What the Heck is a Dry Sump Oil System?

Most production vehicles, whether they are ATVs, UTVs, cars, or trucks, have what is called a wet sump oil system. In a wet sump system, the oil is stored beneath the crankshaft in an oil pan. In a wet sump system, the oil pump sucks the engine’s oil from the bottom of the oil pan up through a tube, and then pumps it to the rest of the engine.

Four-stroke engines are both lubricated and cooled by oil that is circulated throughout the engine lubricating the bearings and other moving parts. After it’s lubricating trip it drains to the sump at the base of the engine under gravity.

In a dry sump system, the oil is stored in a tank typically located outside the engine rather than in the oil pan. There are at least two oil pumps in a dry sump - one pulls oil from the sump and sends it to the tank, and the other takes oil from the tank and sends it to lubricate the engine. In a dry sump, the oil still falls to the base of the engine, but rather than being allowed to collect in an engine sump, it falls into a much shallower sump where it is removed by a second pump and is pumped into the external reservoir where it is both cooled and (also very importantly!) de-aerated. Oil is then drawn from the remote tank by the pressure pump and circulated back through the engine. The two pumps are often referred to as scavenge pumps and pressure pumps.

Dry sump systems have several important advantages over wet sumps systems. Because a dry sump does not need to have an oil pan big enough to hold the oil under the engine, the engine can be placed lower in the vehicle. This helps lower the vehicle’s center of gravity. The reservoir can also be relocated to another part of the car to improve weight distribution. There can also be an increased oil capacity by using a larger external reservoir than would be practical in a wet sump system. An increased capacity also allows the oil to cool and release entrained gasses from ring blow by and the action of the crankshaft. Basically, the oil capacity of a dry sump can also be as big as you want.

In a wet sump system, turning, braking, acceleration, and running across side hills can cause the oil to pool on one side of the engine. Dry sump designs are not nearly as susceptible to the oil movement problems that wet sump systems can suffer from due to these forces. If the oil in a wet sump is forced to one side in the oil pan the oil pump pickup tube can be temporarily uncovered leading to a loss of oil pressure. Because the scavenge pumps are typically mounted at the lowest point on the engine the oil flows into the pump suction by gravity rather than having to be lifted up into the suction of the pump like a wet sump does. Also the scavenge pumps can be of a different design that is more tolerant of the entrained gasses than the typical pressure pump which can lose suction if too much air is mixed into the oil. Since the pressure pump is typically lower than the external oil tank it always has a positive pressure on its suction regardless of cornering forces.

From a strictly engineering perspective the dry sump is the superior solution, however with real-life economic considerations, where vehicles have to be built to a cost, it is usually eliminated as being too expensive. Dry sump systems do add cost and complexity, and the extra pumps and lines require more oil, so maintenance costs rise accordingly.

So there you have it, more than you wanted to know about dry sump oil systems.

Polaris RZR XP - The Performance Details

It doesn’t take much of a look to see the differences between a RZR and the new RZR XP! It’s taller, wider, and longer. That may be simplifying the issue a bit but it’s true. About the only place the XP is the same as the other RZRs is in the cabin. Same seats, same steering wheel, same gauges, same everything.

So let’s take a look at the differences:

Up front is a new tubular subframe designed to hold even longer a-arms. These arms are an additional 2 inches longer than the already extended arms of the RZR S so they can provide 13 ½ inches of wheel travel. That’s a lot of travel, but as Doug Roll always said, long travel doesn’t mean anything if it doesn’t work! In this department, Polaris added a set of Fox Podium 2.0 shocks. These shocks have plenty of height-pre-load adjustment as well as adjustment for compression damping.

Although the front suspension is greatly enhanced, it is the rear suspension that is the most visibly changed! Like many off-road racecars, the rear suspension now consists of a 3-point trailing arm system that provides 14 inches of travel.

