Can using thick oil CAUSE oil consumption?

Despite people saying to go thicker to reduce consumption... What I've seen with people running very thick oil (20w50 and thicker) in more modern engines (1995-pres) is they seem to burn oil badly amongst having other internal problems, compared to those running thinner oils (xW20-30/40max) I've seen a comment on here before regarding all cars burning ridiculous amounts of oil in Costa Rica where 20w50 is the thinnest oil readily available to most people apparently. Same goes here I guess where most people do still believe thicker is better, especially after a couple hundred thousand KM! To the point that the local oil companies such as Nulon and Penrite still make 40w70 (!!!) While they both also make 20 weights and Penrite even make a 0W16. Now the people I speak to running the correct grade oils, usually between 5w30 and 15w40 in most local cars with their larger engines (4.0 I6 and 5.0 V8 in the Falcon, 3.8 Buick V6 and 5.7/6.0 LS V8s in Holdens) seem to burn no or at least minimal oil between service intervals, yet the people that run 20w60-40w70 are topping it up with the nightmare inducing viscosities every week, even if they have less mileage on the engine! I have seen an older UOA of an early 90s Falcon with just 30,000km on it's engine when it was near new running 40w70!! The iron number came back at around 480ppm!!! This indicates massive cylinder bore wear. My last UOA on my Falcon running 10w30 for 8,000km returned an iron number of just 4ppm and all other metals were between 0-4, and burns no noticeable amount of oil between OCIs while being driven fairly hard at 250,000km. I know a couple of people with very high mileage Falcons. One of them has a 2002 with a staggering 960,000km on it's original engine with all it's original internals. It has run 10w40 dino since new at 10-15k OCIs. The other I know had 790,000kms last time I knew and that thing has only ever run 10w30. Both engines still run perfect and don't require a top up in between OCIs, despite the notion over here that "oh you have over 150,000km on your car, here have some 20w50" "oh yours has 250,000km, here try this 40w70!" And I believe this ill advice is where excessive oil burners originate! My guess is thinner oil can get past the rings and slightly line the cylinder walls and prevent wear and metal to metal contact, increasing the life of the engine and help retain compression. Thick oil can't get past the rings and lubricate the bores, causing cylinder wear from metal to metal contact. Another confirmation of this is I've seen an engine that used 40w70 being rebuilt after the pistons and cylinders completely scorched from metal to metal contact! I think there is a happy medium but 20-40 weights are good for 99.9% of engines. I had to add 20w50 Maxlife to slow and engine leak about a month or two ago. It made my engine feel smooth but started slowly on colder mornings, sapped power and I lost nearly 100km per tank! I fixed the leak which turned out to be the timing chain tensioner that had unscrewed itself loose a bit so easy fix.. I changed back to 10w30 and it was even smoother still, which confirms to me it was the MoS2 I started adding since the 20w50, and not the oil being thicker that has made my engine feel and rev much smoother! I would like people's opinions and experiences on this smile
 
I do think it has different effects onmodern and classic cars, my Ford Capri now burns much less oil on 20w50 than it did on 10w40 which is fine because both are specced in the owner's manual, but i remember with my old Ford Escort with a a CVH engine , when i put a 15w40 in it when it specced 10w30 or 40, it made it burn a little more oil and i was pretty baffled by that
 
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1,353
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Brittany / Canada
I always thought thicker oil was sometimes counterproductive, one of my car is specced for 10W40 in normal use and 10W60 in harsh conditions, tried some 10W60 and found it elevated the oil/water temps, so get back to 0W40. Consumption is imperceptible (but it only has 148000Km) with 0W40, was also imperceptible with 10W40 or 10W60. I guess it also depends on the reasons the car is consuming oil, worn out rings, faulty pcv system, leaking valve seals, leaks (lol), etc. Maybe also thicker oil makes a thicker oil film on the cylinders, so when it gets scraped by the rings, there's a greater quantity of oil that is scraped and burned, compared to a thinner oil with thinner oil film? At the end it it more a question of careful balance between flow, thickness of oil film, resistance to shearing within the OCI, and margin for potential fuel dilution. It's also more difficult to find good quality heavy oil, 20W50 are usually the cheapest [censored] you can find, at least in my country!
 
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985
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England
YES in newer cars, probably not in older non rebuilds. Yeabut, it also depends on how long the OCI is! Thick oils (Above max EU spec) slow down the flow rate around the cylinder head and turbo in particular and raise the oil pressure a tad. That can cook up the cylinder head or turbo bearings IF the thermostat is not changed or adjusted to a cool runner. Net result is more top end wear (Fe, Al and Cr), but OK for bottom end (Fe again, Pb and toilet paper). Thin oils do the opposite! What the oil consumption does will vary with the type of oil (German synthoil or Ultra is real good) AND the SAE number (Related to viscosity, or how thick). Generally speaking if the engine is in good condition, they use less thick oil. Yeabut some don't and that is cos either the rings are kaput and the CCV is blocked, or it's one of those new small petrol jobs that is supposed to use 16w20 FS, but some dipstick is trying 0w30 to keep us amused. Net result, more wear AND a higher oil burn rate due to new Gen ring packs and self venting CCV etc. The high oil pressure pushes it out of both ends and that sure will increase the toilet paper consumption! A short OCI results in a thinner average. Too long an OCI might be sort of OK a few times, as the oil thins to start with, BUT then thickens as the detergent/dispersant Add's get used up. That causes the dreaded onset of early Black death (Sludge) symptoms, probably not an issue until past 10,000 miles with a major brand oil unless the injectors are kaput or it has an early model DPF.
 
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7,485
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S California
Automotive engines used in boats probably do well on thicker oil because they live a hard life. In a car you cruise down the road on partial throttle. You get going and then you let up on the gas pedal. Try that in a boat and you stop. In a boat you have the throttle open a lot more all the time or you don't go anywhere. Also boat engines are often down in a hold and the ventilation is nothing like being under the hood in a car or pickup with the wind blowing in the front end.
 
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35,788
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NY
Shell did a study a few years back, and it showed in certain instances [depending on what caused the consumption] that 'thicker' oil can actually cause more oil use. Bottom line is you have to experiment a bit changing oil grades.
 
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1,071
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Wash, DC
40W Wow. That's thicker than most gear oil. it's not just a matter of the oil getting past the rings. It also has to get up past the piston skirts to the oil control rings.
 
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35,788
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NY
Originally Posted By: Gene K
Thin oil for rings. Thick oil for valve guides. At least that's my understanding.
IIRC that's what the Shell study said.
 
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651
Location
Kuala Lumpur ,Malaysia
Originally Posted By: Popsy
It's also more difficult to find good quality heavy oil, 20W50 are usually the cheapest [censored] you can find, at least in my country!
True in asia too. I used 20W-50 many years back because it was the recommended oil for my engine. Had terrible ring wear and some sludging issues. It was burning oil at 240000km, OCI of 5000km, yet it still did not save the engine. Real [censored] of an oil these 20W-50 are. These oils were so bad that they oxidized and thickened pretty quickly. Never going back to those cheap group 1s again.
 
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