I bought a 2002 Honda Accord lx, have replaced thermostat , heater core,
Noticed coolant blown on battery and hoses, coolant leaking from bottom of radiator cap , overflow is now at top and radiator looks dry or low.
Could this be a bad radiator cap?
Do I put coolant in radiator , will it cause overflow to spill over

 

You should fill up the radiator with coolant.

The only way to know for sure is to get a loaner radiator pressure tester from a parts store. Pressure test the radiator to make sure there are no leaks on the system. They also have an adapter to pressure test the radiator cap. The system and cap should hold pressure up to ~15 psi. After the psi rating on the cap, the cap has a valve that releases pressure.

If you find the cap is bad, make sure you get a cap that has the same pressure rating stamped on it. You can't go wrong with the OEM part from Honda.


Here is a video on how to do this.

 

The tester I rented from Autozone had the adapters in it to test both the radiator and the cap. Turned out the cap was still good, but the rad was shot just above the lower seam on the 08 Pilot I used it on.

 

Agree with above posts.



Yes.
Yes on adding coolant directly to radiator in your situation. Buy the pre-diluted coolant, clearly labelled as such.
Only add fluid to radiator when it is cold - like 1st thing in morning. Coolant expands when heated so it needs the overflow tank half empty to have room without spilling out.

 

You need to convince yourself whether the leak under the cap is from a bad seal in the cap vs. a crack, or gouge in the rim of the radiator neck. Either way, it absolutely can result in the radiator going empty while the overflow bottle is full.

The radiator cap's job is to release coolant to the overflow bottle as the coolant expands. Just as important, the cap controls how that coolant gets sucked back into the radiator when the engine cools off.