2003 Honda Civic EX Sedan 1.7L L4 PFI SOHC
* Symptoms:
At highway speeds the temp gauge reads midpoint. Afterwards in stop-and-go city traffic the gauge will climb to highest temp (H), whether the AC is on/off and whether the heater is on/off.
* Troubleshooting:
1) Started car with cold engine. Removed radiator cap and verified coolant is flowing over top of radiator fins once car warms up (good flow, good level) while engine idling in park. Thermostat is opening.
2) Performed exhaust gas leak test, from radiator neck. Results inconclusive. Blue fluid turns yellow for gas engine in presence of combustion gases. (Color turned light green.)
3) Verified fans work. They switch on at 204F every time. Tested 3 cycles.
* Fix Action:
Added coolant through radiator cap (not overflow tank) to top off while engine running.
* Results:
Engine temp gauge stays below midpoint in city stop-and-go traffic.
* Follow-up:
Coolant level is slowly declining. Don't know why. I expect this overheating symptom to recur.

 

Coolant level should NEVER decline. If you're certain you dont have external leaks it has to be going somewhere, and it would sound like a headgasket leak. Make sure your engine oil doesn't look milky.

 

not certain i dont have external leaks (hoses), but havent been able to see any, or the crystallized coolant anywhere outside of where it should be. Oil looks like oil, good, not milky.

Last winter, after the car warmed up, sometimes when i turned the heat on, it would continue to blow cold. this was intermittent, and would only last until i shut it off, and ran it again. not sure if it is related.

 

Heater not working means there's a bubble of air in the top of the engine.

Really sounds like a slow leak in the head gasket. That will not mess up the oil, blow steam out the exhaust or the other symptoms of a major leak. Get the radiator completely full, start cold with the cap off and rev it up, see if any bubbles come out of the radiator.

 

x2,

I've had plenty of bad HG experience with my Subaru.

Could also peer down into the cylinders through the spark plug holes. If one piston head looks really really clean, that's usually an indicator that you're leaking into that cylinder.

If it's a slow leak, I suppose it could last for awhile longer if you keep an eye on the coolant level. Or it could just let go entirely one day and you trash the block and head. It sounds like you're already getting it pretty hot so beware if you want to keep this engine for long. It only takes one overheat to do it in.

 

do honda civics often have this problem with head gaskets?

 

Hi there-- I just went through this problem with almost exactly the same symptoms. There are a million threads out there online about people having exactly the same symptoms (very difficult to diagnose) with '01-04 Civics (mine's an '03 EX). In almost every case it is a small warp in the head gasket which causes eventual pressure buildup in the coolant system and gradual loss of coolant. I changed thermostat, and tested everything else, car even passed an overnight pressure test. I ended up getting the head gasket replaced and it's working fine now.

 

I am going through this same exact scenario now too with my 2003 LX.

Replaced so far: water pump, thermostat (three times!), radiator, timing belt, fan sensor.

I was told by a local shop that it's not the head gasket because they did a chemical test to see if exhaust had been getting into the coolant. Apparently it wasn't because the test was negative. However, when my LX overheats, all of the coolant in the system seems to end up in the overflow tank!

What else would cause that if not the head gasket issue??

 

A bad radiator cap can cause coolant to migrate to the reservoir and not return, leaving the reservoir full but an air space in the radiator. Examine the gasket in the top part of the cap, the one that seals to the top of the radiator neck. Also the hose between the radiator and the reservoir must be airtight. The system depends on a vacuum forming to pull coolant back out of the reservoir as the engine cools.

A bad head gasket does about the same thing though.

Small leaks can be hard to diagnose conclusively because they are small. Here is a test you can do at home. Do this test with the engine completely cold. Squeeze the upper radiator hose, it should be soft (no pressure inside). If there is pressure inside, open the radiator cap to relieve it then re-close the cap. Now start the engine and rev it to about 2500 rpm. Squeeze the hose again, there should be no change. No pressure should build for a few minutes until the engine actually starts to warm up. If you feel pressure immediately, it is from combustion gas that has leaked through the head gasket.

 

These exact symptoms were solved only by replacing the head gasket on my 2003 EX. Some mechanics couldn't diagnose it because they were not familiar with the problem and the symptoms are different that what is typical for other cars. I had my head gasket tested just like you did and the test came back negative; I had to find a mechanic who was familiar with the problem in this generation of Hondas. Go through the motions and check the radiator cap, but don't rely on your shop's diagnosis.