Oil consumption.. compression test results.. help!

dstang01 · Jul 6, 2008

As some of you know, ive been having oil consumption issues with my 5.0, its been eating a litre every 500 kilometers. The car runs great and doesnt smoke on startup, revs or driving, so I was stumped as to where the oil was going. At a cruise awhile ago we were running at 160 kph on the highway and my buddy said he noticed I was blowing some smoke.. its time to get to the bottom of this.

I just pulled the plugs and did a compression test, the compression for all 8 cylinders is 150 to 155. All plugs look clean, except plug number 3 (see pics)

^all plugs look like this except 3

^plug 3

I hope the good compression test indicates my rings are fine (should be with only 110,000 kilometers on the car), so Im assuming my problem is in the valve seals of cylinder 3. My question is, what could be possibly causing my oil consumption/plug fouling? Any insight will be GREATLY appreciated.. I want to fix my stang thanks

Maryland Stang · Jul 7, 2008

I seriously doubt it's a valve seal problem. If plug 4 or 8 had that problem and you get a puff of smoke when you start the car then I would agree. Plug 4 and 8 are usually the first plugs to show a valve seal problem because the heads point down towards the back of the engine and that where oil will puddle the most.

dstang01 · Jul 7, 2008

Maryland Stang said:
I seriously doubt it's a valve seal problem. If plug 4 or 8 had that problem and you get a puff of smoke when you start the car then I would agree. Plug 4 and 8 are usually the first plugs to show a valve seal problem because the heads point down towards the back of the engine and that where oil will puddle the most.

What else could it be? Something with the PCV? Im pretty stumped because compression is bang on.. and that one plug is fouled

90 lx convert · Jul 8, 2008

Compression tests are ok but I'm not sure they give a complete picture of the health of the engine. I wonder if it would help to do a leak down test. Most drag racers leak their motors to check for ring seal, valve seal etc. The loss would be in percent of air pumped in versus how much is lost through the motor. I'm guessing that #3 will be lower. It might help. If nothing else it's another check on the health of the engine. Mike

dstang01 · Jul 8, 2008

90 lx convert. said:
Compression tests are ok but I'm not sure they give a complete picture of the health of the engine. I wonder if it would help to do a leak down test. Most drag racers leak their motors to check for ring seal, valve seal etc. The loss would be in percent of air pumped in versus how much is lost through the motor. I'm guessing that #3 will be lower. It might help. If nothing else it's another check on the health of the engine. Mike

Thats a good idea, a leakdown test was going to be our next approach, but I was just looking to see if these findings can point me in a direction (for example.. one plug is fouled, compression test is fine, car has low miles.. therefore must be something in the heads)

strtrcr50 · Jul 8, 2008

Is it just me, or do you have a rather large chunk out of the porcalin on your bad plug?

neuf · Jul 8, 2008

Like everyone else said, a leak down test is a great idea. Anyone know a ball park figure what one costs?

Blandnuts · Jul 8, 2008

What type of crankcase ventilation system are you running?
What intake are you running?

dstang01 · Jul 9, 2008

There is a chunk of porcelin out of the bad plug

Im running the stock intake, the engine itself is stock, 110k kilometers (68,000 miles)

I am using the stock crankcase ventilation, recently replaced the PCV valve, it looked clean and appeared to be working but I changed it anyways.

Again, after about 315 miles, the engine uses a litre of oil.

The engine is young and unabused, compression test showed 150 to each cylinder. All plugs looked fine, except of course plug 3. All this leads me to believe there is something wrong with the head at cylinder 3.

Blandnuts · Jul 9, 2008

Did this problem happen before or after you replaced the PCV valve?
Check the vacuum lines going to the pcv valve and the one on the filler tube and see if there's signs of oil being sucked up.

Signs of heads being bad (valve guides/seals) usually smoke on start up after the car has been recently ran.

Like mentioned earlier a leakdown test should help out.

Fred

2000wjFUH2 · Jul 10, 2008

My car had a similar problem. The plugs closest to the firewall had more oil deposits on them. there is an oil baffle that wasn't installed with my cobra upper and lower intake, so oil was sucked up into the intake at the back (explains the oil covered black sparkplugs) where it was burned (explains the smoke and increased oil consumption). Since you dont have any mods on your intake, I would deduse you have a problem that would cause the same issues, ie. pcv. Do you have an aftermarket breather on your valve cover? Friend had issues with his cause he didn't install correctly. Good luck.

