Long Term Report - The Polaris RZR XP4 900 EPS

Lessons Learned with a Favorite Four Seater

Written By:

Wayne Davis

There is nothing like the joy of bringing home a new ATV or Side x Side and those first riding adventures together. The trails are always smoother, the riding is always better, and the sky is even a deeper blue on those first outings with your new, made in heaven (or Minnesota, Ohio, Nebraska or Georgia) relationship. Make no mistake, it is a relationship too, and like all relationships, it’s the ability to make it through the tough times that really is the measure of lasting value. Is your new baby just there for the good times at the start, or will it be there for the long haul?

It’s our job to let you know exactly what to expect from every vehicle we test before you hand the dealer a check. That means everything from fit and finish, to durability and reliability, to average maintenance tasks. To find the answers, we use our machines exactly like you do: for weekend rides, to work throughout the week, as hunting buddies, and for any other task we can come up with. One of the most popular models in the last few years has been the Polaris RZR XP4 900 EPS. After utilizing it for more than a year on the trail, here is what we’ve found.

Tale from the Trail

The Polaris RZR XP4 900 EPS was built on the best traits of the previous RZR 800 4-seater, but with a revised chassis, longer suspension, and an all-new motor. The new chassis was designed to be stronger, and to provide longer suspension travel than previous models, while the new ProStar engine brought more power to the game. There was no mistaking it for anything but a Polaris though. As part of their manufacturing efficiency program, Polaris likes to use common parts between models wherever and whenever possible. That meant a lot of existing 800 parts could be found on the new XP4 900 as well.

Polaris did solve a few problems with the XP4 900 and one of the most notable is the use of a better bearing on the driveshaft. It greatly reduced the vibration felt in the front end. However, like nearly all Polaris models, the rubber pivots on the suspension and shocks begin to squeak on cue as if under the domain of divine intervention. The hard way to eliminate the endless chirping is to take them apart and then grease each individually. The easier method is to hose them down with WD-40 or similar light duty penetrating oil and let it work its way into the pivot. Problem solved! Thankfully, our test model was equipped with limited edition Walker Evans Shocks and electronic power steering which, after minimal adjustment to the shocks, handled extremely well on the trails. It’s easy to ride all day under almost any condition unless the trails are extremely tight and twisty. We quickly found out that the harder you push it, the better it sticks to the trail. Chassis reliability was perfect. Engine reliability was another matter, however.

Engine Upgrade

We know the Polaris ProStar engine is a performer, and we’ve never experienced problems with one before. The trouble is, while the engine design is sound, the air intake tract on the XP4 900 can leave it vulnerable. Consider your air filter the first and the last line of defense when it comes to protecting your engine. We love the XP4’s airbox location; it’s easy to get to and service. The flat, pleated filter drops in easily, and like all filters, we were always extremely careful to make sure it was in the correct position. However, the large perimeter of the airbox has few outside fasteners, allowing the assembly to flex just enough that unfiltered air slips by the seal. We don’t believe this circumstance to be common with every XP4 900, but under the right conditions, and in the fine, almost powdery dust common to the trails in some areas, you can scour the inside of your engine and eat away the rings quickly. When that happens often enough, you’ll need to cozy up to your local dealer and beg for mercy during a rebuild. Here is the chronology of our problem:

First oil change as directed by manual.
Oil changes then made at intervals in manual.
Air filter servicing done with and between every oil. Suspension pivots lubricated and grease zerks serviced every couple hundred miles.
Oil consumption noticed at 1600 miles. At 2200 miles, rate of consumption was 1 pint every 125 miles
Engine rebuild at 2200 miles.
Belt also replaced at 2200 miles with Jagged-X kit. Old belt showed little wear, but changed as a precaution

Rebuilding the engine at 2200 miles is not something we would expect with every Polaris RZR XP4 900. We do consider it to be a strong warning about airbox sealing though. There are even several companies that produce an aftermarket seal for under $30 that takes up the gap, and we consider it very cheap insurance against future problems. If nothing else, at least run a bead of grease around each side of the outer edge of the filter to help prevent any possible leak.

Jagged-X Upgrade

As long as we were going to rebuild the engine, we also opted to install the Jagged-X performance kit. The kit consists of valve springs, camshaft, gaskets, primary clutch weights, clutch springs, an SLP dual exhaust and requires a computer reflash. Normally we favor bolt-on kits that we can install, and that most anyone with a garage and a few tools can do themselves. This is not that type of kit. With the reflash, you’re going to have to visit the dealer. Polaris claims a 6hp increase from the kit, and our seat-of-the-pants impression is that it delivers even more. Without a doubt, our improved XP4 900 runs better than before. It pulls harder from the bottom all the way to the top, and although top speed is unchanged, it will get there a lot quicker. The most noticeable area where you can feel the extra ponies though is in loose trail conditions where it never loses power and can accelerate at any speed. You’ll need 91 octane fuel for the higher compression, but overall mileage is unchanged and, if driven normally, is even slightly better.

