Cooling sytem pressure test question

[rgnprof]

I have a general cooling system pressure testing question:

As I'm in the process of putting my 250 back together I borrowed a cooling system tester to test my cooling system for leaks before I reassembled everything. I pressured up my EMPTY cooling system and sprayed soapy water to check for air leaking. It worked and I was able to isolate a serious leak around my heater valve, which I was able to fix by pulling it apart and replacing the o-rings. Pressured it up again and no noticeable, or audible leaks.

My question: Should the gauge hold the pressure in the system this way for a significant period of time without leaking down? I know the tester is designed to be used with a full coolinig system and I know that that would change the pressure in the system onced you pressured it up with air. I notice a pretty slow leak on the gauge - about half the original air pressure lost after 3 hours.

Any thoughts?

Ryan

[Mike D]

Without running the engine to operating temperature and re-torqueing, you won't get a true reading.

A slow leak could be anything from seeping past the unseated head gasket to an actual small leak at the valve in the tester itself.

Do not repeat this test until you have brought the engine to operating temperature and re-torqued. You stand a good chance of blowing out the headgasket around the cooling passages.!

[rgnprof]

That was my plan - I just wanted to try and check to see if I had any serious leaks before I reassembled the intake/exhaust manifold assembly (which is a real pain to get on and off). I already filled it once with coolant and had several leaks around the engine block coolant plate covers and around one of the manifold studs. That seems to be fixed now.

I really don't see how pressuring the system to 13-14 lbs can harm the head gasket though...?

ryan

[Mike D]

On a new head and block it wont. You might have had the head resurfaced but I doubt if you had the block "planed/trued". There are thousands of tiny fissures in the surface. Once you bring the sufaces to an even temperature and then re-torque them you will have a true seal.

It probably wont hurt to run the compression test but why take the chance? It's your dime.

[rgnprof]

Thanks Mike. I was really just trying to make sure I had fixed my leaks before I reinstalled the manifold . I didn't want to have to remove the manifold...again.

ryan