Burning Oil Troubleshooting

[crutch]

I’ve got a rebuilt 347 Stroker that I’ve only got about 1,500 miles on and it’s consuming oil, not sure how to measure it but its quite a bit. Motor was running really rough and when I checked engine it was really low. Wasn’t sure why it was so low since it doesn’t leak much. Did an oil change and it ran good but I’ve been checking oil frequently and its burning oil. A few things I’ve noticed:
* It smokes out the exhaust on startup
* The oil pressure is up over 70 (higher then I’ve noticed it in past)
* Checked a plug and oil on it in the threads (see pic).

I’ve been looking through other threads and seems like it could be PCV, piston ring seals or valve seals. I’m using the Bronco valve covers which have baffles on them and connected the PCV on passenger side to the Holley Sniper vacuum and the other side is just a filter breather. The PCV pulls vacuum when I test it.

From what I’ve read, a compression test and leak down test will help isolate the issue. Is that the next best steps? I guess I should pull all the spark plugs and see how they all look. Any other thoughts/ideas?

A few pics of the engine for reference. Thanks!

 

[oldiron]

My oil pressure gauge shows the same reading, but the mechanical reads around 50. Don't trust the factory gauge to be overly accurate.
Greg

 

[crutch]

My oil pressure gauge shows the same reading, but the mechanical reads around 50. Don't trust the factory gauge to be overly accurate.
Greg

Good to know. I was thinking I should probably verify with mechanical gauge. I’ll do that. Thanks!


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[spap]

When you say consuming a lot of oil, is it a quart per 1000 miles, etc when the motor was rebuilt do you have forged pistons , they can use a little bit more oil. How many miles on the rebuild ?
To me the plug looks like the motor is running rich hard to see if it is carbon or oil.
X2 on the oil pressure gauge mine is the same

 

[1970 Palmer]

I think at this point you would want to pull all of the plugs for a visual inspection. That plug/cylinder looks rich (as was already stated), not burning oil to me. You want to see all the plugs burning the same.

What's the cranking compression on each cylinder? What is the percentage of leak down on each cylinder?

Does it smoke under acceleration (load), or does it smoke under high vacuum (coast)?

You could have something like a bad valve guide, or bad/missing valve stem seals. If the compression and leak down tests are good, I'd look at a bad intake gasket seal, or mismatched intake.

It's all about the diagnosis, one item at a time.

 

[crutch]

When you say consuming a lot of oil, is it a quart per 1000 miles, etc when the motor was rebuilt do you have forged pistons , they can use a little bit more oil. How many miles on the rebuild ?
To me the plug looks like the motor is running rich hard to see if it is carbon or oil.
X2 on the oil pressure gauge mine is the same

I’d guess i probably put 150-200 miles and had to add a quart. This was after I found out it was really low and did a full oil change and filled it up.

Good call on the oil pressure sensor. Just hooked up a mechanical gauge and getting 55 psi at cold and dropped to 49 at temp. I believe I’m running 5-30.

I’ll pull all the plugs for visual inspection and then run compression test.

I have been trying to get my sniper tuned so I’m not too surprised the plugs are showing rich.


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[ugly74]

With the smoke on startup, I’d be looking at valve guides/seals.
Were the heads rebuilt with the rest of the engine?

 

[crutch]

With the smoke on startup, I’d be looking at valve guides/seals.
Were the heads rebuilt with the rest of the engine?

Yep, they are GT40 heads that were rebuilt. I ran it for 10 minutes in the garage while I had the mechanical oil gauge hooked up and it did smoke the entire time. I’ll get it out and drive it and keep a closer eye on the exhaust smoke. Thanks!


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[1970 Palmer]

Yep, they are GT40 heads that were rebuilt. I ran it for 10 minutes in the garage while I had the mechanical oil gauge hooked up and it did smoke the entire time. I’ll get it out and drive it and keep a closer eye on the exhaust smoke. Thanks!


