Piston Slap: What makes a reliable engine?

reliable engine what makes reliability piston slap

Lyle writes:

Hey Sanjeez, I have a question for Piston Slap: What makes a reliable engine?

Like, there are some throughout history that seem to have endlessly positive reputation despite having at least some problems or quirks. Nothing is perfect, but why are some better than others? Is it the design? Production? Materials? Some combination of all three, with a little sprinkling of Chemical X?

Sanjeez (who is really Sajeev) answers:

Excellent question Lyle, and your slow meatball pitch is setting me up for a home run. Thanks for that, so let’s get into why a combination of everything you mentioned makes a reliable engine.

Hello, Vulcanator! Ford

I learned that even the most durable motors have problems at some point in vehicle ownership, stemming from faults in engineering or the supply chain. Even worse, this can happen at any time over the engine’s lifecycle, because it’s just a commodity made by a multi-national corporation. I used to think the 100 percent cast-iron Ford Vulcan V-6 was as tough as they get, except examples at the tail end of its 20+ year history had a defective cylinder head casting that could crack.

My tarnished brand loyalty aside, it turns out that everything matters, especially over time. Cheap out in the supply chain (somewhere, who knows where) and something like this cylinder head defect surfaces. Add the complexity of modern small displacement, low friction turbocharged engines designed to meet government mandates across the globe, and the system is ripe for failures.

And no period of time is safe from blame: Bite off more than you can chew with bleeding edge technology and the early Cadillac HT4100 engine is the result. Tinker with oil change intervals, PCV systems, etc., and sludgy 2000s era motors from VW and Toyota rise to the surface. Subaru boxers have a serious love/hate relationship with the Internet. And when the entire industry seeks less friction in an engine’s short block, oil consumption issues across the board becomes more prevalent.

Now let’s get a little weird …

Chasing down all the fail points will drive you mad, but as a judge in the 24 Hours of Lemons, I learned that presumably durable mills can be downright hapless in endurance races. I’m looking at you, small-block Chevy and various engines from Toyota and Honda that can’t stand being revved for long periods of time. Even the legendary Chrysler Slant-Six has a checkered history in this series, while BMW inline-sixes can take the heat just as well as they do on the streets. (Maybe better?)

Ironically and shockingly, Lemons taught us that the Cadillac HT4100 does pretty well in an endurance race. A Cadillac-swapped Miata is winning races fast enough to hurt some egos in the process. Contrary to the delightfully snarky video above, the HT4500 and HT4900s are one of the better V-8 swaps you can do in this race series. Getting a budget-built small-block Ford/Chevy to be competitive for that many hours on track is difficult, but aside from Ford’s lazy-revving SOHC 4.6-liter mill, the Cadillac is where its at.

And oh boy, does it ever have Cadillac style! (Cue that bass guitar drop!) 

I think everyone needs an HT4100 swap so they can go and “live, love every mile” in flagship style. It proves the point that good engines can be junk, and junky engines can be fantastic.

Frustrated by my answer yet?

Just remember that nothing is sacred, as engineers, mechanics, previous owners, government mandates, and supply chain snafus will find a way to surprise you. No brand is unassailable, no dataset has all the information you seek. So be vigilant on maintenance, buy used vehicles with a service history, and get an extended warranty if your nerves cannot be soothed into submission. Only joking on that last part … probably.

Have a question you’d like answered on Piston Slap? Send your queries to pistonslap@hagerty.comand give us as much detail as possible so we can help! Keep in mind this is a weekly column, so if you need an expedited answer, please tell me in your email.




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    “Reliable” is a pretty loose word anyway, IMO. Too many variables both in the build and the use categories to fit every contingency. For instance, an engine that was “built” with reliability in mind can easily be ruined through poor maintenance – or stupid driving. An engine that was “built” with some inferior parts or processes can be made into a 500,000-miler with a few aftermarket changes made by a competent mechanic. A great, “reliable engine can be made pretty useless if the owner: never changes oil or filters, mis-times it, puts inferior fuel in it, over-revs it by about 5,000 RPM over redline, etc., etc., etc.

    Yeah there should almost be reliability indices for new and 5+ year old vehicles. Problem is, I highly doubt anyone would pay for data on the latter, but we’d get a more complete picture on vehicle reliability this way.

    Reliability is a function of robustness of design, quality of materials and manufacturing, and quality and frequency of maintenance. Failure in any one of these areas will defeat the best efforts in all others.

    There is plenty of room for misunderstanding and misinterpretation of the factors. For example, the typical ‘60’s and 70’s V8 was thought to be far more robust than early 4 cylinder motors from Honda that were 1/4 the displacement and weight of those V8s, but produced twice as much horsepower per cubic inch. Back in the 70’s and 80’s we were conditioned to the more lenient yardstick of oil changes – you could leave that V8 oil for a year, but that could not apply to the more highly stressed 4 cylinder engines without disaster.

    Nowadays small turbocharged 4 cylinder motors under much greater stress put out the power than few ‘60’s V8s could muster. Combine that with ultra-close tolerances and ultra-thin motor oil, and suddenly we’ve got a new maintenance learning curve to wrap our heads around again.

