Chat with an old timer at the truck stop in Flagstaff changed how I check for blow-by

He told me to pull the oil fill cap with the engine hot and at a high idle, not just at a low idle like I always did. I tried it on a 6.7 Powerstroke that seemed fine before, and you could see a steady pulse of vapor I had missed. How many of you guys check it that way, or is that just for older engines?

3 comments

3 Comments

the_claire3mo ago

That dollar bill trick saved me a lot of trouble on my old 7.3.

daniel5113mo ago

Ever heard of the dollar bill test for blow-by? With the engine hot at a high idle, hold a dollar bill over the oil fill hole. If it gets sucked down and stays, your rings are probably still good. If it blows the bill right off, you've got a real problem. That old timer gave you solid advice, it works on new engines too.

the_skyler26d ago

Yeah, @daniel511 is spot on with that test. Tbh, I've had a couple cars where I thought the rings were shot until I did that and it pulled the bill right in. Saves you a lot of stress before tearing into the engine.