LX302 · Jul 11, 2008

Oil problem aside, the fouled plug might be from a bad wire on that plug. Check the voltage resistance on that wire to confirm.

jimilane · Jul 11, 2008

Probably getting oil from the PCV. That's where I usually find the problem. Sometimes people put large vacuum lines on the PCV when they replace old ones. I have replaced the large lines with smaller lines and the oil consumption problem stopped. Just make sure you still have an air flow through the engine by taking the air line that's connected to the throttle body to the oil filler lose from the throttle body while the engine is running, and feel for air being sucked through. Just a little suction is good. If you don't have enough suction through the engine, the engine will start to decrease RPM and run rough after a minute or two.

A leak down would be good too. That way you can see if you are getting extra pressure driving the oil through the PCV system...or somewhere else. I have had this going on before too, more so at the higher RPMs.

Also, I have noticed that if your car is idling a little high, or has a big surging idle, it will suck oil through the PCV.

I have put a clear fuel filter in the PCV line to see if oil is present.

Jim

dstang01 · Jul 25, 2008

Ok.. so I had my dad follow me on the highway today to look for smoke. The car doesnt blow smoke on startup, or when revving in neutral. On the highway, it doesnt blow while cruising, but when I punch it or downshift and punch it, my dad said it gives a sudden burst of blue smoke. Its quite noticeable, but its just a burst and it doesnt continue throughout the whole acceleration. What could this point to?

Also, is there any cons to trying 20-50 oil on my next oil change?

91notchbk · Jul 25, 2008

The consumption you have sounds like worn piston rings.

You have two different sets of rings on each piston. Compression rings and oil control rings. A compression test will let you know how much pressure the piston is capable of building. However, the engine can have excellent compression (which is related to the compression rings) and still burn oil because of worn or carbon siezed oil control rings. The oil control rings are the rings that scrape oil from the cylinder and drain it back to the pan and they control oil consumtion. A common misconception is "if the rings are worn causing blow-by then you will have low compression". However, this is not always the case because the oil control rings may be bad and the compression rings are ok. Sometimes the oil control rings wear out faster than the compression rings. They may also be carbon siezed in the ring groove. In both these cases you will have good compression but you will burn oil. The leakdown test will not test the condition of the oil control rings either. There is no way to test the oil control rings without taking apart the lower end.

The key is blue smoke is present only during acceleration. This is typical of worn oil control rings.

ninety15.0 · Jul 25, 2008

I completely agree with the guy above. You are seeing blue smoke only when you punch it. This blowing oil probably continues while you are accelerating...just not nearly as noticeable. You can't put enough load on the engine when you are just revving it to see the oil. But when you punch it and bring the load up...you will see blow by.

Most likely the oil control rings. Leak down might not even reveal this issue. Have you checked the RMS?

I would try to be as easy on it as possible during the next 500 miles. If you see a decrease in oil consumption, your control rings are the likely culprit.

bentley429 · Jul 25, 2008

Sounds like its the oil rings to me. I wouldnt worry about it, you dont want to know how much oil my car goes through still has good compression. If its not slowing it down why fix it.

dstang01 · Jul 25, 2008

This actually makes sense, I had somebody else suggest this today too. My question is.. the rings must have worn prematurely.. i mean.. the engine is pretty young. If the rings are "carbon siezed" as one of you said, would a good seafoaming possibly remedy my problem?

Another question.. how would this explain my one fouled plug?

91notchbk · Jul 28, 2008

Rings usually get carbon siezed from lack of maintenence. Oil changes every 8,000-10,000K miles. If your car had regular oil changes then Seafoam will do no good. An old mechanics trick is to remove the plugs and squirt ATF down the spark plug hole and letting it sit for a few days. The ATF is high detergents and can remove a lot of carbon on top of the pistons and can work carbon loose on the ring grooves. It will smoke like crazy when it is first started. It is a shot in the dark and will only work if the rings are carbon siezed.

However, in your case it looks as on cylinder is worse than the other. You may be using more through the one and the others may or may not be contributing to the problem. You reallly need to tear the engine down.

dstang01 · Aug 1, 2008

my dad picked up some rislone, he says it might be worth a try to free carbon-seized rings. Anyone have any experience with it? Its been around for a long time.

I was also wondering if I could run a 20-50 oil in my 5.0 to try and slow down the blowby.

Oil consumption.. compression test results.. help!

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