Thermostart Fuel System -- How it works

CurtisJ

New User
Several tractors appear to have a "Thermostart Fuel System", basically, a small container intakes fuel from injector overflow, venting excess fuel to the main fuel tank. Another line, from the bottom of the reservoir, goes to a "Thermostart Plug", that appears to be mounted in the air intake manifold. To me, it appears some fuel would always be drawn into the air input manifold. What am I missing / not understanding here ??
 
There are "dry" and "wet" systems. You are describing a "wet" system that has a fuel reservoir. When you power it, a fuel
valve opens and it lets fuel pass through. When no power, no flow.
 
No Thermostart can work without electric hookup. It has an electric heating coil inside. Some work off the key-switch when
you turn it to the left into "heat" position. Some use a relay. Dry version gets red hot and heats the air in the intake
manifold. Wet version gets hot but also lets in fuel and lights it. Ford, SAME, and Long had wet systems on some tractors.
Case and Allis Chalmers had dry systems on some models. I am sure many others I am forgetting.
 
I know of at least one model of AC tractor that has them. Had a customer 25 years ago have his mess up and dump enough extra diesel fuel into the motor that it thinned the oil really bad. He caught it soon enough to prevent engine damage. He unhooked his. Installed a better block heater and use it over worrying about the thermostart system.
 
There's a checkball operated by a bimetal coil that allows it to open and flow fuel once the heating element gets hot.
 
My White 2-105 and Oliver 1365 have them. There's a wire with a spade right on top of those. When they ignite,you can hear them pop. The White has a separate button,but the Oliver has it built right in to the starter switch so you can either turn it one way to start the tractor without it,or turn the other way part way to ignite it,then turn it all the way to start the tractor with it burning. It's handy that way in real cold weather. It runs a lot smoother if I let it burn for 5 seconds or so after it starts.
 
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The power wire is hooked to the screw. Some tractors use a separate,switch to activate.
Fords are activated when the switch is in the start position. Neutral switch in the
transmission will not let the starter engage if it is not in neutral, So in very cold
weather you can engage the key switch with the Hi -Lo shifter in gear, let the thermostart
heat up and vaporize the fuel, pop the shifter into neutral and the starter will engage and
the vapor will be pulled into the engine.If you had the air intake hose off it would not be
uncommon to see a fire in the intake either, Have seen it many times. Simms injector pumps
also have an excess fuel button that will also help cold starts.
 
You have an electrical activator, push button or key switch position. Applying voltage to the terminal supplied causes the self contained
coil to glow red (orange) hot which heats another spring, which releases "slobbering diesel" onto the red hot spring which ignites the drops
as they fall into the intake manifold.

Suction pressure from the cylinders on the intake stroke suck these glowing ember-fire balls (Great Balls of Fire....Jerry Lee Lewis) into the
combustion chamber where they ignite the cold diesel mist.

Great idea, great functionality, works.
 
The other posts sum up how it operates. That said, if you ever have an engine with a turbo falling on it's face when put under a load, and it has one of these elements, change the element before you do anything else.

I had a customer with that problem on an air compressor unit. It ran fine at an idle but bogged under a load. Turned out the check ball was leaking air into the fuel system when the unit was loaded and the turbo started building boost pressure. The little bit of air in the system would then cause the engine to bog down like it was beginning to run out of fuel. The second it slowed down, boost pressure dropped, and the engine would attempt to pick back up momentarily, and then the cyclke would repeat.

I just about lost my religion figuring that one out, but it would up being that stupid little element.
 
(quoted from post at 10:03:39 11/12/17) I know of at least one model of AC tractor that has them. Had a customer 25 years ago have his mess up and dump enough extra diesel fuel into the motor that it thinned the oil really bad. He caught it soon enough to prevent engine damage. He unhooked his. Installed a better block heater and use it over worrying about the thermostart system.
The AC 170/175 w/Perkins have them. I bought a 175 that had a new engine that started running rough and smoking. I decided to take it to a local shop for them to diagnose. I told them I had another injector pump that had few hours on it. They called me and had me bring the other IP in and installed it. Then they called and said it was running good so I went to pick it up and I asked the mechanic what all they did for my $500 bill. He said he replaced the IP and also disconnected the starting aid system. It didn't take me long to figure out that that was the problem all along, it was dribbling fuel into the air intake...what a waste of $$$. Lesson learned.
 

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