Synthetic 5W-40 safe for summer use?

[Warren96]

My owners manual says to use 15-40 in the winter, and 30 weight in the summer. Both Mobile 1 and Rottela T make a synthetic oil for summer use, and are labled 5W-40. Since even 15W-40 has a noticeable drop in oil pressure in the summer heat, how can 5W-40 be safe for it?

[ZZ]

I have ran Shell Rotella Synthetic for almost 3 years and including the past two summers in my '90 6.2L

The engine seems to be fine with it. I took a 600+ mile round trip last August in 90 to 100 degree weather.

I was nervous when I first changed it over. I heard stories of it causing leaks in some older engines, but mine didn't.

I'm very pleased it. I go 4,500 to 5,000 miles on oil changes now. My truck has around 140,500 miles and it'll use between a quart and a quart and a half between changes.

[moondoggie]

Good Day!

I didn't search for it, & it was probably older than what moved over to our new forums, but I asked the good Dr. this question some time ago. Unfortunately I was asking about 5W-30 Amzoil. The good Dr. made it very clear that 5W-30 was probably a bad idea for summer use, especially if pulling - the mfg. wants to see the "40" in the end of the viscosity rating for our trucks. He additionally made it very clear that 5W-40 (Synthetic Rotella, in my case) was A-OK for all year use.

I've been running this oil in everything I own, plus a few others whose oil I change, with no difficulty at all, although I almost never pull. (This includes my wife & kids' gasser cars.) Interestingly, the oil pressure on my pickup seems to have increased slightly, compared to either the 10W-30 or 15W-40 Rotella I previously ran. These gauges are so poor quality that I don't put much stock in this, but it's certainly better than the reverse situation. ;)

Blessings!

[Dr. Lee]

Brian is right, for summer use the last number, in your case the 40, is the one that counts. And in synthetic oils, the 40 is more reliable because of the heat resistance of the synthetic molecules.

Some users get confused because that think that multiviscosity oils, like 5W-40 get thicker as they get hotter to protect the engine. That is not how the oils work.

ALL OILS get thinner as they get hotter. The multi-vis oils just change LESS as the temperature fluctuates. Your 5w-40 oil will be considerably thicker and more viscous at low temperatures than at high temperatures.

So feel confident to use synthetic 5W-40 under all conditions.

As an aside, my 1984 truck came with a visor label telling me to use 30 weight oil. During 22 years of stupendous improvements in lube oil, never once did GM send me a new visor sticker to upgrade their recommendations! Good thing I have myself to ask about such things !!

[CleviteKid]

. . During 22 years of stupendous improvements in lube oil, never once did GM send me a new visor sticker to upgrade their recommendations! Good thing I have myself to ask about such things !!

You could have asked me, Dr. Lee. I have been hanging around Clevite bearings for YEARS, and know a thing or three about how oil treats them. Give some credit where it is due, and stop trying to hog the limelight. :p

[gvig]

Any disclaimers for a high mile engine? The engine was "worked" at 170,000 so my current engine mileage is 273,800 or so. Don't really know what was done. I bought it with 391,323 on the clock and changed main brgs, rod brgs and oil pump. I think I have a later mod block with oilers for the pistons, at least I had that style of pump. Can't tell for sure, can't see the casting numbers when in the chassis. Pressure now is around 20 idling hot, over 40 running in summer heat.

I tried Rotella synthetic 5W-40 some time ago and the useage went up a bit, engine noise was a bit more, and pressure dropped a bit. It worried me so I changed back to Rotella dino.

How much pressure is indicated as necessary (allowing for flaky oem gauges) for these 6.5's and how much useage is acceptable??

Right now useage is variable, I just pulled my 31 foot fifth wheel from California, over Apache pass, back to Oklahoma, used just barely more than one quart. Around town one quart in 2,000 miles or so.

I don't want to hurt it and a little better lube would be OK, if possible.

[moondoggie]

Good Day!

"Brian is right..." Of course I'm right - I got my info from you, or was it your other half? As I said, Roses are red...

Could one of you two maybe delete my duplicate post? I musta took two moron pills that day. :rolleyes:

Blessings!

(signature in previous post)

[LanduytG]

Something people forget is a synthetic pumps easier and at times will run less pressure. That does not mean its not getting the right amount of oil. I a multi grade oil you want ot look at the viscosity index number. The bigger the number the. Also see if viscosity improvers are being used. Their are some oils on the market that that are marketed as and SAE30 weight but also carry the 10W-30 rate because of its viscosity index being high and allowing it to act like a 10W as well. 30 weight in a synthetic will stand up much better than a 30 weight in a mineral oil. So with that said if I were to use a 30 weight it would be a synthetic only product. Also you have to watch what synthetic oil you buy because most are not a true synthetic. Delvac is one that is along with Amsoil. I am sure their are a few others but for the most part the others are group 3 base stocks which are mineral oil. Group 3 is better but still not the quality of a group 4 PAO.

Greg

[Warren96]

Thanks for all of your replies! I must be out of the loop when it comes to oil recomendation updates.I used the rotella synthetic witch sells at a good price around here.After a thousand miles i haven't had to add any to top it off,the oil pressure is a little lower,and you can still see thru it to read the add oil mark on the stick.But that is probably because of the new gear drive advancing the timing, not the synthetic oil.Thanks again!!

