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Engine oil flushing- why NOT to...
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Author:  drmini in aust [ Sat Sep 04, 2004 8:41 pm ]
Post subject:  Engine oil flushing- why NOT to...
Hey I pulled this off the Austin America site in US, it makes sobering reading.
Kevin G

Thanks to Todd Miller!


Engine "Flush" treatments:
-This was a recent topic on our 1100 email chat group and I thought it an important one to save for future reference. It began when one of our members took their all original car to their mechanic for a "routine" oil change. The car's owner supplied the oil and filter so all the shop had to do was the labor.

Upon removing the drain plug and finding the usual metal shavings on the magnetic end, they told the owner that the engine really needed a good flushing to clean out all the crud inside. The trusting owner agreed.

The shop left the old filter in and filled the engine crankcase with diesel fuel and some oil. They ran the engine for a bit, then drained this out. Still leaving the old oil filter in, they refilled the crankcase with Automatic transmission fluid and some oil. Again, ran the engine for a while and then drained this mixture out. This time, they replaced the filter and put in the owner's supplied Castrol GTX 20w/50.

The engine now has only about 35psi oil pressure warm going down the road, and about 15psi at idle.....prior to this it had 25psi at hot idle, and probably 50 or so at speed.

So, a day late and a dollar short for this owner, here is my 3 cents worth on engine (and transmission) flushes:

-All the engines got the magnetic drain plugs. And, for good reason! Look at all the stuff they catch!! I wouldn't sweat the metal pieces too much. They all do it to some degree and it's just another reason to change the oil more often.

Naturally, there is some suspended crud stuck to the walls of any engine. More so in engines that don't receive regular oil changes, or just get driven around town so the oil never heats up enough to burn off all the impurities. The last thing I want to do is flush
all this stuck crud, down through the engine. Why? Because where does it go?

First, it gets sucked up and run through the oil pump vanes. Guess what that does to the tight tolerances in the oil pump as the vanes get scored. Next it goes past the oil pressure relief valve and can score that piston so it doesn't seat properly. Then at trip through the oil filter where hopefully all of it is caught, and hopefully the oil filter bypass doesn't open due to all the crud that's moving through. If the bypass opens it dumps all this crud directly into the crankshaft and camshaft bearings. On top of all that, the crankshaft and transmission gears sling all this unfiltered crud up onto the piston walls so the pistons now have a chance to drag up and down in it.

Oil pressure is all about tolerances...and keeping them small. Tolerances in the oil pump vanes, tolerances in the crankshaft and camshaft bearings, etc. Once those tolerances start to get big...indicating wear/damage...the oil pressure starts to suffer big time. For example, the crankshaft bearings run on a tolerance of .0015"-.003" By comparison, a sheet of paper is .004" thick. That's why I freak out when I hear about engine flushing. Imagine the diameter of the crud particles (mostly chunks of carbon, which is quite hard) that are being flushed around and they go through the oil pump completely unfiltered. And, if that's not bad enough, oil filters have a bypass function so that they won't clog up and stop oil flow. So, potentially if an oil filter got hit by a boat load of crud, the bypass could open up and allow everything to bypass the filter.......next stop, .0015" clearance at the crankshaft. Ouch!

So, in my opinion, whom ever invented engine flushing (and likewise automatic transmission flushing) is the same guy who wants to sell you a $4,000 engine rebuilt about 6 months from now. And, that's probably the same guy who will say, "Well, that engine's 30 years old, it's probably all wore out inside," when you come back 4 months later asking why it's knocking and has low oil pressure at idle.

But hey, call me paranoid. I say leave sleeping dogs lie.

On the flip side, if oil is getting black before the usual 1,500-3,000 mile oil change interval, then consider changing it more often, do less low speed/short trip driving, and have the carb mixture checked to make sure it's not too rich.

Todd
Author:  Morris 1100 [ Sat Sep 04, 2004 9:26 pm ]
Post subject: 
Wise words from my good buddy Todd!
The owner of the car in the story is a lovely lady and she would not do anything to hurt her cars but she was horrified that her car had lower oil pressure after the oil change.

