djmisio85

Ok, I'm confused...

Admittedly, I'm no engineer... but

I get the glass and water example. OK

The priming bit, what happens between priming with cam sensor disconnected and then connecting the cam sensor and firing up normally? Surely all the pressure is lost and the oil just drains back down.... unless you connect it while cranking?

Also, despite the extra pressure on the bearings when firing, surely, 1 second of priming (or less) with cam sensor connected is going to be safer than 10 -20 seconds of dry cranking right?!

Again, I'm no expert, just curious

APIDavid

iTrader: (4)

There is an oil pressure relief valve that maintains pressure in the system. Plus, there is an anti drain back valve in most oil filters. That is why we all recommend genuine filters, cheaper ones are cheaper cos there's no anti drain back valve in most of them.

So the oil pressure generated is maintained temporarily in the system and at least keeps the residue of oil where it should be. So there is the protection of the oil.

Whereas, when you drain down the system, the first thing to get picked up is the air in the pick up pipe, which needs to be purged before the fresh oil and pressure gets back to where it should be.

David

djmisio85

So the aim of the dry crank priming, is just to get a film of oil all around the engine?

Even with the pressure relief valve, doesnt the oil just go back down to the sump? Does this pressure relief valve open when you do an oil change? (allowing this primed oil to escape?)

Splitpin

No, because aside from other things you have the anti-drain valve in the filter and the position of the filter below the sump oil level to act as the finger over the straw. When you switch the starter motor off, the pressure in the oil system will subside but it won't empty, and so pressure re-establishes almost instantly the next startup. It doesn't empty even if you leave the car sat for days.

Turning the engine on the starter without combustion pressure runs the fuel pump at c. 150rpm which purges air out slowly and progressively. Restarting the engine normally after an oil change results in it turning at 1500rpm within two seconds. Any air within the oil system at that point will be pressurised and blown out through the point of least resistance - which will be a bearing or bearings that are now trying to support the forces arising from a cold running engine.

The questions you're asking have already been asked further up the thread. Worth a good re-scan if nothing else.

No, the pressure relief valve does what it says on the tin - just stops overpressure through the system when the engine is running - at least when it works properly.

Of course not. However, when you take the filter off, you break the fluid lock and remove the anti-drainback valve, allowing the upper parts of the engine to drain out. Next time you take a filter off, undo it very slowly with a drainer underneath and don't allow any of the oil in the filter itself to spill. And then ask yourself where all the oil spilling out over your hand is coming from.

APIDavid

iTrader: (4)

Couldn't have put it better myself. wanna job ?

David

Splitpin

That's interesting - although as you say it's only half the picture without knowing the widths. I see what you say about there being extra reciprocating bits, but on the other hand it'd be interesting to see what if any effect the length of the crankshaft has on bearing loads.

Is it still in one piece?! Whatever's going on here is, I'm sure, a combination of interacting factors. Ultimately the only way we'll know is by modelling or simulating it. We need Richard Hammond and his clever camera show.

Splitpin

Shhh, there are people on here who think you and me are the same person anyway.

djmisio85

Ah, I see

So if anything, filling the oil filter up with oil is obviously the important point

Obviously as some have mentioned, some oil still stays in parts like the crakshaft and oil pump...

So apart from the bearing sizes, what makes a turboed scooby engine so much different to other engines? Why don't other cars need the CPS's disconnected?

Splitpin

Wouldn't necessarily agree with that. The key benefits of filling the filter prior to fitting are firstly that it saturates the filter medium, and secondly, and most importantly, that it puts some oil in a position to do some good more or less immediately.

However, the bottom line is that if you fill the filter but don't disconnect the crank sensor, you still have a load of air in the system if you start it immediately, albeit less than you would if the filter was empty, and "divided" by the oil in the filter.

If you don't pre-fill but do turn it on the starter, you're still going to purge the air out of the system in a controlled way, albeit that it'll take a little longer because you need to pump an extra volume of oil equivalent to the capacity of the filter (about 0.2 of a litre on the current "small" Subaru AA100) into the system before it can pressurise.

On that basis, IMO it's the cranking part that's the more significant of the two, but both together are best.

The pump hardly retains anything. Enough to keep it primed but in total probably not much more than a tablespoon or two. Ditto the smaller galleries and the bearings themselves will retain some but the larger diameter mains drain almost completely. As I said before try taking an old filter off slowly and measure the amount that drains out from above it. You'll be surprised.

Dude, I've said it once, I'll say it again, and hopefully this time you'll pay attention. Questions just like this have already been asked and answered earlier in this thread and/or another one you'll find a link to on one of the previous pages. If you can't be bothered reading through what's already been written, why should any of us waste our time repeating ourselves?

JohnD

iTrader: (5)

As the filter hangs vertically down in the Subaru application, there can be no drain-back of the oil from the entry side of the filter. Therefore a drain-back valve (the rubber 'flap') is not necessary. (unless you roll the car) A number of filters for the Subaru have this valve deleted. eg Purolator, UFI etc.
It may be the case that the reason the Subaru item (who actually makes it?) has this valve, is that it is used for other applications where the filter is not vertical?

JohnD

djmisio85

Ok, sorry to drag up a very controversial thread like this but...

