I know this is a third topic on essentially the same subject but I find that once the initial question is answered in one thread folks often tend to ignore additional questions in the thread.

I am using 10w40 in an old somewhat tired slant six (no telling how many miles are on it). The oil pressere at hot idle is somewhere between 5-10 PSI, and at highway speed I get a good 35-40 PSI so the pump is functioning. This would all be fine according to the 10 psi for every 1000RPM. My question is, is more oil pressure better? The guy at the auto parts store said that I should switch to SAE30, and that my pressure will come up a lot. I live in the PNW where average temperature arnges between about 20F for extreme low and 90f for extremem high. Is this SAE30 good for such a climate?

Mark, the more pressure is good for lots of oil to the bearings, but the tradeoff is the pressure strains the seals and gaskets. When they get age, it will make them prone to leakage. I think your numbers are fine.

When I get my 71 Dart back on the road, I am going to use the 20w-40 Rotella thats designed for diesel applications. It has an excellent additive package and these older motors seems to like it a lot.

I've always felt oil pressure is a bit oversold. As long as you have good oil flow goin through the surfaces, you will be fine

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KenG

I don't think I would put SAE30 oil in my slant but if your having issues with pressure you might condiser something like 20w-50. Before I rebuilt my slant I had the same problems you are having and that's what I did.

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73' Duster 225
<img src="http://longrod.moparpages.com/enginedone.JPG" width=200>

So SAE30 will bring the pressure up you say? I never noticed it before because I dismissed the non multi-grade oild weightsd but it looks that SAE30 is ideal for my climate....? I am confident the gaskets can hold.

No, he said 20W-50 will raise the pressure some. It also puts a strain on the oil pump.

multigrade oil is oversold. keep in mind that when slants where designed there was no thing such as multigrade oil with all those additives. sae 30 to sae 40 (depending on the climate and other factors) where the factory's recommendation. (Sae 30 was recomm, sae 40 if you had a tired motor) If you do lots of city driving use a 20w50 oil since it has detergents that would prevent your engine to build up gunk and residues, if you use at least a 30% highway 70% in town mixed driving you can seriously consider sae 30.

my 2 cents.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Not true!

My '62 Lancer's instruction manual mentions 10W30, 20W40 and 20W20 oils, as well as SAE30. And my July 1964 Chrysler Canada Industrial Slant-6 Parts and Service manual recommends 20W40, 10W30, 10W20, and 5W20 in addition to SAE30, SAE20W, SAE10W and SAE5W, depending on ambient temperatures.
It's entirely possible that multigrade oils didn't appear in constantly-warm climates like yours for many years after they appeared up here, because...well, when the weather only varies from 20°C to 40°C, there's really no need! Up here we have ranges from -30°C to 40°C, so it's natural that multigrade oils would appear in this market first.
All mass-market engine oil, regardless of viscosity grade, contains detergents. Nondetergent engine oil can still be found if you look hard -- it's good for lubricating chainsaw chains, but that's about it. The viscosity grade should be chosen according to the ambient temperatures and the condition of the engine. 20W50 is overly thick for an engine in good condition in most any commonly-encountered temperature range. It is a mistaken notion that heavier oil offers more or better protection to an engine in good condition than lighter oil. All heavier oil does is take longer to get to lubrication-critical parts on cold start, and sap more engine power due to greater pumping losses. On a worn engine with loose clearances, of course, heavier oil can help maintain acceptable oil pressure.

Pretty much everyone reading this who has an engine in good condition should be running 10W30.

An excellent oil info site: http://www.bobistheoilguy.com .

Didn't know that american mopars as early as 62 used multigrade oil. Didn't know either that multigrade oils appeared in the market back in the 60's. We got that in late 70's. In fact, our mopars recommended oil was sae 30. They didn't mention multigrades at all or anything below sae 30.
On the other hand, I told him to use 20W50 since he said that his slant is tired and has countless miles on it. I use 20W50 for lubricating my door hinges. and that's true, all modern oils has detergent. Must have been a brain fart I'm running synt 5W40 on my fresh 10k miles slant, works great, better than the 15W40 I was using. How many miles should I use this synt oil?

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

I don't think I'd run 30w either. The main difference in oils has been elimination of the zinc (and other metals) however I believe bearing materials have been updated to offset this. Aren't silicone derivatives now present in a lot of todays engine bearings and pistons?

At any rate, use a good filter (no Fram!) and religously change the oil, and you should be fine

-Ken

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KenG

I run 10W-40 Quaker state in everything that I have. By the way, do these "high mileage" oils really make any difference or did they just change the name and the bottle and up the price?

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

I run 10w40 in nothing. Too much VI modifier chemistry; too much tendency to sludge.

"High miles" oils contain compounds to swell-up seals. This can reduce leaks in the short term, but the swollen seals wear even faster, accelerating the leak in the long run.

I think Castrol also tends to sludge worse than other brands.

Anybody out there running Havoline?

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

I use pennzoil only because that's what jiffy lube puts in. I don't really have the facilities to change my own oil. I am certain to use pennzil whenever I add oil between changes as I know different oils have different additives. I don't know how different, but I'm being cautious.

Avoid synthetic on older seals. I learned that the hard way.

Synthetic oils leak because the molecules are all equal size. They work great with fresh seals and gaskets. In fact syn is so good that breaking in a new engine requires dino oil to get the rings to seat properly.

Dlantsix Dan
Do the syn's have "seal sweller" additives???

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KenG

Synt oil containing seal sweller additives? so, If I buy for a moment that crap, should I assume that regular oil doesn't swell seals? c'mon, dan, why don't you try the old "I don't like it" instead of that? cardboard or asbestos or cork seal swells in contact with any oil, till one day stops swelling and it looses plasticity and starts to leak cuz it's old 'nuff to leak.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.