I've looked through a lot of threads in here and can't seem to find an answer. I have a 1993 Civic DX with the 1.5 engine. I have had more than my fair share of problems with this car over heating. I've replaced every hose on it, replaced the radiator cap and the thermostat and now that it's cold here in Oklahoma I need my heater to work proper. What I mean by that is it will blow warm to semi-hot air then go to cold and back to warm. Radiator is full of coolant and reservoir has water in it as well. What is weird is that I can be driving along normal and my temp gauge will start to go up and up but if I put the car in neutral and let the idle come down the temp goes back to normal. I have drained and filled and drained and filled the cooling system multiple times and bled all the air out of it. I cannot figure this out to save my life so any help is appreciated. If there's any more details needed, just let me know. Thank you all in advance.

Deon

 

Radiator must stay completely full to the top (check with engine cold and car parked on level ground-- which I guess isn't a problem in OK). If it's always getting a bubble of air in the radiator no matter how many times you bleed it, the head gasket is probably leaking. Start engine cold with the cap off and rev it and see if bubbles come out. There should be no action in the radiator until the engine warms up.

 

Would there be any other symptoms if the head gasket was leaking? I've done all that except the revving the engine with the cap off. When it warms up it pushes coolant to the bottle and when it cools down it draws back in like normal. I just find it weird that the gauge goes up when driving then down to normal when I put it in neutral and let off the gas and then it slowly does it again.... About to sell the stupid thing, lol!

 

Intermittent heat means there's a bubble of air in the system. Often the only symptom of a slow head gasket leak is a buildup of gasses in the cooling system eventually leading to intermittent heat from the heater and overheating.

 

I had the same issue and I found the solution on my car. I have a 98 Honda Civic LX, so you may or may not have the same thing. My car has a heater water control valve in the engine compartment that is controlled by a cable coming from the control box in the passenger compartment. Look in your engine compartment by the firewall for a hose that goes to your heater core. If you see a lever on that hose, that's what I'm talking about! There should be a cable attached to it going through the firewall..if not, your cable broke. All you really need to do is push the lever towards the firewall. This opens the flow to the heater core and you will have HOT heat soon enough. My lever is at the halfway open mark so i have heat that is manageable and not too hot until I replace my cable. I found the cable costs $12 and only can be ordered from a dealer. Let me know if this helped you out!

 

You could take a piece of wire and tie the valve full open until spring. You will still have some hot/cold control because the dial on the dash moves an air door as well as the valve. In the summer in order to get full cold from the A/C the valve has to close fully; this is a common A/C related problem.

The OP's engine also overheats though, suggesting it is a different problem.