I may have finally discovered the cause of overheating in my venerable Deere 2040; something it's been doing ever since I bought the damned thing.

Since a new Kubota 8500M didn't arrive in Santa's bag, I resolved to get to the bottom of the overheating problem. In the process of resolving this issue, I had eliminated several of the potential problems: hydraulics, water pump, belt, fan and thermostat. I had also, run JD cooling system flush in the system as prescribed.

I had good water flow into the radiator and through it and, at one point about 18 months ago, actually pulled the radiator and took it to a shop where they pronounced it fit. This was my first mistake: assuming that the experts knew WTF they were doing.

Going back, I'm now confident it isn't the hydraulic system since, when the engine is overheating, the temperature of the transmission case and joystick return hoses never exceeds 150F or so while, at the same time, the engine is pushing 225-235F and is starting to open the pressure cap on the rad. So yesterday, I pulled the hood off, reinstalled the thermostat and proceeded to run the machine to operating temperature in order to check the radiator for 'cool' spots (ie plugged tubes) with a non-contact thermometer.

During the course of this, I also pulled the overflow hose loose from the filler neck and found that, shortly (5-6 minutes) after the engine was started, I had a slow but steady drip from the overflow. Once pressure in the system climbed a little (10-15 minutes), it was a mechanical pencil lead-size stream. It is leaking at such a rate that it would take 30-40 minutes to lose enough coolant to cause overheating....exactly what I'm experiencing during routine operation except that I thought that overheating was causing the coolant loss, not coolant loss causing the overheating!!!

I've looked at the overflow in the past but, only after the machine was hot. Never once did I see a leak but now I realize that the hose drains into a slight depression in the front axle housing and, I guess, if the engine and surrounding steel is hot, the coolant evaporates and disappears as soon as it hits the depression.

So, I shut down, pulled the cap for inspection and discovered a small crack in a brass apron just under the top of the cap. I also saw that one of the cams on the radiator neck was bent slightly downward, causing the cap to be pulled down tighter on one side than the other. I bent the cam back into place and replaced the cap with a new one but I still have a leak.

Right now I'm thinking that the radiator neck must have a leak in the solder joint between the sealing surface for the radiator cap and the collar that makes up the outside of the neck assembly. This sort of make sense because whatever hit the cap (possibly a falling branch?) and bent the cam downward probably cracked the solder joint as well. Also, a crack in that joint is the only thing that would allow low-pressure (ie less than the cap's rated pressure) coolant to bypass the cap's sealing surface and escape out of the overflow.

The radiator 'experts' simply weren't...apparently, they never tested the thing for pressure integrity. After taking it to them, I assumed that they'd done their job and, at that point, removed the radiator from the equation to follow other rabbit trails.

Tomorrow, I'm on the hunt for either, a radiator shop that can fix that neck or, a new radiator.

Jeez.

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Never a dull moment at Berry Hill Farm.