    As for my daily drives, I’m sticking with the good old mantra – no replacement for displacement and hedging my bets with more frequent oil changes.

    24 hours of racing? Focus on oil pressure and cooling the oil and the engine.

    A small block Chevrolet with adequate cooling and solid oil pressure can take an immense amount of abuse. But the factory cooling systems were never intended for that and nor many small blocks have factory oil coolers. The factory oil pumps were not sufficient to the task and don’t maintain pressure, especially with a high oil temps.

    Our old C50 shop flat bed had a 350 in it and would run non stop hauling, most of the day around 3,000 rpm and WOT. The Radiator was massive and it had a larger capacity oil pan and lots of oil pressure.

    To your point, SBCs do pretty good in Lemons if the cooling systems are up to snuff AND the car has something like a 3.27:1 axle to keep the revs down. But most rev too much, and their teams lack discipline to keep the tach deep in the black.

    I’m guessing your shop truck slowed down and stopped for traffic interchanges, and wasn’t sloshing oil around at 4000+ rpm in high speed sweepers, non-stop for 30-90 minutes between pit stops for 8 hours. But that’s exactly what happens in an enduro.

    Generally there are a group of variables that are in play.

    One is design. How was the engine designed and was it done in a proper way.

    Second is material. We’re the materials up to the task.

    Third is was it used for the intended job. Taking a Cadillac 500 cid racing turning 5500 rpm will result in a failure.

    Over history some engines do better than others. Case in point Olds V8 engines from the mid 70’s to mid 70’s were nearly indestructible in street driven applications. Most out lasted the cars.

    Others like a Vega 4 was a good engine but no sleeve in the engine proved to bring oil use issues. Kia assembly issues is leading to major failures. Honda has had issues on some engines too.

    Many belt driven cams fail because people do not change the, and they fail catastrophically.

    The LS1 engines are proving very durable as little fails or wears out outside some supplier parts in sone tunes.

    The base LS1 are known for 500k to 1 million miles and often out live the vehicle they are in. One C5 is in the Corvette museum with near 900k miles.

    You get the right parts in the right application and show a little care most will last a long time. Even some abuse is not fatal as I have seen some survive people trying to kill them.

    I was told the HT 4100 was the worst engine out there and steered clear of them for years. My current Allante has the HT 4500 and is a solid engine at 150K miles. I think there is a big difference between reliable and perception of reliable. If an engine comes out with some infant issues (as all engines do), they can be very quickly saddled with the ‘unreliable’ brand even if the later engines proved to be very good

    What makes a reliable engine? keep the fluids in it and avoid the timing belt. I suspect what has made the modern engine much more reliable than the engines of the 60s and 70s is that they are much better designed to keep the fluids inside. The owner doesn’t historically have a good track record for maintaining fluid levels. One thing that has kept Diesel engines reliable for years is the fact that they are governered (you cannot over rev them unless you do something REALLY stupid), and they will shut down if certain parameters go out of band. More of this technology has been finding its way to the Otto engine, which plays a big part in improving reliability

    I’d change “keep the fluids in it” to “keep fresh fluids in it”.

    Sometime around 1986 the HT4100 received a lot of internal improvements that made them decent motors. But that was too late for many folk’s perception of reliability,

    Most engine deaths that I have experienced (both personally and indirectly) have been due to a critical fluid running critically low – usually due to a leak. Fresh is a plus, but keeping ’em in there is 90 of the battle. I know people who have gotten high miles on 15 and 20K oil changes – and I’m not talking synthetic

    That’s a very good point! I lose a motor from an oil leak AT the oil pressure sensor, so the sensor never knew anything was wrong…until it was too late.

    That makes a good case for installing gauges instead of “idiot-lights” that only tell you when it’s too late.

    For just a daily driving engine I’d nominate the GM 3800 series, having driven numerous ones over 200k miles with no issues (other than one cracked plastic intake done under warranty 20 years ago). Currently on one I bought 4 years ago with 120k miles and have put 60k worth of commuting miles on in the past 4 years. Runs perfect.

    Transmissions are a different issue though….

    Probably wouldn’t take it racing, but for a stress free cheap daily driver, it’s good.

    The 3800s have two plastic elbows that come out of the engine and go into the accessory bracket (where the fluids eventually terminate in the heater core). These fail, usually by blowing out the corner. Later replacements are now made of metal. If yours are not metal, replace them. I had a 3800 with 230K that was well on its way to 300 when one of these blew out in Pittsburg tunnel traffic and cooked my poor motor

    I’d say “the country you live in” given that reliability can be subjective. I don’t know how many times I’ve heard “Oh, [insert engine here] are super reliable /if you keep on top of the maintenance religiously and only use parts from this one source that’s been on the edge of going under for 14 years/ otherwise watch out, bud.” That, to me, doesn’t say “reliable” so much as it says “I have to babysit this thing to keep it from grenading, but it’ll last 250k miles if I do that.” I’ve run into this with many European cars but I’m sure someone else on this thread’s mileage will have varied and they’ll tell us all about it.

