D-4 7U problems

About 170 deg. F is ideal operating temperature.
Assuming the injector pump travel is adjusted right it sounds more like you have a worn ring problem or combination of worn valve guides and rings.
At low speed there is not enough compression to keep the rings sealing properly and at the higher speed the rings can't keep up with the sealing requirements. Along with worn rings the piston ring lands will also be worn.

If the engine is over fueled I'd expect plenty of smoke which you didn't mention.

Before you go rodding out your radiator, which is a lot of work, I would suggest as a first step of thoroughly pressure washing out the dirt caught between the radiator's air passages. Reverse flushing from the fan side usually gets most of it out. If that is not enough to cool it, then next is to flush the cooling system clean to get the mud and contamination out. Reverse flushing the radiator core from the bottom to the top usually will float a lot of junk up out of the top. Both of these are quick fixes. If these steps didn't totally cure it, nothing much is lost, so now you can take the next big step and get serious with removing the radiator core for rodding it out. When I am brushing with our D4 7U in the woods, about every 4 hours I have to stop the engine and wash the leaves out from the front of its radiator. I have a removable home made screen in the front of my radiator that gets cleaned out about every two hours of operation. With the 44 hydraulic pump in front of the radiator, it make is tough to pull the screen out for cleaning. My John Deere tractor has a corregated screen on its radiator that permits it to operate much longer between cleanings. 😄

Another simple fix for over heating that I found on our D4 7U was a loose fan belt. The fan belt turned the fan OK at an idle, but not any faster when at a working throttle speed. Taking up some fan belt adjustment, fixed that. 😎

i'm not sure i'd pressure wash the fins out. i used regular garden hose pressure with spray nozzle after soaking the fins a couple hours. its amazing how much fine dirt sets up there. its true the chaf screen doesn't keep everything out, only the largest things. good luck.

Thanks for all the ideas gang!😄

You can,t believe how much crud builds up round the outside area of the liners in the blocks where the coolant is if you never had one apart. Also it builds up and plugs the coolant passages in the starting engine block too.This all contributes to engine overheating along with the radiator.By taking the bottom radiator hose off and the block drain open you can flush the block out from a top opening but still you can,t get it a all out.

Here is an example from my D4400 #3 and #4 were badly clogged with rust and debris.

[img]http://c1.ac-images.myspacecdn.com/images02/58/l_0252e6c4a22041f9aca00f39576f72e8.jpg[/img]

Here is #2 which is pretty clean.

[img]http://c4.ac-images.myspacecdn.com/images02/46/l_7040b023cc7d4b6c93bca7aab7b923bb.jpg[/img]