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Overheating 1998 Honda Civic

Hi, everyone. Long time no see. It’s nice to see Carolyn kept my account open. Thank you.

Well, I’m still driving the same old 1998 Honda Civic DX two-door coupe, and I’ve got a problem with overheating. The temperature gauge needle doesn’t get quite to the red, but it’s popping up higher than usual, and I’m concerned to see it getting anywhere near the red. It usually spikes when I get off the highway and stop at a light, but it also does it occasionally in a drive thru, and recently, I discovered that when I give it a little gas in neutral, it brings the temperature gauge needle down to normal.

Here is the history of recent repairs and troubleshooting:

-About 3-4 years ago, I had a leaky radiator replaced, so the one that is in there isn’t very old.
-Last year I had a mechanic replace the thermostat, the radiator fan, and the radiator cap when I started having this problem.
-A few months ago, I had the timing belt serviced (the entire kit, not just the belt), but since the water pump looked fine and the car has so much mileage (275,000 miles), I opted not to replace the water pump. (I regret that now. I usually replace the water pump with every other timing belt, but I’ve learned my lesson.)
-I’ve been to several shops to get a diagnosis, but they have a hard time getting it to overheat at all, so they can’t diagnose it. One guy suggested the water pump might be worn out (inside, without leaking outside). Another guy suggested that “if it was the water pump, you would know it’s the water pump.” Each mechanic has done a pressure test on the cooling system and a flow test on the radiator, and they all say they are fine. One mechanic theorized that I might have a very small head gasket leak, but nobody else thinks that is the case and there is no sign of coolant and oil mixing. Besides, the temperature gauge has never been in the red.
-One mechanic who tried to diagnose the problem recommended replacing the plugs, plug wires, rotor, and distributor cap. After doing that, it is running better than it was, but that didn’t resolve the overheating problem. He also retarded the spark timing, but it is self-adjusting, so it re-advances itself after a couple days of driving. I can hear what sounds like minor knocking, but it’s always made that noise since it was new.
-Everyone who has tried to diagnose the problem says the thermostat is opening and closing as it should, and the radiator fan comes on and shuts off when it should.

I’m done getting second and third opinions, and I’m ready to start throwing parts at it. Do you think I should start with the water pump? What are your thoughts? Don’t tell me to replace the car. I just bought a new motorcycle. :wink:

Typical symptoms of a Honda 4 cylinder head gasket breech.

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@UncleTurbo, wouldn’t there be some oil in the coolant or coolant in the oil if that was the problem?

Hi Whitey! You Don’t Say… Is/Are The Cooling Fan(s) Functioning Properly?

Edit: Oops! " … and the radiator fan comes on and shuts off when it should." I missed it the first time through.

“Typical symptoms of a Honda 4 cylinder head gasket breech.”

These could be symptoms of virtually any car with a compromised head gasket, not just Honda. However, the car is passing cooling system pressure testing.

Was the system pressure tested recently, after this over-heating was noticed?

A bad head gasket can leak, compression, oil, coolant, or a combination. Sometimes you get cross-contamination.

A faulty coolant temperature sensor could cause a false over-heat indication. Air trapped in the cooling system can also cause unsteady readings.

I would have the actual cooling system temperature checked. I would be out in my driveway with my non-contact infrared thermometer checking various locations and at different operating cycles.

Checking the radiator cold and the reservoir reveal no coolant loss at all?


Considering all that’s already been done, I’d flow test the pump. One of the videos in the attached link should help.

You can also test the thermostat by submersing it in a water-filled vessel on a hotplate along with a temp sensor (or lab thermomter) capable of the temp… I’d go for a 300F minimum. You can watch the T-stat open and close as you watch the temp go up & down. For accuracy, be sure neither the T-stat or the temp sensor is up against the side of the vessel.

Confirming that you don’t have a head gasket leak (I don’t suspect one) is easy too. I’ve attached a link to a simple test, what I call a “lab test”.

Why guess when you can test?

I agree with @“the same mountainbike” . Flow test the pump. Your story has all the hallmarks of a pump with disintegrating impeller vanes. As they wear down, they aren’t as good at pushing the water. When you’re driving or you rev the engine, the pump spins faster and pushes water better. At idle it’s no longer able to keep up with the flow rate needed to keep the engine cool.

@CSA, the cooling system temperature was checked, three times by three different mechanics in three different shops. They were very thorough, which is why I consider the diagnostic fees I’ve paid to be money well spent. Our mechanic here at work is convinced I should ignore it and keep driving. EDIT: Yes, it has been pressure tested recently, post-symptom. The coolant temperature sensor was also tested.

@Everyone, so far, it seems like the consensus is something like: If you’re going to throw more money at the problem, check the water pump.

I’m wondering if it would be worth it to employ more diagnostic work and just have the water pump replaced. It’s what I should have had done when I got the timing belt job done.

If it’s a head gasket, I’d probably just keep driving it until it gets worse or sell it and rely on the motorcycle exclusively. I live in Vero Beach, FL now, and the winters are pretty mild. I hate to keep sinking money into this car, but it would be nice to keep it going a little while longer for rainy days.

@Everyone, so far, it seems like the consensus is something like: If you’re going to throw more money at the problem, check the water pump.”

I’m not part of that consensus! I highly doubt it.

If the thermostat is fairly easy to get to on this Honda, I’d throw a new one of those at it before anything else. Almost anytime I’ve replaced a thermostat (using OE part) the temperature gauge needle acts a little differently than it did with the former thermostat.

If you lower yourself to the “throwing parts at it” method of repair then remember the admonition to replace “the easiest, cheapest things first!”

On most of my cars this fix attempt costs less than 10 bucks and takes 10 minutes, even for a DIYer.