    What separates sone engines is what year it is.

    Some see mechanical or engineering fixes. Some supplier fixes and this can change an engine from a boat anchor to a reliable engine.

    The 3800 was a train wreck when it was a 3.8.

    The Early Northstars were great but later had head gasket issues with the changes they saw.

    Jags for years had valve seat issues and were often replaced with Chevy small blocks.

    The cold harsh reality is there is a number of variables that play into long term reliability. Design, economics and just plain engineering or the lack of it.

    Even the best can fail due to a small change, failure or issue.

    I have yet to own a single vehicle that needed major motor work. Any internal work, for that matter. Some accessory items, sure, but nothing that ever would have justified purchasing an extended warranty had I ever done so. I adhere to specified oil change intervals (though sometimes I do change it more frequently when service specials arise).

    Nowadays, I think it helps to also pay attention to others’ reportings of issues. For example, I learned of the two-piece spark plugs in the Ford 5.4 Triton V8 had a tendency to break when attempting to remove/replace them at the specified change interval. I had mine changed earlier and replaced with an updated design.

    Good point, be aware of simple fixes that can improve reliability. Ford 2.5 (and I think 3.0) Duratrch V-6 engines used a plastic water pump impeller that would just disintegrate. Replacing it with a metal aftermarket one was minimal cost and only took about 20 minutes. Reliability improved.

    I’ve always thought that the reason why people think Toyota motors are so reliable is because their drivers never rev them above 2,000 RPM. 😆 Toyota drivers are the slowest (by manufacturer). Have you ever seen. Camry in a street race? 💀

    I just want to point out my appreciation for the very subtle nod to the Powerpuff Girls with the “Chemical X” reference.

    And yeah, if we’re talking 24 Hours of Lemons that’s a completely different kind of durability than driving on the street. I would expect BMW 6 cylinder engines to do pretty well there, and less so on the street.

    As to the original question, design, materials, lubrication are the biggies. As long as there’s no achilles heel in the design or construction those three are the parameters that dictate a long-lived engine. The BMW M10 engine was dictated by the bean counters to have 3 main bearings. The lead engineer fought for, and got, a 5 main bearing design through and the engine was legendary. It was even the basis for their turbocharged Formula 1 engine. You know… the one that made about 1500 hp.

    I’ve owned a few “legendary” motors. Seems proper engineering and manufacturing was the key. Proper maintenance is the cherry on top.

    I worked at a Cadillac dealership in the 1980’s through the mid 1990’s and the HT 4100 certainly kept us busy doing warranty repairs on them. Many camshafts and main bearings were replaced due to coolant getting in the oil from leaking intake manifold gaskets. The cylinder heads were iron and the intake manifold was aluminum with different rates of expansion. You could usually remove the intake manifold bolts with your fingers because the gaskets would compress and loose their seal. The oil usually didn’t look like a milkshake but there was just enough coolant in the oil to reduce the lubricating quality of the oil causing excessive wear on the camshafts and bearings. In 1989, GM came out with a revised graphite intake manifold gasket using thick bevel washers under the intake bolts that acted as “springs” to hold the intake manifold on. This gasket could seal the dissimilar metals and just about all of the mechanical problems associated with the early engines went away. The HT4100 was a good design (for the time) with one fatal flaw of poor sealing intake gaskets. The newer engines (4.5 and 4.9) came with the revised gaskets and they proved to be very reliable.

    High silicon content Swedish Iron in either 1.8 or 2.0 liter forms with serious bearing surface area equivalent to American V8 engines. I’m referring to Irv Gordon’s 680k miles on the factory engine build. Then getting it to 2.8 million miles on the 1st rebuild before another. He finished at 3.25 million miles. Amazing to me is surviving the 125 mile daily drive traversing the Long Island expressway.

    Reliable on the track is not the same as reliable as a daily driver. I drove a properly maintained SAAB 1.7L V4 (German Ford) for 250,000 miles. It had cast iron block and heads but aluminum intake manifold. It was extremely short-stroke but didn’t breathe well enough to rev much. As it replaced the previous 0.85 L 2-stroke that seemed to last about 50,000 miles, I thought it was about as reliable as an anvil (and weighed about as the same).

    I would nominate two inline 6 motors that don’t do anything excellent but do reliability and durability well.

    The Ford 300 incline 6 and the Jeep 4.0L. Neither motor would win any drag races stock but just tough motors.

    My father had a 85 Ford F150 with a 300ci. and 5spd. With lower rear gears he would pull his horse trailer with two mules all day long no problem. It probably helped that the speed limit was lower back in the day! The 300 had perfect balance of torque and reliability to make it all around a good engine.

    In college I delivered meds for a pharmacy that had a Jeep Comache 5spd 4.0L. I would spin the tires all day in first, healthy spin in second and a solid chirp in third. This was after it was beat on for years at 300k miles by a variety of “beat on it like a rental” delivery drivers. I now have a 95 Grand Cherokee rock crawler with a 4.0L and I love it.

    Cheers to the Sixers!


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