Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 10, 2025 ...

8.3 timing case leak ?

September 09, 2022, 01:31:14 pm

Our 8.3 has developed an oil leak that I can't pinpoint yet.  I've thoroughly cleaned the lower area twice now and pretty much ruled out an oil pan gasket and front main seal, I think.  I do see a trace around each oil pan bolt after a 200 mile drive but not enough to get down onto the pan or the hoses below it.    Year before last I had the timing case cover removed and sealed but no joy...

 There's a lot of 8.3s out there and from what I gather the timing case leak ( cracked case ) is a common problem.  It's not leaking a lot BUT it's still getting the area oily eventually. Not on the towed yet though.  The primary spot that gets it first is lower left timing case, hoses below, cross member for front motor mount and then mud flap.

  I'd just like more knowledge about it before I take it in.  And could a Mobil mechanic tackle it. 

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Re: 8.3 timing case leak ?

Reply #1 – September 09, 2022, 01:46:58 pm

Look at the valve cover on the rear passenger side.. Mine has a harness that comes through  the head and is a very difficult area to seal up ( there is a plug and grommet).

Update after... I have changed all the seals around the pulleys on mine and loaded that area with sealant to help the drip but could not get it totally but its close.

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Re: 8.3 timing case leak ?

Reply #2 – September 09, 2022, 03:39:23 pm

Your 02 is probably an electronic engine where our 95 is not so you'd have wiring in places I don't. Just guessing.

 Also I'm not seeing any oil at the top of the block, it's mostly around the lower timing case area....
      I think I'm talking myself into it being the timing case.

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Re: 8.3 timing case leak ?

Reply #3 – September 09, 2022, 03:43:31 pm

The '02 is an ISM yours is a 8.3 entirely different besides the electronics.

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Re: 8.3 timing case leak ?

Reply #4 – September 09, 2022, 03:44:50 pm

Make sure the tube coming from the valve cover top is not plugged, can cause extra crankcase pressure,some call it the slobber tube.

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Re: 8.3 timing case leak ?

Reply #5 – September 09, 2022, 05:35:11 pm

I was almost hoping that it was the slobber tube, almost.  So I threw a pop bottle on it and zip tied with room for air movement.  Nope, no joy there either.  Just a trace of oil in the bottom. ( 200 miles ).

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Re: 8.3 timing case leak ?

Reply #6 – September 09, 2022, 05:40:01 pm

Bob,

No oil from the crankcase breather may or MAY not be indicative of what John was asking.

If the crankcase breather is blocked, it will not blow out oil.

Certainly not suggesting this is the issue, but inserting a small (clean) tube in the bottom of the crankcase breather and blowing will tell you right away if there is a blockage.

Yes, this falls under the "cheap but not fun" diagnostics.

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Re: 8.3 timing case leak ?

Reply #7 – September 10, 2022, 01:55:32 am

Brett.
 Yes that is a check that I could and will do. Hadn't thought of it and to be honest, it never occurred to me that air coming out would also allow air in. 
  It will be something to check off the list. Thanks.

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Re: 8.3 timing case leak ?

Reply #8 – September 10, 2022, 10:40:09 am

Pull the oil dipstick when idling and see if you notice anything coming out,where that slobber tube goes into the valve cover there is a mesh screen,may need cleaning,could the oil be from the hyd system.

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Re: 8.3 timing case leak ?

Reply #9 – September 10, 2022, 12:15:35 pm

Don't seem to be loosing any oil from the hydraulic Reservoirs. But I do loose a quart or 2 in 1000 miles from the engine.    I would think Some of that loss might be coming out the exhaust pipe. 
  Which is part of the reason I'd like to get the leak resolved, so that I'll know how much. Although it doesn't smoke much at all, hot or cold.

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Re: 8.3 timing case leak ?

Reply #10 – September 10, 2022, 05:06:39 pm

A new style gasket is available that goes between the engine block and aluminum gear case.  The hardest part in replacing it was pulling the cam out so you can remove the case.  I believe the leak I had was on the bottom  left of the crank.  Tom  build 4636

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Re: 8.3 timing case leak ?

Reply #11 – September 10, 2022, 06:59:51 pm

Tom.
  Yes that's what I was told as far as the upgraded gasket.  I also heard that there was an improved / reinforced timing case also. 
  And this leak is starting to look like lower left. That area gets it first.    Thanks.

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Re: 8.3 timing case leak ?

Reply #12 – September 10, 2022, 07:28:05 pm

I dealt with a leak for a while that turned out to be the compressor gasket.  Wrong gasket, pulled, installed the correct one per the compressor, not a Cummins item.
Second, 98's sometimes have had the wrong dipstick.
Correct # is 394 5614
Wrong# is 319 5879

The wrong stick will get you over filled and result in blow out. 

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Re: 8.3 timing case leak ?

Reply #13 – September 10, 2022, 08:50:20 pm

Are you sure it's the cam you pull out or just the cam sprocket,pulling the cam is major engine work.

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Re: 8.3 timing case leak ?

Reply #14 – September 11, 2022, 03:19:14 am

I hope it's not pulling the cam but IF.....I watched the right YouTube about it,  pulling the cam is part of it.    Cam is pressed on to the gear or something like that.

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Re: 8.3 timing case leak ?

Reply #15 – September 11, 2022, 10:04:11 am

Will look at my parts book,think the gear is on the cam.

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Re: 8.3 timing case leak ?

Reply #16 – September 11, 2022, 10:29:40 am

How about the pushrods/lifters?

P

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Re: 8.3 timing case leak ?

Reply #17 – September 11, 2022, 10:56:31 am

That's why the cam gear comes off.

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