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Amount of blow-by from oil fill cap question


Soledad

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A few weeks ago I wanted to test blow-by on my 2003 2.3L. I started the engine, warmed it up and then removed the oil fill cap and placed it upside down on the hole. There was enough blow-by to blow the cap up but then it would suck it back down. It was doing it very quickly. I didn't do this for very long though because it was spitting oil out of the hole and starting to make a mess.

I've done this on a few other vehicles and the cap would just lay there with no oil spitting out. But on my wifes 2013 Santa Fe Turbo it does the same thing as my 2.3L.

Is this normal behavior for these higher compression Duratec's or should that oil cap just lay there without moving with no oil spitting out?

I've got a compression tester now but just have not had any time lately to test it due to work and family stuff.

Thanks!
 


adsm08

adsm08

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That sounds unusual for that engine. It will run louder with the oil cap off, and it will spit oil, those are normal for OCH engines. But it shouldn't be blowing the cap around like that, IME.
 

RonD

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Not sure that would be a reasonable test for blow-by on an engine.

Crankcase ventilation usually has a vent hose connected to the air intake system and then often to the oil filler tube.
At idle vacuum is high so PCV valve is closed and vent hose is pulling out any positive pressure.
As engine RPM and load increases vacuum drops and PCV valve starts to open to actively pull in increased blow-by from the load.


A better test is to pull out dipstick, start engine
Use a piece of paper towel or toilet paper on the dip stick tube, should be held lightly in place, but hard to test on some engines because of the fan
 

Soledad

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Ok thanks. I'll have to get a video of it and post it up here soon.

But, I know a compression test is what I really need to do. Just never seen a cap dance like this before.

PCV valve is new and vacuum at idle is a very solid 21in.Hg. Truck seems to run great other than a drop in performance once the engine is fully warmed up.
 

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Compression is fine with 21" of vacuum
 

Soledad

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Cool. Thanks RonD. That does put my mind at ease.
 

MrGiggles

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Every DOHC 4 cyl that I've tried that on move a lot of air and blow oil around. All of which were healthy.

My 2.5 hardly moves any air, but that's a different animal, and I'm not sure if the PCV is working normally.
 

Soledad

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Ok, thanks everybody for the responses! I'm just gonna call this a "DOHC thing" and move on to the next problem.
 
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