I have been fighting with this issue for about a year now. my 2002 honda civic ex is "overheating". i have changed the following:
- radiator
- thermostat (twice)
- made sure fans were turning on
- water pump
- radiator cap
- water temp sensor

heres the problem: I drive for about a good 1hr straight (on the street and freeway) and the needle on my temp gauge starts fluctuating: goes up the the very middle, slowly makes it ways 3/4 of the way up, then comes back down to normal. it keeps doing it while i drive and also when im idle. coolant spills out the top of my reserve tank after this happens. I also noticed that when my the needle starts to go up on my temp gauge, my heater blows cold air. when it goes back down, the heater blows hot air. strange. i have NEVER seen the temp gauge go all the way up to the "H" though & i have NEVER seen any smoke come from my engine. I also grabbed a thermometer and checked the coolant temp after the needle fluctuates and it reads about 160-180. I don't believe its a head gasket- theres no signs of water in oil or vice versa or white smoke out of my exhaust. what could it possibly be? No mechanic has been able to find the problem. any suggestions?? thanks!

 

did you bleed the air out of the cooling system?

 

yup, plenty of times. that was my first thought, air pockets causing the fluctuating temp. but still no luck. but maybe im doing it wrong?

 

Head gasket.



You won't always find oil mixed with coolant when you have a bad head gasket, but you will experience the other symptoms.

 

^^ That's the only thing left really. How many miles are on the car?

 

With the heater blowing cold with the temperature up does sound like an air pocket. Could be water boiling out from heat. Have you checked the radiator? It could be plugged up. If you are not sure, a flow test will confirm. Disconnect the radiator hoses from the engine. Plug the bottom hose port and fill with water. Pull the bottom plug and the radiator should drain in 3 seconds or less. Longer indicates clogging. Also with the radiator empty and the cap off, look down into the radiator. You can sometimes see the cooling pipes cogged up. A radiator shop can rod it out ~$50.

If it is a head gasket issue, oil very rarely gets into the water. It’s the other way around. Pull the dipstick. If water is in the oil, the oil will be gray and thick. Another test is with the engine hot, pull the dipstick and touch the end with the oil on it against the exhaust manifold, if the oil boils or steams, you have water in it.

If it is the head gasket and you are losing water, pull the spark plugs. Sometimes with a bad head gasket, water gets into the cylinder. The plugs will be snow white and clean from the steaming. This will also make the engine run hot.

If you can, check the engine timing. Retarded or advanced timing will cause an engine to run hot.

Another possibility: did you lose power prior to all this happening? A clogged catalytic converter or exhaust line will cause the vehicle to run hot. Under acceleration it will heat up; easy driving it will cool down - causing a temperature fluctuation as you described.

 

I had a similar problem (only for a week though). I thought I may have needed a new head gasket. It turned out that I wasn't bleeding it properly. I didn't get the car bleed until I bought one of those flush and fill kits and cranked up the water hose. It bleed all the air and I haven't had the problem since.

 

If you're convinced that there is air trapped in the system, and would rather try to eliminate that before tackling the other possibilities, get yourself one of these.



I've used it numerous times on a handful of Civics (as well as other makes and models) and I've never had any problem thoroughly burping the cooling system.

Unfortunately, I do not know the actual name of it. It has no name anywhere on it.

 

so how does that work? looks as if the funnel gets clamped onto the filler neck?

 

do a leakdown test if you really think the head gasket is blown. it'll even detect small leaks

 

Has about 160,000 miles >_<

 

Indeed.

Using adapter C and cap C, it looks like this.


Fill the radiator with coolant until the funnel is a little less than half full. Maintain the fluid level as the coolant heats up, thermostat opens, fans kick on (or coolant is normal temp. around 194° F) a couple times... basically until the system thoroughly burps.
When the bubbles stop, turn the car off, put the plug (the red stick thing) in the hole of the funnel and then remove it along with the adapter pieces. Reinstall OEM cap, etc. etc.

 

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