DeanF

iTrader: (1)

Well Is this really neccessary !!!!
You run your engine up to temp, Turn off, Drain your Oil, Remove oil filter, let that drain, Prime your new oil filter (V Important), Screw oil filter up, Fit sump plug Etc, Fill up with oil.You let the fresh oil settle to geta dipstick reading & top up accordingly..
Now the engine has been stopped, for arguments sake say an Hour,
So the bearings/shells etc still have quite a film of oil protecting them & the car starts to pump oil as soon as it starts.
Question.
When you go on your Holidays for 2 weeks & the poor car stays at home, do you disconnect the crank sensor then before starting ??? No, Has the oil had much longer to completely drain away. Yes.
So is the crank sensor disconnection really neccessary , the oil pump will still have oil in it after the sump & filter have been removed .

Opinions Please
Thanks
Dean

scooby_matt

You've opened up a can of worms...or what's going to be a very boring thread

DeanF

iTrader: (1)

Well the Boring bit will help us sleep

Dean

FASTER MIKE!!

calling pslewis one of his specilaist subjects

RON

some may say it's not needed, but i always do disconnect the cps and crank til oil light goes out, then a few more turns just for luck, and as it happens, when i went away for 3 weeks, i did the smae when i got home, call me paranoid i don't care, i'm just saving my engine so i can rag it for a bit longer!! and after-all, it takes what.... 2mins..??

rgv_stu

my scoob is shocking when i change the oil, it takes about 30 seconds of cranking before the oil light goes out!! my previous vauxhalls used to extinguish the light after about 5 seconds.

Kenny.S

Here's my tupence worth, take it as you will but this is my understanding on the subject

I'd say there was a bit of a difference between an oil change and leaving the car standing for a week or two.
When the car has been lying for a few weeks the pick up pipe is still submerged in oil therefore it's very difficult for the oil to drain from the pump, however when you change the oil i think it's highly likely that the pump will drain out and also when you re-fill the sump the pick up will end up with a big gulp of air in it so turning it over without starting helps return everything to how it was prior to the oil change.

I wasn't a believer in this procedure or the pre-filling of the filter but since talking to several respected tuners about it there does seem to be logic behind it.
As i'm sure most of you know the impreza engine has very small big end journals for its capacity when compared to an in line 4. If your average in line 4 suffers momentary bearing journal contact (it's not good on any engine but for the purpose of this ramble!) there is a bigger bearing surface and as such any pressure is spread over a larger area. The impreza on the other with its much narrower bearings will suffer much more damage as the load is applied to a smaller area. The damage may not show up for 10's of thousands of miles but the more marks and scores on the bearings/journals the easier it is for the oil film to break down which can cause the bearing to over heat and when it does, being made of soft material it expands reducing the clearance between the bearing and the crank so less oil gets in more heat until no oil gets in bla bla bla you know the rest $$$$$

Kenny

ALi-B

iTrader: (1)

Anyone care to give me an engine to disband the **** theories?

I'll strip it down, measure wear/damage etc.
Put it back together and I'll run it up. Then drain the oil.

Then start it up run it at idle for 10 seconds WITHOUT oil. (massively exaggerated...most idling engines will prime within 2 seconds)

Strip it down and measure for wear and damage and lets see what we'll find.


It's the only way to prove the theory I'm afraid.....threads like this won't prove anything, time for somone to put their money where their mouth is and show us all who is right/wrong

What if ?

if it goes bang after an oil change, it probably would have gone bang even sooner with worn out crap oil in it. Once the oil light has gone out, oil is circulating and up to pressure, this takes a matter of seconds. It is a very sad day when modern engineering (with residual oils on the surfaces) can be destroyed by not having full oil circulation and pressure for a few (engine off load and ticking over) seconds (at most).

Unlike PSLewis, I would recommend using good qulaity oil though.

Kenny.S

Like i said it's only my opinion not trying to suggest that's it's the route cause of all bearing problems but bearings dont just wreck themselves for no reason.

If you know that your engine isnt detonating, your running good oil changed regularly, you let it warm up properly ie oil temp has equalled out with the water at around 85-90 before kicking it's head in (another highly probable cause of bearing failure) then the only other time that the bearings can come into contact with the journals is during an oil change, am i right or wrong?

For all the time it takes to unplug it and crank it over for a few seconds after an oil change i dont see what the big deal is, it cant do any harm. Call it **** or what ever else you will but ill keep doing it.

Kenny

gareth1

Why does disconecting the crank sensor make any difference? If you are using the starter motor to crank the engine the same movement of the crank and bearings etc takes place as if the engine was on idle. I know it will be at a lower speed but that just means it will take longer for oil to circulate. Do main dealers carry out this method for changing oil?

XR-Wayne

When i had my Defi's fitted they left the oil light dash wire unpluged in the engine bay,

Do i get that reading that the dash light does on the defi's???

Reason i ask is that i was running very low on oil and didnt no coz they unpluged the Wire to fit the defi's and i now dont have a oil light,

Got Oil temp and Pressure.

Stephen Pope

apparently very an@l

jjones

yes the engine is turning over , but without the huge loadings that the internal combustion places on them.

Tone Loc

iTrader: (1)

No they don't, the actual procedure in the service manual also doesn't state you have to pre fill the filter.

I've always pre filled the filter but only done the disconnect crank thing about twice... in 6 years of ownership the engine is still going strong.

You could argue all day long about what you should or shouldn't do, yes a *few* imprezas have failed just after a main dealer service but *many* haven't. You have to make your own mind up.

