dkobayas

Hello,
1998 Civic DX recently bought for son. No vehicle history available. Ran fine for couple months, then had occasional overheating and coolant loss. No drips or unusual noises. Runs fine. With open radiator cap, some bubbling and froth is seen so I suspect head gasket, warp, and/or crack somewhere. Pulled thermostat out as a test (yeah I know not a good idea but we do live in warm Hawaii). Still overheated. Flushed system getting good flow through all hoses, block, radiator, heater unit, both directions. Purged air as indicated. Still overheated. Pulled top hose and started vehicle. Not even a trickle in either direction, even after priming with a hose in case there was an air bubble somewhere. Again, no noises or drips anywhere visible. This has me scratching my head... The water pump is mechanical, has metal impellers, and is driven off the timing belt. It has to be turning since the vehicle runs. Can the entire impeller shear off, or the blades? I'm going in later today or tomorrow, but wanted to see if there is anything else I should check? Anyone seen symptoms like this? Got to get the flow going, then will decide how to handle the bubbling. Thanks. -Don

ezone

Has it been running with just water instead of antifreeze?

Water and rust can literally sandblast (eat) the fins off of the impeller.

Aftermarket pump might have had the impeller come loose, and plastic impellers can crack and let go of the shaft. I've seen a lot of stuff over the years.

dkobayas

Update: Replaced the water pump and timing belt after hellish 8 hour session. The water pump looked surprisingly intact. Confusion. Blades all present, and impeller turns with shaft as it is supposed to. However with new water pump the coolant flow is now apparent when looking into the open radiator now, unlike before. Found that much of the plastic abutting the head was melted from overheating, had to chip it out and remove the dust cover in pieces. Damn! It's running now, stays cool, keeping fingers crossed.
Q1: the A/C fan works as supposed to, but the radiator fan only comes on for ~20 seconds then goes off. Is this normal? I cannot believe there is that fast a response in a sensor to say enough fan. Suspecting the thermal switch, but I don't have a socket that will fit it and it looks too formidable to try torquing with crescent wrench. Bad enough had to go out and buy a deep 17mm just for the motor mounts, and rent the O'Reilly special crank tool, but now need a big socket just for the sensor! Q2: Any tips for getting that sensor unscrewed?

ezone

Radiator fan: If the ambient air temp isn't super hot then the fan can cool the radiator just fine in short bursts. It's a tiny radiator, it doesn't take a lot.

Look at where the fan switch is located too. It's in the stat housing, and that's attached to the lower radiator hose. It doesn't take long at all for the fan switch to sense cooled liquid after the fan kicks on.

I would be watching the computers data list to see what the engine coolant temp really is, and watch where it is when the fan cycles on and off. If temperature stays within normal range, then the fan is probably doing its job.