HELP Huge leak from rear of rebuilt 351w - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 22 Old 05-17-2017, 09:07 PM Thread Starter
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HELP Huge leak from rear of rebuilt 351w

I have a huge major leak from the rear of the motor where it meets the bellhousing. it's very bad Is this the rear main or the oil pan gasket? 3 minutes of run time.

Using 1 piece rear main seal and pan gasket with an aftermarket pan.

Can't drive the car like this...

Whats going on?

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post #2 of 22 Old 05-17-2017, 09:09 PM
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That severe? I'd say oil pan gasket it probably didn't sit right at the main cap "hump" when the pan was installed. I've made the mistake myself once.

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post #3 of 22 Old 05-17-2017, 09:13 PM Thread Starter
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Should I pull the motor again? its a 351w in a fox with a tube K member
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post #4 of 22 Old 05-17-2017, 09:38 PM
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Either pull the motor or pull the trans and bell to see if you can trace the oil...
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1994 GT Vert, 9.75:1cr 359w. Renegade 185. FTI cam, RPM2, 80mm Fox Accufab. 4" CAI. Aluminum flywheel and S/A Romac balancer. Homebuilt exhaust: shorty's with Cats, 2.5" to 3" side-exit oval tubes. MM suspension. Baer/Cobra brakes. The list changes yearly....350rwhp/380rtq and growing.
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post #5 of 22 Old 05-17-2017, 10:16 PM
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Which pan? If it's canton then it's almost a guarantee to be the problem
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post #6 of 22 Old 05-17-2017, 10:22 PM
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PCV yes or no?
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post #7 of 22 Old 05-17-2017, 10:24 PM Thread Starter
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NO pcv im running two breathers
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post #8 of 22 Old 05-17-2017, 11:13 PM
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A PCV will pull some vacuum in the motor, which would help. Not sure why you wouldn't run one, because it pulls fresh air thru the motor which will keep things clean.
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post #9 of 22 Old 05-17-2017, 11:44 PM Thread Starter
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A PCV will pull some vacuum in the motor, which would help. Not sure why you wouldn't run one, because it pulls fresh air thru the motor which will keep things clean.
My intake manifold is not tapped for one.
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post #10 of 22 Old 05-17-2017, 11:46 PM Thread Starter
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Which pan? If it's canton then it's almost a guarantee to be the problem
I don't know if it's canton. I couldn't find any branding.

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post #11 of 22 Old 05-18-2017, 12:48 PM
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Put dye in it
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post #12 of 22 Old 05-18-2017, 01:17 PM
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I found on my block that the rear oil pan bolts are not blind. The rest of them are. Did you use sealant on those rear two 5/16 bolts?
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post #13 of 22 Old 05-18-2017, 01:21 PM
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Tighten the drain plug.
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post #14 of 22 Old 05-18-2017, 03:30 PM Thread Starter
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Tighten the drain plug.
stahp it

And yes i did put thread sealer on the non blind pan holes
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post #15 of 22 Old 05-18-2017, 04:09 PM
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If the leak is that big and you can't find it, time to turn in your wrenches.
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post #16 of 22 Old 05-18-2017, 05:51 PM
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Possible sources; intake manifold to block end rail, oil galley plugs (3), oil pan, rear main seal.

If it's not the intake manifold, I would pull the motor. I had a similar problem, took 3 tries to get it right.
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post #17 of 22 Old 05-19-2017, 08:58 PM
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Did you put thread sealer on the flywheel bolts? Some crank flanges have through holes.
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post #18 of 22 Old 05-19-2017, 09:56 PM
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351 cranks have blind holes. 302 has through and need sealer.
If it is running down the rear wall of the pan, and the flywheel / flexplate is dry, then it's the gasket.
If the flywheel is wet, then it's most likely the seal. With that much oil on the ground, the flywheel and the whole inside of the bellhousing should be soaked.

What type of gasket? What oil pan?

'88 LX hatch. Full MM suspension minus the Torque Arm, Cobra Brakes. Not as slow as it used to be.
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post #19 of 22 Old 05-24-2017, 03:12 AM Thread Starter
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I put my hand inside of the bell from underneath and I didn't feel any oil. It just seems like its on the pan itself. But I am pulling the engine this week. I think it's a canton pan and the gasket I used was a summit one piece. It's grey in color. The U's seem a little bit hard to fit. But the front didnt seem to be leaking. When I pull the pan, I plan to run a nice bead of "the right stuff" along the entire pan rail.

Should I run the bead between the block and the gasket? Or the gasket and the pan?

Thanks for all the helps guys. Really helps me a lot.
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post #20 of 22 Old 05-24-2017, 09:44 AM
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IF ITS THE OIL PAN ......NO NEED TO PULL THE MOTOR.
DROP TUBULAR K MEMBER... PAN CAME OUT WITHIN AN HOUR.
USE THE PAPER TYPE (OIL RESISTANT FIBER MATERIAL) WITH A HONDA BOND SEALER.
LET SEALER CURE OVER NIGHT.

THIS IS THE PROCESS I PERFORMED TO ISOLATE THE LEAK.
INJECT OIL DYE... DRIVE / CLEAN AREA/ PUT ON LIFT OR JACK STANDS.
REMOVED DISTRIBUTOR...FOR MANUAL OIL PUMP ACTIVATION (MOTOR INOP.)
WATCH FOR ORIGIN OF LEAK WITH A UV LIGHT
NOTE: AFTERMARKET OIL PANS PREFER THE PAPER GASKET WITH THE INTERLOCKING RUBBER SEALS

IF NO LEAK FOUND....START ENGINE 5 MIN. THEN TURN OFF (INTERNAL ROTATING ASSEMBLY MAY BE NEEDED TO AGITATE THE OIL)
REPEAT TILL LEAK CAN BE IDENTIFIED

GOOD LUCK.
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post #21 of 22 Old 05-24-2017, 09:38 PM Thread Starter
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Thank you so much. I see the 3 piece seal you are talking about. Seem to work better with aftermarket pans. The motor is 95% out. Otherwise I would have dropped the K member
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post #22 of 22 Old 05-25-2017, 03:10 PM Thread Starter
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This was before I dropped the motor in. Rear main seal depth look ok? I used lucas assembly lube
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