2007 Xterra cooling system puzzler

[drcoastline]

New radiator. The red arrows indicate where I heard air esacpe when I squeezed the upper hose. Also where the glare is on the intake is where I have seen moisture which looked like condensation.

[drcoastline]

Overflow tank

[Scott Douglas]

The area near your thumb looks like it hasn't had an impression made on it by the area with your arrows pointing to it.
Like I said before, I've never seen a system where the overflow tank is pressurized as part of the system. They've always just been a 'normal' cap that wouldn't hold pressure.
I'd suggest laying a straight edge on the rad opening sealing surface to see if it's flat.

[drcoastline]

Originally Posted by Scott Douglas

The area near your thumb looks like it hasn't had an impression made on it by the area with your arrows pointing to it.
Like I said before, I've never seen a system where the overflow tank is pressurized as part of the system. They've always just been a 'normal' cap that wouldn't hold pressure.
I'd suggest laying a straight edge on the rad opening sealing surface to see if it's flat.

I'll check it out. In the mean time from a post (not mine) on an Xterra forum that I found yesterday.

The cooling system on the X is a closed system that doesn’t normally breathe or release pressure during heating and cooling cycles. The reservoir is part of the pressurized volume and acts as both a container for the increased volume of liquid coolant as the temperature increases and a gas separator for liquid coolant. Some coolant normally flows from the top of the radiator through the reservoir to the return path to the inlet to the water pump when the engine is running, whether the thermostat is open or closed. There are baffles in the reservoir to encourage separation of any air mixed with liquid coolant if there is sufficient liquid coolant present.

The pressure relief cap on the reservoir doesn’t release pressure in the system during normal heating. This is different than more common systems that use an overflow bottle at atmospheric pressure. They are filled with liquid and the pressure relief cap opens regularly during heating and allows the coolant to flow into the overflow bottle. As the system cools and the pressure drops the coolant flows from the bottle back into the pressurized volume. These types of systems are normally filled with liquid and don’t have a gaseous volume above the liquid. The pressure build up is more a function of the liquid expanding rather than just the vapor pressure increasing as the temperature increases.

The pressure relief cap on the X has a 16 psi relief pressure. The cap should stay sealed with a 50:50 water to antifreeze mix easily past 250F. If the cap is releasing pressure at a lower pressure then both air and gaseous coolant, both water and antifreeze, are being released from the system. A small volume loss of coolant won’t affect the cooling performance of the system. But if the loss continues it will result in higher temperatures which will accelerate the coolant loss. A leak in the system will have the same effect.

Some thoughts and Observations

The cooling system is essentially a closed volume with two phases, liquid and gas. The liquid is a water and antifreeze mixture and the gas is an air and coolant vapor mix. If the system is in good repair and properly charged with coolant liquid will be circulated by the pump and gas will collect in the reservoir chamber above the liquid. The reservoir is baffled to separate gas trapped in the liquid and prevent it from flowing back to the pump.

If there isn’t adequate liquid, the gas will continue to circulate with the liquid and compromise both the cooling function to remove heat from the engine and heater core’s function to provide hot air. The reduced performance of the heater is probably the first indication that there is a problem.

From observing the system with reduced coolant it is obvious to me that air is circulating through the system, not collecting in some pocket and preventing flow. If it was collecting and preventing flow, an increase from 600 to 1200 rpm wouldn’t clear the pocket nor would slowing from 1200 to 600 rpm allow enough time for air to collect. The temperature change of air from the heater occurs to quickly for air to be collecting in the core. If the is air circulating, it is directed to the heater core from the manifold at the back of the heads before it can reach the radiator. From there it circulates back to the pump. Without adequate liquid the air will continue to circulate

If you are having to add coolant regularly there is a problem that should be corrected. The way the X cooling system is designed there should be minimal loss over time, the system is essentially sealed during normal use. If the system is leak-free and the pressure relief cap is holding the design pressure, the system shouldn’t be releasing air and vapor. The system will pressurize during heating and will de-pressurize on cooling without venting to the atmosphere.

A pressure relief cap that is either leaking at the seal or isn’t holding the design pressure will release coolant over time in the form of vapor. There may not be evidence of coolant being lost so this type of failure is harder to detect. New quality pressure relief caps aren’t that expensive and are readily available.

[Scott Douglas]

Interesting. So they're trying to make the overflow tank do double duty by acting as a reservoir of the radiator.
I wonder what would happen if you closed off the lower hose of the 'overflow' tank at the pump or where ever it goes back into the engine, and ran the hose at the rad cap down to it instead, turning it into a true overflow tank so to speak.
I really don't see how the tank can allow fluid to go back into the radiator when it cools unless it is full to the brim. Even then, how would the coolant be sucked back into the radiator once the fluid level dropped?

[Scott Douglas]

When we picked up our Alfa out in Palm Springs, we had a chance to see how a cooling system really operates. The car was running so hot it was pushing coolant out the cap of the overflow tank. We (my son and I) would stop at every watering hole along the route home and cool the radiator down by pouring water out of a bucket onto it, all the while keeping water in the overflow tank. It was a great lesson for my son as he had doubts about the water going back into the radiator, I think. That was a long drive home, especially for my wife as she was following us in the van. At least she had A/C so was comfortable. It was 114* that day and plenty hot even as the sun was going down.

