Overheating - sludge in radiator/reservoir
 

Alright guys, I'm back w/ another problem, same car. 1994 Civic EX, ~230k.

I recently had the serpentine belt replaced and some other misc. work by a mechanic I trust. During his inspection/repairs, he noticed that my existing radiator cap was "cracked." I had not previously noticed this, however, my car did overheat from time to time, but adding coolant always seemed to do the trick.

Fast forward to now, with the new, un"cracked" radiator cap and I'm having cooling issues every time I drive the car. When it started two weeks ago, it was only when I was sitting still. As soon as I started moving and the air cooled the car, it was fine. Now it's getting hot even when I'm moving at highway speeds.

I opened the reservoir and radiator and the coolant in there is a a thick, BROWN, muddy consistency. It's nasty, and it honestly is the color of diarehha. Obviously this is not cool and it needs to be flushed at the very least, but where should I start fixing this problem? I'm thinking replacing the thermostat is a good place to start. I'm not going to be replacing the head gasket on this vehicle, so if that's the problem, I'm just going to keep driving it until it breaks down.

Any suggestions? If I need to provide more information, let me know. Thanks.

-Adam

I agree. Replace the thermostat, drain and replace the coolant with new 50:50 stuff, and then bleed the cooling system (see diagram).

Also check whether the radiator fan turns ON when the engine gets hot. If it doesn't, the coolant temperature switch on the thermostat housing may be bad. Disconnect the coolant switch connector and jump the 2P connector with a wire. It should now run continuously when the key is turn to ON. If so, replace the switch.

Attachment 23963

Thanks man. Is there any chance of an image/diagram like the one you posted about being available for replacing the thermostat?

That sludge is probably melted rubber.

Before replacing anything, I would remove the radiator cap and coolant drain plug. Start the car, let it warm up, and shove a running water hose in the radiator for a few minutes to remove all the brown sludge.

I don't think water would get the sludge out, I don't think it's that simple lol. Correct me if I'm wrong

The use of a garden hose to force water through the cooling system of a running engine is a well known method for flushing the cooling system of debris.

You'd be better off in the long run replacing the radiator.
It can be really tuff to thoroughly clean a cooling system.
When you flush, be sure the heater is on so it gets flushed also.