'90 MCI 9 8V92 over temp shutdown sequence

[oltrunt]

I would appreciate some help understanding the over temp shutdown. What are the sensors, where are they located and what is their final action in killing the engine?

I don't find any of the "normal" problems like water in the oil, excessive exhaust smoke. plugged radiator core, bad thermostats. coolant loss, or lack of power in my bus.  Yet as soon as I hit 55 mph the temp (on dash) climbs from 180 degrees to 205 degrees and the motor shuts down.  Then as quickly as I can turn the ignition to off and then to start, the engine re starts and the temp gauge again reads 180 degrees.  Then the cycle repeats itself.  Thanks, Jack

[luvrbus]

The sensors are on the T stat housing it is a Kysor system it can have 1 wire sensors 2 wire sensors or 3 wire sensors not knowing which you have, suggest you down load a manual from Kysor  it's a simple system but the sensors do go bad and come in different temperature ranges.The shutdown is not tied to the temperature gauge in anyway.

I am beginning to believe you have a water pump problem like the impeller loose on the shaft 

[bevans6]

just a question, do you have a mechanical or electronic  engine?  Thinking about how it works on a mechanical engine, the shut down sensors (oil pressure, coolant loss, over temp, what ever is hooked up) all go to trigger a relay to open that interrupts power to the skinner valve that keeps the engine shut down air cylinder closed.  As soon as power is removed, the air cylinder is pressurized (assuming the is air pressure) and the engine stops.  Stopping and starting the engine wouldn't do anything to reset that.  The sensor that caused the trigger would have to itself reset mechanically.  Electronic engine is probably totally different.

Brian

[luvrbus]

That is the way it works but I never heard of one resetting that fast usually they need time to cool down it's almost sounds like he has a electrical problem with one of the sensors wiring or a bad sensor sending the wrong reading
 

[Scott & Heather]

Get a laser temp gun and when it "overheats" and shuts down run back to the engine and shoot the Tstat housings. Both of them. Report back your readings. Do you have a rear engine bay coolant temp gauge? This will help sort out if it's a gauge/alarmstat issue or an actual overheat issue. Two completely different paths to chase down. This is coming from experience on my two buses both of which had overheat issues from completely separate sources


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[oltrunt]

Thanks Guys.

Brian, my DD is manual.

Scott, I have done the run with the heat gun several times and checked both thermostat housings and both radiators and just about everywhere else.  I never got a reading over 170 degrees except around the exhaust manifolds.  I do have a rear engine temp gauge which seems to be very slow reacting and always lower than the dash unit though I have failed to quantify the difference.

I'm going to putz around with my continuity tester and a volt meter today and see if I can learn anything.  Jack

[Scott & Heather]

Then it could be your alarmstats. Mine kept shorting out somewhere and killing my bus. I have brand new radiators on both sides, and new coolant and working Tstats so I knew it wasn't overheating. If you are a brave soul, you can disconnect the alarmstats and just leave your gauges connected and see what happens. I replaced my gauge with an electronic one on my new bus and it reads a lot more accurate when compared with the engine bay gauge (also new and mechanical).


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[oltrunt]

Today's results:

The ambient temp was in the 90's today so I had no problem getting the DD up to 170 degrees on fast idle.  I used my infrared thermometer and carefully checked the temp of both heads at the base of the thermostat housing and found the passenger side to be 170 degrees and the drivers side (where the water pump is) to be 160 degrees.  The dash gauge sender is in the passenger side head and the dash reading matched the infrared reading.  The engine compartment gauge which is a bourdon tube affair also from the passenger head read 155 degrees when the dash said 170 degrees.

Is it typical for the head without the pump to run a little hotter than the head with the pump?  Is it because the pass side head is hotter that the temp sending units are in it by design?  If I remove the water pump for inspection what might I look for--a loose impeller?

I also measured the temp of the return water from both radiators  to be 98 degrees.  Both radiator returns of course go to the suction side of the pump.  Jack

[luvrbus]

That is about normal the coolant pass through the oil cooler 1st you don't need to remove the water pump just the snap ring and cover in front on the pump

[oltrunt]

Hello All.  I knew when I bought my bus that  there was a rattling ringing noise on start up of my DD that went away once air pressure went up and the fast idle kicked in---what did I know?

Someone (no doubt Luvmci)  said "it is beginning to sound like a water pump".  The operative word there was "sound".  Once I took the water pump apart and found the impeller free to spin on the input shaft, it became clear to me where the ringing sound was coming from and why.  Like everything else I have checked on this bus, the pump looked brand new save the loose nut on the water pump impeller.  I found a NOS "O" ring to reseal the pump with and can hardly wait until Monday when I can again take the bus for a run to check out this repair.

I've monkeyed with this heating problem for many hours and the loose impeller is the first concrete observation I have made and repaired.  At least now I'll be able to enjoy taking my Toad (Clarence) and his tent trailer, Golden, to the last of the seasons local car shows this weekend.  Jack

[LuckyChow]

Glad you found that, Jack.  Sometimes it's the most unexpected things that are the hardest to find.  I believe you just might have solved your problem.

[luvrbus]

They are bad about that when someone has replaced the seal,LVMCI bus is getting hot also we are going to be trying to solve his problem this month I don't think his is going to be that simple   shoot me a address and I will send you a new square o-ring for the cover

[oltrunt]

Thanks for the offer Luvrbus.  Since I was able to find a NOS "O" ring and get it installed with no leak, I think I'll leave well enough alone for now.  If after taking the bus for a run I find the pump leaks, I'll take you up on your offer.  Thanks, Jack

[oltrunt]

Hello All.  I took my bus out for a little run today.  I drove around town until the engine got up to operating temp (170 degrees) and then hit the fwy for a forty mile run.  I kept the bus at 65 mph and just let 'er run.  The temp never went up at all.  She took the three or four mile 7% grade at 40 mph for about three quarters of the way after self downshifting to third.  The engine began to sound a bit bogged down so I shifted to second and climbed the rest of the way at just under 35 mph.  The temperature never increased.  Both the dash gauge and the engine compartment gauge now read the same and both heads show the same temp with the heat gun--guess the poor thing had been cooling by convection and pretty well I might add other than the over temp shut down at highway speeds.  I really got lucky.  The entire repair amounted to two new thermostats and an "O" ring for the water pump who's impeller had worked loose--less than a hundred bucks.  I know, it's not nice to crow, but---------------------

Whooppee!  Fun to learn new stuff!  Thanks for all the helpful input.  Jack

[LuckyChow]

Good to hear a success story that didn't break the bank!!