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View Full Version : Odd overheating problem that auto repair guys can't fix


SimonMoon5
07-24-2012, 05:26 PM
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.

voltaire
07-24-2012, 05:34 PM
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?

am77494
07-24-2012, 05:35 PM
It sounds like the fans have gone bad

kanicbird
07-24-2012, 05:35 PM
What comes to mind is the cylinder head gasket has failed.

voltaire
07-24-2012, 05:39 PM
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.

Dallas Jones
07-24-2012, 05:40 PM
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.

John DiFool
07-24-2012, 05:45 PM
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.

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

I think this has the cause/effect backwards.

Earl Snake-Hips Tucker
07-24-2012, 06:55 PM
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.I have had this exact problem (but not in a Honda) recently, and this was what he did to fix it.

steviep24
07-24-2012, 07:03 PM
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.

GreasyJack
07-24-2012, 07:22 PM
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.

I think this has the cause/effect backwards.

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

zoid
07-24-2012, 07:27 PM
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.

beowulff
07-24-2012, 07:36 PM
If you rev the engine while stopped, does the car overheat?
If so, it's clearly fan-related.

Senegoid
07-24-2012, 08:21 PM
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.

Gary T
07-24-2012, 10:48 PM
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?"

Philster
07-25-2012, 09:23 AM
Check the radiator fan. The description is SCREAMING for this to be checked.

August West
07-25-2012, 09:57 AM
What comes to mind is the cylinder head gasket has failed.

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.

Kimballkid
07-25-2012, 10:08 AM
As a very last resort, it could be a cracked head.

SimonMoon5
07-25-2012, 04:41 PM
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.

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.



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.

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


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


Uh, don't know. I'll have to check.


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 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.


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.

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

I'd follow the advice here and check 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.

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

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

Don't know. I'll have to check.


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

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.
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.

Okay, I'll investigate, thanks.

mnemosyne
07-25-2012, 04:53 PM
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.

below_gravity
01-29-2014, 09:12 AM
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.

HoneyBadgerDC
01-29-2014, 09:23 AM
Thats avery easy problem to diagnose. I would change mechanics. You simply let the car idle in your driveway watching the temperature. When it gets up too high check and see if your fans are comming on. If they are not comming on find out why. bad fan motors, bad relay?, loose connections. The fans are your problem.

One more question, I have seen many times folks complain there car is overheating when it is not. Some cars have a slightlyhigher spread from when the thermostat opens to when the fan comes on so the gage might go up a bit more at idle than it does going down the road. So how hot is it getting? Does it level out at some point or just continue to climb?

Gary T
01-29-2014, 10:01 AM
Thats avery easy problem to diagnose. I would change mechanics. You simply let the car idle in your driveway watching the temperature. When it gets up too high check and see if your fans are comming on. If they are not comming on find out why. bad fan motors, bad relay?, loose connections. The fans are your problem.It's certainly possible that the fan(s) not coming on is due to faulty fan system components, but that's not necessarily the case. Sometimes the fans won't come on because hot-enough coolant doesn't get to the relevant sensor. A faulty thermostat or being low on coolant can be the cause.

HoneyBadgerDC
01-29-2014, 11:14 AM
I agree with you Gary for the most part. Low coolant especially. But he did say it operated fine at highway speeds or when the car was moving. A thermostat will cause it to over heat no matter what the car is doing . One simple visual test of a thermostat if the car has a temp gage is to simply sit in the drivers seat and watch the gages while it idles. Once the temp starts moving it will climb steady until the thermostat opens. Once this happens it will slightly drop or at least stop mving for a second and continue like this for a few minutes until it heats up the radiator coolant where it will then pretty much level out. I have seen cars where the thermostat opened at 195 and the fans kicked on at 212. This will show up at stop signs by your gage climbing a bit higher than where it normally rides when you are going down the road. I think about a 10 degree spread is more typical.

