2003 Civic- intermittant overheating

About a month ago my daughters 2003 Civic reached 100K miles and we had pur family's long trusted mechanic do the 100K timing belt, spark plugs and water pump replacement.
A couple of weeks later the car's temp gage rapidly soared up during city driving. Not wishing to take any chances, daughter called AAA and had her Civic towed back to the mechanic who'd done the 100K maintenance.
Our mechanic test drove it and told me that he couldn't get it to overheat. There was plenty of coolent in the system and while we discussed it on the phone I suggested that maybe the thermostat was flakey and asked him to replace it. He did that.
The car didn't overheat again for about 8 days, but while on a road trip the temp gage soared up while on the highway. She limped the car to a repair shop where the mechanic there diagnosed it as a failed cooling fan temperature sensor and replaced the sensor.
The car is still intermittantly rapidly overheating as indicated by the temp gage. I showed her how to stop the car, open the hood, and see if the cooling fan was running. She reports that it is.
I suppose that it could be nothing more than a defect in the temp gage system, and the engine isn't really overheating, but the fact that the gage sweeps up over a period of a minute or so and doesn't snap to a new reading has me doubting that.
At this point my best guess is that something is causing the coolant circulation to quit. My limited experience with Civics has me remembering that the water pump is driven off the smooth side of the timing belt, so perhaps there isn't enough tension in the belt to drive the water pump properly and when the belt slips the pump stalls?
Thanks for any leads guys,
Jeff
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Jeffry Wisnia
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On 06/20/2011 09:44 AM, jeff_wisnia wrote:

no, that's the tensioner. the coolant pump is toothed so slippage is not a problem.

much more likely it's the head gasket. open deck blocks like this car just leak exhaust gas straight into the coolant with no other side effects. the subsequent foaming doesn't carry heat away efficiently so it overheats. it's a frequent occurrence with this model and most people don't notice until it gets bad enough to start to overheat.
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jim beam wrote:

Now that makes more sense than my suppositions.
Is there a simple way to confirm that as the source of the problem like being able to spot the foaming somewhere, or maybe by air pressurizing each cylinder through its spark plug opening with the crankshaftpositioned so that cylinder's valves are closed, and looking for bubbles in the coolant?
Thanks,
Jeff
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On 06/20/2011 10:58 AM, jeff_wisnia wrote:

you might be able to get it with a conventional pressure test, but your problem is that it tends to be one-way, and only when hot so pressurizing the coolant and waiting to see if it drops doesn't always show.
another [usually successful] method is to run a chemical test on the coolant. but the kit is massively over-priced given that the chemicals cost only a few cents.
yet another, if you have the gear, is to put a pressure gauge on the cooling system, and run compressed air into the cylinders, and see if you can get a pressure increase on the coolant side. it's usually the middle two cylinders that leak.
i have strong opinions on repair of honda head gaskets that are not shared by the majority of the repair industry. basically do NOT let the head get skimmed unless it's actually warped. and do NOT allow abrasives to be used in the clean-up process. google this group for details.
last thing - if you're not repairing yourself, consider simply replacing the engine with jdm. it's frequently much quicker and therefore cheaper than paying for the extensive labor necessary for strip-down and re-build.
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If you've got a head-gasket leak sufficient to cause overheating, you'd find lots of air in the rad and a reservoir level way higher than normal. Head gasket problems generally result in overheating at idle, not at speed.
Next time this happens, turn the heater and interior vent fan on, full- blast. If this helps, then you have an intermittent circulation problem.
Was the new thermostat OEM or aftermarket?
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On 06/20/2011 12:13 PM, Tegger wrote:

later stages, not early. this might be later stage if it's overheating, but then again, the coolant's been changed with both the coolant pump and the thermostat work, so level is not a reliable indicator.

not a reliable indicator. late stage maybe, but some will overheat on a long hill at full throttle, and be fine the rest of the time.

turning the heater on is "limp home" - it cures nothing. and "intermittent circulation" problems on a honda? i've never seen one.

wouldn't have caused the initial overheats.
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At ANY stage, if the head gasket is blowing.

If coolant is blown into the reservoir and the level in the engine is low, the coolant will only circulate sufficiently when the water pump is spinning fast.

If the problem is poor circulation due to low coolant, turning on the heater will NOT help, which is which is why I suggested that.

I have. Aftermarket thermostat was sticky.
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On 06/20/2011 12:49 PM, Tegger wrote:

sorry dude, that's not accurate. if you drain and fill the rad, there's air in the system. it doesn't blow the fluid out of the expansion bottle, it just burps out through the expansion pipe and away.
same with head gasket - if the gas is not leaking fast, it burps. only when it's leaking bad does it start to foam to the point where liquid starts to fill the bottle.

see above.
when it's running hard, there's more gas getting into the coolant. if it overwhelms the system, the motor will overheat. if it's not running hard, it can usually cope much better. you need a system to be half empty for the situation you're describing, and after a coolant and thermostat change, that's most unlikely unless it's been really boiled.

if the coolant is that low, then yes, you will not notice any heat, but it's not apparent that's what you meant.
i would avoid "intermittent circulation". low coolant is low coolant, not "intermittent circulation".

that's "defective thermostat".
"intermittent circulation" is something like a collapsing hose - honda have a steel pipe on the intake side of the pump so you'll never see one.
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jim beam wrote:

Well, I just picked daughter up at our trusted mechanic's shop where she brought her Civic back in. He found the coolant about 3/4 gallon low, which says to me it's losing coolant at a pretty good clip. There's been no white "smoke" out the tailpipe and no "sweet smell" there either.
Daughter told me that when she had the fan sensor changed "on the road trip" about ten days ago the fellow who did the work had to put about a gallon of coolant in. She said she drove over 300 miles before the overheating started showing up again.
My mammary just reminded me that maybe 20 years ago I located the source of a similar mystery coolant loss. It was a hole in the expansion tank which was causing a loss of coolant, but naturally that wouldn't show up in a coolant system pressurization test.
Wouldn't it be a pleasant hoot if all that went wrong was that they did something to disconnect the coolant expansion hose when they did the 100K maintenance, and then forgot to reconnect it?
I just pinged our mechanic and asked him to look for that.
Jeff
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I'd never use an aftermarket thermostat on a Honda,except for an emergency,and then only until I could get a real Honda TS. The aftermarket one listed for my Integra GS-R was the wrong temp,too;180 degF instead of the specified (IIRC)195 degF proper temp rating. A real Honda TS is not that much more expensive,and it could save your motor.
And watch out for reversed installation of the TS. that's not good.
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