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Author Topic: Air in coolant line on 6v92  (Read 5106 times)
vwb11356
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« on: March 01, 2010, 06:57:21 AM »


I have a 1987 NJT MCI MC9.  I am having a problem with the bus going into shut down.  The coolant level is fluctuating,  but I am not losing it anywhere.  I am getting air in the coolant lines.  There is no coolant in the oil.

Below are a list of things I have tried.
1. Shut off coolant line to the coach and driver heat to isolate the coolant to the engine.
2. Bled the lines from the petcock in the rear between the blower belt.  I have done this with the bus running and off.  I also have done it after any change to verify line is stable and clear.
3. Removed coolant lines to the air compressor to verify it is not blowing air into the coolant.

I have been talking to Luke (from US Coach) and JR (from NC) and they have been a lot of help.  Just trying to see if anyone has any other suggestions.

I am new to this and I appreciate anyy help.
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TomC
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« Reply #1 on: March 01, 2010, 07:06:56 AM »

Usually, cooling systems on trucks and buses are self aerating- meaning they purge the air out of the cooling systems themselves.  To accomplish this, there are small cooling lines at the highest points of the engine-typically on the top of the thermostats-that take the air out of the cooling system since air rises to the highest point.  Check those small lines-I would suggest have them pressure tested to see if they are introducing air back into the system if they are old and cracked.  Also, make sure they are not blocked.  If working properly, air in the cooling system should not be a problem.  Good Luck, TomC
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Just Dallas
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« Reply #2 on: March 01, 2010, 07:13:12 AM »

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RickB
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« Reply #3 on: March 01, 2010, 09:10:35 AM »

The coolant shutoffs to the front of the bus are notorious for stripping out and you end up just turning the spigot shutoff handle without turning off the valve itself.

Rick
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buswarrior
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« Reply #4 on: March 01, 2010, 06:10:25 PM »

Is there an air bleeder on the top of the engine, rear end, down through the hole in the floor from inside, on the coolant pipe heading for the coach heater/defroster?

Check the bleeder on the top of the heater core in the dashboard too.

the air is in there someplace, chase it out!

happy coaching!
buswarrior
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niles500
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« Reply #5 on: March 02, 2010, 02:09:35 AM »

Check your cap for any signs of corrosion - replace if necessary - first things first - HTH
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vwb11356
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« Reply #6 on: March 03, 2010, 09:43:42 PM »

I have the coolant shut off at the 2 vales that allow it to circulate through the rest of the bus.  I think it is isolated to the engine.  I want to get a compression check done.
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luvrbus
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« Reply #7 on: March 04, 2010, 06:04:46 AM »

VW,before spending big bucks on a compression check I would check the water pump and make sure it hasn't sheered a key or lost a blade,if you have problems with water on the top it will show up in the air box drains.   




good luck
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JackConrad
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« Reply #8 on: March 04, 2010, 08:53:42 AM »

A friend had a similar problem on a Saudi MC-5. Water level would not stay up in the sight glass and no sign of where it was going. He replaced the pressure cap, end of the problem.  Jack
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RickB
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« Reply #9 on: March 04, 2010, 01:52:38 PM »

Clifford or Don,

Is this starting to sound like a cracked head or blown head gasket?? Coolant obviously leaking or burning and air in the coolant system. Would an IR gun pickup a bad cylinder thats burning coolant?

The compression check is expensive (around 1K) and has to be done right to be accurate. Motor warm and running at idle.

This one is nagging at me

Rick
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vwb11356
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« Reply #10 on: March 04, 2010, 08:45:36 PM »

I have found the compression check is not needed. 

I am not losing coolant.  It is air in the lines.  When I start the bus the level rises.  Then I bleed the air and the level returns to normal.  It just continues to build pressure when I start or run the bus.  It does not go anywhere else. 

I have only replaced the coolant that has been lost by bleeding it.  I use a tube and run it back into a jug.

How would the pressure cap or water pump cause this.

I am wondering if the only thing to do is check the head for cracks and bad gaskets?

I am new to this and learning a lot.  Trying to find 6v92 manual now.

I appreciate all the help.
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vwb11356
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« Reply #11 on: March 04, 2010, 09:55:17 PM »

I feel like Chicken Little.  "The sky is falling, the sky is falling".  Since my last post I have started my bus and bled the air from the coolant while it ran.  This caused the level to drop.  As the bus ran the level began to rise in the sight-glass,  but did not shut the bus down as before.  I ran it for about 15 minutes after bleeding with no issues.  The level in the sight-glass began to fall to the normal level after a minute or so.  I think this is normal, please tell me if it is not.  The level did not fall back to normal before.