I spoke to the staff at Arai Motorsports here in Japan today. Some of you may know this company, with the boss, Mr Toshi Arai being 2 times PWRC Champion and currently Subarus main rally driver.

The staff knew nothing about the whole "disconnecting the CPS or dry cranking to get pressure" thing...

I'm sure that a company like this would be in the know... considering their success with Subarus, and actually being in Japan and directly working with Subaru Fuji Heavy Industries and STi....

Also, I do see the bigger picture, that it "may" help prevent some "minimal" wear.

Also, it does depend on how long your car cranks before actually starting...

This next bit, I don't know, but is there not a possibility, that the engine is not set to start until sufficient oil pressure is built up?! Its a long shot, but there could be something like this

Also, with this thread,

https://www.scoobynet.com/general-te...-noises-2.html

I read, that someones engine started knocking immediately after starting the engine... how can such big engine wear occur so quickly?!?

APIDavid

iTrader: (4)

Oh dear ! Oh dear ! oh dear !

Here we go again.

The cranking to prime the system before starting is common sense and a recommendation.

I fully accept that not everyone wants to do it, or will do it, or has done it.

My advice is; that if you have the time to do it - it costs nothing and is good workshop practice.

I rang Barack Obama he doesn't do it either.

Gordon Brown will, but wants to tax it if you do.

Frustrated of Warwickshire.

JohnD

iTrader: (5)

David Cameron will not admit either way until after the election!
Nick Clegg just said "What the f**k are you talking about?"

JohnD

APIDavid

iTrader: (4)

joz8968

iTrader: (13)

LOL, indeed.

Splitpin

It's not already built into the cars if that's what you're asking. The ECU doesn't know what the oil pressure is so there's no direct safety interlock to prevent startup.

All there is on the standard Subaru ECUs is a fixed delay between the acquisition of engine timing (and stable rotation on the starter) and the application of fuel and spark. It certainly is possible to increase this delay but it's still a blunt instrument.

Splitpin

Incidentally, I phoned Barack Obama earlier and he told me to "stop building those f*ck*ng houses".

I suspect he might have confused me with someone else.

joz8968

iTrader: (13)

Setright

Dry-cranking is like an Evo outrunning a STi...it's a myth :-)


SORRY!!! Couldn't help myself...fuel the fire ;-)

djmisio85

Well, if Gordon Brown agrees to it, it MUST be BS.... especially if he wants to tax it case closed

My evo outruns imprezas In that case the dry cranking thing must be true

Again, I agree, that it can be done as a precaution, but I think to some people, its like saying, "you should rebuild your engine before every time you drive it... just in case".

Hopper

I started the original thread about Serious Knocking Noises.

Next time you see Toshi, ask him why he thinks my engine failed at 36k miles with a 'perfect' Subaru service history would you?

I have written numerous letters to IM and had no reason whatever put forward from them as to why it happened.

Until then, David and Splitpin are my only source of credible explanation and I for one will ensure that any future oil changes will be carried out according to their recommended practice.

The f***ers at International Motors neither seem to know or care why these things happen, and in fact seem to deny that the problem even exists.

APIDavid

iTrader: (4)

Attaboy hopper.

chrisnorm17

one quick point

How do subaru main dealers changing oil??? they the ones who build the engine they must have tested this????

chris

jef

iTrader: (13)

chris its probably best you read this whole thread,

all will be revealed.

chrisnorm17

hmm
well im unsure but like alot of pople say best be safe its not hard to unplug so ill remember this for next time

karenv7bell

my bro works for Subaru and laughs at this as he has rang tech hq and they do not mention this reck when he dose them and he s been there for 15 yrs , if it was an issue that is so easy to rectify they would make them do it ? , and he showed me to look at oil pressure gauge when senor was disconnected and it was zero ,not until it was connected did it show pressure , try it . he dose fill oil filter up mind .

eggy790

iTrader: (20)

this is the sensor mate

Splitpin

Tanx for the picture Eggy.

Hopper, re. Arai, why don't you put your journalist's hat on and ask the question? It'd be interesting to see if you got an answer out of him:

Toshihiro Arai
Arai Motor Sport Ltd
837-1 Shibamachi
Isesaki City
Gunma, Japan


Some do all of the above, most are probably too lazy Chris. However, Subaru UK dealers are not the "ones who build the engine". The engines are built by FHI or STi in Japan. And speaking of the ones who are too lazy (or dull)...

I'm sure Hopper and other victims of engine failure under similar circumstances will be pleased to hear of a Subaru UK or franchised dealer employee "laughing at this". Would you like to tell us where your brother works so we can phone the service manager up and ask them how they do it? Maybe we could ask for your bro by name?

You're not telling any of us on this thread anything we don't already know. You will never get loads of pressure in the system by cranking the engine on the starter, so I'm not sure what your bro thinks he's trying to prove there. The point is to purge air out of the oil system while the engine's not exposed to running pressures.

Really? Why?

dunx

iTrader: (3)

And the mudjahidden say "die infidel !"

Sorry !

dunx

P.S. I have an oil cooler and even "prime" that before starting after an oil change....

Jamz_

iTrader: (12)

+1, but i think i may have put the pipes on the wrong way round after reading up on the way oil filters work (well i have it piped in to go in at the top and out the bottom, but wanted it the other way round)