Engine life

Maintenance/Repairs
141

EllyEllis wrote:

A 4 heats up faster, thus incurring less wear.

While this may be true in theory, in practice, it’s affect on overall engine wear is likely insignificant.

an engine that turns more RPMs will have more cylinder wear,
but it doesn’t make any difference.

Is that really what was said? I think we can say that a simple count for the number of times a piston goes up and down isn’t the primary factor for cylinder wear.

4 valve engines operate at higher RPMs, forcing them to
run slower would hasten wear and waste fuel.

This isn’t universally true. There are many low-rpm (long stroke) engines out there that have long engine life and are fuel efficient. Other factors are involved.

Higher engine speed helps more than it hurts.

I don’t know where you got this. Higher engine speeds do wear engines faster than lower engine speeds. But that really tends to be a factor with the RPMs that racing cars run at and not typically the RPMs that passenger cars run at.

One person, I’ll not mention his name, said that by shortening
the duration between sparks they had solved the problem with
4 cylinder engines.

This makes no sense to me.

The inbalance of a V6 will cause uneven wear and tear.

Engine designers long ago figured out how to deal with the V6 engine angle quirks. There are no generic V6 engine wear and tear problems.

An I4 is ideally balanced.

This too is oversimplified and often not true. Look how many I4 engines have a dedicated balance shaft.

142

I dunno what the real answer is and don’t suppose it matters, but I believe for over the road constant use, a V6 stands up better. I’ve never used a 4 cyl under continuous use so really don’t know. I don’t buy the faster warm up though as making a 4 cyl better for continuous use. Large over the road truck engines get many hundreds of thousands of miles for some reason. IMHO but do what you want.

143

Hey, Joe, I too do not believe the stuff I said above, but it has been said on here.

144

BMW’s V-10 is only 305.1 cu/4999 cc redlines at 8250 peak hp at 7750. Of course the engine has its roots in F1 but is a production car with a VIN number. That multi-cylinder decision makes for smoothness also. 500hp,what did GM get out of their 305 V-8. Displacement is not all important like it used to be.

145

EllyEllis:
Sorry, I took your reply too literally. My appologies.

Joe

146

You’ll notice that many of BMW’s engines displace 500cc/cylinder (2l I4, 3l I6, 4l V8, 5l V10). I remember some BMW engineer saying something about that being ‘optimum’. That I don’t get.

147

Bing; you just answered your own question about the quick warmup. It’s precisely because big rig engines run continuously at road speed that they last so long, in addition to being well designed. The legendary London taxi has a 4 cylinder engine and many go one million miles before overhaul. They run all the time and are nearly always warm with “wet” bearings; no metal to metal contact.

For a private owner who makes short trips at low speed, a 4 cylinder engine is better, all other things being equal. But, as pointed out by at least 30 posters here, the intrinsic design quality is the most important; forget piston speed as a key indicator.

US manufacturers have a history of making crappy 4 cylinder engines, so it’s understandable that you might be sceptical about small engines.

148

That may have been true in the past, when engines had carburetors and flame distribution at high speed was a key efficiency issue. With modern electronic fuel injection, and precice valve timing, I don’t think cylinder size matters much anymore.

A few years ago I worked on a Marine diesel of 40,000 horsepower with only 6 cylinders! The injectors were the size of one quart coke bottles! This engine was more efficient than any BMW, but had a rated speed of only 100 rpm becasue of the large masses of the pistons.

149

I agree, that’s why BMW’s (very recent) comment about 500 cc ‘optimum’ cylinder displacement surprised me.

150

I am a little confused by how maintaining a higher RPM on an engine HELPS an engine? I would think driving a car at a High RPM would risk overheating the engine, putting more wear on the engine, and ultimately sending an engine of ANY size to an early grave. Please EllyEllis, I’m trying to understand where you’re coming from, but it’s not adding up.
Also, speaking from experience, not all 4s operate at a higher RPM than 6s or 8s, or whatever. I had a Ford Windstar (with a V-6 engine), and now I have a Ford Focus (with a 4), and they both run at the same RPMs. Just the V-6 took less effort to get going sooner. Then again, I’m going by the fact tha both cars run at the same IDLE engine speed.

151

Think of a car as a human being; I use that analogy with my mother-in-law when talking about cars…

The US number one health problem is people eating too much and not getting enough excercise! Cars with large engines that are only driven slowly and do a lot of stop and go, get bunged up! Also, a cold start causes about the same amount of engine wear as 500 miles of freeway driving. Therefore most engine wear occurs from starting and stopping. Similarly, airplanes wear out not from the flying, but from taking off and landing. These stress cycles determing the life of the fuselage!!!

Whether an engine takes longer than another engine to get up to speed is irrelevant. Some of the most durable engines, small diesels in taxis last a million miles!

High RPMs have nothing to do with overheating; the cooling system is designed to handle all that. They overheat from poorly maintained cooling systems!!

152

The inbalance of a V6 will cause uneven wear and tear.

Engine designers long ago figured out how to deal with the V6 engine angle quirks. There are no generic V6 engine wear and tear problems.

YES! they’re called I6’s or flat (or Boxer) 6’s. I’ve frequently heard them called “perfectly” balanced. It takes effort to make a bad straight 6. The old Chrysler slant sixes were legendary. I had a class mate in college with a 350k mi 1985 BMW 325. I know this isn’t exactly the best evidence but I can’t really think of a single BAD straight six… They’re so smooth and torquey. It makes me mad that there are so few out there…

153

jkm416. I would think driving a car at a High RPM would risk overheating the engine, putting more wear on the engine, and ultimately sending an engine of ANY size to an early grave. Please EllyEllis, I’m trying to understand where you’re coming from, but it’s not adding up.
I was just making jest of some of the ridiculous posts on here. I am glad you noticed, not many did. As for them running at the same speed, have you checked the RPMs at 70 MPH on both cars? Most 4s run faster at any determined speed.

154

Running an engine at high RPMs puts it at risk of overheating? I always thought the water pump turned faster when the RPMs went up. I guess I was wrong. I guess cooling systems stop working when the engine spins faster. Imagine that.

I wonder how all of my four cylinder cars survived the southern heat so long. IT’S A MIRACLE!!!

155

Ronman, this is the first thing you said on here that makes any sense. You are right.

156

I see. I stand corrected about cars overheating at higher RPMs. I forgot about the water pump taking care of that. Thanks, docnick and Ron-man. Also, thank you docnick for bringing up the fact that additional stress gets put on cars that do nothing but city (esp. stop and go traffic. eg. LA, NY, etc.) as opposed to cars that do nothing but highway driving. I meant to mention that, but you beat me to it. :stuck_out_tongue:
EllyEllis, thank you for clarifying. Now I see where you’re coming from (really, I do!) And yes, I agree: a 4 DOES run at a much higher RPM at 70MPH than a V6. But I was just talking about idle engine speeds, which I admit is a completely different story altogether.

157

This thread must be a V6…