Well earlier today I was cruising down the freeway at about 75-80mph when I glance down at the temp gauge (mechanical so I have faith in it) and it is running at a little above 240* Now its never gone above 210* except when I would be climbing a stepp hill and then it always cools back down. So I exit the freeway I put it in neautral on the off ramp, the tempature starts to drop, I get caught at the light but it still seems to going down. I pull into the nearest gas station stop, but leave it running, I look under the hood, but I don't see anyleaks. I see where it looks like it may have been leaking near the lower hose but at that moment it is not. I was only about 3 miles away from my house so I drive home. By the time I get home it is near 190* which is where it typically is around town.

After it cooled down I checked my coolant level, a little low, but not much. I changed the lower hose where it looked like it may had been leaking. Replaced the cap cause it was old. I took it for a spin, seemed ok around 190, I get on the freeway and up to speed after a while it creeps up there, around 225* but now the sun has gone down so its not so hot.

Does that seem a bit high it was at 240*, but as soon as I slowed down the temp came down? I have always heard that if it heats up at a stop it is lack of air flow, if it heats up while at high speed it is lack of water flow is this true? Would having a radiator shop clean the radiator possibly help? I'm just trying to see if I am over reacting here or not. It was 115* out today, but I don't have AC, and I run a 180* thermostat so I still think it should be running cooler.

 

I am having the same problem with my truck too lately. Only on the highway it want to heat up. If I am stuck in traffic it will definitly rise up because of low airflow and 1500+ RPMs. I am going to flush and backflush my system soon and see if that helps. See if you are getting a mineral buildup in side your radiator. If there is buildup, then yes difinitly take it to a radiator shop and have it cleaned.