Rep Power: 0

Hey, I just bought a 1999 Honda Civic EX auto.

Drive fine for about a 40 min trip. Got home, CEL came on. Pulled the code, it's a P0420, catalytic converter. I have a solution but my biggest concern is when we got home, I heard bubbling and the reservoir was bubbling.

I filled it up, and made sure the radiator was full (with a new radiator cap).

My concern is that the water pump (& thermostat) is bad, or going bad. The temp gauge doesn't move and the radiator is constant level, no bubbles or anything.

(SIDE NOTE: when my water pump went out in my BMW I was able to diagnose the failed water pump by checking the reservoir and was no fluctuation.)

I appreciate any and all info. I have to get this car fixed and able to drive at least 30-45 min trip, on Monday.

Thanks 😁

 
Rep Power: 210

A working water pump is easy to diagnose. Start engine when cold with radiator cap removed..when it reaches operating temp coolant in radiator should be flowing at a good rate in one direction. If it's not flowing or if it's barely flowing then the water pump is failed or failing.

A thermostat is just as easy to diagnose. A failed thermostat is either stuck open or stuck closed. Stuck open the engine will take longer than normal to get up to operating temp. Stuck closed and it will overheat quickly.

I would start by parking on an incline and burp/bleed the coolant system of air.
Is the new radiator cap you bought OEM? Is the radiator fan coming on when it should?
For the next few days monitor the coolant level in both the radiator and reservoir. If you notice a loss of coolant in the radiator and gain of coolant in reservoir...chances are it's a blown head gasket. A Block Test would confirm a breached head gasket.

As far as the CEL.. Reset ECU by disconnecting the negative terminal from battery, drain residual charge by turning on bright headlights and pump brake pedal a few times, reconnect negative cable.. if, CEL comes back report here.