The advantages of a trailing are system is multifold. First, it provides a more controlled travel and camber gain so that the tire will actually lean in at the top a bit as the travel goes up. That camber allows a longer movement with less scrub. Polaris still designed some camber in the system so that during hard cornering, the tire will lean in and keep from rolling over as much. In addition to better travel, the trailing arm set-up is also a much stronger system for off road use.

And, as on the front, the rear is equipped with long-travel Fox Podium 2.0 shocks with plenty of adjustment for preload and height and adjustment for the compression damping.

 Now for the other very big difference in the XP – the new engine! Designed from the ground up for this machine, the ProStar 900 is a work of art, looking more like something that should be in a racecar rather than a UTV. Oh wait, this is a racecar!

The 875cc twin cylinder DOHC engine now sits in a more conventional direction, with the cylinders and crankshaft running side-to-side rather than front to rear like in the other RZRs. And it’s built for performance, with the pair of 46mm throttle body injectors mounted right next to the cylinder with a very short intake manifold. Also helping to get plenty of air into the engine is a new intake system that pulls air in from the left side of the body and directly into an air box that in essence stores a mouthful of air ready for the engine to suck up when the throttle is mashed.

There’s also a new air filter that has 90%  more capacity than the old-style canister system. And it’s mounted in a box located under an easy-access panel right under the bed.

Polaris also designed a stainless steel exhaust for a freer-flowing path to extract the used air and fuel. All this helps the ProStar to produce a whopping 88hp from it’s 875cc’s.

But wait, there’s more! The ProStar is designed with a dry sump oil system. This allows the engine to sit lower and the oil to be held in a tank away from the heat of the engine’s block. It can also provide a larger oil capacity for better cooling as well. In this case, 3 ½ quarts are held in a finned plastic tank that located under an access panel on the left side of the bed. And that’s also where you check the oil level.

With an eye toward night duning and late-night racing in the desert, the engine is fitted with a large capacity stator that provides an incredible 500 watts at idle, and 750 watts at revs.

There’s also a new CVT transmission with a zero-clearance set-up and helical cut gears for faster takeoff and stronger, more reliable operation.

All of this sounds good but the prove will be in how it works. We’ll take it out for a test next.

These Are A Few Of My Favorite Things!

My Favorites Off-Roaders -

I’ve made no bones about the fact that I love the King Quad. I loved it from the first ride. It had everything I needed – 2wd, 4wd, and 4wd with a front locker. It had a great gauge package. But best of all it was smooth – the engine was incredibly smooth for a big single. And to help in the smoothness department the KQ had a higher ratio transmission that allowed the engine to turn at a lower rpm – something an old guy that liked to short-shift when cruising really appreciated! Of course it still had its Achilles heel, a far too steep of a front caster that caused some steering and handling problems – especially when fitted with better tires.

That caster and handling problem was all fixed with the addition of power steering – not so much as the EPS itself makes it handle better, but the powered steering made it possible for the Suzuki engineers to add in a proper amount of caster!

As the King Quad competitors improved, another feature of the KQ became more apparent – it didn’t have a parking brake in the transmission, but stuck with a simple parking brake on the handlebars. I like this set-up for a couple of reasons. First, when shifting into reverse you never have to try to keep from hitting park inadvertently. And second, sometimes when working or even stopping along the trail it’s easier to simply leave the machine in drive and set the parking brake to keep it from rolling while you reset the GPS, look at the map, or check a fencepost.

I’ve also had a long love affair with 2-seat ATVs. For years I struggled with which one I liked more, the Can Am Outlander 650 or the Sportsman Touring. Both had some advantages and some disadvantages. But with the introduction of the 2011 XP Touring I was able to make a decision. The new Touring with its ADC now goes down hills without trying to swap ends. It now allows me to quickly remove the second seat and have a stable single seat machine with plenty of rear rack space. And as a tourer, the Touring is without competition in the plush, comfortable department.

It’s so good that I can almost overlook the things I don’t like – a single brake lever, the park position in the transmission, and the 4wd system that keeps me from choosing what I want it to do.

