10w-30 vs 10w-40

Messages
69
Location
collierville, TN
thinking the 40 would be thicker and yield slighly higher oil pressure- correct? also would it be too thick for the cold starts? Ill be replacing the sender but it appears that full hot idle is about 15 and id like a lil higher idle..
 

higney85

Thread starter
Messages
69
Location
collierville, TN
o ok- sorry im a newbie when it comes to oil specs.. My main problem is the pressure after its been warm for a while.. so the 40w should bump up that pressure- correct?
 
Messages
4,478
Location
Southern California
quote:
Originally posted by higney85: o ok- sorry im a newbie when it comes to oil specs.. My main problem is the pressure after its been warm for a while.. so the 40w should bump up that pressure- correct?
It might be informative to know WHY you'd wish to bump up the pressure with 10W-40. Racing? Towing? High mileage engine? Hot, arrid region? Just 'cause grampa and dad used it? Don't get me wrong - you probably have a valid reason, but, I also subscribe to the notion that the engineers who designed and nursed your engine through its development aren't idiots, either. (Unsure about the various car makers' marketing departments, though...) Also keep in mind that higher viscosity translates to greater pumping losses through the passages, bearings, and filter. Theoretically, at least, that results in less power and lower fuel efficiency. A healthy engine still within tolerance can maintain sufficient oil film strength even with lower viscosity fluids to "float" heavy bearing loads successfully. Ever skip stones off water? Finally keep in mind that 10W-40 has a higher "elastomeric" content than, say, 10W-30 oil. That means more viscosity index improver content in a quart (or, by extension less actual o-i-l). VIs do NOT lubricate - they only retard thinning from heat. The 10W-40 stuff HAS to have enough VI to cover a 30 point weight spread; the 10W-30, a more manageable 20 points. Since the VIs can be among the first components to oxidize off in hot (REALLY hot) operation, theoretically you could lose both volume and viscosity with the greater spread 10W-40 fluid. (The more VI you lose in 10W-40, the faster you get back to the original 10 weight base stock.) By the way, I'm NOT a mechanic or a lubrication engineer. This is all from "book learnin'" reading, not personal experience. Just a few points to ponder. -Ray Haeffele [ January 19, 2003, 10:34 PM: Message edited by: Ray H ]
 

higney85

Thread starter
Messages
69
Location
collierville, TN
ok well Ray you totally lost me after the first couple sentences [I dont know] (im trying to learn) but ill give my reply to the best of my comprehension.. The *want* for a thicker oil stems from a lower idle pressure and a thought of possibly having a slighly thicker oil may not leak as the 10w-30 is doing ever so slighlty out of what i think is my rear main. I am the type of person who looks at guages alot (its a flying thing i guess) When i see things even slighly off i begin to ask questions. I know the stock guages are inacurate but its better then nothing i guess. Ive spoken with the engine builder and they said a minimum of 6psi is needed for the 4.0L b/c its an inline 6 and is set up to not need high oil pressure... In other words 6psi or greater.. I did some research at the shop that installed the engine and on there books the minimum should be about 13psi and warm idle. I asked about oil weights and i was told the recomended was 10w-30 (duh) but if pressure was low a thicker oil may be beneficial. I will still be swapping out the sensor but would like some added idle pressure once this jeep is up to temp. One thing they did mention was running synthetics in rebuilt 4.0's isnt too smart b/c you will get a lower oil pressure and high probability of leaks (well theres an observation since i ran Mobil 1 for the 500 mile,1500 mile, and first 3K miles before i noticed the leak and lower pressure once the outside temps got hot). I have been running dino oil since then and ran 20w-50 last summer b/c the hotter the temp the lower the idle for me it seems), also the last leak was a gasket leak that i replaced myself. While the pan was off i took a look at all the internals and they appeared clean (including the pickup) and i pulled the center bearing cap and didnt see any wear on it, (reinstalled and put everything back to spec), problems w/ pressure were gone with use of 20w-50 but i heard much more engine noise and swapped back in 10w-30 (once the temps cooled down and the noises went away). As far as the specs of the oil- i asked for an answer and im thankful i got one but its like you answered me really fast in spanish- i get the main points but theres alot in there that flew over my head... sorry for the length [Dual]
 
Messages
43,650
Location
'Stralia
I'm wondering whether we should have "oil flow" guages, rather than oil pressure gauges. If you block all of the galleries, you'll have great pressure, but no flow. Lose clearances, and flow increases at the detriment of pressure. The oil is fed into a (relatively)unloaded area of the bearings, and the pressures from the oil wedge have nothing to do with the oil pressure you have. Provided there's enough oil there. Thicker oil will give you more pressure, by providing more resistance in the ports and galleries. You will probably have a slightly higher film thickness at the bearing.
 
