I have a 1997 Honda Civic with 275,000 miles on it. After driving for an hour or so, it starts getting hot when stopped or nearly stopped. It goes back to normal temperature when I start driving. It does cool down if I turn on the heater. I just changed the timing belt/water pump and put it a new radiator and changed the thermostat hoping it would solve the problem, but it hasn’t. I checked and the fan does come on when stopped. Could it be a cooling system clog that a flush might be able to solve or might it be the head gasket??? Thanks for helping me figure it out.
Wow. You’ve thrown a lot of parts at this problem instead of getting a proper diagnosis. Get the cooling system pressure tested, and check to make sure the fan is working.
I would have had the radiator flow tested before replacing it, considering the cost.
Have you replaced the radiator cap? That’s the one part I would be willing to change with no diagnostic testing.
I am pretty sure it is the fan, based on your symptoms, but don’t replace it until you are sure.
The radiator is probably finished. If you look at it from behind and you see a lot of white or green, the cooling fins are probably rusted away. 15% missing will cause the problem. You should have it inspected with the shroud pulled back if necessary.
The other possibility is that the fan(s) motor(s) may not be working.
Sorry, missed the part about the new radiator, as shadowfax noticed.
I doubt a new radiator would be rusted already unless OP got ripped off.
Check that cooling fan. I know it’s running, but make sure it’s running the right direction. If it’s wired backwards, it will spin backwards, and draw hot air from the engine over the cooling fins.
Also make sure the cooling system is properly bled - an air bubble can cause this.
It could be a head gasket, but it could also be something cheap/free to fix.
it could also be a pinhole leak in a hose somewhere, though you should see steam rising if it’s that.
I tend to doubt it’s a clogged cooling system, because if it was you probably wouldn’t see it cool down when you turned the heater on. All that does is introduce a reservoir of reserve coolant that’s sitting in the heater loop. If there’s a clog, that reserve coolant wouldn’t be able to go anywhere.
If I understand the post correctly, you’ve changed the
and checked to see that the fan was operating properly.
You’ve done a lot of good stuff here.
It is possible that the liners inside the radiator hoses are collapsing and restricting flow. They’re cheap and easy to replace.
You can check for a headgasket leak in a few different ways. But if with the radiator cap off there’re bubbles coming up out the hole when the engine runs, that’s a pretty good sign that you have a breech. The bubbles are combustion gasses getting blown into the water jacket and migrating to the system’s high point. Another way is with a pressure leakdown test of the cylinders. The kit is cheap and should come with instruction.
Does the temperature gauge go into the red zone? If not the engine isn’t overheating. It’s just running a little hotter when sitting and idling which is normal. That little radiator fan isn’t going to push near the amount of air past the radiator as the ram air effect of driving the vehicle down the road. Especially in hot weather.
So as long as the needle doesn’t get into the red zone, the engine isn’t overheating.
Air trapped might be a factor. On my 99 Civic the heater should be set on Hot when you drain and refill coolant because the valve to the heater core is then open.
To eliminate this factor: engine cold, start it and set the heater to Hot. The heater fan is not needed. Put the front of the car up on ramps. Put a bucket where it will collect any overflow of coolant. Open the rad cap. Let it idle until good and warmed up. Top up as needed. Cap the rad.
Put collected coolant in a closed container where living things cannot drink it. You can put the car back level. Next AM check and top up. Probably no more is needed unless there is a leak somewhere.
Thanks for the replies. I just put in another new radiator that came with a cap (shop exchanges for no charge) but it still gets hot. @tester I don’t let it get in the red, I turn on the heater before it reaches 3/4 of the temp gauge. I am concerned by this as before I have never seen the temp needle rise above 1/2 the gauge no matter what.
Try the easy stuff first. Start with a new OEM cap (I know that a cap came with the new radiator, trust me on this). Change the thermostat. “Burp” the system . . . purge the air out of the coolant system. Check to see how long it takes for the fan(s) to come on. Thermostats can be bad right out of the box. Test it before you install it. Wrong caps can screw up the pressure in the system. Air in the system can be hard to find but will burp out with a little patience. Another easy thing to check is air flow. Anything blocking the air flow? Get down on the ground and look around. Good luck! Rocketman