Ok...Intake or Head Gasket Problem?
 

My truck has been burning oil for a few months now and gotten progressively worse...losing a quart every 400-500 miles at this point. And yesterday the engine started misfiring so I decided to finally make time to look into the issue.

Pulled all 8 plugs and #'s 3 and 5 (center two on the driver side) were completely fouled out and covered with deposits from oil. All other plugs were ok. I'm assuming it's an intake manifold gasket issue but was also thinking it could be head gasket.

I think intake because it's two adjacent cylinders, the oil is definitely getting into the combustion chambers, no chocolate milk oil, and coolant hasn't been disappearing any faster than normal.

What do you guys think?

if your not losing coolant i wouldn't jump to the head gasket just yet. Check your compressions before taking anything apart. If those two cylinders are low on compressions its probably bad rings. What year is the truck and what motor?

This doesn't sound like either intake or head gaskets, based on your plug observations.

A compression test as stated above is your next diagnostic step.

97 K1500 5.7 Vortec engine.....but a crate one from GM. Approx 70k on it with Mobil 1 after breaking it in for 5,000 with normal dino juice 5 years ago.

I find it hard to believe that 2 sets of rings right next to each other up and bit it but I'll run a compression test and maybe a leakdown this weekend.

Hold up...I had it in my head you were running an LS1. Disregard my previous post.

Next step I'd recommend is pulling the intake. Save the compression and blowdown tests for later if the intake diagnosis doesn't find anything.

You may find that the intake gasket on that bank is either damaged or wasn't being squeezed uniformly. You'll see a visible impression on the intake gaskets where the intake and head ports locate on the gaskets. Look for uniform depth on the impression outline...chances are you'll see that the bottoms weren't being squeezed. When this happens, the intake ports introduce vacuum into the lifter gallery and oil ingestion happens.

For example...a while back, Holley shipped Stealth Ram intakes that weren't properly machined and they wouldn't seal at the bottoms...causing the intake gaskets to fail and ingest oil down the intake ports on the heads. The intake surfaces were straight, but the angle was wrong.

Just an example of what you might be looking for, good luck and keep us posted.

That is EXACTLY what I was thinking....figured the intake gasket went between those two cylinders on the bottom side and I'm sucking oil out of the lifter valley. I'm going to have to wait another week or so before I'll have time to pull it apart but I'll keep you posted. May run a compression test first anyway.

Intake gaskets or valve seals. Somewhat common for the seals to start going about 80k.

just remember that a compression test or even a leak down test, it may have a false reading with an oil issue, because it will mask the problem < ( the old way was to do it dry and than add oil to a cylinder to see what difference that had on the test ) example if you seing higher compression in those two cylinders than i agree its an intake seal if its lower than the others - rings might be suspect - keep a battery charger on the battery so the starter will see a some what same voltage when cranking - jz

What those guys said. either that, or it is a cracked intake. I guy on NE3G had a simalar problem with a 96 Vortec engine in his Tahoe.

pull / plug the pcv, if there is vaccum in the crank case without it installed you definately have a internal vacuum leak

My buddy that worked at Malouf GMC said that the intake gaskets on the Vortech motors were comon for leaking oil and sometimes coolant from the back of the intake.

yup, more often it is coolant but that is definately a common problem...

Yeah my housemate popped the intake gasket on his 6cyl Vortech a few months back. Was gushing coolant so bad I thought he cracked a head.

Josh I'll try your vac test.....I just tap into any other vac line from the intake with my gauge while I plug up the PCV system right?

Pretty sad I haven't gotten to repair this yet, but the shoemakers kids are always barefoot I guess.

Planning to Sea Foam the engine first to clean out some of the buildup in those cylinders and going to install all new plugs as well.

no, if the crank case has vaccum without a pcv then you definately have a problem..

Ok....so I want to tap into the crankcase where? Right at the hole for the PCV valve?

tap what?? come on Paul dont you work on cars for a living??

haha man I'm a resto guy not a tech. Lately I've been banished to the land of bodywork and paint too.

ok went right through the dipstick tube and with the holes in both valve covers plugged was pulling a ton of vac

Ok so I replaced the intake gaskets yesterday and my vac issue went away, but I swear I still smelled oil after my drive in today....maybe some residual in the intake ports? I'll keep an eye on the level the next few days and see.

Yup, you'll pull the last of the oil residue from the intake runners for a few hours of operation. The reversion inherent to these engines will have been pushing the oil up into the intake a few inches while the problem was ongoing.

A good SeaFoam treatment will speed up the process, and wouldn't be a bad idea in terms of de-gunking the chambers and piston crowns a bit.

Yes I was going to Sea Foam after a bit of driving and then put a new set of plugs in the whole engine after just to get it back up to par. Pulled the plugs on the two offending cylinders last night and only some oil on the threads, electrodes were dry. Still no vac leak either but after 75 miles of driving I'm still getting some oil smell.

If you're not oiling the plugs any more, I'd whip out my can o' SeaFoam at this point and go to town.