But life is more than about handlebars. Being a guy that got his first car (a Meyers Manx of course) at 14, I’ve always had an affinity for holding a steering wheel. I longed for a side by side for years before they came out, even going so far as to be designing a side by side ‘buggy’ out of a Kawasaki Prairie.

So I was excited when Yamaha brought out the Rhino, but I fell in love when I saw the RZR for the first time. Like a lovesick teenager I can remember that first look even today – a great looking, powerful, and 50” wide machine! And I soon found out it was relatively quiet (as compared to the existing Rhino) and handled incredible!

And yes, I’m constantly driven crazy by some of the glaring problems I find with the RZR. Every machine needs a parking brake, something that used to be called an emergency brake because it was a separate ‘mechanical’ system that could be used to stop a vehicle if the primary braking system failed! It would be a tremendous comfort to have a lever to pull when heading down some fast, twisting trail in case a brake line gets ripped and you no longer have a brake fluid to operate the hydraulic system. I won’t even mention how good a nice lever at the right side of the seat is for helping set of a machine for tight corners ;-)

Then there’s the fact that the RZR still sends all of its engine braking to the rear wheels – something that can be extremely irritating on some of those steep, rocky trails I love to explore. That’s something that could be easily fixed with the addition of the ADC system like’s found on the Touring!

But even with those glaring problems the RZR does what no other side-by-side buggy can do – go on the 50” ATV trails. And do it in comfort and with the ability to carry enough camping equipment for the two passengers! So until something better comes along, the RZR is one of my favorite off road rigs. The proof of this can be found in the fact that there has been a RZR sitting in my garage every single day since they came out! The only other machines that can say that are the Suzuki King Quad and the Kawasaki Prairie!

But, my life is more than just riding for fun – living on 20 acres requires something for work – something to haul wood and hay, and tow the rough-cut mower. And living in a small town where things like this are still possible, it’s nice to have something to run to the Post Office, or to the small general store. We’ve used Kawasaki Mules for this for many, many years, with everything from Diesels to Crewcabs sitting here over the years.

It was only recently and as a fluke while at a Polaris new-model introduction that I got to use an electric UTV, the Ranger EV. You guessed it, I fell in love. While certainly not quiet the machine of choice for exploring the trails, thanks to the inability to actually carry any spare volts along in case you run out, it works perfectly around the farm or ranch. Quiet is good in many ways. You don’t upset animals, and in fact actually can here them while you drive by. Perhaps the most noticeable advantage I’ve found to the EV’s quiet operation is when towing stuff – especially something like the rough-cut mower. With no engine sound coming from the EV, you can now more easily hear if the mower is running okay or bogging down, or if you’re dragging it across the field with the blade stopped ;-)

But wait, there’s more! I have one more need. I need something to haul people around – more than just one! For this I need a crewcab something or another. I’ve tried the Mule Transcab. While it’s quiet and good for around the farm or town, it struggles horribly out on the trails. The RZR 4-seater is just too difficult for easy entrance and exit.  The Ranger is too big and wide, so big in fact you might as well be driving a Jeep around. But like Goldilocks I’ve found the crewcab that’s ‘just right’, the Ranger 500!

Yeah, it’s still long, but it’s pretty hard to have a good 4-seater without adding some un-wanted length. Where the 500 Crew shines is that it is narrow enough to fit on many of the trails and it has the suspension to get over them without beating all the passengers to death. And the 500cc EFI engine has adequate power to even climb up the mountain trails with a full load of people on board.

Now here’s where I say that like every Polaris, the crew is not without some glaring faults that if I were the Product Manager that I’d fix. There’s no parking brake what so ever! And, well, that’s it I think. Wow! I think I just amazed myself – I can only find one fault! I better go for a ride and make sure that’s right.

Don’t get me wrong now, there are a lot of good machines out there and something I like to point out to everyone that asks me which ATV is best for them. And maybe that’s exactly what I’ll talk about in the next blog. It’ll help me update the FAQ page on the website.

But for now, you know exactly what I beg the PR folks to allow me keep sitting outside my office ;-)

Just in case you wondered what a Meyers Manx was ;-)

God Bless -

Doug