Outer Limits 4x4 Board

I recently purchased a 2001 ZD30 (R50) Pathfinder(130,000 Km) which is a great truck apart from it's overheating and raising the fluid in the catch tank. I first noticed after climbing a short gradient and about 5 minutes later the temp guage was off the clock and chucking the coolant out of the catch tank. When driven very sedately the coolant level will climb in the catch tank but will take about 8 hours for the vaccum to suck coolant back into the radiator. Ive had the Radiator inspected by a professional (Like new), new water pump and thermostat and pressure cap fitted. I've taken great care to remove any air bubbles on filling the radiator, with the nose as high as possible. Ive checked and tested the airflow meter and checked the variable vane turbo for correct operation. This truck has always had Nissan Long life coolant fitted and changed regularly by dealer (40,000) as well as Castrol magnatec oil every 5,000 Km.
The engine will idle for days without any drama and there is no coolant loss after prolonged idling when the system is pressurised. I'm worried that even after the system has been bled, that gentle flat running at 80-120 Km/h for over one hour will see the catch tank 80% full. If coolant is in the catch tank, then it's not in the radiator header tank. The temp guage now will not pass 1/2 way when driving and hill climbing but the catch tank is always very full and takes HOURS to back siphon into the radiator which worries me that this will affect cooling due to the fluid being displaced. After waiting for the radiator to cool sufficiently (1/2 Hour) before removing radiator cap, there is usually no or very little coolant covering the radiator cores. I'm worried that the next step could be a head gasket!!!
This problem seems to rear it's ugly head after the engine had been under boost/load for a few minutes. As mentioned, I can fast idle the engine without the radiator cap forever and there is no bubbles present, neither is there steam vapour from exhaust or contaminated engine oil.

I appeal to the wisdom of the group for any suggestions and advice to my dillema.

garethb wrote:I recently purchased a 2001 ZD30 (R50) Pathfinder(130,000 Km) which is a great truck apart from it's overheating and raising the fluid in the catch tank. I first noticed after climbing a short gradient and about 5 minutes later the temp guage was off the clock and chucking the coolant out of the catch tank. When driven very sedately the coolant level will climb in the catch tank but will take about 8 hours for the vaccum to suck coolant back into the radiator. Ive had the Radiator inspected by a professional (Like new), new water pump and thermostat and pressure cap fitted. I've taken great care to remove any air bubbles on filling the radiator, with the nose as high as possible. Ive checked and tested the airflow meter and checked the variable vane turbo for correct operation. This truck has always had Nissan Long life coolant fitted and changed regularly by dealer (40,000) as well as Castrol magnatec oil every 5,000 Km.
The engine will idle for days without any drama and there is no coolant loss after prolonged idling when the system is pressurised. I'm worried that even after the system has been bled, that gentle flat running at 80-120 Km/h for over one hour will see the catch tank 80% full. If coolant is in the catch tank, then it's not in the radiator header tank. The temp guage now will not pass 1/2 way when driving and hill climbing but the catch tank is always very full and takes HOURS to back siphon into the radiator which worries me that this will affect cooling due to the fluid being displaced. After waiting for the radiator to cool sufficiently (1/2 Hour) before removing radiator cap, there is usually no or very little coolant covering the radiator cores. I'm worried that the next step could be a head gasket!!!
This problem seems to rear it's ugly head after the engine had been under boost/load for a few minutes. As mentioned, I can fast idle the engine without the radiator cap forever and there is no bubbles present, neither is there steam vapour from exhaust or contaminated engine oil.

I appeal to the wisdom of the group for any suggestions and advice to my dillema.

The new cap wouldn't be the first new part to ever fail. Its cheap and could be as simple as that.
Your mechnic should be able to tell pretty quickly with a Co2 test if its the head pressurizing the radiator. Have you had the radiator out? Did he just pressure test it. Pulled mine and it was 1/3 blocked with leaves and shit that couldn't be seen between it and th air con.

Thanks for the reply... Yep, I've had the Radiator out and it appeared as new so I sent it to a reputable radiator shop where they removed the tanks and inspected/rodded the cores as a precaution, It was like new without any blocked cores etc.
One of the first items that I tried was a genuine Nissan radiator pressure cap as I thought that the seating depth of the origional cap (Not OEM) was not putting enough pressure onto the inside of the radiator filler neck.
As of yet I havnt managed to get a co2 test done on the ccolant and am following this up. Also I've heard that the EGR on the Z30DDTI can be suspect and can cause all sorts of problems with coolant temperature.
I've checked the catch tank and hose/connections for leaks as well as when the engine is cooling down, takes ages for the excess coolant to backfeed into the radiator.
...I feel tempted to replace the catch tank with another that is closer and of the same level to the height of the radiator cap and without the longer hose length.
I have a 3L 2004 Hilux for work and no matter how hard the truck is thrashed, keeps it's cool.
All the problems appear on the Pathfinder R50 to be when the truck has been under boost for some short time.
I have been told that the Z30DDTI engine is not known for spitting head gaskets or cracking heads, but going on the problems in the patrols with pistons etc, I wouldnt be at all suprised.

Fan's working?

I have'nt looked under the bonnet of that model pathy,but if the radiator does sit lower than the highest water point in the head then it still can be air pockets.

Best way I like to do it is use a hose (radiator ) and jam it in the radiator filler,fill her up.....etc

If still overheating.....I hate to say it could be headgasket. Get a pressure check done.