Blow by gases


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Pablo Puma

Sep 8, 2021
A Coruña, Spain
Hi, I am moving this thread to this section because it might be more appropiated:
View attachment VID_20230320_110532.mp4 I don't really have a problem this time with the Puma but I am curious about something I noticed with the PCV system of the 1.7 engine. When you pull out the oil cap while idling (engine cold or hot) you can notice really big pulsations coming out from the head. I am a mechanich myself and I have dealt with quite a few PCV problems and different cars have different pulsations, in some you don't really feel anything, in others the cap is even sucked a little bit and in others the pulsations are pretty strong but I don't know what is normal in this engine or in petrol Ford engines from this era. I don't drive the car that much so I can't relay on oil consumption nor I feel any issues with the engine, it is just pure curiosity, do any of you know how this behaves on any of your cars? Whenever I have time I'll try to post a video so In case it is normal behaviour it will be useful for other members.
Thank you


New member
Nov 25, 2022
Hi Pablo,

Not a mechanic myself, just a self taught dude which has curiosity about cars, but hey here goes my experience on this topic:
I've had my puma for half a year right now, early on my owning I refurbished the complete PVC system, having new valve, tubes and cleaning the oil separator box, and recently I've come back just to check if everything was okey.

I did check as you show on your video, having the engine running while the oil cap was off, and I experienced the same behaviour, big pulsations of air comming out of the fill hole.

As you mentioned, otherwise the engine feels good (though mine drinks a bit of oil regardless 😅), plenty of power and no hessitation. So I might assume this is normal behaviour.

Though as I've said, I'm no mechanic, so if someone else with more knowledge on the matter can answer we will all learn.

Hope you can find this usefull!



Aug 23, 2017
Easy answer, buy or borrow a compression tester. That will tell you the state of play. As the engine wears you will get more blow by and the crank recirc system will dump more into the intake to keep the emissions sensible. If the crankcase is pressurised then I’d suspect things are ‘mid’ life.

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