Radiator cap? coolant leak

Originally Posted by Darwins Child

In April we had a pre-purchase inspection done to Z. The one and only thing noted in the inspection was a leaking coolant cap. After we purchased the vehicle, the dealership handed me a new cap under warranty and I replaced it.

Since that inspection we've put on the vehicle only about 600 km. (The Mobil 1 that I put in shortly after purchase isn't even dirty yet.) Because I assumed (yeah, I know) that the coolant leak had been stopped by the new cap, I did not check if the coolant was still leaking. Yesterday, when I checked the oil level, there was the coolant leak staring me in the face. It is shown in the photos below of the area, the sealing side of the cap and the aluminum coolant pipe's cap-opening.

The rubber gasket on the cap, as well as the sealing ring on the aluminum pipe seem fine to me, but, obviously, something is indeed leaking.

This couldn't be an over-pressurization, issue, could it? Coolant temp is normal. Level is still OK in tank.

Is it possible that the machining of the opening on the aluminum pipe is faulty and not allowing the cap's gasket to press down with enough pressure on the aluminum sealing surface? Should I polish (NOT grind) that sealing surface to a mirror finish?

Today I'm taking the vehicle back to Nissan for their assessment. But before I do that, because I doubt if our Z is the one and only Z to have this problem, I thought I'd ask here if other members of the forum have had this same problem and, if so, what the solution was.

Thanks.

Originally Posted by Jhill

Wouldn't be from over pressure as that would just make the cap open and dump into the reservoir. Looking like more possibly a porous aluminum pipe. I would first recommend using a cooling system pressure tester and leave it overnight (after cleaning the area of course). Then see if you find and traces/wetness around the pipe, flags area etc. it may not show as it may only be happening when hot and the aluminum spreads out. If that is the case they have dye you can put into the cooling system and then check with a black light to find the source. Might even just be a bad hose clamp and wicking onto the pipe, fluids can do some weird stuff sometimes.

Originally Posted by Darwins Child

Speaking of hose leaks and clamps, notice the area pointed out by the arrow in the photo below. If the cap is leaking, why would there be coolant residue on that small pipe in that particular area? Is that pipe ever substantially pressurized during normal operation?

Do you think that Nissan's small and large OEM hose clamps shown in this photo clamp down / seal those hoses against the pipes as well as say traditional stainless steel hose clamps that are tightened with a screw?

I ask because I'm wondering if I should save some time, travel and trouble and replace those two OEM clamps with those I just mentioned, because the more I think about it, the more I think that it is not the cap that is leaking.

Thanks.

Originally Posted by Jhill

Usually the Oem clamps I prefer. Very rarely do I have issues with them. They are also nice because they eliminated the possibility to over tighten. People usually have a bad habit of over torque the screw type, the bands have a sharp edge and eventually cut through the hose. The Oem have nice smooth thick edges and can last a lifetime. Again I recommend cleaning and pressure testing. That will tell you right away.

Side question. Is yours a 2012 +? I can't read the cap but it looks to me like it has the pressure relief in it? If so and you have a 2012+ then that is the wrong cap. The one on the pipe should be solid, no relief and the one on the reservoir should have the pressure relief.