2000 Honda Civic Overheats While Driving

HONDA CIVIC
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MARKRD
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I need help with a 2000 Honda Civic 1.6L SOHC. When I drive the car, I lose heat (inside blows cold air) and the heater gauge climbs (red line). After a few moments, I get the heat inside the car back and the temp gauge goes back to normal. When I check the radiator, the coolant level is down, but the overflow is full. I can pour the excess from the overflow to fill the raditor. Sitting (in driveway throttle in various modes) I can't get it to overheat and seems to run normal. Only can get to overheat when the car is moving. I have replaced thermostat (twice in a month), pump, raditor & cap. Purged the cooling system of air and still get the same result. :? To me seems like a thermostat problem, but have put new ones in with same results. Head gasket or something simple?? I can only drive for a very short distance before it does this. Thanks for any help.
Jan 8, 2007 at 12:19 PM
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BRUCE HUNT
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If the thermostat is new and installed correctly, not backwards, possible to do on some vehicles, I suggest watching the coolant level to see if it drops. I would also check out the plugs to see if they are burning correctly. Note if you smell anitfreeze in the plug hole. Is there any coolant on the plug? Do you smell any different smells out of the exhaust. With the radiator cap open and the engine nice and warm, is there any bubbling in the radiator? After all that you have done, I suspect that the engine has gotten very warm at one time or another and the head is warped causeing the gasket to leak.

Let me know what you find on those questions.
Jan 8, 2007 at 1:43 PM
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MARKRD
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The thermostat is in correct. Same as old one and as per manual. As for the plugs, they do not look like they are burning antifreeze. The color looks good. I do not see or smell "sweet" smell in the head (plug holes) or exhaust. The head gasket is what I was leaning toward but the signs lead me away. Is there anything connected to the transmission besides the oil lines to the raditor? Problem seems to happen when the car is moving. Thanks for the help.
Jan 8, 2007 at 9:33 PM
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BRUCE HUNT
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Has the engine redlined for heat before? If the system is loosing coolant and there is no leak externally, it is going somewhere and the only hole that takes it in and makes it disappear is the engine.

Do you get any bubbling in the radiator?
Jan 8, 2007 at 11:44 PM
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MARKRD
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No redline until now. The coolant appears to be going into the overflow tank, filling it to the top. I can pour this into the raditor and it will fill it. It is not siphoning back into the raditor (even with new cap). This is why I was leaning away from the head gasket but can't think of anything else...I do not see any bubbling (like getting air) in the raditor. I was thinking of an air pocket or blockage, but have flushed the system and purged the air. Everything appears fine. This one really has me stumped.
Jan 9, 2007 at 12:07 AM
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BRUCE HUNT
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A system has the following:

Heater core
Hoses
Water pump
Cooling Fan
Radiator
Thermostat
Temp Sensor
Coolant

That is pretty much it and you have replaced all but the Heater Core, fan and hoses with brand new items. Correct? So, what about the prospects of a collapsing hose? The system should pull the coolant from the overflow back in to the system but it can't do so if the system is picking up air and not allowing the system to pressurize. Be honest here, any loss of power to the engine? This is really pointing big time to the head and the head gasket.
Jan 9, 2007 at 1:45 AM
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MARKRD
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This is true, I have replaced most of the system with new. I did not notice the hoses collapsing, but I have since purchased new ones (everything else is new) thinking I may have a leak in them (sucking air maybe) I keep looking away from the head because I don't see the usual tell tale signs (burning antifreeze, smoke etc..) Wouldn't this overheat when I have it sitting in the driveway idling? Or is there not enough load on the engine? I think I am going to look at this area (compression test etc) a little more. I will keep you posted and Thank You for the help.
Jan 9, 2007 at 3:13 AM
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BRUCE HUNT
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No it would not recessarily overheat. Early signs of coolant burning are hard to find. Good luck!
Jan 9, 2007 at 6:25 AM

Suggested Repair

Suspect a leaking head gasket or warped head even without classic exhaust smell or bubbling. Perform a compression or leak-down test and a combustion-gas test of the coolant. Also inspect hoses for collapse and confirm the system can pressurize and draw coolant back from the overflow.

Conversation Summary

A 2000 Honda Civic 1.6L overheats and loses cabin heat only while moving, then returns to normal. Radiator coolant drops into a full overflow tank and does not siphon back, despite a new thermostat, water pump, radiator, cap, and air purge. Idle testing is normal, plugs look clean, and there is no sweet exhaust smell or radiator bubbling. The expert says early coolant loss into the engine can be hard to detect and points strongly to a head gasket or warped head, while also suggesting collapsing hoses and system pressure checks.

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