550 temp sending unit

[super99]

I don't remember if I asked here or on Talk. The 550 that I rebuilt the motor in, when you start it up and run it for a few minutes, the temp guage goes over and rests right against the red line on the guage. New thermostat and sending unit.I had help so I took the wire off of the sending unit and grounded it and he said the needle jumped all the way over, so the guage should be good, right?? This morning I pulled the sending unit out and put the old one back in and it red lines quicker that the new one. I used an infrared thermometer and checked the hoses and block while it was running and the temp was just about 100°. It would be a pain to do, but I suppose I could take the sending unit out of the other 550 that works like it should and put it in and see what happens. Any way to check any of this different than I have so far to figure it out?? If I parked them side by side and grounded both tractor together and ran a jump wire from the in question sending unit to the guage on the other tractor would it give me a reading to figure out if it's the guage or the sending unit? I'm confused, Chris

 

[RWT]

For what it is worth, I have had problems with new senders not working right with old gauges. For me it is usually just the opposite of your problem.

I believe your gauge is fine. I think you could correct that one with a resistor in the line. You would have to find the value by experimenting.

I did it on an IH truck a few years ago with a variable resistance or a potentiometer. When you find the right place you take it out and measure the resistance and replace it with a fixed one.

This is kind of a my 2 cents but I do experiment and you can think about it. It will be a low value.

RT

 

[rrlund]

I wish I understood electricity better. Those cluster gauges are made for positive ground aren't they? You mention new senders not working like they should. I wonder if there's something about the way that they're made that doesn't match up to the whole positive ground thing?

Just thinking out loud.

 

[RWT]

It seems like the resistance of the sender is not the same as the original. I have a 1650 (well technically I still own a piece of it) that works the opposite of his but I haven't gotten back to it to see if I can correct it. Warmed up it barely moves.

Any of those tractors that came out positive ground the electric gauges are wired for that. As far as I know it won't hurt to hook them backward but they won't work.

I successfully switched an 1800 heat and fuel gauges to negative ground. It was necessary because I have the generator on an electronic regulator (modified ford) and they are negative ground. If you wonder why, the mechanical regulators these days are junk. Electronic works better but I had some trouble on the 1800 with failure. I THINK I solved it. It's been going a while now.

I looked inside of a new replacement heat gauge and those are wired such that I don't know how they work. And by the way, I know enough to be dangerous.

RT

 

[SW3]

I always had trouble with my gauge reading too cold. I replaced the sending unit with a new unit from local AGCO dealer - still had the issue. I finally replaced it with a sending unit from Korves Oliver and it fixed the problem - gauge reads correctly now. They said they run into this problem a lot. Would be worth a call to them. I am still running 12v pos ground on my 550.

 

[Ollie03031]

I have a similar problem with a new sender on my 550. I read somewhere on this forum a few years ago that the sensors from China don’t work and read hot. I need to try a new sender from a different supplier.