Crankcase Pressure

LR Pat

DMAXAMUST
Jan 24, 2015
18
0
0
65
Southeast Texas
I replaced the PCV, but the RMS leaks sometimes, and then go a week or so and does not leak ??? Wondering how much pressure the RMS is rated for ???
 

JoshH

Daggum farm truck
Staff member
Vendor/Sponsor
Feb 14, 2007
13,704
765
113
Texas!!!
I know a guy who broke his nose and orbital socket when his oil fill cap was blown off during an incident while welding a fitting into the lower oil pan. The rear main seal did not leak after being subjected to that much pressure.
 

Burn Down

Hotrodder
Sep 14, 2008
7,092
28
48
Boise Idaho
Cracked/torched piston will blow the rear main out with enough boost:thumb: , even with two 1 1/8" breathers on the valve covers.

The bowed 1/8 steel oil pan was impressive and the fact that the driver kept from totaling the whole car was probably the most impressive of all:thumb:
 

Yellow Jacket

WannaBe Sled Puller
Feb 11, 2009
917
0
16
Waterloo, IA
What are some other symptoms of a cracked piston, ( beside a RMS leak ) ?

With oil cap removed and idling, you will get puffs of air/mist from crankcase...and usually a slight miss or weak cylinder, injector balance rates will show a +7 or other significant # because it sees the poor contribution to engine idle rpm...
 

melms23

Member
Jul 30, 2011
253
0
16
WI
What's the info on the truck? Wouldn't it be fairly uncommon for an lb7 to crack pistons.

The only one I've seen with a cracked piston was an lbz. Fwiw it had only 1 cracked, but 4 had quarter sized chunks of skirt laying in the pan.
 

malibu795

misspeelleerr
Apr 28, 2007
8,230
544
113
42
in the buckeye state
Both my crack pistons were almost complete dead/hard miss with blueish/white smoke out the exhaust and a strong single puff out the oil fill tube both while towing..
 

LR Pat

DMAXAMUST
Jan 24, 2015
18
0
0
65
Southeast Texas
My 02 has a reman 6.6, with 60k miles on it now, ( 279k when I change it ) runs great, only thing is leaking RMS. Changed the PCV, to make sure the crankcase was vented... But it is intermittent leak, so I don't want to change the RMS, until I know why ??? I drove the same rout, same miles,temperature,speed, same RPM. Sometimes it will leak, sometimes it don't ( I even mad sure the weep hole was clear when it was not leaking ).... :mad: