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Old 27-02-2007, 14:58   #1
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Cold Start Heater on Perkins 4-108

I do not use the cold start system as it has never been hooked up. But I decided to see what it would take to get it done. I fould that there is apparently a heater in the correcty place and it has two "tabs" on the top that I assume is where you apply 12 Volts to make it warm up.

BUT,,,,why is there a fuel line coming to it from the top of the filter???

My manual does not show a fuel line!!
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Old 27-02-2007, 15:38   #2
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The Perkins cold start uses an electric element to heat/burn the fuel discharged into the inlet manifold. Use a solenoid when wiring it up as it has quite a high current draw.
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Old 27-02-2007, 20:15   #3
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So in addition to the fuel being injected into the cylinders by the injectors there is also warm fuel being injected into the intake manifold???

The pressure that puts the fuel thru the heater is just the 5-6 PSI of the lift pump and I assume it is blocked unless the heater has been activated. Right.

Are the two tabs, one for heat and one to open the fuel valve and both return to ground from the engine block, or is it both done with one electrical input and the two tabs are + and - 12V.
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Old 27-02-2007, 20:49   #4
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It's a long time since I had anything to do with them and can't remember much about how they're set up but someone here will know. Don't want to steer you the wrong way :-)
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Old 28-02-2007, 02:07   #5
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Look again.
The fuel lines may be actually going to the injectors, which (if I recall correctly) are mounted just below and in front of the glow plugs (which should have a #10AWG wire interconnecting them). The glow plugs are activated (for about 7 to 10 seconds before cranking) by a push-button (N.O.) Switch, which may energise a Solenoid (the glow plugs draw about 6 - 10 Amps each).
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Old 28-02-2007, 08:59   #6
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No, its not going to the injectors. The line comes from the top of the fuel filter to the cold start mechanisum that is mounted into the side of the intake manifold. It is on the opposite side of the engine from the injectors
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Old 28-02-2007, 11:03   #7
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I haven't played with a 4-108. But normaly most engines that use this technique of one single heater in the manifold do not introduce fuel here. It simply heats the air in the manifold and the warm air is then sucked into the cyclinders. The warmer air helps to raise the combustion tem just enough to cause the fuel to ignite. The problem with this was that as the engine wore over time and combustion pressure reduced, it was not as affective as individual heaters in each cylinder. It was often a case of one or two cylinders firing and running for a few seconds before all fired up and the engine ran sweet.
I hind site, there were advantages and disadvantages to both single and multi point heaters.
As for the tube, I really don't know. Does this look factory? or something someone has added on. If I understand you description correctly, not fuel is in this line anyway, just air ??????
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Old 28-02-2007, 14:13   #8
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On my 4-108, you turn the ignition key on first for at least 15 seconds to allow the preheater to work - longer if the engine is quite cold and has not run for a while then turn the key further to engage the starter. This is outlined in the manual - maybe yours works the same way so maybe those leads on it should come from the ignition switch or maybe from the solenoid switch on the starter. Hopr this helps
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Old 28-02-2007, 14:38   #9
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Quote:
Originally Posted by Alan Wheeler
As for the tube, I really don't know. Does this look factory? or something someone has added on. If I understand you description correctly, not fuel is in this line anyway, just air ??????
The tube is 1/4" steel tube with ferrul and nut connections on the top of the stock fuel filter and it goes into the side of what appears to be a cold start heater that is screwwed into the intake manifold just below the flame arrester. The "device has two tabs that take push on spade lugs for wire, similar to the tabs on a water temp gauge or an oil temp gauge and there are no connections to them. If there is air in the fuel filter, I am in trouble....it must be fuel that is coming to the device. It all looks very stock.

My starter button is just one level and there is no key. Just pull the ignition switch out to connect the battery and instruments then push the button and off she goes.
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Old 28-02-2007, 15:26   #10
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Jim, try your search engine...

or here

Yachting and Boating World: Perkins 4-108 preheater
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Old 28-02-2007, 16:12   #11
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Are ya'll ready for the definitive answer?

The 4-108 uses what is commonly called a cigarette heater. residual fuel pressure is bled off from the fuel filter to the heater element. The heater vaporizes the fuel at the mouth of the intake manifold. This provides a warm, preheated fuel vapor directly into the cylinder after rotation of the engine starts.
The 2 wiring conectors are easy. First use 10g wire to a relay it will draw around 20a. The tab closest to the intake and on the large circular disk is the ground or negative terminal. The tab at the outer most position and appearing on the center of the assembly is the 12V + terminal.

Any questions?
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Old 28-02-2007, 16:48   #12
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Thanks, those last two posts answered all my questions. Now while I have the fuel system apart for an overhaul I will also overhaul the Thermostart. Probably wont need it here on the south texas coast, but I hate having things that dont work even if they dont need to.
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Old 28-02-2007, 16:52   #13
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Jim,
Typicly the cold start is actuated by either a reverse turn of the key or a seperate push button.
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Old 28-02-2007, 20:11   #14
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Thanks, I will rig it with a separate momentary contact "Hold it down" button for those rare mornings when it is slow starting. This past winter I was always able to get it started...a couple of times with ether applied very sparingly...but it would be nice to have a factory authorized method.

When I used ether I found a 1/2 second...or less...the minimum I could manage with my reaction time...into the intake manifold, then wait 3 minutes and try, always worked on the first turn. The three minute wait allowed for some of the ether to dissapate. Also, it takes me two minutes to replace the flame arrestor, climb out of the engine room, close the door, replace the steps to the deck then climb up to the helm to try it...#8-)

I have also been told that a rag with ONE DROP of gasoline or a spray of WD40 in it placed over the intake would also work but I was afraid the rag might get sucked into the intake since I had no way to be at the helm and at the intake at the same time.
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Old 28-02-2007, 22:26   #15
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Quote:
was afraid the rag might get sucked into the intake
You are right with that thought. A Rag over the intake is a big no no. Don't even think about putting you hand over the intake on bigger Diesels.
I don't quite see how a drop of Gasoline will cause it to fire, but seeing how American cars seem to explode so easy on TV cop car chases, maybe you have a more potent fuel than we do ;-)
WD40? that would be interesting. Never tried it, but I imagine it maybe more the LPG propellant in the can that is igniting.
As for Ether, it is OK to use it. Just not in long duration. A short squirt and start is fine. Being much heavier than air, I doubt that it would have dissappated much in the few minute of getting to the start button. My main concern with Ether is using it in such a confined space and the fact that the ether being heavier than air, you don't want that stuff settling down into the bilge.
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