[drcoastline]

Ran to Advance today to pick up the new pressure cap. While there another Xterra came in. I talked to the owner explained my situation and asked if I could look at his cooling system. When the vehicle is off the system loses pressure. When you squeeze his radiator hose his radiator makes the same hissing sound at the radiator cap.

[oldE]

Is it just me or is the rubber seal in the rad cap shown in your hand compromised around the 4 o'clock position?

Best
Les

[drcoastline]

Originally Posted by oldE

Is it just me or is the rubber seal in the rad cap shown in your hand compromised around the 4 o'clock position?

Best
Les

It's the photo it's a little coolant on the cap. I checked the cap and flange earlier today.

[mattdavis11]

You need a cap with a deep plunger for that radiator. Over flow cap looks wrong as well.

[drcoastline]

Originally Posted by mattdavis11

You need a cap with a deep plunger for that radiator. Over flow cap looks wrong as well.

It seems this set up is correct. Flat cap on radiator pressure cap on the over flow. I had it as you said it makes sense. This system for some reason is reversed.

This morning I ma going to go through the system of filling the radiator and over flow as described above. Then I will watch and see what happens.

[drcoastline]

Originally Posted by Scott Douglas

The area near your thumb looks like it hasn't had an impression made on it by the area with your arrows pointing to it.
Like I said before, I've never seen a system where the overflow tank is pressurized as part of the system. They've always just been a 'normal' cap that wouldn't hold pressure.
I'd suggest laying a straight edge on the rad opening sealing surface to see if it's flat.

Checked the cap gasket and the flange around the filler neck both appear to be in good shape. As I stated in the response to OldE I had a chance to look at anthor X and the same air sound occured on that one. So for now I am not going to blame the radiator.

[Scott Douglas]

I know I'm not the sharpest tool in the shed, but I just can't wrap my head around the logic of how this system is supposed to work. I'm out of ideas on how to fix your problem other than drive the car a lot longer before going to be tested. Only way I know of to get it hotter short of putting some cardboard in front of the radiator to cut down on it's ability to cool.

[Ayles]

Maybe going back to basics here, but I was able to get all the air out of my Xterras cooling system by using a funnel designed to help burp the system.

I had tried doing it on an incline and couldn't get that to work.

https://www.amazon.com/gp/product/B00A6AS6LY/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&th=1

[drcoastline]

Originally Posted by Scott Douglas

I know I'm not the sharpest tool in the shed, but I just can't wrap my head around the logic of how this system is supposed to work. I'm out of ideas on how to fix your problem other than drive the car a lot longer before going to be tested. Only way I know of to get it hotter short of putting some cardboard in front of the radiator to cut down on it's ability to cool.

No one I know has been able to wrap their heads around this system so you are not alone.

[drcoastline]

Originally Posted by Ayles

Maybe going back to basics here, but I was able to get all the air out of my Xterras cooling system by using a funnel designed to help burp the system.

I had tried doing it on an incline and couldn't get that to work.

https://www.amazon.com/gp/product/B00A6AS6LY/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&th=1

Thanks Ayles, I have used that method as well as the hill and did them simulataneously

[Bob Kontak]

Originally Posted by Ayles

Maybe going back to basics here, but I was able to get all the air out of my Xterras cooling system by using a funnel designed to help burp the system.

I had tried doing it on an incline and couldn't get that to work.

I got it to work with a 2010 focus sideways mounted NA 4cyl. Car ramps. 3500 RPM for 30 seconds. Shut it off for 60 seconds and top off reservoir. Restart. Repeat. Took me three times and heater was smoking hot.

The high RPM's must not give the air a chance to settle into higher cavities. It just sweeps it out of the block and then it goes to the highest point.

I'm not saying it will work on the XTerra. I'm just sayin'.

I say time for another mini trip. Fingers crossed.

[drcoastline]

All that said I think we figured it out fellas. As I said I bought new caps put them in the order per the post I showed above, pressure cap on tank, flat cap on radiator. Checked fluid levels per the recommendation in the post as well.

Took it for a ride today to go pick up a few things. Wala the check engine light went out by it's self. Pulled over kept the engine running checked the hoses hard as a rock. No indication of fluid loss.

I will drive it some more and keep an eye on it.

Thank you to everyone that posted made a coment and suggestions on what to look for, I greatly appreciate it.

Great group of people here lending a hand.

Thanks again.

[drcoastline]

Originally Posted by Bob Kontak

I got it to work with a 2010 focus sideways mounted NA 4cyl. Car ramps. 3500 RPM for 30 seconds. Shut it off for 60 seconds and top off reservoir. Restart. Repeat. Took me three times and heater was smoking hot.

The high RPM's must not give the air a chance to settle into higher cavities. It just sweeps it out of the block and then it goes to the highest point.

I'm not saying it will work on the XTerra. I'm just sayin'.

I say time for another mini trip. Fingers crossed.

The last two times I used your method, it may have contributted? Don't know for sure but thank you for the suggestion.

I used your method, the hill and the funnel all at one time. I figured I would over whelm the system burp methods.

[Bob Kontak]

Originally Posted by drcoastline

I will drive it some more and keep an eye on it.

Good job! Outstanding!

Now you need to find that poor guy at the car parts store and fill him in.