I have already replaced the radiator but it still overheats. It seems to do fine in cold weather or at high speeds on the interstate, but in the city or when I run my AC it just doesn't keep up. I have to keep a gallon of coolant in my car so I can occasionally pull over and replenish what has boiled out. I am not mechanically inclined, but I have been dealing with this issue for 6 months (not so bad over the winter in cooler weather) and my thinking is that it is not a thermostat or a pump issue because the coolant does indeed flow through the engine to cool it off. It's just that it just can't keep up. What else could it be??? Any help would be greatly appreciated.

 

Does the radiator fan work? Unplug the fan switch on the thermostat housing and put a jumper wire in the plug. The fan should now start immediately when you turn the key on. If it doesn't, find out why. Test drive with the fan running constantly and see if there is overheating. If hotwiring the fan prevented the overheating in the city, replace the fan switch.

Note that the A/C has it's own fan which is completely independent of cooling the engine.

 

I have seen the fan turn on and have even herd it, but now that I think about it I don't recall it necessarily turning on at the appropriate times...like when my car is overheating! I will try doing the jump wire thing, but can you please explain how to do that in detail. Not sure what a jump wire is. I am not intuitive when it comes to mechanical things. Any additional help you can give me would be greatly appreciated!!!

 

Basically, you jump (verb) a wire (noun) by inserting a paperclip into the clip on the car, completing the circuit, and kicking the fans on.

Also, make sure you bled the coolant system properly. However, it you are losing coolant, you are either leaking it, or burning it. How many miles on the car? Any white smoke coming out of the exhaust? Whens the last time you did an oil change/coolant flush?

 

ok i will try that. I flushed the coolant when i replaced the radiator three months ago. Last oil change was 4000 miles ago. No white smoke from exhaust.

 

I thought I'd post in this thread because i'm having a somewhat similar issue. Any help is much appreciated.

Here is the skinny.

Last weekend my girlfriend purchased a 1999 Civic EX Sedan. The previous owner was a mechanic and swore that the car was reliable and he wouldn't hesitate to drive it from coast to coast. I"m no mechanic but I've spent my fair share of time in a garage. We took the car for a drive and everything seemed tight. The engine idles smooth and no funny noises coming from anywhere. The previous owner also showed me the timing belt that he recently replaced(Still in good shape) and the old plugs that he recently changed. We drove the car for the first weekend and everything was fine. Maybe 100 miles or so of highway driving.

My gf took the car to work on Monday. On the drive home through the thick road rage traffic the car started to overheat. She called and I told her to pull over and kill the engine before she does any damage. After 20 minutes she started it up and drove it home.

I came over and we topped up the coolant with 50/50. It took about 1 litre of coolant. I let the engine run with the rad cap off and the heat running full blast. I could hear the fan coming on and off. No sweet smell or grey smoke from the exhaust. I told my gf that maybe it was just low on coolant and she should try it the next day. So..the next day it was fine in the morning but started to over heat on the drive home. My gf said it seemed to over heat when she turned on the A/C. I don't know if that makes any sense or if it was just a coincidence. This time the over heating wasn't as bad.. What should I do.. Please help!

 

Pressure test the cooling system in an attempt to find a leak.

Also consider replacing the thermostat and radiator cap and then bleeding the system again.

 

New thermostat for sure. Always change it when there is mysterious random overheating.

Also until this is figured out, it would be good to check the coolant level in the radiator before every trip. Remove the cap only when the engine is cold. If the radiator is getting low (it should always be full to the top) but the bottle is overflowing, replace radiator cap.

She should know how to bypass the fan switch and try that next time it happens. It's quite possible the fan doesn't start every time that it should. Most electrical parts can become intermittent before failing completely. There is also a fan relay which can do the same thing or the fan motor itself.

The A/C puts extra heat under the hood and also more load on the engine, so it will make a marginal situation worse.

 

So I'm in the process of replacing the thermostat. I made the brilliant move of losing one of the bolts for the thermostat housing. Does anyone know if both bolts are the same. How on earth am i going to find a replacement...please help

 

I think they are the same, it's easy enough to tell -- just try the one you have in both holes. Then buy another one like it. It's an ordinary M6 bolt, find at a parts store or hardware store. Be sure to get a metric one.