Ford 7600 Thermostart

[DBakerPE]

I have a mid-80's Ford 7600 diesel tractor with the Thermostart feature. Not sure about specific ID's since the nameplate was destroyed before I got it. It was very hard to start recently so I put an ohmmeter on the thermostart lugs and it reads open circuit. This unit has a shaft about 3 inches long coming out of the intake manifold with a piece of round sheet metal on top of it about 3 inches in diameter. It has two spade lugs that fit to the wiring harness. The penetration into the manifold looks round and smooth. No obvious way to remove it. The replacements I see when searching online don't look anything like what I see on the tractor. Does anyone have experience with replacing one like it?

 

[joecdeere]

picture?

 

[Harry in Ky]

What you're describing sounds more like the sensor for air cleaner restriction rather than the thermostart. Is it threaded into the intake manifold, or into a section of intake tubing between the manifold and air filter?

 

[Tractorboy88]

What you're describing sounds more like the sensor for air cleaner restriction rather than the thermostart. Is it threaded into the intake manifold, or into a section of intake tubing between the manifold and air filter?

X2.

Are you using the cold start advance feature on your injection pump?

 

[DBakerPE]

What you're describing sounds more like the sensor for air cleaner restriction rather than the thermostart. Is it threaded into the intake manifold, or into a section of intake tubing between the manifold and air filter?

Good point. The manuals I have don't mention an air cleaner restriction sensor, so I focused on the first thing I saw on the air intake line with wires connected to it. Is that sensor an on/off switch (so open circuit would be the normal reading with the engine not running)? I'll try to look closer and get photos tomorrow.

 

[DBakerPE]

Yes, the cold start button on the fuel pump seems to be working OK. Just a lot harder to crank this winter than last.

 

[DBakerPE]

What you're describing sounds more like the sensor for air cleaner restriction rather than the thermostart. Is it threaded into the intake manifold, or into a section of intake tubing between the manifold and air filter?

This is the device I initially saw, which is probably the air flow sensor in the intake pipe.


This is looking down on the front end of the intake manifold, which is probably the thermostart. It measures about 1.2 ohms to ground, and the wire to it gets 12 volts when I turn the key to the preheat position, so there is nothing obviously wrong. The tube coming straight out the back goes to a connection near the middle of the block, which I assume is a low pressure fuel line.

I guess I'll just try prewarming the injector lines and intake manifold with a heat gun the next time it's been below 20 when I need to start it.

 

[joecdeere]

you are correct on both pictures, I don't know how long you're holding the thermostart button, but on my 345c it's about 40-50 seconds before you can hear it heat enough to release fuel and ignite.
I tested mine and everything showed OK, but cranking wasn't up to par. I used my laser thermometer to see when it began to heat in the manifold. Now I know how long it needs to be held. Cranks like a charm with the right amount of time.

 

[DBakerPE]

you are correct on both pictures, I don't know how long you're holding the thermostart button, but on my 345c it's about 40-50 seconds before you can hear it heat enough to release fuel and ignite.
I tested mine and everything showed OK, but cranking wasn't up to par. I used my laser thermometer to see when it began to heat in the manifold. Now I know how long it needs to be held. Cranks like a charm with the right amount of time.

I've never heard any sound from mine. Do you hear a flame ignite before you start cranking, or just metal expanding?

 

[joecdeere]

If it's really really quiet out and you're right up at it, I hear the flame start, but mine is lots smaller and closer to the ground.