Our XP4 900 Today

We’ve logged 3850 miles on our Polaris RZR XP4 900 EPS and it still performs great. We’re extremely careful with our oil and air filter changes, and we continue to grease and lube all suspension parts every couple hundred miles. Since then we’re not burning any oil, and the overall condition of the unit is excellent with very little signs of wear.

There have been many other models to follow in the Polaris RZR XP4 900’s tracks, some even from Polaris. After having tried everything else and knowing what the XP4 900 is capable of though, we can say it’s still a serious contender, especially when you consider with a few simple upgrades like the SLP exhaust, a Dalton clutch kit, and an air box seal, you’ll get top level performance without top level price.

Polaris RZR XP4 900 EPS Maintenance Record

Maintenance ScheduleAs outlined in manual or better.

Oil Used Stock Polaris Fully Synthetic as recommended by manual

Oil Filter LocationAdequate – easy to change.

Oil Filter Stock Polaris or K & N

Drain Plug Good access

Dip Stick Good access, easy to read

Air Filter Location Excellent access, easy to remove. HOWEVER, box does not seal consistently between filter and base /lid allowing air leaks and contaminants to pass through unfiltered. This resulted in a major engine rebuild for us.

Air Filter Used Stock Polaris, flat style pleated paper.

Coolant ResevoirExcellent access under front hood. Easy to check

Electrial & BatteryExcellent access - under seat

Engine & Drivetrain

Vavle/Head Appreciable loss of power and compression over time due to air filter seal problem, followed by immediate engine wear. Rebuilt at 2200 miles.

Cooling System No leaks. Maintains coolant level

Shaft Drive No joint failures or excessive backlash

CVT Clutch & Belt Minimal belt wear. Clutch still operating smoothly

4WD System No failures in 4wd system to front end

Rear DifferentialNo leaks or problems

EFI Mapping Excellent starts at all temperatures, no backfire, no hesitation under acceleration.

Engine NoiseNo noticeable increase in engine noise

ExhaustSlight discoloration and negligible corrosion on stainless steel system. Rubber muffler hanger grommet can work free of mounting hole. Donut shaped high temperature gasket between muffler tube begins to disintegrate over time, probably from muffler free play.

Battery Battery still holding charge and cranking cold engine quickly and easily, even at temperatures of 20 degrees F.

Shifting No noticeable change since new

Bodywork & Controls

Digital InstrumentationEasy to read, and easy to use

Levers / Throttle / Switches / Shifter High Quality controls. Throttle has good feel and throw. 4wd button easy to use on dash. Shift lever has positive engagement. Key is easy to reach but out of way.

Seat Cover & FoamAdequate for most riding, although thicker foam and side bolsters that wrap around occupants would be appreciated for aggressive driving. Foam did not break down or take on moisture.

Bodywork Excellent, high quality plastic is pliable and durable. Resists scratches and can take an impact.

Splash ProtectionGood protection from both front and rear fenders. Foot wells drain quickly. Plastic flooring can be penetrated by sticks along trail however.

LightsGood illumination and spread from both front lights which point to where vehicle is headed, but not necessarily into turns.

Suspension

ShocksSoft in stock setting. Good on most trail bumps but front will bottom out, causing rear end to hop. Increase front compression by 1 click. Does have slight body roll.

A-Arms Good durability but pivot bushings squeak when dry. Lube with WD-40 or similar

SteeringVery good in standard model. Excellent and smooth with EPS. (Electronic Power Steering) Calibration of EPS excellent at all speeds

Tires Resistant to cuts but edges wear off rapidly. Stock tires clean out well with acceptable traction in sand, snow or mud.

WheelsTough,cast aluminum. No problems.

Brakes Very good. Excellent, controlled stops at all times.

Chassis

FrameFrame has some flex, but does not beat up riders by being too stiff.

FastenersHigh quality, zinc plated metric. Some use of plastic push-pin fasteners which will become loose after a few in/out cycles.

Paint & Plating Good corrosion protection on frame thanks to powder coat. A-arms and trailing arms tend to show wear first but this is impossible to avoid. Zinc plating on all fasteners and some steel parts

Storage Durable rear cargo deck with integrated tie-down points.