Saint Cad
01-29-2014, 11:39 AM
As usual GaryT gives the best advice for the easiest diagnosis/fix. You may just have an air bubble in your radiator which gives the same symptoms that you describe. While cold, open your radiator cap and pour in some 50/50 antifreeze/distilled water mix. If it take more than a little bit, then there may be a leak somewhere (mine was a bad thermostat gasket). The rest of the posts give some good ideas of where to check for the leak.

Second would be the fan but make sure to have a second person to watch the temp gauge and turn off the car when the temperature starts to spike. This can be done while making sure you've burped your radiator*.


*That what my BIL always called getting the air bubbles out.

Gary T
01-29-2014, 12:12 PM
But he did say it operated fine at highway speeds or when the car was moving.Yes. I wasn't talking about the OP's situation from 18 months ago, but a general scenario where the fans don't operate. Sorry I didn't make that clear.

Senegoid
01-29-2014, 09:53 PM
I had a similar problem that defied solution for several years, despite being looked at by several mechanics in different cities. Finally, my latest mechanic found it.

It was a physically mangled and somewhat melted connector in the wiring between the fan switch (or thermostat or something) and the fan itself. It looked fine on the outside, but if you disconnected the two sides there are looked inside the damage was visible. How it got mangled is unknown.

They fixed that and my car never overheated again.

Isilder
01-29-2014, 10:13 PM
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. .

I know its a bit late, but in future for anyone else

If you think that the water isn't boiling, then maybe its the temperature gauge that is not working properly ??? that is, its only boiling when steam is coming out of the radiator !.

If the water is boiling, then the fans should be running ? were they ? If its boiling when the fans are working, then there must be thermostat problems.


Well , blocked radiators and failed water pumps are easily tested for . There is no way that they can be working "sometimes"...


Perhaps they tested the thermostat it it worked alright, so they put it back in ? But its the thermostat that can get stuck sometimes.!
The electrics can be intermittent too.. maybe the fans only come on at really high temperatures..

Rick
01-29-2014, 10:58 PM
Well , ... failed water pumps are easily tested for.
Do tell...

kaylasdad99
01-29-2014, 11:29 PM
I started noticing this on my 2009 Edge a few weeks ago. And almost always on a Sunday afternoon. Here's the itinerary:

0930 Drive 12 miles to church (surface streets only)

1000 - 1130 Church service

1130 - 1200 drive to Costco (surface streets OR freeway; depending on the store we go to)

1200 - 1330 grocery shopping

Only surface streets are taken on the way home from Costco, but we usually stop at a fast food place to pick up lunch. And I wait in the drive-through. After I leave the drive-through, the air conditioner stops blowing cold air, and the temperature gauge starts approaching the red line. At this point, I turn off the AC, open the windows, crank the heater, and drive for about half a mile or so down the road. This action, without fail, brings the temperature gauge back into the normal zone, permitting me to restore the AC and close the windows.

I have looked into the engine compartment when not overly hot, and found the fan spinning. I have not yet pulled over during an overheat episode to make the same check.

Saint Cad
01-30-2014, 02:10 PM
I started noticing this on my 2009 Edge a few weeks ago. And almost always on a Sunday afternoon. Here's the itinerary:

0930 Drive 12 miles to church (surface streets only)

1000 - 1130 Church service

1130 - 1200 drive to Costco (surface streets OR freeway; depending on the store we go to)

1200 - 1330 grocery shopping

Only surface streets are taken on the way home from Costco, but we usually stop at a fast food place to pick up lunch. And I wait in the drive-through. After I leave the drive-through, the air conditioner stops blowing cold air, and the temperature gauge starts approaching the red line. At this point, I turn off the AC, open the windows, crank the heater, and drive for about half a mile or so down the road. This action, without fail, brings the temperature gauge back into the normal zone, permitting me to restore the AC and close the windows.

I have looked into the engine compartment when not overly hot, and found the fan spinning. I have not yet pulled over during an overheat episode to make the same check.

Does your reservoir have coolant in it? If not, you may have air in your radiator which is an easy fix.

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