Oil Loss in Rebuilt 1970 LS-5

[Tony H.]

Around Sept 1999, I had my original engine rebuilt. Changes from original specs were flat top cast aluminum pistons, high vol/pres oil pump and hardened exhaust valve seats. I have about 3000 miles on the engine. I broke the engine on conventional oil then switched to Mobil 1.

My engine rebuilder said at the time of the rebuild that the intake manifold gaskets were no longer available from GM in the same thickness and would require shaving down the intake manifold if GM gaskets were used. Alternate gaskets were used in this place and the intake remained unchanged. I recently talked to him regarding oil loss and he said the problem may be the intake gasket leaking internally. Before my most recent 300-mile trip, I torqued down the intake bolts and all turned. I did this on a warm engine in two steps in the proper torque sequence. The losses were still 1 quart after 300 highway miles with a few stops for lights and gas.

A fewmonths back, I did a vacuum test and had values of 17" which seemed to indicate normal vacuum with a warm engine. Spark plugs (AC R44T) only lasted 3 months. I'll try the AC R45T but I don't think this will solve the oil loss problems.

Please help. Any and all ideas appreciated!!!!

[Joe L.]

Re: Oil Loss in Rebuilt 1970 LS-5

Tony-----

I think that your engine rebuilder is on the right track with respect to the source of the problem. The induction of lifter valley oil mist past intake manifold gaskets is one of the major reasons for excessive oil consumption in both small and big block Chevrolet engines. However, it is largely unappreciated and not considered whenever such high oil consumption problems occur. I can tell you this for sure: dealing with it on a small block is one of the MOST FRUSTRATING problems which I EVER experienced in my years of involvement in the hobby. Also, I can assure you that NO intake manifold gasket, sealer, or retorquing of bolts will solve it. On the small block that I was referencing, I changed cylinder heads(to brand new GM ones), changed the intake manifold 3 times, had the intake manifold side and end surfaces machined several times, used at least 10 DIFFERENT brands/types of intake manifold gaskets, and used at least 5 different types of sealers, including an aerospace industry-sourced RTV silicone sealer priming compound.

In a futile and desperate attempt to attribute the problem to something else, I used every type of valve seal imagineable. I used stock, o-ring seals alone. I used PC-Teflon seals alone and I used them in conjunction with stock seals. I used Viton positive seals alone and I used Viton seals in conjunction with stock seals. I used umbrella seals alone and I used umbrella seals in conjunction with stock seals.

Then I tore into the engine bottom end. I honed the cylinders and replaced the pistons and piston rings. Since I was in there, I also replaced the rod and main bearings and the oil pump.

None of this did anything to cure the 300-500 mile per quart oil consumption. I NEVER solved the problem and eventually, defeated by it, took the engine out of service. To this day, though, I am pretty well convinced that the genesis of the oil consumption problem is related to oil mist being drawn past the intake manifold lower gasket edge. And, I will also offer that my engine vacuum was about 19" throughout and the engine ran just fine at all times.

I do disagree with your engine rebuilder regarding the intake gaskets. The present GM gaskets may be slightly differently configured than the originals. However, the original gaskets were variously manufactured by Detroit Gasket, Victor, or McCord. You can purchase identically configured intake manifold gaskets from any of them to this day.

[Tony H.]

Re: Oil Loss in Rebuilt 1970 LS-5

Joe,

Thanks for your response. I think. Well, I have a new set of gaskets from NAPA which I plan to install this weekend when I return home to PA (from CT). I hope they solve my problem. If others have any ideas or tips, please chime in. I hope I am able to resolve this problem. I'll talk to my engine rebuilder to see if he has any experience in long-term solutions to this problem when he does come across internal intake manifold oil misting.

Tony

[Patrick H.]

Re: Oil Loss in Rebuilt 1970 LS-5

Hi Tony,

Yes, I am scared by Joe's post too, as I am presently fighting oil use in my 350.

In my case, and maybe not yours, I have a bad oil pan gasket which is scheduled for replacement soon, but also had leaks from the valve covers (gaskets) which were much worse than I expected. My loss is/was approximately the same as yours and Joe's, but did decrease somewhat after I changed to aluminum valve covers (from steel) and new gaskets (after several attempts with new gaskets and sealer on the original steel valve covers). My oil pan leaks bad enough to leave spots on the floor and oil down the bottom of the car, but it still was quite tough to diagnose originally, especially in the first 1500 miles or so.

Hope this helps.

Patrick Hulst