Messages
43,650
Location
'Stralia
Talking flow versus pressure, one very bad bearing could drop the pressure to nothing, and thus take more than it's fair share of the oil, starving the rest. Thick oil shouldn't help you there, either.
 

Patman

Staff member
Messages
21,990
Location
Oakville, Ontario
You should go with a 15w40 over 10w40, as most 10w40s will shear back to a 10w30 pretty quickly anyways, while the 15w40 starts out with a thicker base oil with less VII so it does not shear down as quick. Another consideration is to look at the oil you're using now and see what it's viscosity at 100c is. Most 10w30s tend to sit around 10cst at 100c. If you look at the high mileage 10w30s like GTX HM or Quaker State HM they are closer to the top end of a 30wt, these oils are around 12 to 12.2 cst (12.5 becomes 40wt) These oils are also more shear stable, they don't thin out as easily. Just another thing to consider, you may want to just try Schaeffer Supreme 15w40. This oil has shown excellent results on here. [ January 20, 2003, 05:26 AM: Message edited by: Patman ]
 
Messages
2,480
Higney85, I think your question is valid and we've strayed off a bit. You should be able to safely go to a 10-40 which should be slightly thicker than a 10-30 and will therefore provide the oil pressure increase you're looking for, especially at operating temperature and if there's some previous wear (due to mi. on the engine) and/or oil leakage. As far as the comments re: oil being too thick... Since both oils are a 10 weight, thickness at start-up will be comparable. When hot, the 10-40 will be thicker (which is what you were asking for). As far as the comments above, when an oil is hot, the issues of concern are that it's too THIN, not too thick. This phenomenon is usually a concern at start-up. When the engine and oil are hot, this is when oil pressure drops (as you were witnessing) and thins out in load-bearing areas and extreme heat areas such as pistons, etc. where it BAKES and allows sludge formation and engine detriment. If oil flow was utmost, we'd all be using something as thin as WD-40 with a lot of ZDDP/moly. Flow is slightly slower, but so is the flow OUT of high pressure areas and as Bob previously mentions, it STAYS around when needed to lubricate vs. being squeezed out like water. For the shear comments, the 10-40 should be more robust as it should have more of both VI's and Pour Point depressants which allow it to make the spread, all the while starting with a higher viscosity base oil, thereby not allowing for as much shear-back when used. At least this is my understanding.
 

higney85

Thread starter
Messages
69
Location
collierville, TN
ok so the overall opinion would be that the 10w-40 would be pretty good and possibly a 15w-40? My thoughts would be to use the 15w-40 in the summer and the 10w-40 in the fall/winter (the oil is changed about every 3 months- with the seasons and 3K miles).
 
Messages
8,937
Location
SC
quote:
Originally posted by Dr. T: For the shear comments, the 10-40 should be more robust as it should have more of both VI's and Pour Point depressants which allow it to make the spread, all the while starting with a higher viscosity base oil, thereby not allowing for as much shear-back when used. At least this is my understanding.
I don't think that's the way it works. A pour point depressant isn't going to affect viscosity or VI, it's only going to permit the oil to flow at lower temps. So, a 10w40 probably doesn't use a higher viscosity base fluid. The more standard route was for the 10w30 and 10w40 to use the same base fluid with the 10w40 having more VI improver to cover the spread. However, from what I've been able to read, modern 10w40s don't suffer from this malady as did the 10w40s of old. A higher VI base oil (say a Group II+ rather than a Group II, or Group II with a little bit of Group III) could be used and the amount of VI improver needed may be no more than what was required in the 10w30 using only a Group II base oil.
 
Messages
453
Location
Galveston, TX
Ask yourselves, what do the mechanics put in their personal vehicles? I ask them. It seems that 1/3 use 10W-30. The other 2/3 use 10W-40. Only 1 mechanic I've met had 5W-30 Castrol GTX in his car. But that was in New York City in January 1997. Even he said that he might drop it out at 1,500 or 2,000 miles and replace with fresh GTX 5W-30 because he expected it to shear down and thin out. He said he would change to Castrol GTX 10W-30 when Spring rolled around. South of the Mason-Dixon line, I see most people using 10W-40. I think they are afraid of loss of oil pressure/oil flow in the hot weather. They seem to want a 'beefier' oil. Disclaimer: I do not claim to have polled all car owners in the South. For all I know, some may like to use 0W-20, etc., but I just have not met these guys. :-)
 
