Odd overheating problem that auto repair guys can't fix

Here’s my problem: I have a Honda Civic that has a peculiar way of overheating. It’s fine to drive for a while. And I can drive it on the highway for as long as I want. But once I get off the highway and slow down (or, heaven forbid, stop at a light), the temperature sky-rockets until I get moving again. So, at a long light or in a lot of traffic, I can’t speed up enough and the car overheats.

The guys at the local repair shop have replaced the water pump and the radiator. So those aren’t the problem. Any ideas?

The guys at the repair shop seem kind of stumped. But it also took them three or four days before they realized that the car actually had a problem because it doesn’t just overheat when idling unless it’s been driven around a lot first.

My immediate suspicion would be the radiator fan or coolant temp sensors, but I can’t imagine that the mechanics didn’t check/replace that.

If you’re still driving the car under these conditions, try turning on the A/C whenever you come to a stop or are in slow traffic. Turning on the A/C will turn on both fans regardless of the signals from the coolant temp sensors.

ETA: With the engine running and the A/C on, do both fans spin?

It sounds like the fans have gone bad

What comes to mind is the cylinder head gasket has failed.

Also, besides the turning the A/C on workaround, if you’re still driving this car with the problem, it will also help if you turn the heat on full blast with the vent/outside-air open. Just try to aim the vents out the open windows so you don’t overheat.

I’m sure I don’t need to tell you that over-heating is very bad news. You will want to do everything possible to avoid letting the temp get too high for too long.

Sounds like a problem with the fan switch. The cooling fan doesn’t run all the time and only turns on at a certain temperature, around 180 degress. So you are fine at highway speeds because the fan is not normally running.

Then when you need it to turn on, at lower speeds, it isn’t coming on and your car over heats.

If the shop didn’t check this out go to a different shop.

My '96 Civic had this exact issue for years, and the shops never did fix it completely; after a number of months with no problem it would mysteriously pop up again. Oddly, my friend (who bought it from me 6 years ago) said he saw said vehicle last month (distinctive dent in the hood still visible), still chugging along its merry way somehow.

I think this has the cause/effect backwards.

I have had this exact problem (but not in a Honda) recently, and this was what he did to fix it.

A bad thermostat could cause overheating too. Happened to me once. Sometimes a thermostat could stick intermittently so the problem doesn’t show up all the time.

I would really hope that the thermostat, radiator cap and possibly the coolant got replaced at some point when the radiator and water pump were being changed. Those parts are so cheap and can cause such maddening cooling problems, it’s generally good practice to replace them any time you’re working on the cooling system.

A bad head gasket can definitely cause overheating problems, although it wouldn’t necessarily be at the top of my list of suspects.

I’d follow the advice here and chech the thermostat and fan. Those are the most likely culprits and pretty easy to fix…
If that doesn’t pan out you can start worrying about the high cost possibilities.

If you rev the engine while stopped, does the car overheat?
If so, it’s clearly fan-related.

My car had exactly this problem, and it took several years (and several mechanics in several cities) before it got diagnosed and fixed.

In my car’s case: The electrical wiring leading to the fan has a connector plug somewhere in the middle of it. Somehow, that connector got partially melted/bent/fried, resulting in an intermittent connection. So the fan was running sometimes when it should have been, and sometimes not.

So be sure your mechanic checks all the connectors all along the wiring having anything to do with your fan or related sensors.

Running cool on the highway but overheating at idle are the opposite symptoms of a restricted radiator. Might be time to find a better shop.

I’d make sure the engine was indeed full of coolant and test/verify proper fan operation before even speculating about anything else.

Will it NEVER overheat at idle unless it’s been driven around a lot first? How many minutes/miles constitutes “a lot?”

Check the radiator fan. The description is SCREAMING for this to be checked.

I thought this as well.

If the temperature drops when gunning the engine at idle, check the head gasket.

If the temperature soars when gunning the engine at idle, check the fans.

As a very last resort, it could be a cracked head.

These guys don’t have my full confidence. I suggested the fan first, but they said it was working fine… but that was earlier… Hmm, I guess I should explain the full series of events:

The car was having these problems. I took it in, suggesting the fan was problematic. They said the fan was fine. And they said the car was fine too as they couldn’t get it to overheat, though they did add a little coolant first. And after they gave it back to me, the car worked fine… for a couple of days. So, I took it back…

And I guess they didn’t listen too hard when I explained the symptoms, as they couldn’t get it to overheat while just idling. And they started checking for coolant leaks, which didn’t exist. So, after I gave them the car on Monday, they still didn’t think anything was wrong with it until Thursday when they actually drove it. Sigh.

So, then, instead thinking about the fan, they thought about the water pump (and replaced it) and then also replaced the radiator. And then it seemed to work for them. And then, I took it out for a drive and it seemed okay for about five minutes and then Blam! back to abnormal.

I’m in Oklahoma in the summer. The AC is always on. Though I have tried it turning it off without much effect.

Uh, don’t know. I’ll have to check.

I don’t know if I can survive that. No AC is enough to make me sweat heavily (even with open window). Adding heat… I dunno.

Right, as soon as I see it approach red, I pull off the road immediately.

Well, the replaced radiator was already a pretty high cost possibility. :frowning: But I’ll certainly take this advice.

Don’t know. I’ll have to check.

I don’t know about “never,” but the shop was never able to get it to overheat while idling until they drove it around first. And I’m not sure how much is a lot, since I haven’t been trying to overheat it. Living in a small city, to get to the real city is about a drive of 30 or 45 minutes and then definitely causes a problem. The shop drove to a closer little city (don’t know how far away) in order to discover the problem.

Okay, I’ll investigate, thanks.

My car was behaving much like yours was, though fortunately for both my wallet and sanity, I have an excellent mechanic.

What would happen is that as the car heated up (at idle, slow moving traffic), I’d get temperature spikes, and it would cool back down at highway speeds. After checking on it for a couple of days, there was clearly a coolant leak, though it was somewhat slow. I brought it into the shop and they had difficulty replicating the issue, until the car got hot.

The issue was a loose hose clamp.

As the car heated, the hose would expand, and the clamp wasn’t holding it well enough, and so the coolant would leak.

$50 worth of parts and labour and the car is fine.

Have them check the hose clamps.

Did you ever find a solution? I am having the same problem in my 2005 Civic.

It also overheats if it is left sitting, but its sporadic. It overheated this morning when it was left run for 20 minutes to warm up. It’s 7 degrees F out.