PrrlHKR

2001 Civic EX (VTEC, 4DR, 5SPD) 250xxx

Coolant level goes down after hour-long trips.

The car doesn't leave puddles on the ground (paper under parked car test), and the oil is not milky.

The exhaust does not smell like antifreeze, and I pressure tested the cylinders and compression was great (163,157,158,161) PSI.

I pressure tested the radiator with a tool from O'Reily's and the system did not hold pressure (the tool I loaned was leaking at the radiator connection).

I have to add a decent amount of coolant every time I make a trip - 1/2 a quart before a two-hour round trip.

Replaced the radiator this summer when I overheated while driving up from South Carolina to Pennsylvania. Replaced cap as well

1. What could be causing this?

2. I'm thinking: replace thermostat & gasket as well as water pump. Is this a logical next step?

Thank you.

ezone

When was its last head gasket done?
Typically they lose liquid from the radiator while raising the liquid level in the reservoir. Most overflow the reservoir and puke all over the battery and fans and subframe. This continues until it overheats while driving due to low level inside the radiator.

Typically, they do this DURING the long trips.
If you have to add prior to the trips, yours must be losing liquid during daily drives.


Maybe it's leaking elsewhere, maybe slow enough to not drip on your floor or only leak while moving.


If no leaks, then not a logical step IMO.
Look for leaks there, and evidence of slow leakage (dried trails and dried crustys).

I expect to see 180+ when I do it...... No matter though, could be a bunch of reasons for those results.