Radiator cap? coolant leak
 

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.

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.

Thanks for the input. You may be right about the aluminum spreading or a bad hose clamp. Thanks for the recommendations for testing.

The thing I find interesting is that if coolant is leaking / spitting from between the cap's rubber gasket and the aluminum sealing surface that it is pressing against, I would expect to see some remnant of coolant at least somewhere on the gasket-side surface of the cap that is directly adjacent to the gasket.

But, as you can see on the photo of that gasket-side area, there is none, even on the downward-pointing edge of the cap or any of the aluminum just outside of the convex sealing surface, which is weird. I should have noticed whether this was also the case on the original cap, but, once again, I, as well as the tech who did the pre-purchase inspection, may have made a mistake in assuming that it was the cap that was leaking.

Thanks again.

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.

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.

As the information under my username indicates, we have a 2014. If you look at the leftmost photo of my first post you can see the two removable caps of the coolant system. The one on the lower right of the photo is on the tank, and you can see that it has a pressure designation printed on it at about the 6 o'clock position. As you can see, the other cap - the one in question -- does not have a pressure designation printed on the label. Does this difference in labeling indicate to you that the questionable cap is indeed the correct one for its location?

By virtue of the locations of the dried coolant drops on the engine relative to the small relief pipe, I'm now thinking that it's possible that that pipe has a pin-hole in it, but this would not explain the residue on top of that pipe, near the hose and hose clamp.

Thanks, Jhill.

I just now noticed the warning printed around / near the top edge of the cap's label: "never fix on the reserver tank". Therefore, I think that this is the correct cap for that location.

Yes that is correct. I couldn't see the images clearly on my phone, gets blurry when zooming.

Looking at the image as clearly as I can. Seeing the white around the metal elbow and the coolant stains below it. I suspect the small hose may be seeping and coolant wicking along that bend and then on top of the coolant pipe. Really need to do a pressure test to know.

Thanks! That should nail down what's really leaking.

Also when the coolant is at operating temp and the system gets pressure on it, move the small hose and see if coolant comes out. I had a truck that had a coolant leak and once I moved the hose coolant started shooting out of a pin hole sized hole. I would also get the cap replaced as well. And as people have previously said, fluids can move in crazy ways.

Last but not least, coolant can sometimes seal an area where it is leaking from once it dries up. So try cleaning up the coolant and put pressure on the system.

It's just the hose clamp. Spring clamps get weak over time. Clean off the area, and replace the spring clamps with worm screw clamps. Then see if it continues to leak. You should be able to get a pack of 4 clamps for $2. I'd do that instead of bringing it back to the dealer. Who knows what they will charge you for.

Remember - only work on your cooling system with the car cold (obviously).

Spring clamps can get weak but usually it's the rubber that gets worn causing less clamping force. But yes you can get it tighter with a worm screw clamp. Just do not over tighten otherwise months later you end up with a cut hose. Good idea to use a spring style 1/4 drive screw driver when tightening a worm style, this will prevent over tightening.

More great news! (Maybe more like an update.)

I did as Dreadnaught suggested and after the engine was at normal operating temperature, I wiggled and pulled a bit on the hose near the OEM clamp. There was no leakage, but I also tried rotating the hose a bit and it did indeed rotate quite easily-- too easily, IMO.

So I spent $3.79 on two stainless steel hose clamps, cleaned the tube and the affected area of any remnants of coolant, removed and saved the OEM clamp and, using a manual nut driver, installed the new clamp just tight enough so that I could not rotate the hose using the same effort that had easily rotated the OEM clamp.

We'll drive the car for some more kms and this time, after each and every ride, I'll be checking for remnants of leakage. I'm betting that there will be none. (And because I have placed a bet, there will definitely be some leakage.)

I'm glad you found that leak on the hose. ;) Also, hoses should not move easily. Your clamp was definitely worn out. And as you said, just monitor the area.

Our vehicle was purchased by its original owner in July of 2014, which means that the clamp has been in "hot" service for probably not much more than 2 years. How the heck it could have worn out in 2 years is beyond me. If it was indeed not holding the hose tightly enough, I bet it's because its spring steel was not quenched correctly by its manufacturer, or it was removed at some point and, as a result of that process, the clamp lost some of its tension.

This is why I think that it's best to stick with a clamp whose "squeeze" can be adjusted at will and re-adjusted over time.

This evening my wife and I went on a joy ride (I say "joy" because it included a stop at DQ to get my wife a banana split) that lasted about 45 minutes. No high performance anything, but when we got home I checked the usual suspect and there was no leakage whatsoever, so I believe I may have fixed with a clamp what an expert technician said required a new cap.