What is the explanation for no oil discharge when the oil cap is off?

Asked by dbfl6 Aug 07, 2015 at 10:05 AM about the 2002 Chevrolet Suburban

Question type: Maintenance & Repair

Inadvertently left the oil cap off last time I topped off the engine.  Discovered this shocking omission a few weeks later, to my great surprise, there is no oil discharging from the refill spout, and there was no oil on the hood pad.  There is heat exhausting from the spout, but no oil.

My truck had been experiencing progressive oil loss/leak for a while.  I have suspected that the catalytic converter may be causing backpressure, forcing the engine temp to increase and the pressure, thereby causing oil to finds it way out through seals.

I noticed a reduction in oil loss since I mistakenly left the oil cap off, so I am wondering if my hypothesis about the backpressure could be correct.  Also wondering if there is a downside to leaving the oil cap off if in fact this is allowing pressure relief and reduction in oil loss.  The truck performs fine, with no apparent loss of power, or diminishment in performance.

Thoughts?

3 Answers
223,935

Rowefast answered 9 years ago

Well... Leaving the oil cap off allows dirt to get into the engine, especially on dirt roads. I don't think the catalytic converter is causing this, since the truck is performing fine. The motor needs to breath, check the pcv to make sure air flow gets threw it in one direction, the vacuum side, and look for cracked vacuum hoses and hose that runs to the pcv.

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223,935

Rowefast answered 9 years ago

Also check the breather element, probably needs replacing anyway.

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woodctr51 answered 9 years ago

Some of the older models had/have breather caps for the oil filler tube, you didn't say what year your vehicle is. Mr. Rowefast is 100% correct. I just wanted to throw my 2 cents in.

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