Piston Slap: The Heat Soaked Honda

Sajeev Mehta
by Sajeev Mehta

David Holzman writes:

There was a killer traffic jam on the way into the Holland Tunnel from the NJ [turnpike] last weekend. I covered a mile and a half in about 40 minutes. At the start of that jam, my 99 Accord (manual and 159k) began overheating. When the scan gauge said the temp was 231, I put the heater on full blast, and kept it there, which brought the temp down below 216. (In normal driving, the temp stays within a few degrees of 182.)

In Manhattan, I tried putting water in the radiator, but it only took about 2 cups before it was full. Leaving Manhattan, traffic was thick but not stop and go on the West Side, and the temp remained in the 190s-200s (I can’t remember if I had the heater on or not at this point), and once the highway was clear, the temp remained below 190 and mostly around 182 without the heater on all the way back to Boston–as it had been from DC to the Holland. Haven’t had any trouble driving around town since. Car has a 3 month old t’stat. I took it in, and they couldn’t get it to overheat. Any ideas?

Sajeev replies:

First check your cooling fan, it should kick in around 190 degrees. An easy way to check is to run your A/C, since that normally kicks on the fan too. But I seriously doubt that’s the problem.

On an older car with high miles, I’d guess the radiator is clogged just enough to cause a problem in severe traffic in the summer months. And it’ll be fine every other time. At least for now: get a new radiator if you suspect it is original. This is more important than ever, since most new(ish) radiators use plastic parts that are prone to crack far quicker than conventional metal parts.

Sajeev Mehta
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  • Happycamper Happycamper on Jun 25, 2009

    I'll throw something completely different in the list. I own a '98 Honda Civic, manual transmission. In certain rare weather conditions, it will idle as low as 200 rpm. I too have had the car unexpectedly start to overheat while idling in rush hour traffic. 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.

  • Sajeev Mehta Sajeev Mehta on Jun 26, 2009
    happycamper : 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. 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.
  • Rodster205 Rodster205 on Jun 26, 2009

    As I said before but apparently my words are invisible, I had the exact same car with the exact same problem. It was one of the fans. 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.

  • Altarr Altarr on Apr 12, 2010

    So I found this thread when looking for a solution to my own problem....it is a quite a nunique one and anyone with help for me is greatly appreciated... I have a 2004 Honda. This winter, I would start driving and the temp gauge would go to its normal position, however, I would not get heat AT ALL when driving in the city. Once I hit the highway and the engine began revving harder, heat would blow. Same goes for hills, the heat would blow for a bit but then go away when I took my foot off the gas. Now, flash forward to our warmer weather of spring. When I try to run the heat, the car almost instantly overheats (and no heat to boot) By overheats, I mean the needle is pegged at max. This happens on the highway and in the city. The car will also slowly start to overheat even with the heat off when idling. (like at the slowest burger king ever) Also, even when the heat gauge is at max, there will only be cold air coming out. Any ideas?