Oil pressure opinion

[lombardi]

Just did oil service in my 2ltr spider, noticed the oil pressure has gone up slightly, probably stating the obvious,the reason for this is that prior to change the engine had 10-40 grade oil, in the change i used 15-50, what is better as far as pressure, better to have lower or higher, must state the difference is not much but noticeable, needle has gone from just short of half way to just over half way, am not worried about it, just curious what is better for the engine and mechanicals. regards

[Beatle]

It's obviously good to have oil pressure, but too much can be a problem as well.  Yours sounds perfectly OK. 

Oil pressure per-se is not a definitive guide to lubricity though.  A modern fully synthetic oil may show lower oil pressure, but that oil should provide better lubrication.

Another thing to watch is how the oil pressure is maintained as the temp rises, at higher RPM and at idle. 

Lastly, the guages can read differently between cars with identical true oil pressure.  So don't take too much notice of where the needle sits on your mates car compared to yours.

[lombardi]

Thanks Paul, the original oil was a semi synthetic, whereas the new oil is a mineral based castrol 15-50 gtx for older engines, obviously the engine has done more than 100k re its age thus my choice,engine runs beautifully and idles perfectly, maybe next change might switch back to a semi synth at 10-40, just noticed this 10-40 grading ,there was a sligtht oil usage burn, can confirm there are no leaks as inspected underbody and all good.regards

[Beatle]

Ha ha, no oil leaks.... Now I know your pulling my leg....or there is no oil left in the sump   

Don't fret about a little oil usage.  With modern machinery we've forgotten that engines used to use oil (unless you own a Commodore or Landcruiser of a certain vintage which still do use oil...) and maintenance such as de-coking was commonplace.

Unless you are driving in the snow I'd happily use a 15W-50, particularly if synthetic.

I put 180,000kms on my first Alfa before I stripped the engine down at 230,000 and had used cheap Mobil Super-Drop for all but the first 50,000kms (previous owner).  I think more leaked out of it than it burned, but on strip down there was no untoward wear in cams, top or bottom end.  The little Italian guy who did the work reckoned the secret was to treat them like taxis, max RPM everywhere.  Revs up means oil pressure up....   Not convinced that's a good explanation though.

After it was rebuilt I swapped over to BP Corse+, but only because I'd moved to the NT.  Hot conditions with long runs in the upper rev range (no speed limits).

I have to admit though, I think people get a bit too concerned about oils and as long as you use a decent brand in a similar range to the factory recommendations, you won't go wrong in a road car.   The best oil in the world won't be of any use if it's fouled with soot, fuel and moisture, so if you don't use the car often, it might be better to use a cheaper oil and change it more often than to let expensive oil languish in the sump.   A lot of stuff ends up in oils that isn't filtered out, so the only way to purge it is to change the oil.

[Steve S]

Yep, it all sounds normal. If you use a thicker oil you will have higher oil pressure. Technically your oil pressure, for the same oil temperature and rpm, is proportional to the dynamic viscosity of the oil in the bearings as the bearings are the "restriction" to oil flow causing the pressure. Higher oil pressure does not provide better lubrication or a thicker oil film though.

Edit: I shouldn't post before reading.  15w50 is probably a good viscosity choice.

[lombardi]

Thanks Paul and Steve, Questions about oil in this forum always gets the emotions running, i guess its because whe love our babys and want them to last and chosing the right oils is a cheap decision and easy one if done right.regards

[Beatle]

Some swear by diesel oils for older Alfa engines.  Increased zinc to match the levels current when the engines were sold new.

[lombardi]

Paul , very good point about the diesel oil for older alfa engines, have seen this discussed elsewhere, think on some other forum, do you know of anyone with experience in using the oils and what particular type, think if i remember the shell rimula is popular, please correct me if i am way off the mark as this info is third hand and my memory is not to good nowadays, think its called old age. regards angelo 

[Steve S]

I think Rimula is only diesel rated. Caltex Delo 400 and Mobil Delvac are 2 I know that are dual petrol and diesel rated and are very well respected. Most Penrite diesel oil and also the Repco diesel oil are also dual rated.

Mobil Delvac 1 is a full synth sold here, that would be among the best and expensive. Off ebay you can buy USA imported Shell Rotella T6 and Mobil 1 turbo diesel truck. These are both very suitable for petrol engines too.

Penrite make some very robust petrol oils with potent additive packages. These would be easily as good IMO
Amsoil AMO and ARO series would also perform similar but are very expensive.

[lombardi]

For curiosity sake i emailed Castrol about the zinc content in 15-50 gtx older engine oil, replied that it did have a high zinc content, which i guess comfirms its protection qualities. regards