EliseKStewart

Hi everyone, I'm sure this has been asked and answered a thousand times but I am stumped.

Car: 2002 Civic EX 1.7 SOHC 139,053 miles

Problem: Overheating, heater won't work and fans turn on when AC is running.

*Please note: oil is not milky, no white smoke, no leaks.

Actions we have already took: Replaced water pump and gasket, thermostat, alternator (because a bolt broke), all belts, checked all fluids they are good. Flushed radiator, heater core and motor: no blockages. Checked head gasket by starting motor with cap off, no spitting, bubbling or anything out of the ordinary.

Could be coincidence that 1 week ago my check engine light came on, used an OBD 2 said my cylinder 1 was misfiring. Changed plugs and coils. Light hasn't come on since.

Anyone have any ideas?

ezone

Radiator gets low, then it overheats.
Radiator got low --- and at the same time the reservoir level increased dramatically, or overflowed while driving


Head gasket.

mikey1

all of this was likely a big waste of money,

your head gasket is blown

MN-02-CivicEx

Your post sounds like you've already eliminated the possibility of a leaking head gasket (internal and possibly external?). It's not uncommon for most Motorheads to over-react with a worst case scenario. Considering all your due diligence it could be something as simple as an air lock OR then again an external coolant leak past the head gasket.

Your scenario (heater not blowing hot air) is typical of age old overheating ... "low coolant level in radiator, engine overheating, no hot air when turning on heater fan" with the challenge being to solve the problem. Assuming the head gasket is OK, then the problem is more likely one of the following: (1) Faulty thermostat; (2) An air lock preventing coolant circulation; (3) Leaking coolant hose; (4) Faulty waterpump. And in the scenario already mentioned by ezone and mikey1 the likelyhood it's; (5) An external head gasket leak. First though do a double check of other possibilities.

If it's an air lock, assuming water pump, thermostat, hoses are OK run your EX up on ramps for a couple reasons. Then with the engine idling with radiator cap removed see if you can keep adding coolant until it won't take anymore coolant. This could take several minutes if that's the culjprit. Also with the EX on ramps it's easier to get underneath, if there is an external leak, to see where cometh it from. It could be as easy to fix as a slow leak from the lower radiator hose. If it's a slow external head gasket leak you may be able to see some leakage and/or staining on the engine block.

If you're positive it's not the head gastket and the Water Pump is AOK, you might want to remove the Thermostat to see if the engine still overheats.

If that doesn't work (assuming head gasket isn't leaking) then it would seem some blockage(s) are restricting good circulation around the cylinder coolant passages.