Thermostart question

thermostart definition - a heating element in the
intake manifold with 12v heater and diesel fuel added to create heat. Diesel engine.

Now, my question is when should the thermostart element be active, 30 seconds prior to starting and then turned off or 30 seconds prior to starting and it remains on as long as the engine is in operation?
My manual gives conficting information as to wiring and normal operation. In
my case I am working with a ford 555 tlb.
Thanks in advance for any insight.

I thought only Perkins used Thermo-start? Regardless, you don't turn if off for 30 seconds before starting, that would defeat the whole purpose of using it. It heats the intake air for easier starting. You can usually leave it on while cranking and once the engine starts, it isn't needed anymore. Most systems shut off automatically or are activated by turning the key backwards.Maybe you were reading the manual wrong and it was referring to only cranking for 30 seconds so you don't damage the starter?

On my 655A TLB, the switch is turned to the right for ign. and crank positions. It is turned left and held in the first position for "thermostart" activation, then turned further to the left to engage the starter, while the "thermostart" is still activated.
Then you have to remember to turn it to "ign" position to get elec. to the gauges, etc.

The type of element your talking about is actually considered a 'flame start' element. In other words the element heats and in turn opens a valve allowing fuel to be sprayed on the hot element thereby producing a flame that warms the air going to the cylinders. That being the case the element needs to be shut off once the engine is running. As far as allowing it to heat up prior to starting, it only takes a second or two for one to heat up and be glowing red once power is supplied so the thirty seconds your talking about isn't really needed with this type of heater.

Now if it's one of the ones without a fuel line it's a straight intake heater so it isn't designed to produce a flame to warm the air. In that case it does need to be powered for 30 seconds to possibly even a minute before starting in order to warm the intake air enough to do any good. The same holds true for glow plugs on most engines. Some of the newer ones even keep the intake heater or glow plugs powered for a time after the engine starts just to assist with firing the fuel in the name of reducing emissions from unburned fuel caused by a cold engine. Hope this all answers your questions.

(quoted from post at 18:45:33 02/01/12) I thought only Perkins used Thermo-start? Regardless, you don't turn if off for 30 seconds before starting, that would defeat the whole purpose of using it. It heats the intake air for easier starting. You can usually leave it on while cranking and once the engine starts, it isn't needed anymore. Most systems shut off automatically or are activated by turning the key backwards.Maybe you were reading the manual wrong and it was referring to only cranking for 30 seconds so you don't damage the starter?

Click to expand...

My DB Case had it if the surroundings were quiet you would hear the poof of the fuel ignite in the manifold when it landed on the heat element.

I monitored the voltage on the thermostart. With the key in the normal position and power to the instrument panel there is 12v to the thermostart heater all the time. I agree that it should be turned off after starting. Mine has
burned out and a new is on order. Concerning the key switch, mine appears to be different than the 655tlb but I will check the part number. I may have a bad switch that has been rewired. The schemetic appears to agree with the way the switch is wired now, which has the thermostart element on all the time.

Can you turn the switch to the left? Take the switch out and use a voltmeter to understand how it works and then wire the glow plug to the terminal that turns on when the key is turned to the left.
If someone has put in a switch that is different they probably wired it wrong. Rather then buy a new key switch which is expensive, just buy a button switch that you can hold down while you crank the engine. Actually this is better anyway because you can push the button down and wait a couple of seconds for the glow plug to get hot, and then crank the engine. That's what I did when I lost the keys to my tractor and priced the switch from Ford. I just used the switch out of an old car. When you buy a new glow plug, before you put it in, put the juice to it and count the seconds before it turns red. That way you won't be cranking the engine and wasting battery power, because it won't start anyway until the diesel lites in the manifold.

CAV/LUCAS/DELPHI spec manual lists low, medium, and high flow thermostart units in both 12 and 24 volts, none should be used over 1 minute or there is risk of failure that fuel sealing ball will no longer seat when unit is off. Can usually hear flameup after 15 seconds if in quiet area. Works well if used correctly, safer than ether.

I had MF and Fords (have) with the slobbering flame thrower TS. My 3000 has a button you push to to power the coil whereeas my 4600 had a specific position on the key switch. With the button, you put the key to the on position, push the button and hold it and then move the key to the next position which is start. Once she lights off, you release the button and the TS deactivates.

On the 4600 you went from off to on where the idiot lights lit, to the next position where the lights went out (indicating that you were in the TS position) and the TS was activated. After holding that for as long as you felt necessary, you went to the start position where the TS was still activated. Upon releasing the key, after the engine lit off, releasing the switch caused it to go back to the on position and the TS was deactivated.

On the MF 35 Perikns 3 cyl, I had to install a new one and just don't remember when it was on and off. I would think that anyone with any sense in design would not leave the TS on indefinitely......coming back to me. As I recall the MF had a ccw switch position which was the TS on spot. After you thought things were warmed up you immediately turned the key to start and upon releasing it returned to the on position. The TS activation switch was not in the circuit in the on position.

Mark

I posted the original question about the thermostart. I replaced the TS element because the old one was burned out. I also replaced the ignition switch. I added a pushbutton switch and rewired the circuit so the thermostart element is only active when the pushbutton is on. Works great.
Also had the fuel injectors cleaned and rebuilt. One of the injectors was definitely bad. The 555 tlb now starts good in cold weather, down to about
32F without the block heater. Thanks to all who responded.