Engine shuts itself down.

[peterbylt]

1989 MCI 96A3 8V92TA, mechanical engine.

Engine starts up and runs fine no issue.

Good oil pressure, good air pressure, 175 degrees, no outstanding lights on the dash.

After 10 minutes or so of idling it activates the air valve that shuts it down.

A minute or less after it shuts down the valve pops back to normal and lets me start it again.

I did not check yet, but it occurred to me on the way back from the yard it might be something like a low coolant sensor? Do they have a low coolant sensor?

What else would trigger a shutdown like this?

I am not stuck on the road, discovered this in the storage yard, but I do have a trip planned next weekend and don’t want to be stuck on the road.

Peter

[richard5933]

I had this happen on the low coolant sensor on my 4108 - it would run for a few minutes and then shut down. Got that sensor changed and all was good, for a while.

In my 4108 there were a few systems which had safety shutdown relays, including one for low oil pressure and I believe another for high temp. The way they worked was that once a fault triggered a relay it sent power to another relay with a small bi-metallic heating element. If that stayed energized long enough the heating element bent over and cut power to the system which kept the engine running.

Once that all happened and the engine shut down, it would not restart until that bi-metallic heating element cooled off and re-established contact. Until the fault was corrected it would only run a short time.

Don't know exactly which system your bus has, but it's old enough to have one of these mechanical fail-safes installed. Check your manuals and wiring diagrams carefully to see what you've got.

[Coach_and_Crown_Guy]

The old GMCs had what they called MotoGard and it behaved exactly as you described. Usually there was also an emergency button or spring loaded toggle to get yourself off railroad tracks etc if it stopped. This had to be done BEFORE the engine quit or you were screwed. GM and MCI had a warning light come on, MCIs  would blink for a while before going full on and that was your only warning from MotoGard.

This tracks exactly with your explanation for how it was designed and implemented long before any computers were involved. If there isn't an overrode button already in place it might make sense to add one yourself and have the option of keeping the engine running... as long as you know the alarmed items are in fact still OK.

If it was high water temp you could usually downshift and lower the temp and the warning light would go out. Been there, done that. I think I'm not a fan of the whole "low coolant" sensor idea. I've heard too many cases from many brands and experienced them myself where the low coolant alarm comes on and causes trouble when in fact there isn't anything wrong and the levels are fine. More crap to go wrong is what I usually say.

We lived for years without any sensors and just always made sure to check every day and could usually spot any leaks or incipient problems from how the temperature acted while driving. That's what made a professional driver, he knew his vehicle and how to drive and care for it.

[niles500]

In my experience 90% of shutdowns on 8v92's are from low coolant fwiw

[luvrbus]

Check the skinner valve on the back wall ,they will start bypassing the air and shut down,it easy to check the shut down syatem,on the right side of the engine there are 2 senders on the t-stat housing 1 for temperature and 1 for high temperature shut down disconnect those if it shuts down it is the skinner valve on the rear wall ,be sure the rear start switch is in the right positions too if not when it builds air pressure it will shut down .The low water sensor on the surge tank will not shut a non DDEC engine down in a MCI that I know of but you can bypass it with a paper clip to check it,if it has one .most just have the sight glass to check the coolant level

[niles500]

Although he said mechanical, I'm assuming an '89 TA is  DDEC; May be wrong

[peterbylt]

I tested all the sensors and skinner valves all appeared to be working as designed.

The wires had been repaired on some of them, I redid any questionable connections.

It continued to shut itself down after a few minutes.

If you were sitting in the driver’s seat and looked real close, it quickly flashed the overheating and low oil pressure indicators at the same time while it shut down.
 
The temperature on the dash and on the gauge in the back never got over 180, the oil pressure was right up where it should be on the dash and the mechanical gauge in the back.

The coolant was low, I looked at all the sensors on the Bus and in the manual, I could find nothing that indicated there is a coolant level engine shutdown.

None the less, when I added approx. 2 gallons of coolant the issue went away, I ran it for over an hour and drove it for 20 miles, no Issues, very strange.

So there must be a coolant level shutdown somewhere I cannot find, probably a good thing.

Now I need to figure out where the coolant is going, last time I checked the coolant level was when we did a 500 mile trip in September, I had not checked it when we got back, I don’t see any visible leaks anywhere and there is no water in the oil.

Niles500,

It is definitely a Mechanical engine, not a DDEC, probably the last of its kind installed in an MCI, in 89 you could get it either way.

Sometimes when I see some of the things you can do with a DDEC I wish I had one, but most of the time when I see the issues that can occur because of the DDEC, I’m quite happy with my mechanical engine.

