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Author Topic: Need help/advice for a friend regarding 6v92 oil usage  (Read 2708 times)
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81 MCI 9 smooth side 8V71 Allison 754

« on: June 09, 2009, 06:14:41 PM »

Hey all,

Just got back from a ride in a friends 83 MCI 9 with a 6v92 in it and I need your help in giving him sound advice/ideas to get to the bottom of a serious oil usage issue. He has been going through ALOT of oil. Last week he drove about 100 miles roundtrip and used a gallon and a half of oil, so with that in mind I went for a ride and drove it, it smoked a bit blue at idle and layed a HUGE cloud of whitish smoke for about a hundred yards or so when we first took off and then it cleared up and it had serious power for a motor that seems to be on it's last legs. It out pulled my 8v71 by a wide margin. So here's what i know so far:
The blower looked brand new on the inside no evidence of leaky blower seals, the turbo had no visible oil seal issues on either the intake or exhaust side. We didn't remove the access covers to check the airbox/piston rings. The part of the story that messed with me was, I drove this bus less than 25 miles today and there was probably close to a quart of oil already in the airbox drain canister!!

here are the things that make it more interesting:

the dipstick is obviously not stock, it is totally a different color and has home made hash marks for full and low.

there are some leaks around the alternator and there seems to be another fairly substantial leak that we haven't been able to trace yet. Have any of you ever seen a detroit leak that bad through anything other than a main seal?

Also, he has been running 15-40 weight oil in it. He figures he has added about 8 gallons since he bought the bus so it must be totally diluted by now.

Here was my advice to him:
Call in the serial # to DD and get the correct oil capacity for the engine.

Fill it with the correct weight oil.

Drive it for awhile and see if he was possibly way over full of motor oil. I did check the dipstick against the cranckcase /oil pan and it seemed to align with the actual junction instead of an inch below that which is what I have come to believe is "normal". What are the real chances that he is severely overfull with oil making it leak like this?

All of you far more experienced busnuts out there has it been your experience that once they start throwing this kind of oil out the spitter tubes that motor failure is imminent or can he get through the rest of the summer? The motor had good oil pressure and was running strong and cool.

Am I just trying to avoid the probability that his rings are just worn out here??

I felt bad for him when we opened that airbox drain canister... It was frightening how much oil was in there from the little bit of driving we did.

Made me miss my old simple normally aspirated 8V71...

I appreciate in advance all the sound advice/ideas I know you guys will give my friend,


I will drive my Detroit hard... I will drive my Detroit hard.
Tim Strommen
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« Reply #1 on: June 09, 2009, 06:27:37 PM »

Also, he has been running 15-40 weight oil in it...

This sentence makes me cringe especially on an '83 6V-92...  he may need new main bearings by the time he gets the right oil...

Easy-ish thing to look at is the air-box ports - these are cover plates along the side of the block between the exhaust manifold and the oil sump - the air-box drain lines (to the air-box drain sump) should either go into the block next to one of these plates or if it was retrofitted, may actually be run into one of these plates.

Pull these cover plates off with the engine stopped, and take a look in with a flashlight.  You should be able to see the cylinder liner (looks like a can with holes in the side when viewed through the air-box ports).  If you slowly crank the engine by hand (a helper can help with this - make sure the fuel rail is set to "stop"), you may see one of two things:

1) oil will be coming out of the liner holes - this generally indicates that the rings at the bottom of the cylinder are bad, allowing oil from the crankcase to enter the intake system.

2) oil will be coming out from the edge of the liner itself where it meets the block - this indicates the liner seals are shot and need to be replaced.

If either of these is the case, you buddy is probably looking at an in-frame at the least (you need to pull the heads off to fix either one).  This kind of problem is something to catch good and early - oil can feed the engine enough to run-away... (I've never seen a 92's piston get blasted into the concrete below it - I imagine it's quite a sight Shocked).

While you're poking around in there if you happen to have a mechanic's mirror, take a look into the cylinder liner holes and look at the inside of the cylinder walls (the piston must be rotated down to the "intake" position for this).  If the walls look smooth as glass, the upper rings are probably OK, but if there are visible vertical scratches - the upper rings are probably shot (scraping the walls with the broken edges).

« Last Edit: June 09, 2009, 06:33:52 PM by Tim Strommen » Logged

Fremont, CA
1984 Gillig Phantom 40/102
DD 6V92TA (MUI, 275HP) - Allison HT740
Conversion Progress: 10% (9-years invested, 30 to go Smiley)
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« Reply #2 on: June 09, 2009, 07:05:20 PM »

Rick, pull the air horn off the blower and check for oil running down the inside with a flash light even with the blower looking new I have saw rebuilt blowers leak more than the one it replaced.
He may have broken oil rings or piston pin retainers came loose and you cannot see those from the air boxes also have him check the air compressor it will amaze you how much oil it will use. The valve guides may worn too
DD will use more oil running 15/40 than a straight 40 w but he is not going to destroy the mains using 15/40. Most 6v92 hold 6.5 gals with the filter       good luck
« Last Edit: June 09, 2009, 07:17:01 PM by luvrbus » Logged

Life is short drink the good wine first
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Currently in Northeast Ohio

« Reply #3 on: June 09, 2009, 07:16:26 PM »

Ok I know i'm "new" to the bus scene but i've always had Powerstroke ford pickups, Literally 5 month's ago I purchased a Reman turbo for it b/c mine was beginning to leak coolant and do the "white cloud" when spooling up...upon installing my "reman" the situation became worse! I thought the Heads where blown. turns out the Turbo was leaking oil and coolant internally! I looked like the batmobile! anyway hope that helps ! I'm with Luvrbus on this one check em out!
« Last Edit: June 09, 2009, 07:19:02 PM by ekhedge » Logged
Angola Coach Conversion "Aesop's Tortoise"
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« Reply #4 on: June 09, 2009, 10:23:04 PM »

Rick -

Your recommendations to your friend are right on the money.  Educate him about the correct oil for a two stroke.

As Luvrbus stated, 6.5 - 7 gallons is a normal oil/filter change for a two-stroke in a coach.

Work with him to try and mark the dipstick properly - it is VERY possible that he's been over-filling the crankcase. 

Educate him also about the best time to check the oil level - in the morning, before he fires it up for the first time.  Second best is 30 - 45 minutes after shutting it off - NOT while you're putting fuel in it!

Might also check the slobber tubes to see if they're plugged.

Try the simple things first, before getting really greasy!

FWIW & HTH. . .


RJ Long
PD4106-2784 No More
S13406 1978 MC-5C Converted
S14947 1980 MC-5C Shell
Cheney WA
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« Reply #5 on: June 09, 2009, 10:35:52 PM »

Using 15w-40 is not a problem on the bearings.  It is the rings that will prematurely wear out, or get stuck-hence either a worn out engine or excessive oil usage.  I suggest he open up the side box covers and inspect the cylinder liners for scoring, rotate the rings to see if they are loose and if there are any cracked ones, then refill with straight weight 40w and remark his dip stick.  Up and beyond that, if nothing changes, time for some new cylinder kits.  Good Luck, TomC

Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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