emergency engine shutdown Detroit diesel

[buswarrior]

No, air pressure is used to shut it down, not keep it running.

Low or no air, the engine can't be turned off.

Happy coaching!
Buswarrior

[neoneddy]

Usually they need air to shutdown, without air they will run even with power off.

[chessie4905]

I hate to think operating coach with air pressure so low it could trigger engine shutdown. What about brakes?

[buswarrior]

I hate to think operating coach with air pressure so low it could trigger engine shutdown. What about brakes?

Ha! Chessie, we are so behind the times... nobody worries about compliance or its connection to practical matters as mundane as brakes. I learned all this on the internet, cuz i am failing at being hip...

Happy new year and

Happy coaching!
Buswarrior

[richard5933]

so the skinner valve supplies air to keep an air solenoid from shutting down the engine?  If so, could low enough air pressure trigger a shutdown.  This thing had air leaks all over and the lady who sold it to me had to gun the engine for 15 minutes to get air pressure to build up enough to release the parking brakes.  So is it possible that letting up on the throttle while going down a hill could lead to the air pressure to drop enough to stop the engine?

No. You could have a catastrophic loss of air in the system and the engine will not automatically shut down. The brakes should automatically apply though, so be prepared for the bus to come to a pretty quick stop if they are working.

Before you go down a wild goose chase looking for a system fault which might have caused the engine to shut down, have you confirmed that everything with the Skinner valve controlling the shut-down cylinder is functioning properly?

The Skinner valve is an on/off switch for the air going to the shut-down cylinder. As long as it has power, there is no air flowing to the shut-down. If the Skinner loses power for a moment, air will flow to the shut-down cylinder and the engine will stop. Even if power is restored to the Skinner right away, the engine may still shut down due to the time lag of the air cylinder releasing.

So, please let us know if you've confirmed the Skinner valve is in good condition and that the wiring is solid. It's possible to test the Skinner valve with the engine not running as long as there is air in the system.

[tombuchanan]

that's been my plan to test it but I'm in wisconsin and I don't see that engine starting until temps rise a bit.  I'll post again when i'm able to test it.

[tombuchanan]

any advice on best way to test?  start the engine and jiggle the wiring on the valve to see if it triggers the shutdown?

[richard5933]

Where in Wisconsin are you? I'm in Waukesha County, and if you're near to that maybe I can lend a hand when you get to the point of trying to start it and do some testing.

The Skinner valve that controls the shut down air cylinder won't really do anything until you have air in the system. That's actually a problem with the air-powered engine stop - if you need to shut off the engine before enough air has built you'll have to do it manually as the shut-down cylinder won't do anything.

Once the bus has air built up, if you flip the switch (or turn the key, or do what ever you do to shut off the engine) the Skinner valve will send air to the shut down cylinder to move the governor to the 'no-fuel' position. Once the engine is off, if you turn it back on but don't start it, you should hear the air cylinder venting and the governor snapping back to the 'fuel' position.

You don't even need to run the engine at this point once things are aired up. If you have a way to air up the bus without running it, you might be able to test it without even running the engine. Turn on the switch and watch to see that the shut-down cylinder vents and backs off. Then with the switch still on, start jiggling wires to see if you can make it extend the shut-down cylinder again. There might be a time-out on this system. Mine will keep the governor in the 'fuel' position for about a minute before it times out and I have to power off briefly and start again.

[neoneddy]

I'm in the Twin Cities area, if you're close to the western side I might be able to come by.  I'm not too much of an expert, but I've dealt with a few issues like this.

[dizzyg44]

If I may ask, how long of a time between the shutdown and restart?

Not sure if the mc9 has the same feature as my mc8 but at about 200 degrees the engine shuts down to protect itself.  I've hit this a few times when I first started out before I learned to drive by the thermostat not the speedo....

I saw also that you mentioned that your manual said it doesn't have it, possibly aftermarket?... people do weird things to these buses during their life....

[neoneddy]

If it’s real close to 200 , I’d restart as soon as possible to get it to cool down.

I had mine do it once in a construction zone up a hill in SD. I had no where to pull over, so I shifted down and held the master switch in. It kept running then the alarm stopped and it cooled down on its own with the higher RPM.

In my opinion, letting an engine sit and cool is worse than running it to cool. The pistons and liners all have heat that is now not being carried away by water, so they will actually increase in temp before coming down. You’re better off getting it to high rpm and low load to get it cool, keeps everything moving.

[luvrbus]

If it’s real close to 200 , I’d restart as soon as possible to get it to cool down.

I had mine do it once in a construction zone up a hill in SD. I had no where to pull over, so I shifted down and held the master switch in. It kept running then the alarm stopped and it cooled down on its own with the higher RPM.

In my opinion, letting an engine sit and cool is worse than running it to cool. The pistons and liners all have heat that is now not being carried away by water, so they will actually increase in temp before coming down. You’re better off getting it to high rpm and low load to get it cool, keeps everything moving.

Good advice they are supposed to shut down at 210* when that happens most of the time the temperature keeps rising till they are cooked well done  ,The 1st warning buzzer (205*} or lite should be kept in good working order it will save you big $$$$ 

[tombuchanan]

thanks for the offers of help, but i'm in central wisconsin.  it finally warmed enough to start it so i tried wiggling the wires on the valve while it was running and nothing happened.  but, it hadn't run long enough to reach operating pressure so I'll have to try that again.  As for temp, I believe it was around 200 when it happened.  is that really hot enough to trigger a shutdown?   it restarted after about 4 minutes

[buswarrior]

The first issue, the dashboard gauges on these old buses are notoriously inaccurate.

Using the infra red heat gun on the pipes, down thru the floor into the engine room at the back, while actually making driviing heat, let's you "re-calibrate" what the gauge really means.

For instance, mine was good at 180, and rose quicker than the real temp beyond that, so 195 or so, was really 190, but they are all different.

An old detroit 2 stroke that is really showing 200 degrees has approached the precipice... you really don't want one that warm...

Happy coaching!
Buswarrior

[luvrbus]

 2 strokes do fine at 200 degrees that is normal temp 195* to 200* on generators with 2 stroke but in a bus that doesn't give you much room for temperature rise ,Sean Welch ran his 8v92 in his Neoplan for years at 200*but he watched it close