Oil Loss 93 5.7 TBI

Pjhanlo · Jul 23, 2024

Having a lot of oil loss in my
1993 c1500 5.7 TBI
No leaks on the ground. Had exhaust smoke which I originally thought was Valve seals which I’ve since replaced.

Exhaust is no longer smoking but I am seeing similar oil loss. I have to add around 2 quarts every time I fill up at the gas station.

I’ve seen some threads about it being possible PCV related and disconnecting my PCV hoses I can see there’s a good bit of oil in the vacuum hose.

How do I diagnose and fix this?

Thank you,

Schurkey · Jul 23, 2024

Pjhanlo said:
1993 c1500 5.7 TBI

Pjhanlo said:
No leaks on the ground... ...I have to add around 2 quarts every time I fill up at the gas station...

...disconnecting my PCV hoses I can see there’s a good bit of oil in the vacuum hose.

How do I diagnose and fix this?

You've already partially diagnosed it. You have insufficient baffling at the PCV valve, or you have wildly excessive blowby.

The blowby might be diagnosed by seeing fumes escape from the "fresh air" tube from valve cover to the spacer between air cleaner and throttle body.

Any chance this engine has cheap-crap "dress-up" valve covers? Lack of baffling in the valve cover is a prime reason for PCV-sourced oil loss.

Pjhanlo · Jul 23, 2024

Schurkey said:
You've already partially diagnosed it. You have insufficient baffling at the PCV valve, or you have wildly excessive blowby.

The blowby might be diagnosed by seeing fumes escape from the "fresh air" tube from valve cover to the spacer between air cleaner and throttle body.

Any chance this engine has cheap-crap "dress-up" valve covers? Lack of baffling in the valve cover is a prime reason for PCV-sourced oil loss.

Valve covers are OEM. Recently replaced the valve cover gasket when doing the valve seals. But the issue was occurring prior to that as well.

Could it be a bad PCV valve?

I will check the fresh air tube when I get home tonight.

Schurkey · Jul 23, 2024

Pjhanlo said:
Valve covers are OEM. Recently replaced the valve cover gasket when doing the valve seals. But the issue was occurring prior to that as well.

Restricted oil-drainback holes due to sludge build-up?

Pjhanlo said:
Could it be a bad PCV valve?

Possible. Somewhat unlikely, but worth checking.

Pjhanlo said:
I will check the fresh air tube when I get home tonight.

OK.

Pjhanlo · Jul 24, 2024

Schurkey said:
Restricted oil-drainback holes due to sludge build-up?

Possible. Somewhat unlikely, but worth checking.

OK.

Checked fresh air tube, didn’t notice any fumes but the hose is lubed up with oil. Vacuum connections on the breather hose and on the PCV are brittle and cracking. They’re less than a year old.

Where can I located the oil drain-back holes?

someotherguy · Jul 24, 2024

Each end of the cylinder head. If oil change intervals have been neglected, they could be sludged up and invisible.

If they are sludged up, be careful cleaning them up. Start with a shop vac and nozzle attachment and try your best to avoid knocking the crud down into the engine.

Richard

Pjhanlo · Aug 24, 2024

someotherguy said:
Each end of the cylinder head. If oil change intervals have been neglected, they could be sludged up and invisible.

If they are sludged up, be careful cleaning them up. Start with a shop vac and nozzle attachment and try your best to avoid knocking the crud down into the engine.

Richard

Apologies for the long response.

One of the oil drain backs was non-existent. The rest had some residue.

Once I opened the blocked one and cleaned the rest out it seems to be much better.
I’ve filled up at the gas pump twice now and no oil loss noticeable.

Thank you to everyone

Oil Loss 93 5.7 TBI

Pjhanlo

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Schurkey

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Pjhanlo

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Schurkey

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Pjhanlo

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someotherguy

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Pjhanlo

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