Caterpillar 3126 engine - any good? Lugnut?

Sure. By varying the amount of turbo boost and fuel injection parameters (timing etc), you can vary the maximum horsepower. There's no such thing as a free lunch though, tuning it for more horses will probably reduce fuel economy, increase emissions, and perhaps reduce engine life.

I worked on Caterpillar stationary generators with the turbocharged 4 cylinder version of this engine. It wasn't computer controlled, however. From what I know of computer controlled diesels, the turbocharger wastegate is controlled by the computer. The computer can be programmed to hold the wastegate closed more and increase the boost pressure along with also increasing the fuel flow. That 6 cyl. is intercooled, so you wouldn't get into an excessive EGT problem and damage the turbo. The increased air and fuel increases engine output. I won't comment on the reliability of that particular engine, but the 4 cyl. Cats I maintained were dead solid good engines. However, they always ran at a constant governed speed, unlike your application. I'd be interested to hear what others think of the engine.

Garrett Fulton

Many identical engines these days can be set to various hp levels to suit the customer and application. They may need details, such as a bigger intercooler, at higher levels, but they may indeed not. In this case the hp is set by dumping a flash file appropriate to the hp level into the CPU of the engine. Nothing more to it than that. Certain manufacturers may inhibit tuning in this way though. I know it can be done with smaller Cat engines like the 6 litre Perkins 1000 series electronic engines but have no direct experience with bigger versions in this respect.

Huw

The Cat 3126 is a solid engine in an application like this at that HP rating. It can easily be re-rated as well as changing max engine torque, rpm and a multitude of other controls including the cruise control and max road speed attainable. Many of these parameters are set to the owners wishes while remaining under warranty. All of these settings can be altered by a Cat service tech with a laptop computer with the correct software. Hell, here in the states, drivers can usually find someone at a truck stop willing to step it up for a little cash. Cat engines in highway applications with regular maintenance are easily capable of 500k miles before overhaul. I know of many that are now approaching 1mil miles w/o overhaul. Keep in mind that some Cat engines require crank bearing maintenance replacement at 300k miles with no further major maintenance. In a bus/RV application, this should be an outstanding power plant. I will give one word of caution on the Cat engines. They have a natural vibration as do most Diesel engines. The vibration characteristics of a Cat engine tends to cause some chaffing of engine related wiring around the starter unit on the left side and in the area where they are sometimes in near/in contact with fuel lines. This can and has resulted in several fires on the 3126. Inspect these items closely and regularly and, correct as needed.

Lugnut

Caterpillar is the top of the heap among diesel engine builders in that size category.

In all fairness, the modern Detroit 4-strokes like the Series 60 are excellent engines and on a par with Cummins and Caterpillar. So was the

2-stroke 6v92 in its day... 40 years ago. But 2-strokes are pretty much steam-age technology now. There are millions still out there and they'll be running for another 50 years, but I'm not sure I'd go looking for one in a motorhome. Maybe an old road grader or dozer to use on the ranch, but not a motorhome.

You know Lugnut - if you were a 20-year-old good-looking, blonde female you could have my babies just for saying that. (Are you?) Hell - even if you're a brunette....

Seriously - music to my ears mate. Thanks for your help and same to everyone else who commented.

I'm interested in this 'adjusting the hp' technology I have to say. How did I manage to get so old and senile and still not know about that? Maybe this explains why so many engines I have checked out seem to advertise varying hp despite looking like the identical machine to a novice like me. It's been driving me crazy. So what's the deal with the trade-off in torque? For example, if I had just driven accross the plains and was about to cross a pass at 7,000 ft or whatever, would it be a good idea to up the hp or would that lose the low down torque? And if I adjust the hp right down to the lowest - say 200 - does that take a lot of strain off the crank, or doesn't it work like that? From what I understand of the Australian interior I could be doing a lot of distance on fairly flat, empty roads. What would be my best bet in those circumstances - high hp or low? Bearing in mind I'm not in any hurry and I want to absolutely look after the engine? (My life could depend on it I hear tell) I'm presuming low as possible, but it seems the world of diesel engines is vast, mysterious and full of surprises.

I've read that Cats are a lot more expensive to repair (than DD's) if they screw up but then if they go 500k between o/h then it's a chance I'll take.

Cheers Graham (aka A W-S)

The power and torque curves can now be manipulated easily by computer as well. In some applications, maybe yours, it is advantageous to have a very steep torque rise, say 35 to 40%, to the extent that the engine becomes a 'constant' or even a 'rising' power unit. That is, looking from the rated speed downwards [and assuming you are at least familiar with the general shape of power and torque curves] that the power actually rises as the load forces the engine revs to reduce. Say 200 hp at rated speed of [say] 2200rpm yet as revs drop the power rises to a peak of around 240hp at 1900 before dropping gently to still give 200hp at 1600rpm, just above the peak torque point of perhaps 1300rpm. This engine would perhaps be described as having a broad constant power spread or as having a significant power bulge or [correctly] as having both characteristics. Clever eh?

