Hi all,
 
recently bought new oil for my MK1 Escort Van with a 1300 Crossflow and was suggested by the person serving me that synthetic oils are not recommended for older engines. I ended up just buying the Mineral oils but was just wondering if anyone could shine some light on weather synthetic oils are ok or not, including both the gearbox and diff as well.

Thanks

I've been told the same thing and only use mineral oil in my Mk2 RS. Not entirely sure of the reason either.

Doing some reading on the net and a common reason people believe its not recommended is because it eats away at seals. Apparently modern engines are able to have synthetic oils due to the seals being re designed in a way that allow them not to be worn away from the oils.

How true is this thought because I would like to use synthetic if I'm able to without damaging anything.

Most of the issue will be the grade of the oil.  Synthetics are typically thinner for modern engines with smaller oil passages.  I am not aware of a 20W50 in a full synthetic for example.  Its the last number in the grade that is the most important.  I use Castrol Edge full synthetic in my Pinto track engine in 10W60.  If you used say a 10W30 it would rattle its brains out.
I knew a guy once that put 5W30 in a red motor VB commodore.  You could hear the rattles from across the street.  There wasnt anything wrong with the engine, just being an oler engine they dont have as tight tolerances so thicker oil is required.

I just got a 3J LSD and they recommended using fully synthetic 75W 140 grade diff oil.
 
Matt

What about the HPR 15 by Penrite? Fully Synthetic with a viscosity of 15W60. There shouldn't be any problem with running that oil in my Escort? 

Is it also true that over the many years a engine like mine has been using mineral oils it should have a thorough flush out of the oil due to there being a build up of grime inside the engine and if not done prior to changing to synthetic oils this grime will become dislodged by the  synthetic oils and can potentially block your engine up? 

Full synthetic is fine for g/box & diff, but debatable for engine.
I was told by a Castrol tech that full synth is not recommended for older valve trains, especially if high spring pressures. So, just in case that's correct, I use mineral (Penrite HPR30 20W/60) in my club competition pinto.
 
Cheers

What's so bad about older valve trains that makes full synth no good? 

Its not the oils base that is the issue, the problem is that most modern oils carry specific certification, to gain these certifications oils must comply with numerous things. One of these things is the zinc (and other)anti wear additive content within the oil, zinc has been targeted as a 'bad' pollutant and has hence been reduced in oils as anti pollution measure with every new certification. The engines mostly affected are those with flat tappet/lifter arrangements(anything non roller), pinto and xflow included.
I have personally used penrite in all my engines for a long time now of which all have a decent zinc content, with excellent results. So for any old school engine Penrite hpr30 is highly recommended as it has a very high zinc content as well as correct viscosity, and not a bad price either.
 
So its not really mineral vs synthetic but rather what is actually in the oil.