My 97 Cavalier has had a slow coolant leak lately, which I discovered a couple weeks ago when the engine started overheating and I found the coolant tank empty. I refilled it with water and it’s only lost a couple inches from the top since then.
So I borrowed a Motorad pressure tester to see where the leak is coming from, and the only source I could see was from the cap. It feels like I was able to get the tester onto the coolant tank pretty securely, and pressure does build a little bit before starting to leak, but I suspect maybe I’m just not get the tester secured as well as I’d hope. Could a faulty cap really be a likely source of the coolant leak?
Yes! with hoses that old it may be time to look at how tight the clamps are, and condition of the hoses. Cleaning the cap and filler neck or replacing the cap might be all it needs.
Are you saying that you used the adapter on the Motorad tester to test the radiator cap and it failed, or that the tester did not seal to the radiator properly to allow the tester to pressurize the system?
Generally you don’t lose enough coolant to really notice it through the radiator cap. If your cap has a rivet on the top you should be able to see steam coming through it when the engine is hot and running.
Leaks from hoses can be hard to find. Sometimes there’s a weep hole on the underside of the water pump near the bearings that will show leakage. It’s there so you can see a leak before the outer seal blows and dumps most of the coolant. With the engine off you might see some coolant on the pulley from behind it. Inspection mirrors can be handy there.
You may have a firewall mounted regulator valve to look at.