Strange oil consumption issue

Comporange5.0 · Jul 30, 2011

I just had my block bored .030 over and rebuilt with new reman GT40P heads, forged pistons, comp stage 2 cam, new ford lifters, scorpion rockers ect... Now it is 2500 miles old and it is still burning about a quart of oil every 200 miles or so. Two plugs were totally shot and covered in oil. (cylinders two and seven) Always smoke on high rpm decell or after full throttle. I pulled the heads off to check everything and I found the lower intake to be loose. I figured that was the issue. I still pulled the heads to clean them and I lapped all valves too. Everything appeared perfect (new seals, good guides, good seat contact pattern, etc...) I put it all back together very meticulously and I still have the same issue. Lots of smoke on a high rpm decell and plugs two and seven oily. I did a compression test too, all within 160-170 psi. I pulled the PCV hose out of the back of the block and plugged it, and went for a quick drive. That did not appear to help. There was what I would consider a lot of blowby coming from the breather on the valve cover (also carried some oil with it) with the PCV hose disconnected. I am really stumped on what exactly is wrong here. Could it still be rings on those two cylinders even though they did ok on a compression test? Any ideas??

Thanks!

BlownFiveLiter · Jul 30, 2011

Plugging the PCV probably exacerbated the situation, if anything. The pressure would have nowhere to go after that, and would start looking for other places to escape (rear main seal, valve cover gaskets, etc.). My best guess would be that there's oil in the upper intake that's getting down into those cylinders. Does your lower intake have the baffle and screen under the PCV valve? It could very well be bad intake gaskets, too. You'll probably have to perform a leak down test, so you can find the source of the oil. Short of disassembling the short block, I'm not sure what else to recommend.

BlackGT89 · Jul 30, 2011

If you are confident that the rings and re-bore was done correctly, and the proper break in procedure was used, there is a good chance the problem could be in your heads in the form of bad or improperly installed valve seals. On some engines I have seen the valve seals actually get dislogged and ride up the valve stem. The tip off would be a lot of smoke after extended idling, or smoke after engine braking (high intake manifold vaccuum conditions). Go down a long grade with your foot off the accelerator, and then pop the gas to it, if you get a huge puff of smoke, it could be oil getting sucked past your valve stems into the cylinder. It should clear up for the most part when you are moving along at a steady pace.

Comporange5.0 · Jul 31, 2011

Thanks for the responses! I guess the only thing left is for me to take it back apart and inspect carefully. Maybe somehow I missed two bad valve guides, its a lot better than rings! I'll let ya know what I find

93stang burden · Jul 31, 2011

i have my 331 that was coating the itakewith oil. i just went ahead and and put 3 small breathers on it and solved my issue. 1 on the pcv, 1 on each of teh valve covers about 25 buck at autozone cure it for me. i had even bought a differnet intake and put in new screens everything and it wouldn't fix it.

Comporange5.0 · Jul 31, 2011

Well, I took the valve covers off along with the lower intake and both of the cylinders that have wet plugs have intake runners that are wet with oil. Even the injector caps on those cylinders are wet with oil. The whole intake and PCV valve are a bit oily, but that may be normal with a PCV system but I am not sure... I do have a new pcv valve, new screen, and a breather on the passenger side valve cover. The valve seals are still in place, so it looks like I may need to add breathers like 93 stang burden or there is a bigger issue with valves or rings. Still pretty stumped here

BTW, 93 stang burden, how much oil was that causing you to burn before you fixed it?

rainey27 · Jul 31, 2011

i had the same problem on my 342, come to find out that it was a freeze plug under the lower intake at the back beside the whole that drains the oil back to the oil pan. so it could be that is it carb or efi. because on my it wasnt in there so it sprayed oil right up on my pvc valve and it was sucking oil up into my intake and back through the motor.

93stang burden · Jul 31, 2011

mine is only a weekend driver so i really have no idea how much oil it was. I had even tried a oil catch can and it was catch to much. but trust me it was too much for me. i was sick of oil. it would even run back down my to my throttle andleak out of the back down to he headers. but trust me try getting those 3 breathers and give it a shot it worked for me and was only like 25 bucks

Comporange5.0 · Jul 31, 2011

Ok, I am now thinking it is probably the PCV system after a lot of reading considering the intake is covered in oil. I will probably either install another PCV valve or vent them all to atmosphere. It may also be a bad guide that I somehow missed when installing the valves.

RangerJoe · Jul 31, 2011

My buddy had the same exact problem as Rainey27. The machinist, who is very good and just made a mistake, missed the oil galley plug in the back of the lifter valley, just underneath the PCV Valve. He was sucking oil right in the intake. He began to pull the motor thinking it was the rings, but when he took the Hpipe out, oil poured out. Luckily the machinist knew what was wrong as soon as he called him. Easy fix, just a pain in the rear.

Beasty306GT · Jul 31, 2011

run the pcv into a oil seperator

ID89GT · Jul 31, 2011

Hmmm my car is doing the same thing. Fresh rebuilt 351. Put all new valve stem seals, didn't do anything. Mine mainly smokes out the passenger side, but it smokes horrible. And it also doesn't start smoking untill its fully warmed up, then it starts pouring out the tailpipe.

JungleJoe · Jul 31, 2011

I would be looking into the rings also as mentioned above.....

ID89GT · Jul 31, 2011

Ya thats what I was originally thinking. Pulling it apart this next weekend to rering it. But if its possible its something else then I would want to check that as well. I want this problem fixed

JungleJoe · Jul 31, 2011

I know what ya mean man. . .

Comporange5.0 · Aug 3, 2011

Well I actually measured the guides. On the bad cylinders they were at a clearance of .008" Supposed to be less than .003. There is my issue haha.

BlackGT89 · Aug 4, 2011

Glad you found it, ha-ha ! That high vaccuum (especially on decel) will pull the oil right past if there is too much clearance there.

Comporange5.0 · Aug 10, 2011

After a few expert opinions, I tore the engine down. Apparently it is not possible to draw that much oil past the valve guides. Glad I did because i found four sets of oil rings that were not in the correct positions and four broken lower compression rings. Hopefully I will be able to re-hone, re-ring and go!

JungleJoe · Aug 10, 2011

That sucks! well, nothing to do but get it back together...

ID89GT · Aug 11, 2011

I'm pretty sure I figured my problem out, oil was leaking at the intake at the number 3 cylinder. Turns out the intake itself had a low spot so had it milled down and also got a thicker intake gasket set. Hopefully it fixes my problem

Strange oil consumption issue

Comporange5.0

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