Need help with major oil leak...

[Slonaker]

To make a short story long, my 305 blew a quart of oil all over the bottom of the truck in a 25 mile trip several months ago. I couldn’t figure out where the oil leaked from because everything on the truck leaked at the time. I was about to pull the engine apart, so I did not really worry much about the leak, especially since it never happened again in several hundred more miles of driving.

I recently replaced my cam, pushrods, lifters, and all the seals and gaskets in my engine except for the rear main. I figured that whatever leaked that one time would have been fixed, but it was not. It has now lost a quart of oil in a 60 mile trip, and almost a half a quart in a 25 mile trip.

The truck runs well, and does not leak on my driveway. It does not leak while idling. When I drive it, though, it covers the entire bottom of the truck with oil. The oil appears to be coming of the back of the engine because the front ¾ of the engine is clean. The oil is not leaking from the intake or the valve covers, both of which have new gaskets anyway. The oil pressure sending unit is new, replaced while I had it pulled apart, so that seems to rule it out. It appears to be blowing past the rear main, but only while driving.

I talked to a mechanic friend about it, and he says that a malfunctioning PCV valve will cause a SB Chevy to blow oil past the rear main while driving. This weekend I replaced the PCV valve and the hose that connects it to the carb. I have verified that the PCV rattles and is connected to a good source of vacuum at the front of the carb. When I disconnect the PCV valve from the hose, the engine immediately dies from the massive vacuum leak. I also made sure that the aluminum tube that goes from the valve cover to the air cleaner is clear and clean, and replaced the rubber seal at the valve cover and the rubber hose at the air cleaner.

After all of this, it is still blowing past the rear main while driving. Remember, it does not leak on my driveway, and there are no visible leaks while idling. I cleaned everything up around the rear of the pan this weekend, and with 20 minutes of fast and slow idle in the driveway, there was no visible leakage.

Does anyone have any suggestions about what might be making it blow past the rear main? Is there anywhere else it might be coming from?

Slonaker

[PHOENIX]

everything is cool with the oil filter and connection?

[Slonaker]

I tightened the filter and drain plug a little more last night, just in case. It did this before and after I changed all of the seals, and the filter has been replaced twice (before and after cam break-in)since it first did it, so I suspect neither of them are the problem. I will probably throw another filter on it just in case, though. I like to try easy and cheap solutions before difficult and expensive ones.

Slonaker

[old Rusty C10]

id gunk it all down one more time and then leave it idle in the drive maybe at a higher rpm than idle but not that much see if its being forced out at a high pressure other than aseal or the oil pressure switch i cant figure it out either

[79BIG10]

Check your connection at the oil pressure sender again. I've had a leak there where it didn't look like it would do anything but when you go the wind blowing into there it would decorate the underside.

[Slonaker]

The oil pressure sender has been replaced since the first time it spewed. It is not likely that both would leak that much. I'll check the oil pressure switch that controls the choke again, though.

Thanks,

Slonaker

[86SILVERADO]

My guess is you put the wrong seal in the rear of the oil pan. There are two different sizes you probably used the thinner of the two when you needed the thicker one.

[TROYLV]

check your exhaust system. a plugged up exhaust will cause excess crankcase pressure, which will cause the rear main to leak at off idle rpm. tail pipes and mufflers have a way of collapsing at realy bad times. you can check your manifold vacuum, if it is low this is a good indication of a restricted exhaust.

[1FaastC10]

how about trying some tracer dye? i used it to track my trans leak on my TA. you just add it to your oil, run it for a while, and then shine a blacklight on it, and it shows up. you dont have to change the oil or anything, as it wont hurt anything being in there.

[phantom dually]

I have seen a few leaks at the distributor without a gasket present. Probably not the case but just a thought.

[bigblock73]

Originally posted by 1FaastC10
how about trying some tracer dye? i used it to track my trans leak on my TA. you just add it to your oil, run it for a while, and then shine a blacklight on it, and it shows up. you dont have to change the oil or anything, as it wont hurt anything being in there.

I agree with ^^^^

I used this method once, it clearly showed me where my oil leak was coming from. I added it to my oil, drove the truck for less than a day, shined the backlight on the engine...whalla...oil leak from rear of the valve cover (I6). Its that easy.

[Slonaker]

Where would I get this dye? Is it available at a regular auto parts store?

Thanks for all the suggestions. I'll keep trying to find out why it is leaking over the long weekend. It has been unusually cold here this week, in the 30s, and that has slowed me down a bit working on it in the dark after work.

Slonaker

[Slonaker]

A machanic friend suggested I spray everything down with brake cleaner and get it completely clean. He said to take it on a short trip and look underneath for oil and do this over and over again, going a little farther each time, until I spot the leak.

It worked. I spotted oil leaking from the side of the oil pan gasket, of all places. I bought a new pan gasket Friday night, but then twisted my ankle Saturday morning while exploring a junkyard. I haven't been able to replace the pan gasket yet since my ankle is bruised an swollen, but I hope to change it out in the next couple of days.

Thanks to everyone for their suggestions.

Slonaker

[ChevyGuyBC]

MAN LISTEN TO ME RIGHT NOW I BET I CAN HELP YOU! THIS HAPPENED TO ME WITH MY MALIBU! YOU READY?????

their is 2 holes on the front of the engine on the passenger side, they NEED to be plugged, those are oil gallery holes for the fuel pump pushrod. plug those and youll be fine!

it took me a few weeks to figure it out too but i got it

make sure its no longer then half inch, try quater inch 9/16 corse i belive..

but don't go too deep or it will hit the rod.. also you can use washers like i did if you can't get a short bolt

your welcome, and if thats not it..it could also be your intake gasket, mine did also leak from the back down onto the headers and burnt hope i helped ya

[Slonaker]

Thanks for the info, but it isn't leaking there. It is leaking from the pan gasket, and my block uses a pan gasket that is dealer only... Just my luck. $57 for a pan gasket.

Slonaker