Engine warm up poll.

[Chuck Dye]

A long time ago I read somewhere that most engine wear was at startup, and I always intended to bugger up the ignition switch on my '72 240Z so that  it would crank without ignition for a few seconds to get the oil pressure up a little before lighting the fires.

Next, you'll have us back to compression releases.  

It has been 36 years since I last drove a truck with a compression release.  The drill was to release compression, spin up oil pressure on the gauge, then release the release to light the fires.  The boss paid attention, few drivers blew the drill more than twice.

[slingshot]

I crank my vehicle up and when the oil light goes off, I drive normally. I know people that let their vehicle idle for a couple minutes.  I can see that in the winter or cold months, but see little gain other than perhaps the heater generates heat a bit quicker once you are driving.

[Tallpine]

Next, you'll have us back to compression releases.  

It has been 36 years since I last drove a truck with a compression release.  The drill was to release compression, spin up oil pressure on the gauge, then release the release to light the fires.  The boss paid attention, few drivers blew the drill more than twice.

Starting my old Cat diesel, you always turn it a while with the pony motor with the compression released and fuel off until the oil pressure came up.  Meanwhile the pony motor was circulating coolant and theoretically warming the cylinders.

Finally when you think she's ready, you give it some fuel and drop the compression release.  If everything works right, you get ignition on at least a couple cylinders to keep the diesel going until it warms up and runs smooth.  The darn pony motor was so loud that you had to watch the smoke to be able to tell whether the diesel was running or not.

The flywheel engagement mechanism on mine was so worn that I had to hold it in gear until the diesel started, so it really was something of a black art 


One sawmill that I worked at had an old IH engine that started on gas and then switched to diesel.

[Boomhauer]

My Cat dozer has a hand cranked pony motor. And hydraulics? What hydraulics? Cable lift is where its at, with the two winch control levers whacking you all day

[drewtam]

It's a 5.9 liter engine...   So while I don't have the equations, I know that this increases the temp rise....  :)

What's really amazing is the fact that at a 17.0:1 compression ratio, The air temp at TDC is *HOT*...   Making some basic assumptions - moderate boost on the turbo giving me 2 atmospheres pressure at intake...  And assuming a *really* good intercooler that knocks intake temp back to 100 F...  At TDC, the air temperature goes up to almost 1300 F....


Man I love diesels... :D

Me too.

100F is a little optimistic, I usually see air to air aftercoolers achieve the 45 to 50C (113F to 122F) range at full load. Jacket water aftercoolers are obviously hotter since they track with coolant temp, they'll be around 110C (230F).

Your 15psi-g boost estimate seems a little low too, but maybe more typical for real old engines, with old turbo tech. Modern heavy duty engines are usually in the 25 to 45psi-g range. Of course, with 45psi gotta drop the compression ratio to keep cylinder pressures in spec.

[AmbulanceDriver]

I was guesstimating more in the cruise mode than WOT and load....  But looking at specs for my truck (1996 Dodge Ram 2500) max boost is 15-18 psi....

[Tallpine]

My Cat dozer has a hand cranked pony motor. And hydraulics? What hydraulics? Cable lift is where its at, with the two winch control levers whacking you all day

Mine was the rope start.  You put the knot in the slot, wrap it several times, and pull.  Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat.

It had a cracked rotor and none had been made for a few decades.  Super glue helped for a while.

It must have been quite the big deal in 1938 as it did have hydraulics.  It was really complex to operate.  It would go up or down.  Or down or up. 

[cosine]

Regarding engine warm up, I just get in and drive. If it's cold out I'll often start it five minutes before I leave, but that's because I hate driving in a cold car and I want to wait a few minutes for the cabin to warm up.

[230RN]

Your 15psi-g boost estimate seems a little low too, but maybe more typical for real old engines, with old turbo tech. Modern heavy duty engines are usually in the 25 to 45psi-g range. Of course, with 45psi gotta drop the compression ratio to keep cylinder pressures in spec.

Some of that depends on altitude, too, no?  Up here, we're at about 5/6 sea level pressure, that is, about 12.2 PSIA.  And are you sure about the psi-"g?"

The reason I ask that is because the boost gauge in my gas-powered Audi would read just about "5/6 ths" of 1 ( 0.8-ish) with the ignition on but the engine not turning, so I assumed it was reading absolute pressure.  It would go up to 1.2 or 1.3 (17.6 to 19.1 psia) with it floored.  Given the German penchant for precision, I suspect it wasn't far off, even though it wasn't reading pressure in psi, but absolute atmospheres (Bars).  Just wondered --I don't know much of anything about commercial diesels.

My Cat dozer has a hand cranked pony motor. And hydraulics? What hydraulics? Cable lift is where its at, with the two winch control levers whacking you all day.

I betcha you speak DOS, too.

Mine was the rope start.  You put the knot in the slot, wrap it several times, and pull.  Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat. Repeat.

D'ja ever watch any videos on cold-starting aircraft radial engines?  Quite a process.  Just video-google "radial engine startup."

Terry

[Boomhauer]

I betcha you speak DOS, too.

A little bit, or at least I did. I also remember Ataris.

[Chuck Dye]

I don't know much of anything about commercial diesels.

All of the trucks with intake pressure gauges that I have driven have had turbo boost gauges, psig, not absolute pressure gauges.  Those were of U.S., U.K., and Swedish manufacture.  The MAN, Deutz (air cooled!) and Mercedes I drove were either naturally aspirated, or without such gauges.  The Cummins ISX I currently drive gauges out at about 32 psi, tops.  Other Cat and Detroit Diesel engines I have driven peaked at 45+psi.  I view those gauges as largely entertaining guesstimators, barely better than idiot lights.

[drewtam]

Some of that depends on altitude, too, no?  Up here, we're at about 5/6 sea level pressure, that is, about 12.2 PSIA.  And are you sure about the psi-"g?"

The reason I ask that is because the boost gauge in my gas-powered Audi would read just about "5/6 ths" of 1 ( 0.8-ish) with the ignition on but the engine not turning, so I assumed it was reading absolute pressure.  It would go up to 1.2 or 1.3 (17.6 to 19.1 psia) with it floored.  Given the German penchant for precision, I suspect it wasn't far off, even though it wasn't reading pressure in psi, but absolute atmospheres (Bars).  Just wondered --I don't know much of anything about commercial diesels.

Terry

Yeah, sounds like your audi gauge is reading absolute pressure in either bars or atmospheres. My aftermarket boost gauge on my miata also reads in absolute pressure, except the dial face labels atmospheric pressure as 0, boost as +psi and below atmosphere as inHg vacuum. Gasolines almost always have an absolute pressure gage because they throttle the engine. As a result, during idle and low load, the intake manifold will be below atmospheric pressure.

During coasting/slowing down, in gear, foot off the gas, my injectors will shut off, and the idle air circuit will close. Manifold pressure will drop to ~1-2psi absolute. During 800rpm idle in neutral, then engine will draw ~5psi-a at the intake manifold.


Diesels, on the other hand, typically do not have an air intake throttle at all. Therefore, the diesel intake manifold never goes below atmospheric pressure... so why create a gauge that measures what never happens? Probably saves 1 cent to not have the gauge spring calibrated for that.


The absolute pressure from the turbo will depend on the altitude. For a wastegated turbo, the full boost gauge pressure will stay constant with altitude. The wastegate works on a spring and diaphragm system, and so it takes a consistent force to open it. The force is caused by the pressure differential between atmosphere and boost. The wastegate mechanically works exclusively on gauge pressure.

Except for fancy gasoline engines which like to use electronic wastegate controls. Then the workings are slightly different.

[Tallpine]

D'ja ever watch any videos on cold-starting aircraft radial engines?  Quite a process.  Just video-google "radial engine startup."

Only recently did I learn that some radials had a hand cranked flywheel for starting.  Before that, all that I had ever known about was hand-propping.   

[230RN]

Gasolines almost always have an absolute pressure gage because they throttle the engine. As a result, during idle and low load, the intake manifold will be below atmospheric pressure.
...
Diesels, on the other hand, typically do not have an air intake throttle at all. Therefore, the diesel intake manifold never goes below atmospheric pressure.

Ah!  Good points, and thanks.  

Good explanation there.

I love being iggerent.  Means I have to learn something every day.

There was something goofy about the  waste gate on my (bought used) Audi.  It  didn't "regulate" boost at all, the boost sensor just shut off the fuel pump if I  over-boosted.  I guess it was stuck shut.  Soon as I hit 1.4 Atm (or Bar*), the engine died until I let up on the gas.  I learned to kind of feather the gas to just below cutoff if I really wanted to move out. (Typically, when entering EB I-70 from Kipling --hairy-assed  entrance ramp.  Dang, I loved that car!)


'Speshully for Tallpine:

http://www.youtube.com/watch?v=WkPFRpbSU9o

Note all the smoke.  Catches fire sometimes.  

The "pony motor" is dressed in black in this one:

http://www.youtube.com/watch?v=ROnb5ouBjNc

Terry

* http://en.wikipedia.org/wiki/Bar_(unit)

[drewtam]

Wastegates rarely fail. It probably just had a bad boost control solenoid ~$50.

[230RN]

^

Oh, heck I only paid $500 for it ('87 5000 CS).  Was really in great shape, only  couple of things wrong.   

Cheapest operating car I ever owned.  31 mpg, yet powerful, and after someone rear-ended me and totaled it, insurance was only about $36 a month (no collision any more.)  I red-and-amber taped up the rear lights and put the bumper back on sorta right, and drove it for another five years. And for the most part, I didn't kick in the turbo very often.




<Back to topic, I guess.>