PT Masthead

 

PT DIY Guide to Improved Fuel Economy

 

September 2005

I began work on this guide a few weeks ago. Little did I know how much life would change after Hurricane Katrina visited the Gulf Coast last week. The loss of life is unprecedented, as is the extent of the damage. Historically hurricanes have had little economic impact except for the area that is directly impacted. However, unlike prior Hurricanes Katrina is and will have lasting effects on the U.S. economy. The most significant national economic fallout is due to Katrina's impact on key energy assets along the Gulf Coast. An amazing 30% of the nation's oil supplies flow through Louisiana. The Gulf Coast is the source of about 10% of the nation's refining capacity, so gasoline prices have soared. Some analyst's project average pump prices to be $3 per gallon or more during the upcoming Labor Day weekend and to rise a bit more in the fall. Crude prices have also spiked and appear poised to go higher since production in the Gulf is shut in and this represents 25% of domestic capacity.

With gas prices breaking all previously held records in many areas of the country there are a few things each PT owner can do to help ensure that they are obtaining optimal fuel economy with their vehicles.

If you think gasoline is expensive here in the U.S. check out this MSNBC article (PDF) which discusses how much gasoline costs in other countries.

The majority of owners who write to us at PTDoItYourself.net report that they purchased their PT primarily because of the unique look of the vehicle, not for the fuel economy. Of course, as recently as a year or two ago, gasoline was reasonably priced, which made the PT's mediocre mpg numbers somewhat disappointing, but still palatable for most owners. However, what was acceptable then is no longer acceptable today. We need a plan to improve our fuel economy and or reduce our fuel costs, so that our 15 gallon $45 fill-up goes as far as possible when were out on the highway.

Not sure what your mpg is, or how much you spend annually on fuel? Click here before reading any further.

We're anxious to hear about your mpg results once you've implemented some of the recommendations provided below. Please use this form to report results, or review the latest feedback reported by owners here.

Fuel economy is affected by a number of factors, some of which we have little control over and others we can change or improve upon. The biggest factor is the vehicle we choose to drive and its fuel economy characteristics. We can't do much about that, other than exchanging the PT for a vehicle with better fuel economy, so let's try to focus on ways to maximize our fuel economy with the PT.

One fuel saving approach that each driver can apply is to modify their driving habits. Here are some commonsense tips to consider and implement during your daily commute:


Always keep safety in mind when experimenting with new driving habits, not to impede traffic, etc.

 

Other Fuel Saving Tips

 

Aerodynamics

 

Cash Back Gas Credit Card

 

Excessive Idling

 

Extra Cargo

 

Fuel and Octane

 

Terrain and Weather Conditions

 

Towing


 

Mechanical Condition of Vehicle

The mechanical condition of a vehicle plays ones of the most significant roles in determining fuel economy. If you've owned your PT for awhile and followed the factory recommended maintenance schedule you're probably in pretty good shape, but your diligence places you in a small select group of owners.

Unfortunately, many owners perform little or no maintenance until a problem arises, at which point the cost of the repair and daily operational cost of the vehicle far exceeds the amount of money they would have spent on periodic maintenance. Under inflated tires, vacuum leaks, faulty thermostats, worn spark plugs, malfunctioning engine controls, poor wheel alignment and transmission issues are among the conditions that cost consumers millions of dollars in wasted fuel on a daily basis.

The following are some of the diagnostic checks that a technician will typically conduct for poor fuel economy:


Let's look at a few things we can do, check or repair ourselves (DIY), or economically have serviced by an auto professional to improve MPG on our PT's.

 

A/C System

 

Engine Cooling System

 

PCV Valve and Engine Air Filter

 

EGR Valve

 

Oxygen Sensors

 

Spark Plugs

 

Oil, Viscosity & Filters

    Dirty oil reduces mpg by one mile per gallon and hastens engine wear. As engines wear, they loose compression, and then efficiency. Changing the oil at regular intervals reduces engine wear on internal engine components and can increase fuel economy.

    The correct oil filter can influence a vehicle's mpg. Clogged, incorrectly applied, or substandard quality oil filters can reduce mpg. It is important that oil filters are changed at regular intervals and meet manufacturer's specifications to protect vital engine parts and optimize oil pump performance.

    We recommend that you change the oil and filter change every 3,000 miles to prolong engine life and improve mpg.

