weird performance issue

[arno]

I have been searching the forum for the last couple of days and before I have done some research on the net but cannot identify this problem or any threats that are related to the strange problem I have.
This problem has been there since I bought my 2001 GU2 3l TD about 6 years ago.

Maybe somebody has read upon this and can pinpoint me in the right direction.

When start driving the performance and power is poor but after about one hour and half I can notice a significant increase in performance.
When I say poor I mean that driving up a slope hill (highway) the speed drops from 110 to about 90k's/80k's, and thats without towing or anybody in the truck. Sometimes I have to go back to 3rd gear to keep that speed.
As an example I have been to Canberra picking up a car on the trailer and on the way back it suddenly started to pick up power and was able to keep a 110 and sometimes even more. overtaking at this speed was also not an issue at all.
When switching off and on the engine the performance keeps the same.

I understand that any issue requires troubleshooting but where to start with this???
I am in the process of getting a boost gauge installed so I can have a bit more details of what is going on but I dont wanna start throwing parts at it for no obvious reason.

Fuel, air filter and MAF sensor have been replaced without any difference. I can also tell that it has had regular service done.

I would be stoked if anybody can give me some directions even that I have provided not a lot of details.

Cheers, Arno

[threedogs]

Hi Arno , I think you need to NADS your Patrol or at least fit boost and EGT gauges,
that way you can see whats going on with your Patrol, even swap your ECM relay
with your air con relay.
Do one thing at a time and see how you go.
If your IC is oily chances are its leaking, replace it with a tigged and tested one

[mudski]

Yeah check the intercooler mate for leaks. If it has a really small pin hole leak in it, when the motor gets hot and warms up the intercooler the hole might close up due to expanding metal. And when its cold the hole is larger. If you understand my train of thought on this...
A tell tale sign off a leaking intercooler is oil deposits on the core. Especially on the underside of the cooler. First thing I'd look at.

[arno]

Thanks guys will check your suggestions this weekend!