oil leak

by McCauley5983 Thu Aug 09, 2012 5:10 pm

ok have a 400 sbc recently rebuilt and cant figure out why its losing oil it doesnt smok and i can see seepage around the bottom of the back of the oilpan and the transmission looks pretty wet and i can see a lot of oil on the cross member. it almost looks like the bottom of the head gasket is seeping oil and there are droplets on the underside of the plug boots. it doesnt smoke and runs really good no loss of power im lost any help would be greatly appreciated

by Joe73 Thu Aug 09, 2012 6:00 pm

Spray the whole underneath with some light cleaner like purple power or simple green. Hose it off and check it after driving it a couple of days. You should be able to see where its coming from. I would doubt its the head gasket. If thats the area, I'd lean more towards a valve cover gasket.

by JB2wheeler Thu Aug 09, 2012 6:58 pm

I spent big bucks to build my engine and it started leaking after a hundred miles. I have not even checked to see where it is coming from. I chalked it up to using royal purple synthetic oil. It is not the breakin oil. That stuff is really thin and its hard to hold. JB

by Biomedtech Thu Aug 09, 2012 10:10 pm

Got the same problem, used to the old days when you used a rubber seal at the front and rear of the intake.... Haven't got the hang of creating your own yet with rtv

by ant7377 Thu Aug 09, 2012 10:12 pm

Is the motor vented properly ? Could it be blowing out of the breather ? Are you using a PCV? I had/have this porblem on my 350,Its got some blow by but I had a defective breather on it and oil started coming out the dipstick tube. But when I blew into the breather to see if it was clear-it wasnt.

by 2fat2fly Fri Aug 10, 2012 12:38 am

billy-ray wrote:ok have a 400 sbc recently rebuilt and cant figure out why its losing oil it doesnt smok and i can see seepage around the bottom of the back of the oilpan and the transmission looks pretty wet and i can see a lot of oil on the cross member. it almost looks like the bottom of the head gasket is seeping oil and there are droplets on the underside of the plug boots. it doesnt smoke and runs really good no loss of power im lost any help would be greatly appreciated

I agree with Joe73 , clean it up, maybe put it stands to run then look to find your problem.
check up thru the tunnel area and look at the rear of the intake, any oil sender in the area, valve covers, rear oil pan seal, you may have to spend some time but you'll find it.
GOOD LUCK !!!

by Tom77 Fri Aug 10, 2012 7:22 pm

ant7377 wrote:Is the motor vented properly ? Could it be blowing out of the breather ? Are you using a PCV? I had/have this porblem on my 350,Its got some blow by but I had a defective breather on it and oil started coming out the dipstick tube. But when I blew into the breather to see if it was clear-it wasnt.

X2 same here.

by dragons_lair59 Fri Aug 10, 2012 8:31 pm

oil sender make big freaking messes too

by McCauley5983 Fri Aug 10, 2012 10:00 pm

It's got a PCv ill check it out this weekend

by 77mali Sat Aug 11, 2012 10:20 am

In addition, after you clean it up, check the rear of the intake manifold. If the sealant is not in there properly it will run down the side of the cylinder head and follow the contours down to the plug wires and exhaust manifold areas. Check that the dist clamp is tight also and you can see the gasket that's supposed to be there, just in case.

by 77ElClassic Sat Aug 11, 2012 11:54 am

The machine shop that worked on my sb400 used a thread chaser to clean all the bolt holes on the block. There is one bolt hole on the lower front-right side that I think was a hold-over from the old front motor mounts used in the 50s. When the shop cleaned that hole, they apparently ran the chaser all the way through into (or almost into) the fuel pump chamber. I kept getting oil all over the lower part of the right header, cross-member, floor pans, but never could find the leak. Drove me nuts for a couple years until a buddy suggested I plug that hole. I guess oil would seep out of that hole at higher RPMs and the wind from the fan blew it back.

by McCauley5983 Sat Aug 11, 2012 5:36 pm

Ya I found that one already Mad

by pila Sat Aug 11, 2012 9:56 pm

That hole that intersects with the fuel pump push rod bore, is normally plugged with a short bolt. It's also handy when replacing a fuel pump. A long threaded bolt can be used to hold the fuel pump push rod up, while the pump is installed, using just a light torque on the bolt to hold the push rod.

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