It might seem strange to be getting a cold weather starting tip from a fulltime RVer who, except for that brief flurry at Smokin two years ago, hasn't been snowed on in 10 years until today, but trying to start a 3126/C7 in even mildly cold weather is as difficult as starting a PSD in frigid temperatures, which is probably why I read on Pocket's thread that only half of the Denver school buses started the other day! That would be the half without a 3126/C7!

Here's a trick I've learned, and several "technical" explanations as to why it works. First of all your best chance to get started in cold weather is to be successful on the first attempt. Of course the battery will be drained some for each subsequent attempt, however, there's an even more important consideration than that, but I'll have to bore you with some graphs to help explain it.

When you crank a cold engine to start it, the pistons, cylinder walls, and cylinder head, all absorb heat energy from the compressed air. The reason a diesel starts without activating its glow plugs or AIH after its been warmed up to its full operating temperature is that with a warm engine there's minimal heat energy transfer from the compressed air to the hot cylinder walls. The graph below...

http://h1.ripway.com/ernesteugene/DG1/3 Adiabatic.jpg

...is for a for a warm start, and note that from 50* BTDC to TDC the top "pink" curve of cylinder air temperature is well above the approximately 500F temperature required for auto ignition of #2 diesel. This graph...

http://h1.ripway.com/ernesteugene/DG1/4 RPM 100.jpg

...is based on an intermediate heat loss assumption for a colder engine, and now you don't hit the required 500F temperature for auto ignition until about 16* BTDC. Also note that 2.5 HP at the flywheel is needed to crank the engine, and this seems correct because I think a starter motor draws about 200 Amps which is (200)(12)=2,400 Watts, and that's 3.2 HP of electrical power. In any case hand cranking like in the old days isn't the starting tip that I'll eventually give!

The point of these graphs is that if too much "heat of compression" gets absorbed you don't achieve the required 500F temperature for auto ignition. If you've ever stepped out of the shower all wet you've felt the "latent heat of evaporation" effect as your body heat gets absorbed by the film of water on your skin to make it evaporate, and this same effect occurs on a second start attempt due to all the wet volatile fuel that's left coating the cylinder walls from the first attempt!

So here's the tip! The best way to get started on the first attempt is to wait for 20 to 30 seconds after the "AIH" or "Wait To Start" light goes off before cranking the engine. This allows your battery to recover its surface charge so that you get a little faster cranking RPM which in turn builds more "heat of compression"!

Normally my engine off battery voltage is about 12.4 volts, after my AIH light extinguishes it's about 11.7 volts due to the current drain of the AIH, but if I wait about 20 to 30 seconds the battery recovers to about 12.2 volts, and then I crank. I also monitor the MAT during this recovery period, and it continues to increase even though the AIH has been turned off by the ECM! Both of these effects that are achieved by the 20 to 30 second wait before cranking increase the chance of a successful first start!

On my new CAT C7 I've got a VMS 240 CL made by SilverLeaf Electronics, Inc. http://www.silverleafelectronics.com/?q=node/14 , and it plugs into the data link port to access data from the engine ECM and tranny ECM, and among many other parameters, I can monitor a real time display including a time histogram log of battery voltage and MAT!

The two pics below show the beginning of a "major event" here in Las Vegas called "snow", and it's looking like I'll be needing my cold weather starting tip if I'm foolish enough to venture out in this stuff!

http://h1.ripway.com/ernesteugene/Snow1.jpg

http://h1.ripway.com/ernesteugene/Snow2.jpg

 

So much for finding a nice warm spot in the desert to ride out the winter.

What you say makes sense, but we're running glow plugs that operate independent of our WTS light. The glow plugs can stay on up to 120 seconds after key on, but the fuel pump only runs for 20 seconds. Even though the truck is supposed to hold fuel pressure for 10 minutes, there still might be a concern for fuel pressure bleed off.

Otherwise I agree 100% with what you're saying. I recently got my wife an 01 F250 since she wanted a 4x4, and when her truck wouldn't start the other morning, I simply had her turn the key on, then wait for the glow plugs to cycle off so the batteries had enough voltage to get the truck started.

I've never considered fuel on the cylinder walls having a cooling effect. I would have thought the cooling affect stepping out of the shower was more in line with wind chill that didn't have any affect on metal objects, but from a heat absorption aspect, I guess that makes sense. Nice to see your graphs back on FTE.

 

Eugene! I'm not so sure I'd call that snow...but go venture out in it, you'll be fine. Just no hot rodding.

Edit: Cool little hauler you've got yourself there too. I like it.

 

Good thorough stuff Eugene. Nice to see you around again.

 

My neighbor taught me that little trick last winter (he's got a -94 F250 psd)......I never let it go quite so long as 20 or 30 seconds.....But 10 or 15 (after the wait-to-start light goes out) anyway.....And it DOES seem to start better when cold.

Good advice.

 

When it gets down to the single digits, I wait a good minute before starting. usually watch the track time on the radio. Doing this I have never had any problems starting it. Even when it has been below 0. Looks like we are supposed to be down into the lower single digits this weekend.

 

ernesteugene? Your 3126c7 hard starting in cold weather.Have you tested your AIH to make sure the grid is working correctly.Update your heater and there is also an update on the injectors for hard starting in cold weather!

 

That is what I do as well I wait a minute or so and have not had any problems starting it other that when my GPR went south...Most of the time(well if I am at home) I plug the truck in if it is going to be down to 0 or colder (or should that be lacking heat)....

 

really sounds like freight shaker didn't add enough battery power for cold starts

 

Could be batterys are getting used up.

 

When I still had the 7.3 and it was cold out, I would almost always wait 20-30 seconds after turning the key on before starting it. It always started on the first try and without a lot of cranking.

 

Good to hear from you again Gene. I usually cycle the key through one Gpr cycle, back it off for about ten seconds, then key on until the WTS light goes off. I may be wearing out my GPs prematurely but it starts so much better with some heat in there.
It doesn't seem to matter when cold though as far as the smoke goes, like Kris has seen, but it cranks and starts every time. My truck smokes like a chimney when cold. Starts fine, idles fine, just smokes like hades.

 

I notice a slight hum after the glow light goes out. I waited until that hum stopped and it fired right up this morning in 18*F.

The engine block heater is plugged in tonight.

 

With regard to the wind chill effect, there's a boundary layer of air surrounding exposed skin that provides thermal insulation against the loss of body heat. Since the wind disrupts this boundary layer you loose some of its thermal insulation value when your skin is directly exposed to the wind. The "wind chill index" attempts to adjust for this loss of thermal insulation, but this index is very nonlinear because a relatively low wind speed is all that it takes to "blow away" most of the boundary layer, and then it takes a much higher wind speed to further thin out the boundary layer.

On the other hand, the "latent heat of evaporation" is the amount of heat energy that needs to be absorbed by a substance to make it evaporate or vaporize so that during a second start attempt "heat of compression" energy is being used to vaporize the old fuel left over from the first attempt to start as well as to vaporize the new fuel for the second attempt to start! For Kerosene it takes 108 Btu of heat energy to vaporize each lb of fuel. Well now that I've been "blackballed" from the "CAT RV Club" forum I've got a little more free time, and I'll eventually get around to doing the post to address your comment on my TDG thread about the effect of having more cylinders.

 

I haven't tested my AIH, but it seems to be working ok because I use my fancy "SilverLeaf box" to monitor the battery voltage and the MAT. After key on the AIH light illuminates, the battery voltage falls from 12.4 to 11.4 volts, and the MAT starts to increase. After the AIH light extinguishes the battery voltage slowly recovers to 12.2 volts and the MAT continues to increase. Even after the battery voltage levels out the MAT is still increasing, and I wait for the MAT to level out before cranking.

I took my truck to a CAT dealer to have the exhaust brake programmed into the "latch mode" and at that time my April 2004 ECM was re-flashed to the latest 2006 version which among other things was supposed to fix a "high altitude" starting issue.

Do you happen to know anything about the 3126/C7 fuel system? In particular the HEUI pump and the fuel pump. The 2006 engine has a "fuel pressure sensor", but my April 2004 version doesn't. I learned this because after the re-flash I got an error code for a faulty fuel pressure sensor. It turns out that the ECM program has a yes/no check box asking if a fuel pressure sensor is installed, and checking no fixed the problem. I'd like to see if I can install a fuel pressure sensor on my 2004 engine and check yes?