Oil - which?

[metric_thumbs]

I bet this has been done to death before, but here goes:
What oil (in the sump) for my 924 CGT?

Do you guys worry about oils with high scuff additives - ie the stuff you do not find in modern oils?
Special turbo oils?

 

[924nutter]

The 924 cgt is blessed with a different material for the cam followers or tappets, presumably to be compatible with the material used in the clear-chill casting for the camshaft, who's valve-timing, alas, remains unaltered from the normally asiprated engine. A direct quote from the original orange service spec booklet (well I would have one wouldn't I?) says only this about oil. "HD oil for internal combustion engines, conforming with API classification SE or SF. For all year operation, (oil change every 10,000 km) (sic) MULTIGRADE OIL of viscosity SAE 15W-40 (after approval) or in summer SAE 30, in winter SAE 20, for constant temp.
-15 deg C to 0 deg C. SAE 20W 20
SAE 10w for temp. below -15 deg C

 

[metric_thumbs]

Thanks for that - mmmm - chill cast surface - you are exactly in the area I was thinking of myself.
In the 80s oil had lots of additives (zinc and phosphorous comes to mind) which helped with the high pressures seen when a cam pushes on a flat tappet. As modern (mostly American) regs require that manufacturers remove these noxious substances the shear resistance is much lower. As most modern engines have differently profiles tappets, or hydraulic tappets or rollers this lack goes un-noticed. But in my old engine I wonder if I need some oil with these additives in it.

Anybody seen or heard of tapet wear at relatively low mileages "" ie 30,000?

 

[geoff Ives]

Let's keep this simple.
Your car is a turbo. 924 Turbo's (including CGT) are fragile especiall where oil is concerned.

Use a synthetic oil and change it reasonably frequently or use a GOOD semi synthetic and change it VERY frequently.
I do the latter.

 

[924nutter]

Not me. When my belt went I only replaced three followers that had been dented by the stationary cam as the piston struck the valves and pushed the followers on to the lobes. The rest were in good original condition with no pitting or for that matter no weraring through the hardened surface of the camshaft. The engine had at that time done 64,000 The article for that has been in Porsche Post. The technical specs came from the service manual update from 1981.

 

[metric_thumbs]

Me thickie - now lost
AFAIK - modern synthetics do not have all the old additives which keep the shear resistance of the oil high. And high shear resistance is good when you have flat tappets and a normal profile peak on the cam.
924nutter - pointed out that the turbo engines have a standard cam (I guess it has a low overlap and so OK with a forced induction) so the cam will not have high acceleration on the opening ramp and so the shear on the oil is moderate.

Do modern oils suffice because the turbo engines do not shear the oil above their working limit?

Or - is 924nutter saying no to that?? And saying that normal non-synthetic oil is fine, and the high shear given by the older additives is not needed.

If the standard tappets are well chill cast, I would accept their wear characteristics are acceptable even on those moments after start up.


In the Beetle world, on powerful engines with knobbly cams and double springs and ratio rockers we have to go to tool steel cam followers to guarantee that there is no wear. Get the combination wrong and followers can wear out disastrously in 3000 miles - and that is not a one off

 

[geoff Ives]

You problems are not the tappets. The problem with the 924 Turbo is the destruction of the oil seals in the turbocharger due to heat AFTER the engine is shut off. This is a well known problem and was only sorted on the 944 turbo that continued to circulate oil after shutdown.

Advice given is to let engine run for a minute before switching engine off and to use high quality oils ( preferablely synthetic) and change it frequently.

I use 70% full synthetic and 30% semi synthetic the reason for this is that my car leaks full synthetics and likes a spot of semi. I also change oil at 4,000 miles and oil filter at 8,000 mile. If I did track days I would use semi and change it every track day.

On our cars heat is the problem.

 

[Tam Lin]

ORIGINAL: metric_thumbs

Me thickie - now lost
AFAIK - modern synthetics do not have all the old additives which keep the shear resistance of the oil high.

Not sure about the shear resistance, but I thought the main reason to avoid latest spec API SM synthetics is that in an effort to be catalyst friendly, they have cut down the percentage of ZDDP, which is a no-no for (our) old engines. For suppliers, try http://www.opieoils.co.uk/, they seem to offer sensible advice, and deliver quickly.