Working on a 05 Honda Civic cars runs great has 185,000 on it automatic transmission. I can drive all day on the highway wont overheat, as soon as I get off the highway it goes right up and overheats. If I sit in park and rev it 2-3 grand the tempature will start to go on. That led me to believe it was the water pump. Took that off today water pump is perfectly fine. I have changed the coolant temp sensor, radiator fan switch, now going to be water pump and timing belt. I block tested the car to see if exhaust gases were getting in the coolant (blown head gasket) and it came up negative. No excessive water in the exhaust, no sweet smell nothing. Is there another test I should do to see if its a blown head gasket? Leak down test? Compression test?? Could the radiator be clogged?? Please help?

 

Do the fans come on? Have you changed the thermostat? Does the heater always work?

It's not the water pump. If the impeller of the pump is still there, it's going to work.

 

yes the fans do come on, i have read on all data that it says that the radiator fan switch is on at 196-203 degrees and off at 5-15 degrees lower than the tempature it came on at. So basically even with the engine overheating its possible for the fans to not come on and stay on trying to get the tempature lower? both fans will come on and stay on though when the a/c is on.

 

Your problem seems similar to my son's 98 Civic CX with 176K miles, which is in North FL and I am in South FL.

When he drove the car to SO FL this past weekend, he had upper hose ruptured and lost coolant. The temp gauge hit red as he drove into a gas station, next to the highway.I got the call from him and I changed the hose on the spot, filled the radiator. I looked for a bleed valve but this car does not have one. I thought the radiator will be filled as the engine does a few cycle of hot and cold as long as coolant is in the reservoir.

While he was in town, he drove it couple of times. Never had overheating problem. Then as he was to leave to NO FL, I checked coolant level in reservoir and it was full to the cap while coolant level in radiator was somewhat low. I filled the radiator and told him to watch the temp.

He said when he got off high way driving back from SO FL to NO FL, the temp gauge hit the red. But, as long as the car is moving the temp is lower on the gauge.

He checked the fan for proper operation the following day. He says it comes on with engine in operating temp and cycles. So I know the radiator fan switch is good as well as the fan. There is no external leak. I told him to change the radiator cap to new one, and see what happens. This was yesterday.

So, I don't know if it worked or not, yet. He has not called me since. I hope it did work, other wise, I am thinking of thermostat change would be the next step.

Oh, cylinder compressions were in 160s about a month ago when I checked. Color of coolant is green as it should.

Changing radiator cap may not be the answer to your problem or his problem. But, since your case resembles my son's and I thought it will be interesting to find out your solution.

 

OK on to the other questions I asked(*). Have you changed the thermostat? Does the heater always work?

(*) It also wasn't clear, do the fans come on when the engine is hot, without turning the A/C on?

 

He did change the radiator fan switch but it could be the fan that is faulty. And as maachan suggested, a bad radiator cap could adversely affect idle circulation.

Regarding the thermostat: My experience has been that if the thermostat is stuck closed, coolant temp will climb, even on the highway. This never happened with my Civic but I assume it would.

 

These situations seem like my son's 2002 Civic. The temperature gauge runs pretty normal at operating rpm and highway speeds but after warm-up climbs quickly while idling. The heater works normally, until the temperature climbs, then it stops putting out heat. We just changed the thermostat today after two days of symptoms – but the problem still exists. No visible external cool leakage. What's significant about the heater quitting during overheating?

 

I just had the same exact problem with my 2004 Honda Civic EX (140K miles). I recently replaced the accessory belts and when I drove to work and back the car was fine on the highway and when I was driving the car but as soon as I stopped at a light or the engine was just idling it would red line.

I took it to my mechanic and they replaced the termostat and O2 (oxygen) sensor. I just drove it to work and back today (>100 miles) and no over heating.

I highly suggest you have the thermostat replaced and possibly your O2 sensor (the one that sits right in front of the engine and connects just below the manifold.

 

Are you losing coolant / is it full?

Very small holes in the system (mainly the radiator) allow coolant to escape and basically dry or evaporate so it can take a long time before you actually see a drip. All the while you're still loosing coolant.

Have you had to add any lately?