@CSA, the cooling system temperature was checked, three times by three different mechanics in three different shops.”

And… ?


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Good to hear from you again OP! If I had this problem and was certain the coolant was actually overheating (verified not a gauge/sensor problem), and was sure the radiator cap was ok, before replacing the pump I’d

  • Look for bubbles in the radiator
  • Do a chemical test on the coolant for combustion gasses
  • Replace or at least check the operation of the thermostat in a pan of hot water
  • Remove the top hose of the radiator and make sure that coolant really starts pouring out of that hose when the thermostat opens. It should be a strong flow, almost like turning the garden hose on full.
  • Air bleed the cooling system

If all that checked out ok and the symptom remained, I’d replace the pump. Of course if the flow test showed weak flow, and the thermostat checked ok, no need to question further, replace the pump.

Thank you, everyone. I’ll let you know what I decide to do and how it turns out.


If you want to be quite sure if you have combustion gases in the coolant . . .

Have a shop use their 5-gas analyzer. You remove the radiator cap and idle the engine, then you hold the probe above the opening, and let it take a sample. I believe you’re looking for elevated hydrocarbon levels.

It won’t tell you exactly how the combustion gases are getting into the coolant, but at least you’ll know that something has failed and is no longer sealing.

Another thought . . . I’ve run into a few bad aftermarket thermostats that just didn’t work properly. Even though they weren’t stuck one way or the other, they didn’t work

Well, I finally bit the bullet and had a new head gasket installed. A mechanic I work with volunteered to do the job for a case of beer, and he told me to order the OEM kit for $180. Then, the day before we were going to start the work, he bailed on me. Keep in mind I didn’t ask this guy for help (he volunteered), and I warned him it was a big job when he volunteered, but for some reason he didn’t believe it was a big job when I said it. I even offered to pay him. I also didn’t pressure him to do the job. I let him set the date so I wouldn’t be in the awkward position of nagging him. He really set me up and then hung me out to dry.

Fortunately, I found a shop that would use my parts. The head was warped, but only slightly (about 3/1000 of an inch) when they sent the head to be planed.

So I could pick up the car after hours, I went by the shop on Saturday to pay them and get the keys. On Monday evening, a friend took me to pick it up. The car ran so poorly I turned around and left it there, putting the keys in the night drop-off box with the comment “Please test drive the car and then call me.”

The mechanic reset the spark timing. While the car sat at the shop, the timing had been retarded to the point where the engine could barely run. When I picked up the car for the second time, it ran fine, so I drove it to work. On the drive home, the car ran fine, but the next morning, it ran as if the spark timing had been retarded again. Since I was on my way to work when it happened, I pulled over and let the engine idle until the timing could self-adjust. This morning, it acted up again, so I let it idle until the problem passed and I drove it to the shop. The mechanic checked it out and everything looked fine, but I hadn’t let it cool down overnight, so he couldn’t figure out what had happened.

If the problem happens again, I’m going to drop the car off in the evening so everything is cold when they check it out the following morning. What is happening is likely temperature-dependent.

Do you have any idea what the problem could be? I was thinking it might be a loose adjustment screw, or a loose connection to the ECU, but the mechanic checked those things.

EDIT: Oh, and they did confirm I needed a new head gasket. They can’t guarantee it will solve the original symptoms, but the head gasket on the engine was shot.

First off, I’d stay away from the co-worker that bailed on you.

All head gasket jobs are a large job, involving removal of many items just to get at the head.
Exhaust manifold, intake manifold, many of the components driven by the serpentine belt, etc. etc.

Unless you are doing a simple flat head 4 cylinder engine from the pre 60s era…it’s a big job.
Any real mechanic would know there is a lot involved.

I think he is the type that brags that he can do anything, but when the work is in front of him…he’s lost. I’d stay away from this guy unless it’s a simple repair…like changing a tail light bulb.

The problem that you have now is most likely a simple chore of the mechanic going back over his work. I presume that he either forgot to plug in a sensor or other electrical component, or a vacuum line got pinched off on the process of installing the head.

But without the vehicle in front of me…that’s just a guess.


hmmm … well removing the head involves removing the timing chain (or timing belt), so maybe something is amiss w/the valve timing. Does this car use variable valve timing? If so, check the associated solenoid. If there’s a simple way to check the valve timing with a timing light, maybe start there. Also the distributor – if a 98 has one – may have been removed, so that’s another place to look. The ignition module too, check those connections. There’s probably an electrical ground connection from the head to the chassis, or to the engine block, so check that. If nothing simple pans out you’ll have to check the cylinder compression.

Edit: Check the crank and cam position sensors, at least a visual check that they are wired up correctly.

Your friend isn’t a mechanic. Any decent mechanic would know a head gasket replacement is a major job. This guy is a poser, meaning one who talks the talk but doesn’t walk the walk.

Jeeze, tough crowd. It’s possible the friend who offered the free help bailed when he found out it wasn’t as simple a job as he assumed. That doesn’t make him a cad. It would have been different if he’d started pulling parts off the engine and THEN bailed, but if he’s otherwise a good friend I’d let it go.

Well, it appears all is good with the car. Since the mechanic made the latest adjustments yesterday morning, the car runs like normal. The valves are even quieter. It ran like a champ as soon as I started the engine this morning.

I appreciate the feedback. If the symptom reappears I’ll drop it off at the shop at night so they can check it out the next morning.

I have to ask, did anyone check the interior of the hoses? A partial delamination could cause these symptoms.

And since you had the head off, did you replace the water pump? That would have been an opportune time to do that.

Glad your 98 Civic is purring like a kitten again OP. Best of luck.