McCormick B450 - Temp gauge - How does it work?

[brazosdog]

The B450 has a gauge that comes off the peg when I turn the key on, and it never seems to move even when the diesel tractor has been running for 20 minutes (and it’s 100 degrees out right now).

How do these gauges work? There is a single green wire that attaches to a bolt on the head. It’s totally electric somehow. How can I determine if the gauge is good or bad or if the sending unit is good or bad or if it’s anything else?

How do I test this type of gauge?

 

[Jim.ME]

The B450 has a gauge that comes off the peg when I turn the key on, and it never seems to move even when the diesel tractor has been running for 20 minutes (and it’s 100 degrees out right now).

How do these gauges work? There is a single green wire that attaches to a bolt on the head. It’s totally electric somehow. How can I determine if the gauge is good or bad or if the sending unit is good or bad or if it’s anything else?

How do I test this type of gauge?

The green wire is not attached to a bolt on the head. That wire is attached to a sending unit which provides a variable resistance ground, which changes resistance, as the engine temperature changes. with power to the gauge, ground the sender terminal on the gauge and see if the needle moves full scale. You need to be sure the other terminal on the gauge is getting power.

You can remove the sender and suspend it in a pan of water. The resistance should change as the temperature of the water rises.

 

[brazosdog]

Ok, so is there a fuse in that thing laying on my oil filter housing? I can get that separated but not get anything out.

Also, the gauge sits “dead” when tractor is turned off and key is off. When tractor is off and key is turned on, the gauge perks up to basically the far left of the temp range.

Edit to add: I just disconnected that wire and hooked an alligator clip to it and grounded it out with power applied. The gauge does in fact move full sweep.

 

[Jim.ME]

Ok, so is there a fuse in that thing laying on my oil filter housing? I can get that separated but not get anything out.

Also, the gauge sits “dead” when tractor is turned off and key is off. When tractor is off and key is turned on, the gauge perks up to basically the far left of the temp range.

I expect that is just a type of connector, not a fuse holder. You should be able to tell if it has a fuse in it or if the wire ends touch inside it.

How it acts key off or on is not the issue. Grounding the terminal at the gauge eliminates the possibility of a broken wire. If the gauge goes full scale, you can try grounding the wire at the sender. If the gauge moved when grounded at the gauge but not at the sender, the wire is likely bad. If it goes full scale in both tests the sender is likely bad. You asked how to test it and I gave you a method to try.

If you decide to change one or the other, you need to get a replacement unit that operates on the same ohm ranges. The other option is to get a kit with the gauge and sender in it and replace both.

 

[brazosdog]

Thanks!!!

Ok. I grounded at the sender and the gauge went full sweep. I think we’re good from there.

Might be the sender or maybe I haven’t gotten it up to temp because I noticed the gauge now read coole than it did an hour ago when it was running. Maybe it does work and I just havnt gotten the tractor hot enough. I wish I knew the ohm to temp conversion on it.

 

[Jim.ME]

Thanks!!!

Ok. I grounded at the sender and the gauge went full sweep. I think we’re good from there.

Might be the sender or maybe I haven’t gotten it up to temp because I noticed the gauge now read coole than it did an hour ago when it was running. Maybe it does work and I just havnt gotten the tractor hot enough. I wish I knew the ohm to temp conversion on it.

I would expect to find it in the service manual for the tractor, if anywhere.

 

[BarnyardEngineering]

Thanks!!!

Ok. I grounded at the sender and the gauge went full sweep. I think we’re good from there.

Might be the sender or maybe I haven’t gotten it up to temp because I noticed the gauge now read coole than it did an hour ago when it was running. Maybe it does work and I just havnt gotten the tractor hot enough. I wish I knew the ohm to temp conversion on it.

Diesels, especially older diesels, tend to run cool unless they are being worked. Sitting idling or puttering around the yard will not get them warmed up.

 

[brazosdog]

Diesels, especially older diesels, tend to run cool unless they are being worked. Sitting idling or puttering around the yard will not get them warmed up.

Yeah, that's what I was thinking. Might not be a bad idea to get it running for 20 minutes or so and then stick a thermometer in the radiator just to be sure though.