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Nissan Patrol ZD30 GU III
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Hey all,

i have a ZD30 DI with a 3 inch intake & exhaust running a cross country intercooler & remapped. Im getting a coolant issue as the water seems to be getting into the second over flow tank and then theirs air in the system... im certain the head & the head gasket is good because the car runs perfect no smoke and the oil is good.. ive bought a new thermostat and new radiator to suit. If anyone could help that would be really appreciated
 

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07 Black Patrol 3.0 / 04 Grey 3.0 Patrol / 01 3.0 Patrol
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1,417 Posts
Check for any leaks, first thing to check is the expantion overflow cap.The cap has a spring which can weaken over time and open too early. It's not too common but i would buy a new cap first just to rule out the simple things.
It's unlikely an external leak like a hose etc because then you would just be loosing coolant and not pushing it out.
Long story short the system is been pressurised and it shouldn't be. When engine is up to full temps the top hose should be soft to touch,if it's hard then the system is been pressurised.
Unfortunately these show no symtoms of head damage at all only what you are saying are the early ones. 9 out of 10 times when the water is been pushed out in to the smaller tank it's the head or just if you are lucky the cap!!
Now if the coolant level was just going down there could be many things to check like a leaking hose or clamp.
Just about the only other thing to do is change the radiator as it could be slightly blocked,but again this would cause overheating.
Another rare one is the oil cooler (behind the oil filter) sometimes these can crack and cause the system to pressurise.Rare too but it happened to me once and i didn't catch it on time and it then cracked the head after too much loss of coolant over time.This was years and years ago on my first Patrol (2000 model) this showed no symtoms only what you are getting,we done a leak down test then on the rad and indeed it had combustion gasses in the cooling system.
 

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Premium Member
2003 ZD30 Di Patrol (The rare Gold one)
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25,595 Posts
If you have replaced the thermostat + radiator and the pressure cap on the header tank is good and sealing well then I can pretty well guarantee you its either the head gasket or the head. Water pushing into the reserve tank and out the vent is a classic sign of this. This issue has no effect on power or engine temp. (Unless of cause you run out of water in the radiator.) Won't cause smoke or water/oil mixing either.
From cold. How long does it take for the top radiator hose to go hard after starting the car? If it is pretty well immediate then you definitely have a blown head gasket or cracked head. Not difficult to fix. Just a PITA to remove all the crap that's in the way so you can do the job.
Up until last week when I switched over to driving my Commodore to work instead of the GU. I had to transfer 1.2L of coolant every morning before driving the 16km to the office. Will pull it apart and fix it after xmas as I'm putting a extra high double carport up beforehand. Trust me you don't want to do this out in the open during summer. Expecially with the bonnet on which you have to do if you don't have a roof above you.
It's around a 12hr job if you can work at trade speed. Expect it to take double that if you are learning as you go. I'll do it in 16hrs as I have to take frequent breaks due to my back injury.

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GUII ZD30DI Wgn
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46,884 Posts
Hey all,

i have a ZD30 DI with a 3 inch intake & exhaust running a cross country intercooler & remapped. Im getting a coolant issue as the water seems to be getting into the second over flow tank and then theirs air in the system... im certain the head & the head gasket is good because the car runs perfect no smoke and the oil is good.. ive bought a new thermostat and new radiator to suit. If anyone could help that would be really appreciated
It maybe worth pressure testing the system before moving on, how much coolant is being pushed into the secondary tank? If only small amounts and it is not being sucked back into the system when it cools I would check the hose from the top tank to the secondary tank, if the hose clamps are not sealing correctly they may not leak as there is no pressure there but they may suck air as the system cools down. Also to get right back to basics make sure the caps are in their correct position. Worth a look anyway.
 
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