Help Disabling MC-9 Hot Engine Shutdown But Leaving Telltales

Debo · November 27, 2016, 04:38:26 PM

Hi guys,

I've always left my hot engine shutdown system operable, but I'm rethinking this after a trip from North Carolina to Maryland this past week. My engine shut itself down after the alarmstats falsely triggered a hot engine condition. Two redundant gauges showed me that the engine wasn't hot, so I coasted off the road, unhooked the sending units, and went on about my way having no further problems.

I'd like to replace the alarmstats and keep the telltale lights and buzzer, but disable the engine shutdown part of it. I've got a redundant engine temperature alarm, so I'm not really concerned about not noticing a hot engine until it's too late. I'd like to keep the factory warning system operable though. I know from the schematics that it's possible to keep the telltales and disconnect the shutdown, but that's the part I need a little help with. Can any of you MCI electrical guru's look at your schematic pages and tell me which wire to disconnect from which stud to disable the engine shutdown? I tried to attach the pages, but they're too large for the site. Any assistance with this would be greatly appreciated. It was a great trip, by the way. The bus ran like a very large sewing machine, and other than the false hot engine shutdown, not a hiccup. Thanks again for any assistance.

Bus: 1981 MCI MC-9
Engine: 8V-71N
Transmission: Manual 4-speed Spicer

gumpy · November 27, 2016, 05:19:11 PM

Remove the wire from stud 13, rear junction panel, that goes to the shutdown relay, terminal 7.

Keep in mind, this disables shutdown for low oil pressure and level as well as low water, too.

Debo · November 28, 2016, 02:45:25 AM

Cool! Thanks very much Craig. That's pretty much what I thought, but I wanted someone who knew what they were talking about to verify.

I'm pretty fanatical about checking gauges as I'm going down the road, and the telltales and alarm will still function, so I'm not too worried about the engine's ability to decide when it should shut down on me. I also have one of those great Engine Watchdog alarms that uses a thermocouple bolted to each side of the block to measure temperature, so if for ANY reason things start to heat up, I know about it. I don't think I even have a low water sensor, but I might look and see if the wires are there so I can add one and have the alarm.

Thanks again. I really appreciate this.

daddysgirl · November 28, 2016, 05:30:41 AM

Is there a jumper also between 13 and 45? If so, would 45 also need to be removed? And is there is a buss bar between 44 and 45? I have a double rectifier on 44...one for engine stop, one for hot sensor. Then there is 53...stop relay contact 5, and switch line side (6)?

luvrbus · November 28, 2016, 06:20:58 AM

? why not just buy a new alarm stat and keep the shut down system intact,they don't cost but 30 bucks

gumpy · November 28, 2016, 06:25:39 AM

Quote from: daddysgirl on November 28, 2016, 05:30:41 AM
Is there a jumper also between 13 and 45? If so, would 45 also need to be removed? And is there is a buss bar between 44 and 45? I have a double rectifier on 44...one for engine stop, one for hot sensor. Then there is 53...stop relay contact 5, and switch line side (6)?

There is a wire between 13 and 45, but there is no reason to mess with it. If you remove the wire from 13 to the relay coil, that disables the shutdown while leaving the rest of the circuitry intact, which is what he wanted.

There is a busbar between 44 and 45, and yes there should be double rectifier on 44 as you indicated.

Relay contact 5 supplies power to terminal 53 in the run circuit. Should be left alone.

Again, his desire is to leave the warning and telltale circuits functional while simply removing the engine shutdown option. Removing the wire from 13 to the relay coil ground is the easiest way. There is probably a wire from relay terminal 8 to relay terminal 2 which could have been removed, instead.

gumpy · November 28, 2016, 06:34:45 AM

Quote from: luvrbus on November 28, 2016, 06:20:58 AM
? why not just buy a new alarm stat and keep the shut down system intact,they don't cost but 30 bucks

That would be my choice, too. A failed hose clamp could drain the engine of coolant in a matter of minutes. A comfortability with driving can keep you from seeing a high temp long enough for damage to occur. The engine shut down will get your attention immediately. Just like the guy who's oil sensor blipped the shutdown in AZ the other night. I imagine when the engine shutdown triggered, it got his attention immediately and that's when he saw the oil light.

BY the way, there is a way to defeat the shutdown by holding the start button in. This allows one to get the bus off the road, but it depends on having a working fuel pressure switch on the starting circuit.

B_K · November 28, 2016, 06:49:35 AM

Craig you are right about suddenly loosing coolant!
On one of the 05 Setra's we had I blew a hose once and the shut down killed the engine before I knew I'd blown the hose!
40 gallons of coolant all over the highway and the back of the bus before I even knew it!
Sure was glad for the shut down!

BK

gumpy · November 28, 2016, 07:00:17 AM

Quote from: B_K on November 28, 2016, 06:49:35 AM
Craig you are right about suddenly loosing coolant!
On one of the 05 Setra's we had I blew a hose once and the shut down killed the engine before I knew I'd blown the hose!
40 gallons of coolant all over the highway and the back of the bus before I even knew it!
Sure was glad for the shut down!
BK

I had a clamp break on the first bus I bought. I was taking it on it's monthly run to warm things up. Got back and parked on the curb and walked around to find a puddle forming in the gutter. I followed the trail back about 3 miles. Fortunately the hose stayed on the pump, but it ultimately would have become a major problem, and I don't think the safety shutdown system was working on that bus. That was before I knew anything about buses.

Debo · November 28, 2016, 09:26:47 AM

Yeah, maybe I'll give the shutdown system another shot. It was comforting knowing it's there. It sure was a rude thing to just have the power yanked out from under you like that for no real reason though. I'll give it another go and see what happens.

I was always going to buy new alarmstats and fix the warning system, but disconnect the shutdown part. And yes, I know about the override. Cliff, where are you getting the alarmstats for $30? The only place I've looked, they were $66 apiece. If I can get 'em cheaper, I'm all about that.

luvrbus · November 28, 2016, 09:31:13 AM

My Napa guy where I live orders those in for me but they are not the Kysor brand

Debo · November 28, 2016, 09:47:00 AM

Cool. Thanks. I'll check with my NAPA folks and see what they say.

luvrbus · November 28, 2016, 10:03:33 AM

Mine here is a commercial store they don't many auto parts just mostly the commercial stuff

buswarrior · November 30, 2016, 07:56:38 AM

Every busnut should maintain and test the various alarms as part of the preventive maintenance, and especially soon after acquiring a new to you coach, the collective experience proving that any previous owner is to be highly suspected for bypassing or otherwise screwing the stuff up...

Engine shut down systems are for protecting the owner's capital from ignorant hired labour.

The busnut is the owner, how far are you going to drive with an alarm showing?

Upon a warning alarm activating, I will decide when and where, on this bit of road, the propulsion is going to be turned off, not some 30-40-50 year old bits of wire down the back?

happy coaching!
buswarrior