Look for benchmark optimum fuel consumption figures of around 200g/kW/h or better in the mid range at full load. The drawback with those constant power engines is that because they produce such huge power and torque at low revs they tend to drink fuel at near the same rate at full load whatever the revs because they produce the same power at low revs than at high. The power and torque produced at low revs is phenomenal though and very suitable for applications that are normally described as 'heavy duty'. This is partly because the torque rise is so high that as load increases and consequently the revs decline and speed also decreases in proportion [assuming no gearchange] the power declines at a lower rate than the requirment for power. In other words they really lug to the extent that some Cat engines used in earthmovers and generally run near rated speed are virtually unstallable in work.

For instance, consider a dozer pulling a ripper through a tough spot needing

30% more power than the surrounding area. If the dozer is pulling near its maximum effort at 2200rpm in the lighter soil and it hits the tough spot you would think a down gear change would be needed to pull through. This is not the case because as the dozer enters the tough spot then it will inevitably lug down. If it is pulled down to say 1600 rpm then it will have slowed forward motion by 30% and so wil require near that much less power to proceed but the engine [as I indicated above] is still producing the same power as it was at 2200rpm. In fact under such a peak load it would not lug it down to 1600 but you can easily see what the characteristics and the practical effect of such an engine is from this illustration.

Huw

The Cats are expensive to repair but, if you run a long term cost analysis, most Cats are no more expensive than any other and give a dividend in up time because of reduced major maintenance.

As far as the power goes, the vehicle and engine manufacturers just about have it down to a science when it comes to power requirements for a specific application and operation based on your expectations.

As far as high altitude operation, I don't believe you will see much performance degradation in a turbocharged and intercooled engine as long as it does not overheat. These engines sense manifold pressure and temperature and adjust turbo and fuel delivery to both maintain power output and safe engine operating parameters. The best thing to do is let it do it's thing while you drive and observe before you make any changes. You may be happy just the way it is. Then again, you may subscribe to the premise that a lot of power is good, more power is better, and too much power is just right. Fuel consumption only counts if you are paying.

(Speaking of fuel mileage, you may be able to have the ECM data downloaded which would be a good idea before finalizing the deal. It will give you a printout which includes all the sensor alerts like overheating, low oil pressure, engine operating hour, road mileage and fuel consumption/mileage to date. That may be interesting reading for you before purchase.

Lugnut

I bought a new dump truck in 99 with this motor. It currently has

215,000 miles on it with no engine work ever. It does however (and always has) use at least a gallon of oil between changes, sometimes more if it's worked very hard. I usually try to change it around 6,500 but have gone a little further if doing a lot of work on the highway as apposed to dusty conditions. My empty truck weight is approx. 22,000 lbs. & a loaded weight of around 55,000. I average 7-7.5 mpg but would get a little better than that if empty & on open road. I live & work in a mountainous area (2000-3500' elevation) Red line is about 2600 rpm & I've never exceeded that. It will easily run 75 mph & be around 2400-2500 rpm. Mine was set at 275hp from factory & can be turned to 300 but Cat techs say it will not increase torque, only use more fuel & I'd probably never see the power difference. They wanted 1 hours labor ($71 at the time) so I didn't bother with it & as someone said it's only a matter of plugging it up to a laptop for 5 minutes. This type engine won't accept an engine brake but you can install an exhaust brake. Take it from experience it's a complete waste of money. This probably won't be an issue with a motorhome anyway. It always slows when starting up a hill but you can make up for it going down the other side! It's just not a "massive power" engine but it is a decent one in my book. I could see it doing a great job in a motorhome. Keep in mind the weight's I'm dealing with as apposed to what your RV will weigh. It will surely carry it along just fine. FWIW, mine has an 8LL trans.

I've heard that some Cat motors adjust the HP rating while on criuse (advances the timing or something), this is not one of them according to Cat. They also told me to expect 450-500,000 miles before doing an "inline" on the motor. If it goes this far I'm buying another truck! Hope some of this helps!

The bus is an 11Meter Hino (I think that's about 37ft) with a car trailer behind that, so it's a fairly hefty beast. I don't know what it weighs in pounds, in fact I'm not even sure what a pound is anymore - the rest of the world went metric about 30 years ago you know - but I'm pretty sure it won't be anything like the weight of your dump truck. I'll be dawdling along anyway. I liked a quote I read from a long-term 'full-timer' in Oz: "My first trip round Oz took me two years, the second one just over three years, but on this trip I'm just going to take my time"!

Thanks to you and everyone for your help - all very interisting stuff.

Cheers Graham