GQ radiator pressure build up?

[mikeD]

G.day people having trouble with pressure build up in my 11/95 build date
4.2 deisel patrol to the extent that it is blowing either hoses or expanding radiator tubes either side of radiator core. Now i.ll give you a run down on what has been done to date to try to fix/find problem.
Initial symptoms heating up more than normal underload takes longer than usual to get back to normal operating temp.
New radiator 3 core instead of 2 start of hose blowing.No hose blowing prior just heat.
Try..
New radiator hoses
New thermostat(genuine nissan)
New radiator cap (genuine nissan)
New viscous hub (genuine nissan) old one cactus
New gaskets water pump & thermostat
Alright for about 3 weeks radiator develops leak pull out go back to place of purchase pressure test no sign leak under 20psi pressure.
Radiator back in vehicle goes another 3 weeks. Develops leak again radiator again pulled out visible distortion of inlet side tank hence leak this was figured to be possibly caused by blown head gasket. Off to the spanner men for testing of head gasket. Neither confirms or denies blown head but head removed & crack tested several times all negative so head reco,d and re assembled road test ok but still hint of pressure.
So vehicle driven by myself without incident for 400-500ks highway & suburban driving for 3 days,4th day short journey radiator inlet hose blows again GRRRRR.
So back to the spanner men for pressure releif ideas. Try diferent radiator cap no pressure at idle BUT pressure when pushed to upper operating temp & present after aswell now. So of too radiator man disassemble inlet end radiator check for clear even flow present check with clearing rod clear. Reassemble & reinstall test drive no pressure on suburban drive but increase in pressure when pushed after hill climb.Cracked block is one diagnosis but no water in the oil or gas in water that will show any way starts easily when cold.
Now i know it is a very long winded question but I am slowy turning grey & losing hair so any suggestions, answers, questions,ideas,funny jokes would all be appreciated.

CHEERS MICK...

[Dozoor]

Maybe porous block or head ,
Go to the nissan club site and ask of simaler symptoms.
I know of some motors in perticular such as the small bloke 400 chev.
these and some others made in a certian period had porous blocks and would show simaler symptoms as a cracked block or head, but the symptoms whern't as savage.

Anyone else clues?

Larry.

[mikeD]

Thanks for the reply Larry. Funny you should mention a porous block as the head service technician at central coast nissan mentioned this as a possible cause. Have you personally experienced this. I,ll try the nissan club site as you suggest got get this thing sorted as its my work vehicle which i am losing confidence in it.

CHEERS MICK...

[2car]

Sell it and buy a Toyota.

[Juzza]

Was the head pressure tested when it was off?
If not it may be that it was porous, just crack-testing may not show this!

[bazooked]

take an oil sample to a lab and get it tested ie cat sumtimes if ya cant pick up head leaks via a visual or tk tester its the last resort.had it happen here to a diesel hilux.

[Brad]

Now the cooling system is a sealed unit and to get a pressure increase like yours there must be a leak or restiction in the system.
- Pressure test it for a long period of time, like a leak down testput leave it for at least an hour. There should be no reduction in pressure.
- Does the 4.2 have water jackets ? I had a 3B which got a slight fracture in the jacket and it acted lilke a one way valve. Would let the pressure into the system but no water into the oil.
- Did the problem only begin when the radiator was upgraded ? If so what size veins has it in comparison to the 2 core ? There are many different types of 3 cores, maybe the one they used is restricting it to much so pressure builds up.

Have you still got your 2 core ? If so I would be putting it back in and seeing if it does the same thing as the 3. From your above info I get the feeling that it use to over head but not over presurise.

I hope this helps..

I know the 3B drove me nuts when the jacket went and every Tom, Dick and Harry offered advice and I still got no where.

Stick with it, it is after all just a machine...

[dangerman]

Have you taken it back to the Radiator place again ?? They say?

Id actually try another Rad place, I had a problem with my car one place couldnt fix, then another fixed it first time....

[Punchy]

air lock i would imagine...

Or a possible water pump issue

[Carl Coight]

It sounds like a blokage in your cooling system. Try a radiator frush, or perhaps pull your oil cooler off, i am pretty sure they are water cooled and it may have some crap in it. Perhaps reminants of manufacture of the new radiator.
One of the fitters at work had a simmilar problem and it was his oil cooler. (they are located in the block behind the oli filters)
Carl

[mikeD]

Thanks for the replies Carl, Punchy, Dangerman, Brad, Bazooked, Juzza. Engine is not pressurizing at present but have noticed slight water usage over the last 2 days. But still running just a little bit hot for my liking. 2 Car Ha Ha Ha very funny i did ask for jokes.