your radiator might not have the coolant flow it once had,might be time for a new radiator..

[denman]

I'm with Jambo on suspecting the rad, .... a rad flush chemical may improve the coolant flow but replacing the rad is not vary expensive even with new antifreeze and hoses. Failing that, a good external cleaning of the rad may help air flow. You should hear the rad fan cycling on-off at idle in hot wx. , ...