The secret to long life with mini engines is change the oil every 3000 miles or sooner.
Author:  drmini in aust [ Sat Sep 04, 2004 10:01 pm ]
Post subject: 
Mine gets oil change every 1500 miles and a new filter every 3000, religiously.
Cheapest thing you can put in a motor, if you want it to last.
Author:  mrcooms [ Sat Sep 04, 2004 10:17 pm ]
Post subject: 
What OIl filter do you guys use?
last time i used a Valvoline one and i have forgotton the model number.

good informative article.
Author:  Morris 1100 [ Sat Sep 04, 2004 10:30 pm ]
Post subject: 
I run Ryco filters, I have never had any problems with them except for the Cooper S air filters that they kept making thicker and thicker!
Author:  drmini in aust [ Sat Sep 04, 2004 11:01 pm ]
Post subject: 
I get the Coopers or Unipart spin-on ones from Karcraft, made in UK.
Ryco are good, but I've not seen these type lately at the right price.
I do use Ryco in the Laser and EA Ford.
Author:  mrcooms [ Sat Sep 04, 2004 11:18 pm ]
Post subject: 
I think i should go for a trip to karcraft everyone seems to talk about them but i havent been yet.
is it basically a werehouse and you ask the guy at the counter for the parts u want?
Author:  drmini in aust [ Sun Sep 05, 2004 5:42 am ]
Post subject: 
Yeah that's right. Basically, they are importers & distributors. Lots of Mini places buy off them and resell.
Address is 9 Egerton St, Silverwater. 8)

Mon-Fri only..
Author:  Anto [ Sun Sep 05, 2004 10:38 am ]
Post subject: 
Yeah that article makes a lot of sense. The only time I 'flushed' my engine was when I put the new gearbox on at the start of the year, after the old one (well, the drop gears actually) had disintegrated. All I did was put a new filter, filled it with GTX and some Nulon oil flush, let it run for a while, then ditched it all and put a new filter and new oil. Strangely enough, no crap really came out so I don't think I actually needed to do it. I always figured the oil filter was the bit designed to catch all the crud, so frequent oil/filter changes would keep the engine clean.

Anto.
Author:  Minimad [ Sun Sep 05, 2004 1:32 pm ]
Post subject:  Re: Engine oil flushing- why NOT to...
drmini in aust wrote:
So, in my opinion, whom ever invented engine flushing (and likewise automatic transmission flushing) is the same guy who wants to sell you a $4,000 engine rebuilt about 6 months from now. And, that's probably the same guy who will say, "Well, that engine's 30 years old, it's probably all wore out inside," when you come back 4 months later asking why it's knocking and has low oil pressure at idle.


I am not sure about the autos in minis, but I ALWAYS get the auto flushed in my V8 commode.( Not a spelling mistake :wink: )
The reason being that the converter, pipes and cooler hold about 3L of oil!!

So it only makes sense to flush this out with new auto fluid. They don't 'run' the auto when they do it, they just hand pump the new fluid in unit the old is changed. The V8 tends to really kill the auto fluid between services (20000Km) as it is my tow car.

Auto is still holding together after 180000Km of flogging.

Note: Desiel for desiel motor.........Auto fluid for automatic........why would you let some arse muchanic use it as oil in your motor :shock:

Minimad
Author:  68matic [ Sun Sep 05, 2004 3:33 pm ]
Post subject: 
can someone explain
what does oil pressure have to do with a good runing engine,
and what are good limits for it? (what if i dont have an oil pressure guage?)

thanks doc for the lightening article
what if the oil is really dark? does it mean we should ignore it in the a-series engines and just change more often until clean?
Author:  drmini in aust [ Sun Sep 05, 2004 3:54 pm ]
Post subject: 
Best way to flush a motor IMO is give it more regular changes with 20W/50.. 8)
I don't know who the mental giant was that decided to use ATF in an engine. Heck it's not even oil- it's glycol based.. :shock:

Duc, oil gets dirty for a few reasons:
1. Blowby past the rings if motor is worn.
2. Sludge coating in motor, because PO didn't bother changing it enough.

Bear in mind the `black' in the oil is mostly carbon particles small enough to go thru the filter element. So it really won't hurt anything.. it just shows the oil is doing its work. :wink:

BTW I find it gets dirtier sooner if you run a Weber or Dellorto- but I don't care... :P
Author:  68matic [ Sun Sep 05, 2004 4:05 pm ]
Post subject: 
gotcha
and what importance has oil pressure on the engine?

i thought that about ATF too... it smells and feels like brake fluid and thats washable off without soap
Author:  drmini in aust [ Sun Sep 05, 2004 4:22 pm ]
Post subject: 
Normal oil pressure (hot & revving) on most Minis is around 60psi, Cooper 70psi. I'd say on an old motor 50 is OK, if it gets down to 40 the bearings or pump are on the way out.

Idle pressure- anything over 20psi is OK. Depends what grade oil and how hot it is... :wink:

Autos (even old ones) should be around 60-70psi hot- they have a humungous pump, compared to all others.. :P
Author:  J_A_M [ Sun Sep 05, 2004 9:48 pm ]
Post subject: 
Thanks Kev. I have never believed in flushing oil, and this is why. Everyone should take note.

Someone once told me ages age that the engine build up deposits actually help seal your motor, not only the rings but some gaskets as well.
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