    Oil & Filter Service Maintenance Schedule

    Schedule

    Mileage

    B – All Engines

    Every 3,000 miles.

    "Viscosity" refers to how easily oil pours at a specified temperature. Thinner oils have a water-like consistency and pour more easily at low temperatures than heavier, thicker oils that have a more honey-like consistency. Thin is good for easier cold weather starting and reducing friction, while thick is better for maintaining film strength and oil pressure at high temperatures and loads.

    Most modern motor oils are formulated from various grades of oil so the oil will have the best characteristics of both thick and thin viscosity oils. Multi-viscosity oils flow well at low temperature for easier starting yet retain enough thickness and film strength at high temperature to provide adequate film strength and lubrication.

    As a rule, overhead cam engines (OHC) typically require thinner oils such as 5W-30 or 5W-20 to speed lubrication of the overhead cam(s) and valve-train when the engine is first started.

    Most vehicle manufacturers today specify 5W-30 or 10W-30 motor oil for year-round driving. Some also specify 5W-20. Always refer to the vehicle owners' manual for specific oil viscosity recommendations, or markings on the oil filler cap or dipstick.

    An SAE viscosity grade is used to specify the viscosity of engine oil. With the PT's double overhead cam (DOHC) engine, only use oils with multiple viscosities such as 5W-30 or 10W-30. These are specified with a dual SAE viscosity grade which indicates the cold-to-hot temperature viscosity range. When possible and appropriate for your area of the country and driving conditions use 5W/30, instead of 10W/30 oil. 5W/30 oil is thinner and will improve your mpg by 1-2%. Look for motor oil that says "Energy Conserving" on the American Petroleum Institute (API) performance symbol to be sure it contains friction-reducing additives to reduce internal engine friction.

    Synthetic oils are oils that are refined to a much higher degree than ordinary oils and generally have greater viscosity stability, lower pour points and can withstand higher operating temperatures. Synthetic oils are advertised to improve cold starting, reduce friction, reduce oil consumption and improve fuel economy and performance, but they typically cost about three times as much as regular motor oil. They are especially good for turbocharged and high output engines, but are not recommended for breaking-in newly rebuilt engines. For maximum protection users should stick to their normal oil and filter change service intervals when using synthetic oils. A number of PT owners report using synthetic oils in their Cruisers and their comments are very favorable towards these products.

    Review the oil and filter replacement guide for additional information. The guide also includes a list of recommended aftermarket oil filters and procedure tips.

    Pit Area Resources

    Oil & Filter Guide
    Oil Pan Guide

 

Tire Pressure, Balancing and Alignment

    According the USDE, every pound per square inch (psi) of under-inflation on all vehicles in the U.S. wastes nearly 4 million gallons of gasoline a year. Under inflated tires increase road-resistance, which can reduce mpg by 5% for every 8 pounds a tire, is under inflated. For every 10% that a tire is deflated tire wear increases 10%.

    Underinflation also makes a tire run hot. Increased flexing of the sidewall increases the temperature of the tire, which in turn increases the risk of a tire failure and blowout. They also break traction more easily than one which is properly inflated, which can cause skidding during braking or hard cornering, or wheel spin when accelerating.

    When inflating a warm tire add about 4-5psi to the recommended tire pressure and verify the pressure when the tire is cold. When checking a cold tire, follow the recommended tire pressure posted on the Tire Inflation Pressure Label provided with the vehicle (usually on the rear face jamb of the driver's door). Cold inflation pressure is obtained after the vehicle has not been operated for at least 3 hours, or the vehicle is driven less than one mile after being inoperative for 3 hours. Weather conditions also affect air pressure in a tire; it increases in warm weather and decreases in cold weather, 1-2 pounds for every 10 degrees of temperature change.

    The domestic PT Cruiser utilizes 34psi per OE tire and the GT (Turbo) 38psi per OE tire. A quality air pressure gauge is recommended to check tire air pressure. Tire pressure should be checked cold once per month and more frequently when the weather temperature varies widely. After checking the air pressure, replace valve cap finger tight.

