4Cyl. Engines vs 8Cyl.

[buster]

Generally speaking, wouldn't a 4cyl engine (like mine) running at 3K rpms @ highway speeds be much harder on the oil then an 8cyl engine running at much lower Rpms? It seems the 4cyl. really test an oil from the higher rpms they generate.

 

[Mike242GT]

Buster: You would think so, wouldn't you? On the other hand, lots of 2.0-2.5 liter 4 cylinder engines have sump capacities and use oil filters which are approximately the same size as their 4.5-5.0 liter V-8 counterparts.

 

[Whimsey]

I tend to agree with you. My 2.0L 4 cyl Zetec engine is turning at a higher rpm @ a set speed in the same gear than my 4.6L V-8 in my truck. Both being OHC engines with the 4 cyl being a Dohc and the truck being a Sohc I would think the 4 cyl engine is harder on the oil and could shear it down more. Whimsey

 

[Whimsey]

Good point Mike. My 4cyl engine has the a very similar size oil filter versus the 8 cyl engine, FL200(4) and FL 820S(8). The total oil capacity according to the manual is 4.5 qts/4 and 6 qts/8. But I still would think that the oil is being "worn" out faster/sheared in the smaller motor. That is unless you tow heavy loads in the heat with the V-8 I assume. Whimsey

 

[Quick_lude]

I would definitely say that 4 bangers typically are harder on the oil than 8 cyl engines. But as we know there are exceptions to every rule..

 

[Shannow]

I'd say that the 4 bangers are generally running at a higher mean pressure than the 8s. In other words, the 8s run at very low manifold pressures (meaning low cylinder pressures and temperatures), and lower revs than the 4s. Theoretically, an engine is most efficient at W.O.T., so I'd guess that the most economical engine would be foot to the floor at cruising speed(and tuned as such). It would probably eat oil, and wouldn't last to any great degree.

 

[mkosem]

One thing you may want to consider tho..... 8 cylinder engines have more moving(and thus wearing due to friction) parts in them. 8 cilinders, double the number of cam journals, double the number of crank journals, etc. wouldn't that contribute to additional wear? --Matt

 

[JohnBrowning]

Well I do not see alot of difference today. The bigest factor in my mind is that inline engines suffer less blowby then V or W configuration engines. The thrust side of a V/W engine cuases abnormal wear and interferes with ring sealing after 50,000-60,000 miles. This might be offset some by today by almost all engines being tilted for packageing though. The inline engines tend to have stiffer blocks and prevents block flex. Most vechiles today run 195 degree water temp and have simalar oil capacitys in alot of cases example 2.7 4cyl ina Toyota Tacoma holds close to 6 quarts of oil v.s. 4.7 Dodge V8 holds 6 quarts. The difference is in filter size if you run same filter both hold 6. I do think that rpm plays a role but most manufactures are gearing vechiles for gas millage and this means low RPM's in overdrive. In the old days it was common for 4cylinders to turn 1500-2000 RPM's more then V6 and V8 engines at Hwy speeds but this is less common today. I think that one reason that 4 cylinder engines tend to be harder is more a funtion of load. Most manufactures are put more load (weight to Hp/Torq.)on their economy cars then on anything with a V8. A good example would be a 1.0L 3 cylinder Geo Metro with 4 grown men in it trying to climb a hill at HWY speeds compared to a V6 Nisaan Altima climbing the same hill with the same 4 men. I belive that the heat saturation of the engine s would be comencerate with their load ratio/Duty cyle!!! If you throw in things like extreme temps or dirt then you get into residual subsytem capacitys like cooling, filtration etc........ I hope I made since!!!

 

[Patman]

quote:

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Originally posted by mkosem: One thing you may want to consider tho..... 8 cylinder engines have more moving(and thus wearing due to friction) parts in them. 8 cilinders, double the number of cam journals, double the number of crank journals, etc. wouldn't that contribute to additional wear? --Matt

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It would show up as a higher ppm of wear metals in the UOA, but take into consideration that because it's coming off more parts, the wear level in comparison to a 4 cylinder probably evens out. IOW, 8ppm of iron in an 8 cylinder engine is much like 4ppm of iron in a 4 cylinder (if they are of similar metal construction that is) When I had my 98 Formula with the 6 speed transmission (with it's .50 overdrive!!) and it's stock 3.42 rear end, the rpms at 60mph were only 1300! Even when I modified it later with a 4.10 rear end, it only revved at just under 1600rpm at 60mph. My current Formula has a 3.23 rear end and an automatic trans with a .70 overdrive, so it revs at about 1900rpm at 60mph.