Peter

[niles500]

Well I guess I was half right 

Check the weep hole on the back of the water pump. It will slowly leak enough to cause what you've described, if the pump needs service. Fwiw hth

[luvrbus]

There is no low coolant shut down on a MCI with a machinal engine ,some have a tale ,tale light on the dash like Tom's C does for low coolant ,You testing  and moving wires around probably cured your problem .On a 8v92 pull a oil sample and check for coolant and take it out of play they will leak coolant into the crankcase along with the water pump as Niles stated and silicone hoses are bad about leaks in cold weather 

[richard5933]

There is no low coolant shut down on a MCI with a machinal engine ,some have a tale ,tale light on the dash like Tom's C does for low coolant ,You testing  and moving wires around probably cured your problem .On a 8v92 pull a oil sample and check for coolant and take it out of play they will leak coolant into the crankcase along with the water pump as Niles stated and silicone hoses are bad about leaks in cold weather

Are you sure that this wasn't an option? Not sure how MCI did it, but my GM came with a number of items that weren't normally installed but had been specifically ordered on my bus from the special-order catalogue. In the wiring diagrams for the GM there are pages and pages of these often-rare items. It took me a while to understand why my buses wiring didn't follow any of the standard wiring diagrams, and it wasn't until Luke and Bill helped me find the 'special' pages that things made sense. Seems likely that MCI also did lots of special orders for things like this.

I remember reading about how during the 70s-80s companies started to rely less on driver experience than in previous decades and started to automate more and more stuff like this.

[luvrbus]

Are you sure that this wasn't an option? Not sure how MCI did it, but my GM came with a number of items that weren't normally installed but had been specifically ordered on my bus from the special-order catalogue. In the wiring diagrams for the GM there are pages and pages of these often-rare items. It took me a while to understand why my buses wiring didn't follow any of the standard wiring diagrams, and it wasn't until Luke and Bill helped me find the 'special' pages that things made sense. Seems likely that MCI also did lots of special orders for things like this.

I remember reading about how during the 70s-80s companies started to rely less on driver experience than in previous decades and started to automate more and more stuff like this.

[luvrbus]

Are you sure that this wasn't an option? Not sure how MCI did it, but my GM came with a number of items that weren't normally installed but had been specifically ordered on my bus from the special-order catalogue. In the wiring diagrams for the GM there are pages and pages of these often-rare items. It took me a while to understand why my buses wiring didn't follow any of the standard wiring diagrams, and it wasn't until Luke and Bill helped me find the 'special' pages that things made sense. Seems likely that MCI also did lots of special orders for things like this.

I remember reading about how during the 70s-80s companies started to rely less on driver experience than in previous decades and started to automate more and more stuff like this.

 

I never seen one before on MCI,they did have option for a low water idiot lite and a idiot lite for low oil level ,there  is no stud # in the rear or front panel for one ,MCI used the off shelf Cadillac / Kysor system with a sight glass on the surge tank, GM had there own system ,you have to remember MCI was owned by Greyhound they did not vary much 

[peterbylt]

To follow up on this issue.

I topped off the coolant and put clean cardboard under the engine and ran it for a while.

After bringing it up to temperature and going between forward and reverse a few times I started to get some wet spots on the cardboard.

On the back of engine on both sides of the block just below the exhaust manifolds there are 1 ¼ inch elbows with rubber hoses attaching to 1 ¼ copper pipes that go up to the top of the engine and forward. Old photo shows the hose (green) on the curb side.
   
On the driver’s side behind the Air cleaner, in a hard to see/get at spot that hose had cracked, when idling, stationary, or off, the hose was mostly sealed, although it would seep slowly, when driving or loaded it would leak more, any leakage would just fall away from the engine with no sign.

I had to pull the inside floor hatches and have an assistant shift the bus from reverse to forward to finally spot it.

After spotting I checked the curb side, although not leaking it was showing signs of deterioration so I replaced both sides, these rubber hoses are quite close to the exhaust manifold that probably contributed to the issue.

I do inspect all the hoses regularly, but had not inspected this one.

On my MCI 96A3 I had to remove the air cleaner and housing to replace or even see this hose, the curb side is much easier to get at.

With both of those hoses replaced the cooling system is once again maintaining the level in the sight glass, now I need to replace the antifreeze.

Still don’t know why Low coolant will shut the engine down, it never overheated, but approx. 3 gallons down will shut the engine down.

Peter   

[Iceni John]

If those coolant hoses are close to the exhaust, it would help to put them inside some heat-resistant sheath such as Techflex Fireflex to prevent the rubber deteriorating again.   I use sheathing like that on all hoses close to hot stuff, and I also make simple heat shields from two pieces of thin SS sheet:  that also helps a lot.

John