Here is one difference from today:
I have needed to charge my batteries, but did not have a large enough charger.  I purchased one today and now have the front battery to a higher level than it has been since this problem began.  This all began after the bus sat in cold storage for about 1 1/2 months in the coldest time of the year.  Could this all have been becasue the DDEC was at a low voltage?  I am not sure about this and I know it is a reach, but I thought I would give as much info as possible. 

Is there a thermostat or something that could have casued this also?  It is starting to warm up here (around 40 the last couple days).  Could this have any effect?


Sorry for the long post.  I hope this may help point to the problem.  Or did I just get lucky and it ran for a few minutes.

Thanks
Vince
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RickB
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« Reply #12 on: March 05, 2010, 06:13:15 AM »

Vince,

I got your email and after revieweing this post I'm not sure we're dealing with the same issue. I haven't actually been out to see what is happening with my motor but first off my motor is out of the bus on a stand. We filled the motor with water, it will just keep recirculating it inside the block until the thermostats open which we haven't ran it long enough to have that happen. But it seems that I may be getting pressure through a crack in the head or a blown head gasket. I'm going to video it for review later today and hopefully put a pressure gauge on the coolant system to see what kind of pressure we're getting inside. But my mechanic sure seems to think that all is not well in my motor. It is all specualtion until I can get out there and see it for myself but I will definitely keep you informed.

As far as your issue, I have never noticed alot of fluctuation between starting and running coolant levels but certainly the system pressurizes itself due to the rising temp of the coolant. I have read many time that it is a no no to run your ddec ecu to below certain voltages but I do not have a ddec so I'm not qualified to even venture a guess.

Sean is pretty darn knowledgable when it come to electrical issues. Maybe ask the question on the board what are the issues I can expect to have with lo voltage in my ddec.

Just a thought

Good luck with this

Rick
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luvrbus
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« Reply #13 on: March 05, 2010, 07:23:41 AM »

Vince, may not be your problem but a bad water pump or bad seals on the thermostat or anything else that causes a turbulence in the cooling system will cause air pockets



good luck
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NJT5047
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« Reply #14 on: March 05, 2010, 07:17:50 PM »


Vince's bus appears to be pumping air into the cooling system within a few seconds of firing up the engine.
The thermostats would have been closed, the pax heater gates are both closed, the air compressor has been shunted away from the cooling system, and the DDEC set a "high coolant level" code (16) and the water level substantially increased in the surge tank.   
Also sez he can hear air bubbles 'boiling' up into the surge tank following cold shut down.  My bus doesn't do that even when shut down hot...only noise is oil dripping back into the crankcase.   
IHMO, the engine has been bled satisfactorily.  I've got an identical bus and it bleeds within a few seconds.   Some engine combos may not, but these NJT systems are easy to bleed. 
For a time, as I understand, Vince would start the bus and it would shut down due to either high or low coolant within a very short period...long before heat expansion would increase the water column.   
The DDEC isn't likely related to the problem.   Nor the water pump or thermostats.  Water pump isn't doing any great thing anyway until the thermostats open.  Although, a DDEC sensor fault could be the problem.  Ex NJTs are famous for setting bogus "Low Coolant" codes.
My bus is still in 'winter storage'...what Vince needs is someone to crank an MC9 and see what the water level does.  I've never paid any attention to what the sight glass does when the engine is initially started...it may surge up and down.  May not.   I set it and forget it. 

I'm with RickB....the problem sounds like a cracked head.   
No water in the oil.   That may change. 
And maybe no problem at all...?   Or maybe a faulty high water sensor?
The bus seems to be functioning for now, and my thoughts would be drive it and see what happens.  Unless coolant becomes obvious in the oil or the engine begins to miss--or overheats, nothing will be worse for the wear. 
If the bus does begin to miss, an infra-red tem gun will ID the cylinder.     
Vince, make sure the dash water temp guage is working correctly.   The dash sender is the automotive looking temp sender screwed into the pax side thermostat housing.  One wire sender.  Ground the wire and the guage should move to "hot" when the ignition is "on."  The engine doesn't have to be running to verify that the guage works.  It it doesn't move, check the wiring at the guage, if patent, change the guage (remember that it is a 24V guage).  If it moves, but doesn't read when hooked up to the sender, replace the sender.   
The DDEC will shut down on "Hot Coolant," "Hot or Low Oil Pressure," and "Low or High Coolant."  It will shut down with bogus sender signals too. 
See if you can read all of the codes.    On a DDEC I, the codes are lost if the DDEC fuses are pulled or the batteries disconnected.  Turning off the battery master will not depower the DDEC ECM.   Keep in mind that some of the DDEC wiring is always "hot" if working on the bus wiring.   This is true for the 'Distributor' (engine unit), and the ATEC and DDEC ECMs. 
Whaddaya think bus peoples?    Huh

Good luck, JR



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JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

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