99 infiniti I30 , is there a coolant leak or not ?

Question

my coolant reservoir was empty ,and I thought i was hearing knowcking from the engine ,so I took the car to firestone and , told them the synptoms , they suggested a perssure check , dun know what that means , so after the diagnosis was done , they came up with the following results ,
1) the sytem pressure was 20 Psi
2) no leaks found
3) temp guage below half
4) oil dipstick has dark brown color
5) no white smoke on the engine start
6) heard no knocks in the engine.
7) they found moisture on the oil cap
the firestone people did not know how to deal with this ?
so they toped off the coolant in the reservoir and the radiator
but told me to keep an eye on the level in the reservoir. now what I am afraid is if there is a leak internally ,its going to damage the engine ,so i dont know what to do ?
how can a coolant resevoir be empty if they found no leaks
my car is at 137 k and ran fine until i thought i heard knocking sound , but i guess it isnt knocking but stallin

Answer 1

The big question is, why are you taking it to Firestone?
Moisture on the oil cap can come from condensation when you take the car on too many short trips. The biggest thing you need to know is how low the coolant in the radiator was. If it was empty, you have a problem. If you have a blown head gasket, it can blow the coolant out of the system in no time.
For now, get an oil change and do what they said. Keep a close eye on the oil level and color and watch the coolant level. There might not be anything wrong.
Don't trust the temp gauge to tell you you're getting low on coolant. If the fluid level drops below the sensor, it won't work right.
And take the vehicle on at least ten mile long trips now and then to get it good and hot so you burn off the moisture and acids in the engine and exhaust.

Answer 2

Well the coolant is 50% water so it will evaporate some. I wouldnt be so worried by the moisture on the oil cap unless you start noticing it in the oil. If you are really worried about it you might want to take it to an actual repair shop. Firestone is more of just tires and preventitive maintenence not diagnosis and repair.

Answer 3

They are saying it isn't an external leak, and there are no signs of a blown headgasket. They should have run a test to check for gasses in your coolant reservoir to verify a head gasket or warpage of the head, but you can get a radiator shop to do that.