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greg124Posted - 13 Feb 2018 : 21:15:14
The Saab handbook which came with my car states that the engine oil should be 10W30 or 10W40 to API SD.
I currently have in stock 5 litres of 20W50 mineral oil (the green stuff like old Duckhams) to API SE, which I use in the Alvis.
There is also 1.5 litres of 10W40 Semi-synthetic to API SN left over from servicing the 900. If I buy another 5 litres of this, there will be just about enough to change both the 96 and the 900 (which is due soon) - However, is the modern additive package going to wreck anything in a V4 engine?
Would I better going for the closer additive package even though the oil is a heavier weight?
I'm not concerned about mineral vs semi-synth as the oil will be changed every year at about 3k miles or less
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pchristyPosted - 21 Feb 2018 : 09:54:03
I can't comment on zinc, other than to restate that my current engine has done around 50,000 miles on "modern" semi-synth oil + molyslip without ill effects. Molyslip has a plating action, depositing itself on areas of high load and forming a protective layer. It certainly seems to work on bearing surfaces well enough, and the tappets have never needed more than a minor tweak at 6,000 service intervals.

And whilst I would agree that modern metallurgy - not to mention manufacturing processes - have come a long way since our engines were designed, an awful lot of "old" engines continued in production well past their sell-by date! (BMC "A" series?).

I wouldn't worry too much. These motors are as tough as old boots - except possibly for the balance shaft bearings! Just chuck in a decent 10W-40 semi-synth and add a dash of molyslip and you'll be fine.

"Duct tape is like the Force: It has a light side and a dark side, and it binds the Universe together!"
greg124Posted - 20 Feb 2018 : 20:41:47
Thanks Rhys
I've been doing a bit of research and it's Zinc Dialkyldithialphosphate. Don't chemists just love long words. ZDDP will suffice for us.
In the good old days before catalytic converters oil companies put about 15ppm of the stuff in engine oil (retrospectively referred to as Full Zinc), and it was jolly good at reducing wear in areas such as the valve train. However it 'pollutes' cats, and by API SL it had been reduced to 8ppm. With modern metallurgy this is probably fine, but what effect does it have on the wear rate of our old engines which were presumably designed to run at 15ppm? Is it desirable to achieve 'Full Zinc', if so which is the best way, or is something like Molyslip a safe alternative?
RhysNPosted - 16 Feb 2018 : 16:14:57
The additive, or content you are looking for is ZDP.
greg124Posted - 15 Feb 2018 : 12:50:25
Thanks Andy. An electric fan is part of the long term plan.

I have found another oil of the specified weight which is described as being for muscle cars ie. American V8s of the same era, which should therefore have a suitable additive package. Emphasis on 'should' as I have so far been unable to download a data sheet
andydeans3Posted - 14 Feb 2018 : 18:45:26
Another tip, with regards the balance shaft bearing. Fit an electric fan, this allows you to fit a shorter fan belt, which I think places less side load on the balance shaft, and so, hopefully, less wear on the balance shaft bearings.
For oil, I've almost always used Castrol GTX. Semi Synthetic. I am currently trying Millers Classic Piston Eeze. This on a recommendation from Steve Broadhead at Malbrad.
As Peter has already said. Use Molyslip as well.
My oil pressure runs at 52 psi hot, cruising, 20 to 25 psi tick over.


1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro
greg124Posted - 14 Feb 2018 : 16:18:44
Thanks Pete.
I suspect the reduced amount of zinc (can't remember the exact compound) added to modern oils won't help balance shaft bearings, and the engine has done 118k miles with no evidence of a rebuild, so on balance think I'll try the 20W50 which is described as suitable for classic cars from the 60's to 80's.
I've got an oil pressure gauge ready to fit.

Good tip about the fan belt. I do that on all my cars to protect the alternator/dynamo bearings
pchristyPosted - 14 Feb 2018 : 14:43:42
When I had my original V4 back in 1969, I always ran it on 20W-50. I don't recall ever seeing 10W-40 back then! That was one of the "blue" engines, which ran at fairly low oil pressure. The engine had nearly 100,000 miles on the clock when I sold it, and was still running like new, though it did have the balance shaft bearings done at around 50,000.

My current car, with a Vege rebuild engine runs on 10W-40 semi-synthetic, and has done around 50,000 miles on that now, around 35,000 of them in my ownership. This engine runs at a much higher oil pressure than the old "blue" engine, so is more suitable for thinner oil.

One proviso: Following the balance shaft bearing failure on my original car, I've always added Molyslip to the engine oil. The balance shaft bearings are not very well lubricated and the molyslip helps protect against this. Also run the fan-belt as slack as you can get away with (the pulley is on the balance shaft, not the crankshaft!).

As a guide, the "blue" engine only ever showed more than 40psi oil pressure when stone cold in the middle of winter! Most of the time it hovered around 38psi on the motorway. My current engine normally shows 60 psi on the motorway, and on a cold winter's morning will go over 90 when just started! If you have an oil pressure gauge fitted, these should give you an indication of which oil is best, but if the book says 10W-40 for yours, that is what I would use. Don't worry about it being semi-synth. I do recommend molyslip, whatever else you put in it!

"Duct tape is like the Force: It has a light side and a dark side, and it binds the Universe together!"

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