GoHardrGoHome

I have a '02 Civic LX where I cannot get air to blow out the left-hand dash vent. Can someone tell me if there piping behind the dash for this or is it one big box with several vent doors, i.e., I don't want to start taking things apart until I know what direction I'm going. I suspect a service manual would show a diagram of the system but I don't have access to one.
Also, it's been rather cool this last week and I've been using the heater. When I stop at a light and the engine idles down my heater starts blowing cold air! What's the reason for this? Could it be a water pump that just isn't efficient at an idle?
Thanks for any suggestions.

sumdewd

Vent? Not sure. A service manual would definitely help. Have you checked the cabin filters lately? And stupid question, the vent is not closed, right?

Check your coolant and/or bleed the coolant with the thermostat set to hot. See what's going on with it since the heater cores are run off of the engine coolant. Have you ever had issues with overcooling?

Also, these cars have a tough time blowing headgaskets left and right. If you have phantom coolant loss it can be a headgasket pressurizing the cooling system and pushing coolant to the overflow. Lack of coolant makes it so the heater core doesn't really work too well.

GoHardrGoHome

The cabin filter was recently checked...all good. All the other ports, i.e., defroster, floor, and mid-level vents all blow good air. And "no", the vent door is not closed.
I'll have to look into the coolant issues tomorrow. Note that this car has only been in my possession for about 2 weeks so I don't know a whole bunch about it. So far, I haven't noticed any coolant loss. I'll check on the level again tomorrow.

sumdewd

I wish you luck. My buddy's 2002 EX has been nothing but bullcrap for us since we purchased it. One of the first things we noticed was that the heater didn't work very well, so I hope you don't have a headgasket issue. Keep us posted. I might be able to find his service manual somewhere to assist further.

GoHardrGoHome

Ok, got the vent issue resolved. Linkage was disconnected on the vent door. As for the loss of heat at idle...I haven't figured it out. The coolant level hasn't dropped a bit since I last checked.

NDNV

Lack of good hot heat from the vents is what was the first indication I had a head gasket problem. It is a well known issue for these engines and is a major repair. Once repaired the heat is hot enough from the vents that holding your hand in front of the vent will become uncomfortable in no time. Night and day difference.

GoHardrGoHome

Checked the coolant level myself today (a friend was helping the other day) and it was a bit low (approximately 3/4 of a liter). Likely air in the system. Filled and burped the system. All seems fine now. I'll take it for a drive to work tomorrow and verify if the heat is now blowing properly...and that I don't lose any coolant from a head gasket leak.

sumdewd

How full was the expansion tank? It'll likely work for a while, then gradually get worse until you need to add coolant again. It may keep doing this in shorter cycles as the headgasket gets worse (if it is indeed the HG) You may wish to test the coolant for the presence of exhaust gases. A shop may be able to do that for you, or you can buy your own tester.

GoHardrGoHome

The expansion tank was full but the radiator was not. Seemed kind of odd to me since I thought the fluid from the expansion chamber should have been sucked back into the rad when the system cooled down. I'm going to see if I can buy a tester. When I brought the engine up to operating temp yesterday I did not see any exhaust gas bubbles in the radiator. I hope that is a good sign I'm going to pay closer attention to the coolant fluid level over the next few days and then take the necessary action as required.

sumdewd

Full expansion tank and low radiator coolant levels are red flags for a blown headgasket. A bad radiator cap or other leak could also cause similar issues.

Get the tester, and start making plans in the back of your mind to take the car off the road for an engine swap or full HG job. You may also wish to rent a cooling system pressure tester. I don't think the prognosis is good, especially if there are no apparent leaks. And don't assume it's going to be fine for a while since it's starting to cool down outside. HG leaks don't work that way but if you catch it early enough you might not have to machine anything.

Be extremely careful at this point if the tester says you have a blown headgasket. That coolant temperature sensor can only read an accurate temperature if the coolant is present, and now it might be putting exhaust vapor in there. It's usually too late if you start to see the temp gauge spike. You may also run into a situation where the sensor doesn't pick up on the actual engine temp, and it makes the car run like crap or refuse to start.