Can you determine oil grade using oil pressure?

[kilou]

Hi all,

I did get several suggestions of oil grades for my old Volvo engine (atmo) with over 200K: 0W40, 5W40 or 10W40. I do understand the differences between these grades and the fact 0W and 5W appear "better" for cold starts and winter. However although all these oils are SAE40 when hot, they have different viscosities when cold with a 10W being thicker than a 5W and so on. Now Volvo recommends a 5W40 for that engine but that is for a NEW engine and certainly not for a 200K miles one. To my understanding it may be perhaps better to run a 10W40 (even in freezing cold Switzerland winters) rather than a 5W40 in that old engine. The main point is that I can get a high mileage oil (Valvoline Maxlife) only in 10W40 here, not 5w40.

Therefore would it be possible to figure out if a 10W40 is fine even in winter by using an oil pressure gauge??? I mean if I get a proper oil pressure on cold start, it should mean the oil grade is OK with 10W. A 5W may produce a low oil pressure when cold (not to the extent of lighting the oil light in the dashboard though...) and that would mean the oil is too thin when cold for my "worn" engine. Does this make sense?? I would move to a 5w40 grade only if it is really better but I do believe a 10W40 high mileage oil with seal conditioners may be much more beneficial to even a full synthetic 5w40. Afterall the 5w40 grade is good for new engine and perhaps no more for a 200K miles one....

Glad to get your opinion on that.

 

[Gary Allan]

Your oil pressure will be too high (if one were to use that as an indicator of suitability) with 0w-10 @ 100F ambient. Every oil is too thick at start up.

 

[Captain_Klink]

your Volvo is not "old", it's still a baby. my mitsubishi has 275k, 1995 model, and i feed it a steady diet of 5w30 semisynthetic.
your engine is not "worn", it's barely even broken in, you're worrying too much. 200k for a volvo is nothing. and 5w40 is always better than 10w40, no matter what the age of the engine: the problem with oil at startup is that it is too thick.

"high mileage" oil is mainly a marketing ploy to extract more profits and lighten your wallet - basically what they do is they increase the viscosity, so if your rings are worn then less will get by the rings, and you think you have done something, when you really have done nothing.

 

[bepperb]

How cold does it get where you live, in winter?

Gary is right, any oil will have very high pressures when not at operating temp, you won't be able to get any useful info from a pressure gauge, since the pressure correlates with the temp of the oil and you have no accurate way to measure that.

I'd be a little leary of a 10-40 in winter here, it gets down to about -30 celcius when I'm up north in the winter time. But a HM could have advantages for you, and if you're ok with the cold (or it doesn't get that cold where you are) I wouldn't hesitate to give it a try.

 

[ARCOgraphite]

If I lived in Switzerland I dont think I'd be choosing Valvoline Maxlife.

 

[mechtech2]

kilou - If you are going to use an 'X'-40, use a 0-40 or 5-40.

 

[demarpaint]

As others stated oil pressure will be very high with cold oil, and you need all the help you can get when temps dip very low. Like mechtech2 said use either a 0W40 or a 5w40. I would use the 0W40, opinions vary.

 

[kilou]

Volvo originally recommended 15w40 or 10w40 for that engine. Haynes manual recommends 10w30, 10w40 or 15w40.....seems weird why they don't mention 5w40. The engine is from 1997, maybe that was an "old" design with large tolerances no?

 

[CATERHAM]

Yes you can use your oil pressure gauge as a guide in oil selection.
First you need to know the minimum safe oil pressure at maximum rev's. A good guide is 10 psi per 1000 rpm. 6500 rpm therefore would translate into 65 psi or 4.5 bar.
From the sound of things you are running a 40 wt oil now so you can see where you're at presently. I suspect you've got more than adequate oil pressure. In the winter oil temps tend to run lower which means even higher oil pressure so you can comfortably run a lighter oil while maintaining plenty of oil pressure.
I think you should be able to run a high VI 0w30 or 5w30 with no problem.