 

[mrchecker]

quote:

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Originally posted by JohnBrowning: The thrust side of a V/W engine cuases abnormal wear and interferes with ring sealing after 50,000-60,000 miles. This might be offset some by today by almost all engines being tilted for packageing though.

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This is an old wive's tale that dates back to the old Ford flathead V-8's. ALL engine configurations have sideways thrust on the pistons, it has nothing to do with the angle of the cylinder, only the direction of the engine rotation. Do Subarus and Porsches wear out their cylinders on the bottom? Does jacking the back end of your car up make it go faster since it's always going downhill?

 

[Gary Allan]

quote:

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ALL engine configurations have sideways thrust on the pistons

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Although this is true in a "static" sense ..there tend to be distinct differences. The "V" configuration tends to have a shorter rod length to stroke ratio. That is the amount of reactive thrust tends to be "less". The longer the rod to stroke ratio ..the higher the torque. This is due to less angular deflection ...and, hence, less lateral thrust.

 

[JohnBrowning]

MRCHECKER if this is an old wives tale then why do all V configuration engines wear their cylinders out of round much faster the inline engines? Why is blowby more pronounced in V configurations at 120,000 then in similar inline configurations. You also note more taper in their bore. If not thrust then it must be block flex!!! I have to admit though that common sense would seem to dictates that the side of the case with the most force applied must also wear faster. Gravity is going to be pulling the one side of the piston and ring directly into the case at all times even when at rest while it will also be pulling the high side portion of the ring away from the case at all times. The ring rotates but the case and piston does not. The side with more friction has to have more wear! It is also common to see more scuffing on one side of a piston then on the other side. I was never taght this. I have observed this and tried to reason the cause. I have no hard science (double blind controlled study)to back up my observations. It would apear though that history is on my side. The longest lasting engines both gas and diesel have always been inline configuration. It is also common place to refresh an inline engine with a rering job in developing nations/thirdworld where a V engine almost never responds well or long to this.

 

[metroplex]

Engine life is almost directly proportional to piston speed. The faster your engine runs, the more wear there's going to be - unless its a rotary engine, those things can take a licking!!

 

[sbc350gearhead]

Inline configurations are inherently smoother running than v type configurations. The rod/stroke ratio probably plays a large part in the equation. The advantage of a longer rod is a controversial topic as the longer rod weighs more and increases stress on the reciprocating assembly in high winding engines.

 

[Greaser]

How would a Jeep engine fair?Straight six,cast iron block and head,8.8:1 compression ratio,two valves per cylinder,6 quart capacity in oil,does around 2,200 rpm at 70 mph..yet it has had high iron counts at almost every UOA...just thought I'd throw this into the pot

 

[Quick_lude]

My 4 cylinder engine redlines at 7400rpm.. and revs at 4,000 at 140km/hr.. but my gearing is quite tall in 5th.

 

[JohnBrowning]

greaser I have no clue. I really do not know much about DC products interms of long term durability. I have read some of you UOA and I found the iron to be alramingly high. If it is just ring wear your bore is proably not wearing much at all. I know that traditionaly Chrysler casst their blocks with a harder allow with much finer grain then GM or Ford. The only thing I can figure about your Jeep engine is that they must be useing really soft ring material THe Dodge slant six was an incredable engine for durability. It was not uncommon to see cars with the slant six in them go 200,000 miles when the V8 were lucky to make it past 80,000 miles. I have seen quite a few with 300,000 miles. The Ford 300 inline six was the same way. Toyotas 3.0 inline six was also an incredable engine. THe Cummins Turbo diesel usedd by Dodge is also known to last 300,000++ miles.

 

[Greaser]

Yes John..lots of memories of the "good ole' motors"..where you can actually see the oil filter,water pump,starter etc..not covered with a plastic sheild...the 4.0L had been around for a long time now...many people on a different forum I frequent have way over 200,000k and still going strong with this engine...I think the high Fe levels are due to the fact of the entire engine being cast iron...not a alloy head on a cast block..so may-be the wear on the head componants contributes greatly to the iron count...who knows?