    Have your tires properly balanced and keep the vehicle "in alignment" to obtain the best mpg. As tires roll a certain amount of drag occurs. Due to alignment geometry, a front wheel drive vehicle's (PT) tires tend to move in an inward fashion as the vehicle moves forward. As the tires move in this inward fashion, tires experience greater amounts of drag and resistance, which accelerate tire wear and decrease mpg. If the wheels are as little as a 1/4" out of alignment, mpg is further reduced by another 2%. To counteract these effects, alignment geometry is statically adjusted toe-in or toe-out so that the vehicles tires roll in a straight, non-scuffing, and least resistant manner. If a tire is unbalanced, the unbalanced dynamic forces cause the tire to run eccentrically. This eccentric movement causes reduced tire traction. The loss of traction results in a power loss, thus mpg is reduced. Additionally, unbalanced tires accelerate tire wear.

    Driving with the parking brake not fully released can cost a mile or two per gallon on a car that normally delivers 20 miles per gallon.

    Review the guides below for additional information.

    Pit Area Resources

    Tire System Guide
    Tire & Wheel Diagnostic
    Tire-Pull Diagnostic
    General Tire Information
    Top 10 Issues List

 

Transaxle – Auomatic & Manual

    The transmission is probably the most neglected component on vehicles today, which is surprising given the cost for repair or replacement.

    Heat is the number one cause of failures in transmissions. The transmission oil is critical for lubricating the transmission and reducing friction. When the fluid breaks down and loses its viscosity, it no longer effectively lubricates the transmission. This causes premature and excessive wear and results in transmission failure.

    Transmission fluid is designed to last many thousands of miles under normal conditions. However, one of the most important factors affecting the life of the fluid and the transmission is the temperature of the fluid. Overheated fluid forms sludge and particles of carbon that can block the minute passages and lines that circulate the fluid throughout the transmission. This causes the transmission to overheat even more and will lead to eventual failure of the transmission.

    Some cars come from the factory with coolers that help with the temperature. The transmission oil flows through the cooler as air flows across the cooler to lower the temperature of the transmission fluid. The PT's automatic transmission oil cooler consists of an internal oil-to-coolant type, mounted in the radiator lower tank, and an external air-to-oil type, mounted in front of the radiator. Rubber hoses connect the oil coolers to the automatic transmission.

    Anything that puts a load on the engine can cause the transmission to heat up and speed the deterioration of the fluid. Towing a trailer, idling in traffic and climbing long hills is all hard on a transmission. The graph illustrates just how much transmission temperature affects the life of transmission components. Fluid that lasts 50,000 miles at a temperature of 220°F, will only last half that long if the temperature is consistently 20° higher.

    Maintenance schedule B recommends changing the automatic transaxle fluid/filter each 48,000 miles, and manual transmission fluid at the same intervals. Under maintenance schedule A there is no maintenance recommended for either transaxle. We agree with other transmission experts who recommend changing the fluid and filter every two to three years or 30,000 miles, or once a year or every 15,000 miles if a vehicle is used for towing or other severe service use.

    Transaxle Fluid & Filter Service Maintenance Schedule

    Our Schedule

    Interval/Mileage

    All Engines - Normal Service

    Every 2-3 years or 30,000 miles.

    All Engines - Heavy Service *

    Once a year or every 15,000 miles.

    * Used for towing or other severe service use.

    Check the transmission fluid level and condition every 6,000 miles or 6 months, which ever interval arrives first. Under extreme usage, or if a problem exists, the fluid should be checked at shorter intervals

    Thumbnail

    On the manual transaxle PT check the fluid level by removing the fill plug. The fluid level should be between the bottom of the fill hole and a point not more than 3/16" below the bottom of the hole. Add fluid, if necessary, to maintain the proper level.

    To properly check the automatic transaxle fluid level on the PT the following procedure must be used:

    1. The vehicle must be on a level surface.


    2. Start the engine and curb idle for a minimum of 60 seconds.


    3. Fully apply parking brake.


    4. Place the gear selector momentarily in each gear position ending with the lever in (P) Park.


    5. Remove the dipstick and determine if the fluid is hot or warm. Hot fluid is approximately 180F which is the normal operating temperature after the vehicle has been driven for 15 miles. The fluid can not be comfortably held between the fingertips. Warm is when the fluid is between 85-125F.


    6. Wipe the dipstick clean and reinsert until seated. Remove the dipstick again and note the reading.

    A. If the fluid is hot, the reading should be in the cross hatched area market HOT between the upper two holes in the dipstick.

