here ( holland) there is an oil disccussion going on again:
one specialist say .. never put synthetic oil in our old corvettes (C3) just use mineral 15W40 or 20W50  .. but  another one say better to put an synthetic oil in

been doing some reseach on this forum and see lots here use indeed a synthetic oil. 
something what took my attention too was the claim that oilcompanies nowdays  don't use  or atleast use less zinc  in their oils.  and from what i understood  that is not very good for our oldies.
solution is to use oil that is used for diesel engines which contain more zinc??

and further what viscoity to use
now i have shell mineral oil 15W-40 in my vette

the owner manual (1978 c3)  say  for a temp range  0- 100  degrees F  use 10W-30 or 10W-40.
and 5W-30 for temp range of -20  to 60

so to my idea.. 5W-30 synthetic wouldn't be such a good idea .. too thin ???

(i heard from a friend with a 1981 vette his manual mentioned 5W-30 for the range 0-100  ..)

and another further remark i got here.. when i  change my oil  from mineral to synthetic i best use first a half synthetic  oil for some time .

to make it short:

should i go to a synthetic oil  with viscosity  5W-30 , 10W-30 , 10W-40 ?

or should i stick to my  shell mineral oil 15W-40

or get an oil for diesel engines (viscosity?) (synthetic or dino?)

i saw that in usa there is shell rotella for diesel:
Shell ROTELLA® T SAE 15W-40
Rotella® T Synthetic SAE 5W-40
Shell ROTELLA® T Single Grade
Shell ROTELLA® T Synthetic-Blend

should i use  an half synthetic( first time)?

we don't have the rotella here.. but probably something similair

T.I.A. you for any input

art-corvette

I think you should stay with  what is called for in your owners manual for that year. Just my 2 cents..Your seals and engine was built to use what is recommended..

Good to here from our friends in The Neatherlands, I used to be stationed in Vokel Air Base, and lived in Udan.  Most of thoses Iv'e talked to recommend Non-synthetic 10W-30 as a good all weather oil.

that is 10W-30 , 10W-40  ..... but.. the mineral oil i can find here is only 15W40 ... so should i go to a 10W- ..  what might be a synthetic/half synthetic..or  that oil for diesel engine which contain more zinc ?

art-corvette

This is proabably one of the hottest debated issues among mechanics/enthusiast...I use synthetic in everything I have...my diesel, a 77 comp. ski boat, the whole families gas vehicles and my 76 Vette. If your engine is in good shape it will love the synthetic. If your engine is in poor health I would not use synthetic (it will burn more oil and leak worse than it already does).

What ever you do do not mix synthetic with mineral oil.They are basicly two different animals. I would not use synthetic in a high mileage engine because you will be using a lot of it through leakage (it will flow through old seals easily) and buning off through the (worn)rings. At the higher cost of synthetic you might not want that. If your Vette does not leak now you might try synth. It will help you engine with less friction and heat generated.Just watch and for any leaks that may start. Try it you may like it. I use it. I like it.custom762007-05-15 17:26:06

I'm hearing the reduction of Zinc or even the absence of it is really hurting the older engines. It's ok on the newer roller motors, but it's wiping out cams on the older cars.

If you ever desire some of the benefits of synthetic oil without going all the way, read the label, newer formulas are compatible with our usual petroleums. Experts feel it might be a waste to use full synthetics in older motors with lesser tolerances than todays tighter designs. Hence , the recent blends. aceinthehole2007-05-15 20:32:28

[QUOTE=daveb12]I'm hearing the reduction of Zinc or even the absence of it is really hurting the older engines. It's ok on the newer roller motors, but it's wiping out cams on the older cars. [/QUOTE] aceinthehole2007-05-15 20:24:57