99 Honda CRV Overheating

Hello All - I recently bought this vehicle. When turning the heater on, the engine overheats. There is evidence of coolant in the grooves of the air ducts. The heater will blow cool air as if the coolant is not circulating through the heater hoses. I haven’t changed the thermostat as it seems the engine would run hot whether the heater is on or off. The engine runs at normal temperature when the heater is not on.

If it’s like my 1999 Civic, there’s a valve on the engine side of the firewall that opens and closes as you move the heater control from Cold to Hot. See if this is working. It may need the engine running to work.

You may have low coolant. Set the valve to open (heater to Hot), turn on the cold engine, remove the radiator cap, and top up the coolant while letting it run long enough for the thermostat to open. Catch any overflow in a pan and dispose of properly. Coolant is poisonous to animals who drink it. Also fill the overflow tank about half way. Cap the radiator, turn off the engine, and let it cool. Check to see if the overflow tank has drawn down. Open the rad cap and see if coolant is all the way to the top of the neck.

Coolant in the air ducts is evidence the heater core is leaking, or has leaked in the past. Was it replaced? Did someone add a sealer to the cooling system to try to plug the leak?

A head gasket leak is also possible, but check these items out first.

What do you mean by air ducts? Are you talking about the intake duct behind the wiper blade, or are you talking about the vents inside the car?

The duct (plumbing) that connects to the air filter housing.

To Shanonia - The head gaskets were changed about a year ago. If the gasket was leaking, wouldn’t it run hot all of the time, not just when the heater control is set to hot?

Coolan in the air filter ducts and it only overheats with the heater on??? Doesn’t anybody screen these posts :).

Oldtime11 is spot on, the first thing to do if figure out what’s causing the coolant turning up in the air ducts. That’s not supposed to happen, and whatever’s causing the leak could depressurize the cooling system, but only when the heater is turned on. A depressurized cooling system will almost always overheat.

If that’s not the overheating cuase, first things to suspect are the radiator cap, low coolant, or air in the cooling system.

I’m gonna spitball here and guess OP means the coolant is on the outside of the air intake (the grooves being the bendable part of the intake tubing).

I’m gonna further spitball and guess OP has a leak somewhere in the heating circuit before the lines get to the firewall. He turns on the heater and the leak depressurizes the system while spraying coolant on the intake.

OP should get the car up to temperature and then (while wearing face protection) open the hood and have someone throw the heater on while OP looks to see where the stream of coolant is coming from.

A depressurized cooling system will almost always overheat.

Well, when my daughter’s Cavalier had an external coolant leak from the head gasket, I rigged the pressurized coolant reservoir cap to run vented to atmosphere. She drove it another year without overheating before dumping the car. 50% antifreeze boils at about 227F.

I’m going to suggest that you check the heater hose where it enters the head just below the distributor.