    B. If the fluid is warm, the fluid level should be between the lower two holes, into the area marked WARM.

    C. If the fluid level shows low, add sufficient transmission fluid to bring to the proper level. Do not overfill.

    Low fluid is the primary cause of transmission problems.  On the automatic transaxle operation with an improper fluid level (too much or too little) will greatly reduce the life of the transaxle and of the fluid. If the fluid level is consistently low, suspect a leak. One way to locate a leak is to slip a piece of clean newspaper under the vehicle overnight, but this is not always an accurate indication, since some leaks will occur only when the transmission is operating.

    Other leaks can be located by driving the vehicle. Wipe the underside of the transmission clean and drive the vehicle for several miles to bring the fluid temperature to normal. Stop the vehicle, shut off the engine and look for leakage. Keep in mind that the source of the leak may or may not be where the fluid is located. Airflow around the transmission while the vehicle is moving may carry the fluid to some other point.

    When adding or replacing fluid it is critical to the performance of transaxle that you use the correct type. Only transmission fluid of the type labeled Mopar ATF+4 (Automatic Transmission Fluid–Type 9602) should be used in the 41TE automatic transaxle and G288 (GT Turbo) manual transaxle. Use of improper or substitute fluids can cause shift problems, torque converter shudder and/or transaxle failure.

    Two types of fluid are available in T350 manual transaxle equipped PT models, dependent upon where the vehicle was manufactured. Always add or replace fluid removed or lost with the fluid the transaxle was originally built with (Mopar Transaxle Lubricant Type MS 9417 or ATF+4 Automatic Transmission Fluid Type 9602). Do not mix fluid types. Use of improper or substitute fluids can cause shift problems, torque converter shudder and/or transaxle failure.

    Along with fluid level, it is important to check the condition of the fluid. Mopar ATF+4 (Automatic Transmission Fluid) when new is red in color. The ATF is dyed red so it can be identified from other fluids used in the vehicle such as engine oil or antifreeze. The red color is not permanent and is not an indicator of fluid condition. As the vehicle is driven, the ATF will begin to look darker in color and may eventually become brown, which is normal. ATF+4 has a unique odor that may change with age. Consequently, odor and color cannot be used to indicate the fluid condition or the need for a fluid change. A dark brown / black fluid accompanied by burn odor and or deterioration in shift quality may indicate fluid deterioration. When the fluid smells burned, and is contaminated with metal or friction material particles, a complete transaxle recondition is probably required. The transaxle should be inspected by a qualified technician to locate the cause of the burnt fluid.

    Vehicles with a manual transmission are a little more fuel-efficient than vehicles with automatic transmissions. A PT with an automatic transmission will average 5-11% poorer mpg than a PT with a manual transmission that is used correctly. A slipping automatic transmission will loose another mile per gallon

    All automatic transmissions use a torque converter to couple the engine and transmission. Torque converters are not 100% efficient. Some energy is lost between the input (the impeller) and the output (the turbine) sections. Internally, torque converters use a one-way clutch device to multiply engine torque at low engine rpm's.

    This action aids in an automatic transmission vehicle's acceleration capacity. Once turbine speed is approximately 90% of impeller speed, the one-way clutch race spins on its own axis. At this point, the converter is said to be "coupled hydraulically." Under these conditions, up to 10% of the engine's output power could be lost to the torque converter's internal slippage. This accounts for most of the mpg difference between a standard and automatic transmission vehicle. This energy loss is transmitted to the vehicle's radiator and shed as heat.

    Torque converters developed in the mid 70's had a "lockup" feature added to reduce this energy loss and improve mpg. The PT utilizes a lockup Torque Converter Clutch (TCC) which is described as a standard torque converter. The impeller and turbine rotate at about the same speed and the stator is freewheeling, providing no torque multiplication. By applying the turbine's piston to the front cover's friction material, a total converter engagement can be obtained. The result of this engagement is a direct 1:1 mechanical link between the engine and the transmission.  The engagement and disengagement of the TCC are automatic and controlled by the Powertrain Control Module. The engagement cannot be activated in the lower gears because it eliminates the torque multiplication effect of the torque converter necessary for acceleration. Inputs that determine clutch engagement are: coolant temperature, vehicle speed and throttle position. The torque converter clutch is engaged by the clutch solenoid on the valve body.

