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Thermostart explanation

H

Hayburner

Member
Can someone please explain the operation of a thermostart?

After talking with a few guys, I discovered I have one on my 5000. I saw where it is installed in the air intake, but believed the key switch had been changed at one time making it inoperable because the manual says you turn the key a certain direction to operate the thermostart.

After reading some and talking to others, I found mine is operated using a button. I checked it out last weekend while doing other work, and there is voltage to it with the button pressed, but it did not seem to operate like I thought it should.

I see other references in the archives to a fuel line going to it, which mine has, but I wonder if mine is plugged.

Can someone please explain how it works?

TIA
 
It makes a small fire in manifold. Theres a valve that opens with heat and lets small amount of fuel drip in then glow plug sets it on fire in turn generates heat to help engine start.
 
(reply to post at 19:42:17 03/24/10)
Click to expand...

Thanks Shaun. Do I hold the button in until it starts? or not longer than 15 seconds? If I test it with the intake hose off, what should I see? Just smoke? I'm not sure how long to hold it in or how much fuel should come from the line. Also, do I only do this while cranking?
 
On my 1967 5000D with Thermostart I have to turn the key to the left from the "OFF" position to activate the Thermostart unit. The key is spring loaded back to the OFF position and I often have to hold it for 1 minute to get a big enough fire in the manifold to start the engine. I can stand on the right side of the tractor, reach the key with my left hand and touch the manifold with my right hand to feel how hot it is getting.
 
There is a fuel supply from the return to tank line(it"s tee"d to the thermotart fuel line). There is a power supply that heats a grid. When you switch it on, it supplies power to the grid, the fuel dribbles over the heated grid and is ignited. This warms teh incoming air charge.
 
There is a fuel supply from the return to tank line(it"s tee"d to the thermotart fuel line). There is a power supply that heats a grid. When you switch it on, it supplies power to the grid, the fuel dribbles over the heated grid and is ignited. This warms teh incoming air charge.
 
If properly operationg engage thermostart for 15-20 seconds then immediately crank engine. They do go bad, heating coils burn out, fuel lines stop up, etc. They also fail open where they leak fuel into the intake when the engine is running. I heat for 15 and crank for 15 then repeat until it starts. With a new thermostart unit sometimes you can actually hear them light off the fuel the second or third time you heat in a cycle.

It should be warm to the touch after 15-20 seconds of preheat. If not I'd remove and check it.
 
If you listen carefully when you're holding the button/key you will eventually hear a 'poof' in the manifold after 15-25 seconds depending on how cold it is, etc. When you hear the poof, you know the fuel has lit off. Crank immediately.
Basically, all that unit does is heat a coil. When it gets hot enough a bi-metallic spring opens a small valve that dribbles fuel on the valve... and the poof is the fuel igniting and burning in the manifold.

Rod
 
HB:

The thermostart device actually burns a small amount of fuel in the intake manifold to preheat the intake air.

The device has an electrical heater that heats a heat sensitive valve allowing a small amount of fuel to flow by gravity onto the heater where it is ignited. As Rod says, if you listen carefully you can hear the fuel ignite if it is working.

Many/most thermostart devices on older tractors do not work for various reasons.

Verify adequate flow of fuel from the line to the device. If there is fuel to the device and the heater element works but the fuel will not ignite, the orifice in the device is probably plugged. The devices are not expensive and easily replaced.

Dean
 

Thanks for all the responses guys. The longest I tried cranking while pushing the button was about 20 seconds....now I know I should push the button and wait before cranking.

I'll have to check mine Saturday to see how it works. I know there is voltage to it and it smoked slightly when I pressed it then ran around to see what was happening. I didn't press it long enough to see if fuel came out though, so I'll have to get some help to see what happens.
 
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