I am losing coolant somewhere. No visible leaks. I rented a pressure tester yesterday and need to know how much pressure to put in the system for a 95 lt-1. The radiator cap is 18 lbs. TIA

 

I personally would go no more than 15 to be really safe.

 

I had the same problem. Losing coolant, with no visible sign of where it was going. Nothing coming out the exhaust, nothing in the oil, no oil in the coolant. I could see no leaks in hoses or on the radiator. I borrowed a pressure tester, and it would hold 18 lbs just fine for several minutes. One hot day, I came out of the allergist's office, and saw a puddle under the car. I raised the hood and could see coolant all over the right hand side of the engine and engine bay. I started it up, and then I could see there was a crack in the radiator plastic on the passenger side. I can only guess it was leaking when it got up to operating temp, and would evaporate before I could see a leak. I guess the crack finally got big enough for me to see without it being hot and pressurized. Cure was a new radiator.

Good luck.