    The PT's TCC clutch will not engage until approximately 35mph and after the shift into third gear. Other factors may prevent a converter from locking up.

    Besides the vehicle speed sensor indicator, a converter may not lockup for any of the following reasons:

    1. Engine temperature too cold - most converters will not lockup until the coolant reaches about 120°F.


    2. Overdrive unit locked out - when an automatic overdrive is "locked-out" the torque converter lockup feature will also be locked out. Overdrive lockout would normally only be used when pulling heavy loads, thus the converter is logically "locked out."


    3. Under low engine vacuum, heavy part-throttle acceleration is an additional power demand which could result in the engine lugging. To prevent engine lugging, which could result in serious engine damage, a sensor determines if low manifold vacuum exists.

    Typical lockup converters connect these sensors in a series creating a "string" arrangement. That is, if one sensor gives a "no" signal then the converter will not lockup. Therefore, for most converters to lockup, the following must be present:

    1. Coolant must be at or above minimum temperature.


    2. Transmission selector must be in "O" or "OD" overdrive if an overdrive vehicle.


    3. Vehicle must be at or above minimum 35mph lockup speed.


    4. Transmission must have shifted into the third gear.

    A converter may fail internally, which will reduce mpg and affect vehicle performance. If the one-way torque converter clutch slips, then the vehicle will characteristically have very poor acceleration. Mpg will be significantly reduced since engine torque is not being multiplied during acceleration. A vehicle with a slipping one-way torque converter clutch will experience a 20 to 30% decrease in fuel economy.

    A one-way torque converter clutch that does not release is a second type of torque converter failure. Vehicles with a non releasing one way clutch will accelerate normally but at a decreased top speed. The failure results in a 30 to 50% reduction in mpg. Top cruising speeds are lowered to 40 or 50 mph. The transmission may shift normally even when the one-way torque converter clutch slips or fails to release properly!

    Lockup torque converters may exhibit additional fuel-eating malfunctions. Sensors for temperature, speed, selector position, and engine vacuum may fail. Internally, the lockup device itself could fail or wear out. Whatever the malfunction, mpg will be decreased.

    Technicians usually hear the complaints of "poor performance" and "low mpg" and need to be able to identify a malfunctioning torque converter or a lockup torque converter that fails to lockup.

    Review the guides below for additional information.

    Pit Area Resources

    41TE Automatic Transaxle System Guide
    T350 Manual Transaxle Guide
    G288 Getrag Manual Transaxle Guide
    General Transaxle Diagnostic Guide

 

Fuel Injection System

The PT's 2.4L engine utilizes a sequential Multi-Port Electronic Fuel Injection system. The MPI system is computer regulated and provides precise air/fuel ratios for all driving conditions. MPI systems generally offer smoother performance, more power and improved fuel economy when compared with other fuel injection systems such as TBI (Throttle Body Injection) technology.

Over time, a buildup of fuel deposits can cause partial blockage of the fuel injectors. The injectors need to be cleaned, if an engine is experiencing any of the classic symptoms of dirty injectors, such as lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power, poor fuel economy, and higher hydrocarbon and carbon monoxide emissions.

Review the guides below for additional information.

Resource

Fuel Injection System Servicing

 

Gas Saving Devices

We have discussed a number of practical steps each consumer can take to increase their MPG. However, inevitably, as gas prices spike we often see an increase in new “gas saving devices” advertised on the internet and in print magazines. Most of these companies promise to increase our fuel efficiency by simply installing their nominally priced devices on our vehicles. The Federal Trade Commission and other groups have tested many of these devices and warn consumers to be wary of any gas-saving claims for automotive devices or oil and gas additives. Even for the few gas-saving products that have been found to work, the savings have been small.

Review the articles below for additional information on gas saving devices.

Resource

FTC - "Gas-Saving" Products: Fact or Fuelishness?
Consumer Reports - Gas savers: Do they really help?
FTC - Bogus Fuel-Saving Device Sellers Settle FTC Charges
Wikipedia - Fuel Saving Devices
Popular Mechanics - Looking For A Miracle
ABC News - Tips To Save At The Pump ((PDF)
Fuel-Saving Devices Not Worth The Money
ABC News - Can A Pill Reduce Your Gas Costs?
Fuel-Saving Devices Put To The Test

 

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