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Flushing with semisynthetic
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trampintransit



Joined: 09 Aug 2010
Posts: 166
Location: Edinburgh

PostPosted: Wed Jul 13, 2016 10:17 am    Post subject: Flushing with semisynthetic Reply with quote

So....the motor's ( '59 Armstrong Siddeley 4litre ) not turned over for an age. There's a bit of sludge in the gunk that's come out. I've got some best quality classic multigrade to go in, but I'm thinking , why not run it for 15mins with some cheap oil , then change the filter and drain and put the classic oil in.
Somebody else just said " Don't flush with synthetic oil , you'll damage the shells"

Really?. Surely 15mins at idle with a semi isn't going to damage anything?
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petermeachem



Joined: 23 Sep 2013
Posts: 358
Location: Chichester Sussex

PostPosted: Wed Jul 13, 2016 2:21 pm    Post subject: Reply with quote

I have no idea, but I like the last sentence!
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trampintransit



Joined: 09 Aug 2010
Posts: 166
Location: Edinburgh

PostPosted: Wed Jul 13, 2016 3:37 pm    Post subject: Reply with quote

Bad, bad man! Smile
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peter scott



Joined: 18 Dec 2007
Posts: 6221
Location: Edinburgh

PostPosted: Wed Jul 13, 2016 8:32 pm    Post subject: Reply with quote

I've been running my SS on synthetic for the last 10k miles and the oil pressure is as good as when I put the shells in.

Peter
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goneps



Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand

PostPosted: Thu Jul 14, 2016 1:07 am    Post subject: Reply with quote

As I understand it, and I don't claim any expert knowledge, modern oils such as synthetics are unsuitable for old engines for a couple of reasons:

1. They lack the zinc anti-wear additives (ZDDP) essential for engines with conventional tappets where scuffing and shear are factors.

2. They are highly detergent, which means foreign matter is kept in suspension to be removed by the efficient full-flow filter all modern engines have, but old engines don't. Most oldies make do with a simple gauze, which will let through particles that can score the crank journals and bearing surfaces.

How (2) will affect a relatively modern 1959 engine I'm not sure, but even if it has a full-flow modern-type filter there is still the matter of excessive valve train wear. Personally I wouldn't use any oil with an API rating greater than SF (ie. SG and higher).

As for the original question, if sludge is coming out with the oil you need to drop the sump and give it and the oil pump a good clean out. After that I'd run for a few miles with a cheap oil (API of SA to SF), then drain and fill with the classic oil.

API rating is usually found in the small print on the back of the container.

Richard
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jp928



Joined: 07 Jun 2016
Posts: 247
Location: Australia

PostPosted: Fri Jul 15, 2016 4:34 am    Post subject: Reply with quote

There are quite a few oils around with high ZDDP levels, so that part should not be an issue, UNLESS they also have high detergent levels, as in Diesel truck oils marked HDO. I do agree it would be good to drop the sump and make sure its all clean inside, and the pump pick up is clear of debris and sludge. Starting with some cheap oil of the right viscosity makes sense, but I would crank it without spark until you see oil pressure up before actually running it. Some users of modern cars with hydraulic tappets that tend to clog up (rattle on start up) eg MX5, fill the sump with half oil, half diesel fuel (or even paraffin) and idle them for a while to flush out gunk.

jp
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goneps



Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand

PostPosted: Fri Jul 15, 2016 4:46 am    Post subject: Reply with quote

ZDDP has been progressively reduced virtually to nothing in oils intended for modern engines because it depletes the platinum in catalytic converters.
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jp928



Joined: 07 Jun 2016
Posts: 247
Location: Australia

PostPosted: Fri Jul 15, 2016 5:42 am    Post subject: Reply with quote

Yes, but it IS around. Mobil do a line intended for Diesels with ~1200ppm, but its detergent is probably too high for older cars. Jag engines need it badly after overhaul, so find out what they use. Penrite here in Oz do a good line in high ZDDP, so there will be a source in UK - Castrol claim their Classic line is appropriate, also without high detergent levels.

jp
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goneps



Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand

PostPosted: Fri Jul 15, 2016 6:16 am    Post subject: Reply with quote

Agreed, JP—the only way to be sure is to get the information directly from the manufacturer. Penrite, for instance, have technical data sheets on their web site, and an excellent toll-free advisory service for Australia and NZ. Better safe than sorry...

Richard
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trampintransit



Joined: 09 Aug 2010
Posts: 166
Location: Edinburgh

PostPosted: Tue Aug 23, 2016 9:27 pm    Post subject: Reply with quote

I understand that non-zinc oils are a bad idea in high shear, older motors, but surely not for 15mins just to flush it out.
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goneps



Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand

PostPosted: Tue Aug 23, 2016 11:40 pm    Post subject: Reply with quote

It's your engine, of course, so entirely up to you, but personally I wouldn't chance it. Once you've gone through the microscopic case hardened layer on cams and tappets you're on the road to rapid wear regardless of what oil you use.

Which makes more sense—a few quid wasted on the right oil, or a few thousand and all the attendant grief for an overhaul?

Richard
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emmerson



Joined: 30 Sep 2008
Posts: 1257
Location: South East Wales

PostPosted: Sat Sep 17, 2016 9:19 pm    Post subject: Reply with quote

For what it's worth, when I had the V8 rebuilt in my Range Rover the builder put in fully sinthetic oil, which I was not too happy about.A few hundred miles later the oil light started to flicker on very low tickover, say when drive was engaged, but held on the brakes. Everything checked out OK, but it still bothered me, so against the engine man's better judgement, I changed over to pure mineral oil of the same grade. (5/50) The light has never showed since.
I'm a bit of a Luddite I'm afraid, and like things natural where possible, so my oil has to come out of the ground, not out of a factory!
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colwyn500



Joined: 21 Oct 2012
Posts: 1741
Location: Nairn, Scotland

PostPosted: Sat Sep 17, 2016 11:14 pm    Post subject: Reply with quote

emmerson wrote:
.
I'm a bit of a Luddite I'm afraid, and like things natural where possible, so my oil has to come out of the ground, not out of a factory!

The base for both conventional and for synthetic oils comes out of the ground. Very Happy and all oils will have been through an "engineering" process.
As far as I know, the "synthetic" crudely (no pun intended) refers to the fact that all of the molecules of lubricant have been synthesised to be identical. In simple terms, imagine trying to surf on a board over a surface covered in lots of different sized ball-bearings and then doing the same thing over identically sized bearings. The identical ones are the synthetic and in addition to giving better lubrication and heat-transfer,they also have a hugely increased resistance to breakdown of multigrade action and are more impervious to being damaged at high temperatures.
I have those misgivings about the lack of anti-shear additives especially since I do relatively big mileages in my little Fiat. But I'm gambling like I have had to with using unleaded petrol, that on balance, the greater sophistication of the modern oil formulae will give longer life to the engine.
12,000 miles and counting.......
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