As another poster said ANY speculation or other testing is pointless until the owner takes FIVE SECONDS and turns on the A/C and looks at BOTH fans. If BOTH are not running, problem solved. If both are then you can chase bubbles, leaks, water pumps (very unlikely) etc.

Thermostats open when coolant in the radiator hose reaches a certain temperature, it’s not about water pressure (singularly). But that’s besides the point.

What you are saying is not very likely, I don’t think any motor can idle at 200rpm, no matter what your tachometer says. But if I’m way off base there, you might have a point: what you said is a big problem for modified cars running performance engine pulleys.

I took a while, but I figured it out. When the car idles at 200 rpm, the water pump might not generate enough pressure to open the thermostat. Simply tapping the gas pedal will generate enough pressure. Try this next time, it might solve your problem.

Uh, no. The fan(s) will come on when the engine exceeds a preset temperature to prevent the car from overheating. If they don’t start to run until after the temperature is too high, something else is wrong.

I really think the fan, relay, temp sensor, etc are all more likely than the radiator itself. Interesting to note that sometimes with an electric fan setup such as this, turning the A/C on may force the fans to run, causing the engine to return to normal operating temperatures. This will not work if the fans are bad or ther A/C system is dead, but if for some reason engine temperature is not engaging the fans, commanding A/C is supposed to command the fans to run all the time to force air across the condenser coils.

It’s not your thermostat because if it was, it would either be stuck open and the car would not overheat but wouldn’t get to proper operating temp in the cold (which you would have to wait til winter to find out), or be stuck closed and the car would overheat all the time.

It could possibly be a fan, but you can’t tell from idling because often the fan will not need to go on until you are in an overheat situation. You would have to get the car to the point where it is overheating and then see if your fans are working. However if your radiator hasn’t been replaced in more than a few years I would suspect that as the most likely culprit. New York City is very dusty, more than almost anywhere else and I think it clogs radiators quicker, plus I needed to change my oil more often, but that’s another story.

An outside possiblity: Was the new thermostat installed correctly? (I don’t know if this particular one could be installed backwards)

BTW, an easy/cheap DIY fix to replace the fan with one from Advance/Autozone, but make sure to get one with the blades and shroud already on, then just unbolt, yank out, slide in the new assembly, bolt it down. Don’t forget to plug it in though!

Old brass/copper radiators used to split their soldered seams.

They both fail fairly regularly when they get old, there’s just no good way to “repair” the plastic ones like we used to do with metal ones.

1) Make sure the radiator fans are clicking on and going at a rapid rate. Just let the car idle and wait until the temp starts climbing. If it doesn’t click on past the 215 degree mark, you will either need a new relay or assembly.

2) Squeeze the hoses. Are they extremely soft? Do you smell or see any leakage? That too can be a problem.

3) I replaced the radiator on my Camry after 10 years… just as cheap insurance. Go to radiator.com and you should be able to order one for less than $100.

4) Flush out the fluids if you haven’t done so already. You can actually buy a manual excavator for $50, remove the radiator cap, and just start pumping away until it’s dry. Start the vehicle up for a minute and repeat a couple more times.

Let us know how far you go… best of luck.

Bad water pump — impellers are made of plastic and disintegrate.

On this car (and virtually all Hondas that I can think of) the water pump impeller is stamped steel.

Personally I don’t find modern plastic & aluminum radiators any more trouble prone than the old brass & copper ones. Thirty years ago it was common to see vehicles pulled off on steep hills due to overheating. Now it is rare.

Bad water pump — impellers are made of plastic and disintegrate.

Bad t-stat.

Clogged rad.

Bad electric fan.

Bad fan electric temp switch(sensor).

Collapsed rad hose — very common with lower hoses.

Air leak into the engine causing a lean mixture.

Bad head gasket, cracked cylinder head.

When it comes to a radiator that’s over 8 years old (in my experience) with high mileage, its only a matter of time before the plastic parts crack and the radiator dies.

I’m all about making cars lighter and better, but I do miss the days of 100% metal radiators.

If it was original equipment, I’d skip the flushing and just replace it, as it is unlikely that a ten-year old, well-used radiator is going to be saved with any amount of maintenance.

In the future, I’d take better care of the cooling system. Four years without maintenance on a ten-year old vehicle’s cooling system is a bad idea. Newer cars can handle longer intervals, but I wouldn’t let it go too long on a ten-year old car. I’d be flushing it every couple of years.