Q: I’m currently running a Chevy 350 that I’ve assembled myself using a 4-bolt main block bored over .040″, a cast-iron crank, forged pistons and rods, moly rings, World Products angle-plug 64cc cylinder heads, and a bunch of other goodies.
I’ve put about 6,500 miles on it, and it starts right up, runs great, and makes plenty of power.
The problem is that it uses about a quart of 20W50 every 100 miles!
The engine doesn’t appear to have any leaks, and I don’t see any smoke coming from the tailpipe. However, I’ve noticed that the oil pressure reads 80 psi at road speed and only 40 psi at idle, and that the spark plugs all show a dark line about 3/8-inch wide along the insulator.
Can you help me figure out what’s going on?
A: Sounds like a great setup! Let’s see if we can figure out where that oil is escaping.
If your 350 is running as well as you say, then the chances are good that your rings are fine, but it’s still worth a look.
Start by checking each cylinder for leakage.
A bad ring will yield decreased compression in that cylinder, and you’ll be able to hear the compressed air from the tester escaping into the crankcase. If the rings turn out to be bad, replace them with a new set of moly rings.
Your cylinder heads could also be the culprit.
On most aftermarket heads, the rocker arm studs thread into the intake runners, making it possible for oil to get sucked down into the threads. If this turns out to be the case, that could be where some of that oil is headed.
To solve that, simply remove each rocker arm stud and apply Teflon® tape to threads before reinstalling them.
This should keep your oil from taking any unwanted detours.
Sucking it up pcv put in baffled escusion
Nice it’s gonna say blowby
I had a similar problem it turned out to be the bolt hole on the front of the block that goes through to the fuel pump pushrod. It only came out at speed so I couldnt see a physical leak. Just another place to look.
Make sure your pvc system is set up properly so as the engine can breath. {Pcv valve one side and vent on the other valve cover} Otherwise internal press will push oil through rings.
I had the same oil burning frequency with a 350 engine that had been rebuilt by the former owner. I tore the engine down and found that the oil ring expander ends had been overlapped so there was not enough tension on oil rings.
bolt hole in front of block where fuel pump bolts on.thats caught a lot of people out.
It’s the rings or the valves / valve seals…
I had one to do that when moly rings were first introduced and what I found out was the cylinder walls had to be finished with extremely fine stones. I finally wrapped 400-600 grit sandpaper around the hone to polish the walls. Also make sure you have positive valve seals on the valves. Excessive bearing clearances with the oil pressure you’re running could lead to excessive oil going on the cylinder walls and overloading the rings. The other replys are also good items to check.
I used 14 quarts of oil doing the HRPT with my Chevelle last summer. It’s a 400sbc, I did see blue oil stains accumulate on the bumper above the tailpipes so I was sure it was burning oil and not leaking oil. When I replaced the carb with the Holley Sniper I removed the intake and found the runners were coated in oil, it was simply sucking oil from the lifter valley up into the intake. New gaskets fixed the problem.
Just an update, I thought I fixed the problem, but alas she is still burning oil. Had to rebuild after I spun 2 bearings, still burning oil (3 qts/500 miles). I have checked my PCV, baffles in the valve covers. Has all new rings (correctly checked/aligned the gaps). Machine shop redid valve seats, checked guides and installed positive stop seals. I’ve double checked sealant on the rocker arm studs, and currently trying the old umbrella style seals on 1 cylinder. Not a drop leaking anywhere I can find. Slight smoke out the tailpipe, more on left bank.
For the engine you have I would ask why you need such high oil pressure. Chevrolet designed that engine to run on much lower oil pressure. You may be overloading your rings.
I agree with Sam and Todd. If you do not have a good crack case evacuation system, PVC valve or vacuum system this will defiantly contribute to this problem. I do not understand why people think they need so much oil pressure. If you must, use a high volume pump to increase oil flow but I recommend staying with a Melling standard oil pump with a new pickup kit. You will be just as happy and less problems
lets put a vacuum gauge on it & make sure we dont have a intake gasket sucking oil. pull the pcv valve out of the valve cover & put your finger over the grommet(after plugging the vent side-on other valve cover) if it’s pulling a vacuum u have a intake leaking & pulling in oil from the valley. seen several run decent & pull from the valley.
Updates? You will get various miles/qt depending on how you drive if you have low tension rings.
Got a small block 350 that a relative said they got running but it pissed all the oil out of it. It’s currently sitting in an old s10 two door
I have not seen a single mention of seals. At 80 PSI with a 2 piece rear it will slowly piss out at speeds and then seal up at idle. Also check the balancer. Last place to check is the thing no one ever suspects, the pressure sending unit. This is especially true if you have it raised up a bit. Vibrations can cause the riser to crack, not enough for a gusher but just enough that it will piss out at high RPM. You also stated that you are getting a black ring on the plugs, check the cover gaskets. SBC valve cover design is piss poor at best. I had a machine shop cut a slight groove in the surface on mine and with teh steel reinforced gasket it sealss up nicely
Why are you running such a thick oil? 10w30 should be more than adequate. I wouldn’t run more than 10w40, 20w50 is overkill.
Valve stem seals leaking
Could be the intake manifold sucking oil I the lifter valley
I’ve read posts on another site that if the heads were milled, it can cause a misalignment on the intake manifold, causing a poor seal on the lower side of the intake ports. It causes a vac leak and sucks oil into the ports. Solution. Is to mill the intake to mate flat with the heads. HTH
You’re exactly right Tom, and Jeff Smith actually explores that misalignment here too, you can click here to read the article: Ask Away with Jeff Smith: Lining Up Intake Manifold Bolt Holes on a 427 Chevy
I got a 350 and don’t know why but I got oil coming out of existence value on cylinder 7 what is the cause anyone know
I have oil leaking from the driver side of my 350, it’s brand new got Millars racing engines to build it for me. Looks like it’s coming from just under my valve covers. What kind of seals are there that would be leaking oil that I should try to fix?
pull the PCV vacume hose off the carb & check for oil.