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If it smokes under heavy load, it's likely rings. Your more interested in the compression difference per cylinder than the actual number you get. They should all be within 15% maximum difference. It could be something as simple as a broken ring, on a engine that new.

If it smokes more under coast (like 3000 rpm in second gear then let it slow down). This causes high vacuum and pulls oil past the loose guides, or bad oil seals. A bad intake gasket seal could show up with this test.

You need to accurately diagnose the problem before you tear into the engine so you have a good idea of where to look.

 

[Broncobowsher]

Oil pressure has nothing to do with consumption.
Do you have a baffle under the PCV?

 

[crutch]

Oil pressure has nothing to do with consumption.
Do you have a baffle under the PCV?

Yep, I’m running the bronco covers the vendors sell and they have baffled on both sides.


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[73azbronco]

Correct pressure PCV?

Rebuilt 347. Like it was a 347 and then was rebuilt, or built into a 347 and new to you as a new 347?

 

[SevenT]

Oil Consumption

crutch,

I remember the first generation 347 stroker kits were notorious for consuming oil because the landing for the ring on the botton was so close to the wrist pin. Hopefully it is guides and umbrella seals in the heads and not the pistons themselves. Just my .02. Good Luck.

v/r,

SevenT

 

[crutch]

Correct pressure PCV?

Rebuilt 347. Like it was a 347 and then was rebuilt, or built into a 347 and new to you as a new 347?

How can I verify the correct pressure on the PCV? I have the part number I can grab but is there a way to size the PCV to the 347?

This was a 1996 explorer block that I had an engine builder build into a 347.


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[Broncobowsher]

What intake manifold gasket was used during the build? Been a little while since it cropped up last but the Felpro 1250 (I think) was rather well known for failing between the intake runner and the valley. Internal vacuum leak and sucking oil spray out of the valley.

 

[Apogee]

What intake manifold gasket was used during the build? Been a little while since it cropped up last but the Felpro 1250 (I think) was rather well known for failing between the intake runner and the valley. Internal vacuum leak and sucking oil spray out of the valley.

...and if this were the case, you could expect some difficulty in getting the EFI to tune properly due to the vacuum leak.

 

[blubuckaroo]

Actually that plug looks pretty good.

The PCV baffles on most aluminum valve covers are just a cheesy metal plate. Not nearly as well designed as the baffles on the old steel valve covers.

And, yes. The wrong PCV valve can cause oil consumption.

Check the PCV line to see if it's got oil in it.

 

[oldiron]

Some years ago I had a rebuild that slurpped oil like crazy, to the point that it would build up on the plugs and physically bridge the gap and kill that cyl within 500 miles. Every test was perfect and showed no problems. Turned out to be the "rebuilt" cylinder heads. The machine shop had done a poor job on the valve guides, but it never smoked a bit. Hope that's not your issue, just relaying my experience.
Greg

 

[73azbronco]

Stock gt40's, no special rockers or such? Do you have stock gt40 valve cover for the right side?

I'd tend to think not enough baffle, or bad valve guide seals at this point.

Should not have been smoking since first start, mine never has, I look to have same intake as yours. I am using the FMS taller canted valve covers with the baffles they provide, no oil use.

What is you vacuum pressure at idle?

 

[crutch]

I have the valve covers as shown here: https://www.cjponyparts.com/scott-d...DuMXxtJDAljzz6qZOn6dktxYF4tXE5DsaAldLEALw_wcB

But just noticed that they state: *These valve covers are not for use on EFI engines. and says "Clears most roller rockers".

This is a roller block from a 96 explorer with GT40 heads and I'm running Sniper EFI.

Just pulled all the plugs (see pic). It's interesting because on most of them the ceramic is half black and half grey, not sure if that says anything.

Going to run compression and then will validate vacuum reading. I had an exhaust shop fix a leak at the collectors recently and he said I had 12". The sniper has MAP but its in kPa. I'll get some readings on this.