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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: gwcrim on July 22, 2023, 02:12:41 pm
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The engine: 400 SBC
The area: top rear of engine (of course)
The leak: at least a quart (or more) every thousand miles.
It leaked on the original build. I took the intake off and tried to reseal. It leaked. Then I had the engine out again and the builder reassembled. And again, it leaks. Three attempts, three failures. Each time the end of the intake was sealed with RTV only. No gasket. When I removed the intake it didn't appear that there was a leak around the RTV. When I reach around with my fingers, they come back dirty and a little damp.
There is a gasket on the distributor.
Oil pressure sender is a brass tube and a brass elbow and the gauge sender on top. I sealed the joints with teflon tape.
There is oil along the bottom of the cylinder head nearly to the front of the engine but for the life of me, I can't find a leak at the front. Could the oil wick frontward?
The intake manifold is a Edelbrock Performer RPM. It's a VERY tight fit. I can barely get the manifold bolts started in the heads. Takes maximum effort. Could this issue somehow be causing a leak?
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You mentioned the Intake manifold fits tight. Look closely with a bright flashlight and see if it looks like the seals are being squished out at the front and back. I have had to get the intake manifold machined down in the front and back in the past because when torqued down it would push out the rubber seals on the ends. They do not always fit right. That can definitely cause a leak. If that is good, I would clean up the engine well, run it and look for a leak while it runs. From what you said, it should leak enough for you to find it.
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Buy a uv flashlight and run ultraviolet dye in the oil.
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I actually did the UV dye. The block is painted original light blue in color. Everything glows. I even got a bore scope camera to take pictures. I'm going to take a closer look at the oil pressure port since it's a much easier fix than taking the manifold off. I think I may tap into the block down by the oil filter.
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Could it be in the realm of possibilities that the oil is leaking from the drain holes in the head? The heads are Promaxx aluminum ones.
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Greater than one quart per thousand miles is quite a bit. Is oil puddling on the ground, under the engine? The "drain holes" in the cylinder heads are internal to the engine passing oil from the rocker arm areas back into the lifter valley. Are these the holes to which you refer or are there external holes (post pics)?
Pick up some aerosol engine degreaser foam and thoroughly lather the offensive areas then hose them down and let it drip dry. When water is no longer dripping off the engine (and into your eyes), use the dye, UV light, and yellow filter goggles to find the leak source(s). The goggles produce a HUGE improvement in leak detection so don't neglect them.
If you were saying that the engine paint fluoresces, it should be a different color and easily discernable from the bright yellow-green of the dye. Again, the filter goggles could make the difference in success vs failure.
Make sure the brass fittings that support the OPS aren't cracked and leaking under pressure. Check the valve covers carefully for leaks from the gasket areas, especially if they are aftermarket covers. Remove the stamped steel flexplate cover and, using a good flashlight, check for oil on the back of the block and the front of the flexplate. Both should be dry.
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It leaves a couple 3-4 inch oil stains when I park it. I change the oil every 5k miles. It's used 4-5 quarts in between.
I can try yellow goggles but the real issue is that it's nearly impossible to see the back of the engine.
The valve covers are sealed. I check them on occasion.
Now that I have the oil pressure situation remedied I'll try and eliminate the OP port as a source.
I **REALLY** hate oil leaks.
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Fluid leaks are always a pain. Use an articulated mirror. They are inexpensive and available in several sizes and shapes at O'Reilly.
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It's expensive as a tool, but look up Ferret cameras.
They broadcast their own wifi to the app.
It has paid for itself over and over again, avoiding mass heartaches.