I have a 2003 Civic EX with 60,000 miles. It started overheating and the heater was blowing cold.. First mechanic bypassed the fan relay, I put a new relay in..no change. Next changed the thermostat, fan temp switch, no change. Lower rad hose was not heating up, fan not going on (though the fan was good). After my son had driven the car after mechanic number one had "fixed" the problem, we bring it to mechanic number two, who has the car a week and tells me I need a new engine or major rebuild because he has seen the head gaskets go on these and the car had overheated. Meanwhile there are no other head gasket symptoms, smooth idle, no smoke, no bubbles on the dipstick,no oil in the coolant. I take the car home and it sits for a month, I'm not convinced it needs a head gasket, though looking at You tube videos of bubbling coolant with the radiator cap off is starting to make me think it is the head gasket. I go to mechanic #3 because I have done everything I know and maybe mech #2 is right. We go through everything again..he's not convinced it's the head gasket..maybe the radiator??.but it's not clogged. Then we notice the expansion tank has crystal clear water in it ..no antifreeze... We remove the expansion tank and the inlet at the bottom is completely clogged. Clean it out..problem solved!!!!! The temperature gauge sits right below half and I have plenty of heat!

 

what the hell was it clogged with?

 

Good question..just sediment collected at the 90 degree elbow and my crack mechanic #1 didn't do a thorough flush/check..there was nothing coming through that expansion hose.

 

hm.... possible stock leak residue? has anyon ever put stop leak in your cooling system? because that would be a big no no.

 

No stop leak that I know of...it wasn't like there was a bunch of sediment on the bottom of the expansion tank, just something got in there..I got the car 20,000 miles ago at 40,000, now at 60k i hope all the bugs are out..

 

Mixing coolant types from Honda coolant to the store-bought standard green coolant or GM orange coolant, will cause gelling and clogging.

 

What is so special about Honda antifreeze that it cant be mixed with other antifreeze?.

 

Chemical composition. When mixed with standard store-bought coolant, it tends to gel and turn to a molasses like substance.

 

with that being said, i would run a coolant flush through the entire system, and then run water through it until it runs clear, and then i would fill the rest up with honda coolant. thats just me. some people wouldnt run water through the system, but i just want to make sure everything is out.. debris, gunk, etc...

 

You are totally right..the car has been fine for a month , last night my son calls me and it's over heating again.. I check the expansion tank hose and this time the fitting between the two hoses was clogged, kind of greyish gooey stuff. then I notice that the antifreeze is yellow not blue. So a total flush of the system is in order with a refill of the blue antifreeze that Honda recommends. there must be a mixture of different types of antifreeze in the engine from mechanics using whatever they had around.. and it does clog the system.. I never paid attention to antifreeze colors..always thought the Prestone yellow stuff was good for everything..this is my first japanese car and i'm learning. Thanks

 

prestone isnt bad, to be honest. you will just have to do a flush at least once a year. years ago, people thought it to be okay to mix any coolant and they'd be fine. i've heard that mixing orange with the green or blue or yellow, generally causes the goopy sediment build up. orange was generally used got fords and chevy cars/trucks. i dont know what color it is now, nor do i care. haha.

 

well this is good info for people that didn't know gel could form by mixing coolant. After switching to prestone from honda ima keep an eye out.