[Robyn]

Well just my 2 cents worth
I recently overhauled one of our 6.5's and it had been run with Amzoil 15-40 for 200K plus miles.
The thing was in very good shape as far as crank and block. The crank went back in with just a tanking and a polish. The block got tanked and lightly honed.
The issue I have with these fancy oils is that one cant always get them if need be when traveling the super slab and the cost out on the road can be stagering for a gallon of oil.
I run class 8 trucks for a living and we run Rotella T 15-40 year round.
I use this same oil in all the smaller trucks too as well as the 6.5's in the Suburbans now after the rehaul.
We have millions of trouble free miles on all the big rigs.
I can but a quart, gallon or a bucket of that stuff almost anywhere and the price is as good as it gets. The little rigs get a can of STP with each oil change. Oil pressure on the 6.5's will run 50 running cold to 40 warm and idle at about 20 hot which is right where they should be.
I have never seen any real reason for all the magic numbers with the oils. ie 5-40, 10-30, 20-50 and so on I believe that much of it is marketing and really has no advantage one way or another.
We have an 86 GMC crew cab here at the ranch with a 454 and its never had anything in it other than Delo 400 30weight and the thing has a buttload of miles on it and runs sweet. It runs 60 psi down the road and idles at 40 hot.
Guess its what ever you feel cozy with.

[Dr. Lee]

Brian, I took care of the double posting. The Clevite Kid does NOT have moderator privileges, so don't bother asking him to do ANYTHING.

Robyn, you obviously give your trucks good maintenance, which is the most important thing for durability and longevity.

We did a survey of the members many years ago, and found lots of engines that had gone over 300,000 miles on good diesel mineral oils Rotella-T, Chevron Delo400, Castrol 15W-40, and Mobil Delvac 1300. I have never felt the need to run synthetic engine oil in my truck, because I don't have to ever start it below about 55 F, don't tow anything in FLAT FLORIDA, and there is no steeeeeeeenkin' turbo to coke up with heat soak.

[Robyn]

Dr Lee
I was taught from an early age about letting the turbo cool for a bit prior to turning the engine off, especially after a long hot run. I still see folks that run their diesel PU, SUV, ect in and shut it down boom and I wonder how this impacts the turbos on these little rigs.
My 94 sub had been on Amzoil since new and I kept it up after I bought it. The turbo had a load of carbon in it too. Was a crazy thing, when I was ready to drop the turbo back on after rebuilding the engine it had sit wrapped up on a shelf for almost 2 months and it felt sweet when I took it off. I could not turn the bloody thing and had to soak the thing in Skunk piss to get it loose. I took it all apart and cleaned it well and but it back together and it works fine.
There was absolutely nothing wrong other than a wad of carbon on the hot side. I am thinking that the long sit allowed the carbon to draw moisture maybe and swell some biding the wheel.
The bearing was fine and the shaft was smooth as a babies butt. All the seal rings were good to go. I had never seen one do that before.
The only real thing I am not happy with about the synth oils is the cost and availability on the road. one does not dare mix that stuff indescriminately with regular oils. Sort of like mixing ELC coolant with regular Glycol. OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOH that makes a mess.
RC

[dieselrealtor]

I switched to the Rotella 5-40 synthetic about 1.5 year ago. If memory serves me correctly I noticed an easier start in the winter, it burns less oil now (1 qt max 3000-4000 miles) even when towing.

I didn't develop any leaks, which I was concerned about.

It seems that my mileage might have picked up a smigen, when I went full synthetic in the tranny, transfer & diffs, but it has been a while & I have a hard time remembering last month.

My pressure hot is around 40 down the road, around 20 idling.

One thing that I did experience with synthetic from years ago (Mitsubishi, turbos & twin turbos), when we went into the engine on one that had been running synthetic, there was virtually NO sludge, varnish or other build up in the engine, it looked new while on the other hand, engines running conventional oils allmost ALLWAYS had some sort of varnish, buildup or in high heat conditions some sludge.

These were apples to apples on change intervals & maintenance. I am no scientist & I don't have the knowledge & understanding of how the chemical composition is different, but I was sold on the results.

[Robyn]

The lack of sludge and clean is what I found with the Amzoil.
Wear was negligable too.
I wont knock any of the synth oils as they do what they say they do.
I guess I am just old school and dont like to have the need to carry oil with me on the road.
I use pacific pride when I travel and I can always get a gallon of oil from a vending machine at the pump island there. With Petroleum I dont worry about brand too much if its diesel rated in it goes.
I always use Rotella T 15-40 in the big rig and when out and about some places have Union 76 brand and some have Delo and I have mixed the three now in my Cat for 11 years and 520K miles and it still purrs nice.

[CleviteKid]

D
My 94 sub had been on Amzoil since new and I kept it up after I bought it. The turbo had a load of carbon in it too.


All that carbon just MIGHT have been soot from an aggressive pump setting, and some spirited driving, and not necessarily from decomposed oil ! ! ! Whatdaya think, Robyn ? ? ?