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My honda is over heating

I have a 96 honda civic that I can’t seem to figure out why its overheating. I’ve changed the water pump, thermostat, radiator cap, and cleaned the system a number of times. It only seems to overheat when I’m on the free way and up to speed. When I get to my destination I see that the water overflow is full of water like to the top of the filler, so the water is being ejected out of the system. It also seems to have a lot of pressure in the system. Please help.

This is a situation where distinguishing between cause and effect may be very difficult, but the outcome is the same. My theory–subject to change with more information–is that you have a bad head gasket and/or a warped cylinder head, and that hot exhaust gases seeping into the cooling system are leading to both high pressure and high temperatures in the cooling system.

How does a head gasket and/or a cylinder head sustain damage?
Frequently, as a result of overheating.

So–it is very possible that an initial incident of overheating from a relatively benign cause (like a bad thermostat, or a defective cooling fan, or low coolant, or using water instead of coolant) resulted in damage to the engine, and that damage is now resulting in continuing overheating problems.

Based on the information you provided I’m in agreement with VDCdriver. I suggest you have a mechanic test for a leaking head gasket.

If you are getting an overpressure situation in the radiator then you already have a bad head gasket. It probably occured after your first major overheat. When the gasket fails in this manner you are literraly leaking cylinder pressure into the cooling system…this will make your overflow fill up and well…overflow. This is your issue…

You can fix it the right way…which is the RIGHT WAY…or you can use Blue Devil for $60.

If you are keeping the car fix it…if not then Blue Devil it…I know 3 cars that are still going strong after Blue Devil 6 years later…they had the same issue you have.

Your head gasket is definitely done…when you get this overpressure and lose coolant into the overflow it creates an air pocket in your system…which compounds the hoverheating issue you are having…Textbook head gasket failure…

I am the tech manager at Prestone and a mechanic. It sounds like you have a leaking head gasket. Highway speeds just force combustion gas into the cooling system and fill up the overflow. You need to pull the cylider head, have it checked at a machine shop and reinstall with new gaskets.

Once again you come through VDCdriver. Iam going to troubleshoot my radiator problem based on this answer. I heard the Blue Devil works terrific, your thoughts?

Going in another direction for a moment I might suggest a clogged radiator because sometimes cleaning or flushes will simply not dislodge the gunk in there.
Some radiators can only be cleaned by removing them and having them vatted out at a radiator shop.
By this point though you’re usually better off just replacing the radiator as the radiator shops around here get about 75 dollars just to vat one out.

Another possibility could be iffy cooling fan operation if this problem occurs when using A/C, Defrost, etc. but does not occur when the HEAT position of the mode control is used.
Just something for consideration anyway.

This happened twice on my Honda Civic. Both times the culprit was a clogged or poorly flowing radiator. The 2nd time I sold it.

I am unclear how that diagnosis came about but maybe there is a flow/pressure test that can be performed.