Tony.

DeanF

iTrader: (1)

To have an engine turn over freely, you should infact remove the Plugs as there is still considerable load from the compression, Try turning one over by hand without the Sparkys removed !!! Not easy


DEan

Bob Rawle

Think about this, the oil pump has to lift oil from the sump, push it up to the top of the block into the oil gallery's before the oil gets to the bearings or anywhere else, so if the car is stood then all that oil also stays put, when you do a change the oil in the gallery's and above the pump thats normally trapped there drains out, so now you change the oil and fill the filter, thats great but you still have a big empty sppace to fill before the bearings see any, so cranking with the sensor disconnected fills that void with oil and channels it to the bearings albeit at low pressure before you fire it up, otherwise there is a short period of almost dry running (just some residual film).

Unplugging the sensor prevents the injectors firing fuel into the cylinders and stops the ignition also.

I know of at least one main dealer who sensibly adopted this practice and have seen NO bearing failures following service since, prior to they did.

cheers

bob

pug32

Looking at doing mine on thursday, anyone got a piccy showing where the crank sensor is? I have never done this on previous cars owned but will do it anyway!

scooby_matt

It's the white plug underneath the alternator

[Davey]

You dont need to prime the filter and you dont need to crank the engine..

You'ed never crank the engine fast enough on the starter to get the oil flowing at a pressure to keep the crank afloat in the bearings anyway! And there will already be oil deposits on the engine components to keep it lubed on the initial start up..

Its a normal car with normal needs, not some majestic being that needs special treatment!

scoobfan

And that's from a expert, not some keyboard mechanic !

Rob

[Davey]

Well thats its, thats the end of that.. end of story, he's right, everybody is wrong, done, dusted, finito, goodbye, astalavista, bing bang bosh the case is closed from now on when ever I change a filter I will prime the filter, pray to the gods and use my special spanner because a main dealer does it so it must be right?

scooby-tc

iTrader: (2)

pslewis

An updated, Modernised **** Oil Procedure is now out:-

1. Remove Oil Filler Cap, 'SLOWLY' - take at least 15 minutes or the threads will strip and the exhaust will fall off within a week.

2. Carefully jack up the front of car, make sure that only the 'special' car jacking points are used or the steering wheel will be upside down next time you see it (the special jacking points are only known to a select few, not the main dealers!)

3. Locate the Sump Plug, do this using an Inspection Lamp with a 40W bulb - do not, under any circumstances, use a bulb of Higher Wattage or the splash cover under the engine will melt and minute pieces will be sucked up into the MAF. Immediate engine failure will occur within 5 miles.

4. Undo Sump Plug whilst humming 'Oil Be Home For Xmas' - do NOT sing any other song or the Radio will never tune into any local stations again and the aerial will need to be replaced at the next service.

5. Allow Oil to drain into a Tupperware Perspex Jug - use only perspex as other plastics react with the old oil and particles travel back through the draining oil molecules and attack the Big-End Bearings.

6. Whilst Oil is draining run around car 15 times in a Morris Dancing Outfit with the Special Subaru Bells attached to shoes.

7. Remove Oil Filter by unscrewing anti-clockwise 5 times, then clockwise 2 times, continue until filter is free - failure to do this will result in the new Filter not filling up with Oil on start-up.

8. Take Oil Filter that you have been soaking overnight [you DID soak it overnight with regular ½ hour top-ups – didn’t you?] If you did not soak overnight please do NOT continue any further – a Filter not soaked for at least 8 hours will not be ready – the Subaru Impreza Filters have a known weakness known only to the select few. The weakness results in HeatSoak within the Intercooler and engine failure.

9. Start filling the engine with Oil – ignore the Oil Subaru recommend, they don’t know as much as the ***** – Oil costing less than £35 for 4 Litres should NOT be used under any circumstances. The more expensive the Oil the better! Cheaper Oils are Hydro-Cracked, EthoNotol BaseStocks removed from the bottom of the chip fryer in Bills Fish’n’Chip Shop!

10. Now it gets complicated, the engine start procedure - remove the spark plugs, coil packs and battery - remove the seats and rear boot/tailgate – remove the carpets if the service is also the CamBelt Service (the CamBelt will snap unless this is done) ensure Octane Booster is removed from tank as it might spontaneously start the car when you are not ready - take the drive belts off - turn engine over, s....l....o....w....l....y - engine should be turned over at least 67 times to ensure adequate Oil film coverage.

11. Return all components and start engine whilst whistling the theme tune to TITANIC ................ if you are VERY lucky the engine will not shoot a con-rod through the block (this normally happens to MY96 cars which are MicaPink in colour with Gold Wheels) - but ALL Model Years can be affected equally.

12. If the engine started without any problems, then don't be smug as the MAF sensor will blow up your engine within 3 days in any case!

--------------------------------------------------------------------

Do NOT do as Subaru recommend and as the Main Dealers do, which is:-

Change Oil – Change Filter - start engine - check for Oil drips - return to customer!!

Pete

fatmanscooby

FPMSL

[Davey]

Have you got that in PDF format so I can print it out and add it to my service folder?

I think we need one for the cambelt change

scooby_matt

That's the first time I've actually laughed at anything Mr Lewis has every written (provided he did write that himself).

pslewis

It is all mine ..... its a few years old now but still gets a chuckle!!

Pete

pslewis

pm me your e-mail and I'll send you it in WORD format?

Pete

pug32

cheers fella