Messages
378
Location
West Coast
Highney. The Jeep 4.0 responds well to the 15W-40. I concur with Patman. I have run Delo 15W-40 very successfully in my Jeep. These engines have a lot of piston slap too. The 15W-40 will significantly reduce this.
 

higney85

Thread starter
Messages
69
Location
collierville, TN
well to keep everyone in the loop i ordered a bottle of auto-rx and will be running that for 1000 miles with a motorcraft FL-1a filter and then swapping in 15w-40 oil. Ill also be swapping oil the pressure sender and ill tighten up the oil pan bolts and hopefully the leak will stop. Thanx all
 

higney85

Thread starter
Messages
69
Location
collierville, TN
ooo before i forget.. When i swap filters can i go on and fill it back up to full using the 15w-40 or should i just use the 10w-30? Over this engine's lifetime it has had about 2 bottles of STP oil treatment and 2 bottles of STP stop leak and both did there job but i am wondering if these will all get cleared out. I used about 1/2 bottle of stop leak and oil treatment with an oil change so i didnt use too much i dont think. My oil leak always appears about 1500-2000 miles after the oil change and the leak is just enough to put i drip on the bottom of the bellhousing so its a small leak but id like to make sure everything is clear and the Auto-rx does its job and i can just run a good oil and filter and not haveta deal with it. Also what would be the best oil to run (the 15w-40 variety) thanx
 
Messages
11,006
Location
Canberra ACT Australia
On Saturday I changed from 10W30 w/Auto-Rx to Delvac 1 5W40 with approx 3/4 litre M1 0W40 TS added (leftovers) and reduction in general noise particularly in rocker area is very noticeable. First time I've used a CAFE viscosity oil (was the only straight dino I could find) and it will certainly be my last. Patman even you seem to agree LS1 need high end 30 or maybe 40 for reduced wear? IMO any 30 is not good and even more so if engine has a few miles on it.
 
Messages
22,188
Location
Colorado Springs
So, despite the fact that the majority of manufacterers now call for 5w-30 and 10w-30 weights, you all think that's no good and recomend 40 weight oil? I've always heard from mechanics that 10w-40 is a really bad weight of oil, especially in engines that don't call for it, because it shears back very easily. Most indicated to use 10w-30 for moderately hot weather and 5w-30 for cold weather. One mechanic I know said to change 5w-30 much sooner, say 2,000 miles, as it thins out very easily. He said to still use it though in winter for quicker oil pressure etc. I have no freakin clue now what the best weight is [I dont know] since some of you guys think thicker is better! Ahhhhhhh, what do I use? My 5w-30 penzoil is almost at 3,000 miles, do I go with 10w-30 now, even though it occasionally gets to about 10 degrees F here?
 

Patman

Staff member
Messages
21,990
Location
Oakville, Ontario
quote:
Originally posted by sprintman: On Saturday I changed from 10W30 w/Auto-Rx to Delvac 1 5W40 with approx 3/4 litre M1 0W40 TS added (leftovers) and reduction in general noise particularly in rocker area is very noticeable. First time I've used a CAFE viscosity oil (was the only straight dino I could find) and it will certainly be my last. Patman even you seem to agree LS1 need high end 30 or maybe 40 for reduced wear? IMO any 30 is not good and even more so if engine has a few miles on it.
Yep, I am confident that the LT1 and LS1 would get better wear with a high 30/low 40wt oil. I'm not sure if I'd want a mid 40wt or higher though. But something in the 12-13cst at 100c range. I still don't believe there are too many engines out there which will actually see lower wear numbers with a 50wt oil though. But I will admit there are precious few 20w50 and 15w50 reports on here. I'd love to see someone do a comparison between a 20w50 and a 10w40 in their engine.
 
Messages
378
Location
West Coast
quote:
Originally posted by higney85: ooo before i forget.. When i swap filters can i go on and fill it back up to full using the 15w-40 or should i just use the 10w-30? Over this engine's lifetime it has had about 2 bottles of STP oil treatment and 2 bottles of STP stop leak and both did there job but i am wondering if these will all get cleared out. I used about 1/2 bottle of stop leak and oil treatment with an oil change so i didnt use too much i dont think. My oil leak always appears about 1500-2000 miles after the oil change and the leak is just enough to put i drip on the bottom of the bellhousing so its a small leak but id like to make sure everything is clear and the Auto-rx does its job and i can just run a good oil and filter and not haveta deal with it. Also what would be the best oil to run (the 15w-40 variety) thanx
It shouldn't matter.
 
Top