Well as you all know I tackeld the whole headgasket replacement on my Z several months back. It's been running great ever since too! I have to tap the throttle a little bit in the morning to get it to start on the first try but, other than that I don't really have any mechanical issues, big ones at least. I do see a thin seam of moisture where the block and head meet though, It doesn't leak and it doesn't grow bigger. The car doesn't overheat but it does run hot and coolant system seems to have too much pressure once the car warms up. Is it possible that the headgasket is leaking enough for pressure to slip into the coolant system? I've replaced the radiator cap, the thermostat, the water pump is good, I had to bypass the heater though because those hoses had a pin sized hole one day on the way to work. It's at least 95 in the day here so I haven't worried about a heater yet.

The coolant is new too because I ran a system flush a few weeks ago, in which you add the flush and fill up the rest with distilled water, then you drive the car for 3-5 hours on and off. You then drain the system and flush it with hose water, fill up with hose water let idle and warm up, then drain and fill up with appropriate mixture of coolant and water. I've never seen anything odd in the coolant system though, no streaks of oil,fuel, etc. The coolant didn't smell burnt or look discolored and my oil fill cap doesn't have that milky residue that gives away a blown headgasket.

Although I only had a pointer style torque wrench on hand so that's what I had to use, perhaps I could just retighten the head studs with a much better torque wrench and see what happens?

Just to recap,

New coolant
New radiator cap
New thermostat
System has been flushed
Water pump does work. . . wait, aren't you supposed to see coolant rushing through the radiator whenever you tap the throttle while the radiator cap is off? I used to see a noticable movement but, not so much anymore. Water pump actually might've gone out but, wouldn't it make a loud noise or wouldn't the car get reaaaally hot?

 

the water should flow with the rad cap off only if the thermostat is open (up to temp) or if you have no thermostat installed.

I have had experience with an overheating Z. It overheated only on the freeway but temps would drop at lower speeds. I replaced the thermo and flushed the radiator. In the end, replacing the radiator solved the problem. The flushing just didn't clean it out enough...

its still hard to say if your head gasket is blown. Can you run a compression test? That may give some info, maybe not though.

 

I don't think the headgasket is blown, . . . yet because the car runs great and I haven't seen any difference in performance between this car and my last Z, except that eventhough this is a 2+2 it feels more torquey. The radiator definitely needs to be replaced though so I should probably start looking for a good quality but, low price replacement.

Even with the thermostat open I still didn't see much fluid movement in the radiator but, I think in 100 degree weather in florida if my water pump was busted I'd have blown up by now because this was weeks ago that I noticed and I drive more than 300 miles each week.

I can do a compression test this weekend.

 

there is always the possibility of the fins on the water pump being corroded away so it still works but doesn't flow well. I think someone found that happened on a 4-cyl L-series that sat a while... but it seems to be a very rare problem.

This car is an 81, right? 1981 had the 3.9 rear while the 1979-80 had mostly 3.54 rearends. So the lower gearing helps a little with torque and the 1981+ engines had slightly higher compression. Its good that it seems more torquey.

 

It's a 1979.