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Hi all. First post. Having temperature gauge issues with my 2004 Civic LX - 225,000 miles. Even though I recently (last week) replaced Cooling Fan, A/C Condensor Fan, Coolant Temp Sensor and Cyl #4 Coil, the temperature gauge is still fluctuating - - all the way to the HOT line, after an hour of driving. However, the car has not actually been running hot, nor has it overheated, at all. Any ideas, suggestions and help would be GREATLY appreciated! Thanks.

 
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Radiator coolant level is low?

 
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Not really. Have added about half a gallon of water to the radiator over the past week.

 
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FYI: After all of those replacements and money, my mechanic said he "thinks" it's the computer telling the temperature gauge that the car is running hot, but it's not running hot or overheating. Please help. I'm at a point where I have to junk my car over a fluctuating temperature gauge and I really don't want to do that.

 
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01-05 are high candidates for head gasket failure..... look at the MANY, MANY post on this formally 7th gen (01-05) site.

 
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Mechanic says that if it were the head gasket, the car would actually be overheating. It's not.

 
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Uh huh. Where did all that water go?


NOTE: The entire cooling system only holds about a gallon and a half of liquid. The loss of less than a quart can lead to very obvious overheating problems. The overheat is very obvious on the gauge in front of your eyes, and the overheat really is happening inside the engine even though you haven't seen a huge cloud of smoke (yet).

If you were in the cold you'd have been complaining your heater output is weak.



Your mechanic is incorrect, and if he believes what he tells you then he will not be able to correctly diagnose your problem.


Your mechanic is broken. Replace mechanic with someone who doesn't guess.

Find a mechanic who has lots of experience with this particular engine and it's shortcomings.

Or start reading up on how your blown head gasket needs to be diagnosed.
Almost everything you need to know is in the first two posts of this thread: https://www.civicforums.com/forums/36-mechanical-problems-vehicle-issues-fix-forum/340759-overheating-mysterious-coolant-loss-common-causes-reference.html





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Thank you for responding ezone.

 
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You said you've added a bunch of water to the cooling system, but you didn't say where it went.. Have you found leaks yet? Enough leakage to explain the loss of a half gallon? I'd expect puddles on the floor of the garage if it were leaking that fast, and you would have mentioned such.
That led me to suspect the head gasket is leaking, typical for the engine.

You can start with filling the cooling system and burping all of the air pockets out of it,
fill the reservoir to the max line
Drive it....the temp gauge should be stable as long as the radiator stays completely full and the fans run when they are supposed to.

Once the level starts dropping, the temp gauge will go up.
When the leakage rate is very slow it may take hundreds of miles before enough liquid is displaced out of the radiator to become noticeable.

Many people report the fans don't run even though the temp gauge shows overheating, which can be expected due to the location of the fan switch in the system.

 
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I have no idea where the water is going. No puddles that I have seen. According to my mechanic, my radiator passed pressure test when he was replacing the fans. Thanks again for all of your responses ezone.

 
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Ezone, this is my mechanic's response when I asked about possibility of head gasket blown, "sounds feasible, but the fact that both sensors for the computer and the fan are in the same coolant orifice, I can't understand how if that's what was going on, it's not affecting the cooling fan switch."

 
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He doesn't understand how this system is designed.

Visually the sensors appear to be located very close together, but if one were to take the time to study how the liquid flows within the housing where those sensors are located, one would understand they are completely separated, they are really at opposite ends of the liquid circulation design. (There is more than one passage within that housing)

The temp sensor for the computer (and the gauge) takes its temp reading as the hot liquid exits the cylinder head,

but the temp switch that turns on the radiator fans senses liquid coming out of the bottom radiator hose after it's had a chance to be cooled within the radiator.

Because of this, the fans can take an extremely long time to turn on, and a light breeze blowing through the front of the car can sometimes keep the radiator cooled enough to negate the need to run the fans.

When coolant level in the radiator is low--- there is 'localized overheating' within the engine, the cylinder head can get extremely hot due to lack of liquid within it, and the temp sensor the computer reads is really reading accurately, you see the gauge say it's overheating.
The water exiting the cylinder head really is screaming hot....but by the time it passes through the radiator and makes its way to the fan sensor, it's cooled enough to not turn the fans.


But none of this will explain why the coolant is mysteriously disappearing.

 
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IF the head gasket has it's typical small leakage problem, it will probably pass every last check your mechanic can think of.


Most people (mechanics included) can't figure out these head gaskets without help, or until it becomes a catastrophic failure.

Many people throw every part they can think of at the car to address overheat problems (fans, switches, water pump, radiator), and maybe even a heater core if you complained the heater blows cold at stops......never figuring out the root cause until after they run out of money.

 
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Ok ezone, I've relayed all your information to my mechanic (except that I should replace him lol). Having the block test done tomorrow, but I'm pretty sure I will soon be in the market for a used 2011-2015 Honda Civic LX.

Thanks again!

 
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Many of these head gasket failures can't be found using that test.

If failure is found using that test, great.
If it passes the test, that only means he needs to do a different test to prove it.

See the previous linked thread about overheating common causes. In the first post there are two videos. The longer of the two videos (about 11 minutes or so) is a demo of how I find these on the first try, and it was done in real time.

 
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WOW!!! What is the answer! This is my car exactly..I'm going crazy over this problem ..lol..really!