Got lazy and ran the blowby test with just my hand instead of a gauge

I was out on a job last week in Lubbock checking out a 6.7 Cummins that sounded a little off at idle. Didn't have my blowby gauge handy so I figured I'd just cup my hand over the oil fill and feel for pressure. Seemed fine to me so I told the guy his engine was good. Well he brought it back two days later after it started smoking bad on the highway and I finally put a proper gauge on it. Read 12 inches of water at idle and almost 20 under load. Lesson learned - stop trusting hand feel for blowby, it's way too easy to miss something until it's late. Any of you guys ever get burned by skipping the proper test?

3 comments

3 Comments

laura_wilson4d ago

Yeah that hand test tricked me too on a 5.9 once, cost me a engine.

sean484d ago

See, what gets me is nobody talks about how the engine temp itself can mess with the hand test. If the engine is hot and you just shut it off, the oil is still cooking inside and the level reads false. Cool down time matters way more than people give it credit for. You need at least 10 minutes minimum, but I let mine sit for 15-20 before I even think about checking. Then the hand test works fine. Trying to do it right after shutting down is what gets people. That 5.9 was probably warm and the oil looked good on the dipstick but the true level was off by a whole quart. Been there, it's a nasty surprise waiting to happen.

luna2614d agoMost Upvoted

Ouch, did the dipstick look fine when you checked it?