2001 Diamante Fuel Consumption, A/C Settings, Alarm, Headlight Intensity and More

[john_chicago]

Fuel consumption of a 2002 Diamante with 57,000 miles has doubled. Most miles are from highway use and vehicle condition and maintenance is excellent.

Fuel efficiency was at about 38 miles per gallon at 2100 RPM which yields about 50 miles per hour. A general result was about 120 miles for every quarter tank or 4.5 gallons when 80% highway and 20% city operation occured. Engine RPMs are normal and there is no engine labor but something seems to be causing the engine to consume more fuel. I have not detected any leaks when the vehicle is stationary.

There seems to be some oil consumption of 10w-40 oil. Dipstick always read full--even to the day of the oil change. Now it is at midmark and I am concerned since the engine is always operated at low RPMs of about 1900. the Diamante engine is a low RPM engine providing torque early and maximum power at only 5000 RPM. As a side note, being a 3.5 liter engine, it should be capable of producing more power at higher RPMs as other engines do. The Infinity 3.5 liter engine yields about 280 HP at 7000 RPM. The Diamante's about 210 at 5000. This engine has capacity for more speed and work.

When selecting HVAC settings of dash vents and floor vents circulation, there is no flow from the floor vents. Is this normal in this setting? Dedicated floor vent flow is good along with all the other settings and combinations. Perhaps there is a compromise when two vents are selected, but not receiving air from the floorwell vents does not seem right.

Alarm tends to activate---horn and lights engaging---suddenly. A few times over the years the alarm erroneously activated when inserting the trunk key into the trunk lock as if the system did not recognise the key. Any thoughts?

Headlight illumination seems to be dim and shallow since the car was new. Is this a problem or just a design issue inherent in Diamantes?

At 57,000 miles, the transmission fluid has not been replaced and would like to replace it at 60,000 miles. Is it a problem to drain the transmission fluid only by opening the drain plug and not removing the pan? Will all the fluid be removed? Is there a filter in this transmission? Also, will this type of transmission have an issue with this procedure being done?

Is there a way to prevent the power antenna from extending to save wear on the mechanism since there is an additional diversity antenna imbedded in the rear window and since the mechanical antenna might still receive enough signal even while retracted.

Thanks for your help about this lengthy post.

[lileisme21]

Hey, I saw that you seem to be having the same problems that I am having. I have been doing ok with gas mileage for a year and a half that I've own the car. I have a 2001 Mitsubishi Diamante LS by the way. But the past 6 months, my gas gauge will be at say a quarter of a tank when I pull into the drive, but as soon as I start it up again the next day or something it will only go up to the line before the quarter of a tank line and seems to go down more and more with each time I start the car waaaaay more than it should be doing. I'm not sure what is happening. I don't have a leak and I know gas gauges usually don't go down showing how much gas you've used unless you've driven for a long time, such as a long road trip, or when you restart the car, but this just doesn't seem right. Also, my headlights dim after I start the car and when I push the gas pedal they brighten up until the RPMs go back down and they dim again. I thought it was my battery, but it seems to be in working order with no problems. So, I'm not sure if this is a defect with the diamantes after a certain amount of time, but it's starting to cost me A LOT at the gas station. I've had to put 10 bucks in my tank every single day. And I don't drive but 20 miles a day IF that... and 10 bucks at this time gets me 4 gallons. So, I'm getting about 4 mpg. I'm not quite sure when you posted this, I didn't get a chance to look, but I was wondering if you had discovered a resolution because I REALLY need one. My car runs great and I haven't had any problems with it ::Knock on wood::. I just would like to get this resolved and start saving some money. So, if you have any advice you could get me I'd really really appreciate it. Thanks. My email is lileisme21. I HOPE that you can help me. Thanks again.
Eric - Illinois

[lileisme21]

Hey, I drive a 2001 Mitsubishi Diamante LS and I saw that you were having the same problems and me. My car had great gas mileage for a year and a half after I bought the car, but the past 6 months, it's been using a LOT of gas. I know a car's gauge usually doesn't go down unless you've gone on a long road trip or when you restart the car, but something just doesn't seem right because from how much I drive in comparison to how much it goes down just doesn't match up. I have been having to put 10 bucks in my tank everyday and I dont' drive but 20 miles a day, IF that. And 10 bucks here these days gets me about 4 gallons, so that's saying I'm getting mpgs. That just really doesn't seem right to me. Also, with the headlights. They will brighten up when I start the car, but as soon as the RPMs go down they dim. When I push the gas pedal they will brighten up and dim as the RPMs go down. I thought it might be the battery, but that's in working order with no problems. I'm not sure when you posted this, I forgot to check it, but if you've discoved a resolution sincek I'd REALLY REALLY appreciated some insight. I'd like to start saving some money at the gas pump. My car's been great to me with no problems ::Knock on wood::. So, I'm not sure if these are defects that this certain car has after a while or not. So, if you could help me out, I'd really appreciate it. Thanks... My email is [email protected].
Eric - Illinois

[john_chicago]

Hi Eric,

The dimming headlights might be caused a partially malfunctioning alternator. The lights in my 2001 Diamante appear to be dim, to me, since I bought the car new and I find the same problem of illumination with a 1997 Honda Accord, 4 cylinder, non-Vtech engine. I think I was just accustomed to the the better positioned headlights on my 1990 VW Fox which I still drive and feel it offers better illumination than the Diamante and Accord. But I think your headlight issues might be related to an electrical output problem from the alternator. But I think that a Diamante's properly operating headlight system is inherently inferior to that of other vehicles. I often use the Diamante's high beams to have the similar illumination field that is available with my 2004 Honda S2000's low beams. But no front lighting combination from the Diamante will equal the natural brightness of the S2000's High Intensity Discharge, HID, headlamps. But I still feel that even simple halogen headlights that are properly positioned are very comparable to the more expensive HID and Xenon lighting systems.

Recently, lower fuel consumption has been elusive on my Diamante. I have been noticing about 10 miles to the gallon during daily city driving of about 3.5 miles each trip, 4 trips a day and about 6-7 start-ups a day along with one 15 minute idle time to achieve proper engine temperature in near zero degree Fahrenheit temperatures.

Past city driving results were at about 20 MPG. But the car has achieved 38-40 MPG at 2100 RPM, 50 MPH. The Diamante has a a low RPM engine with early torgue. If the transmission had a 5th or 6th or even 7th or 8th final gear type ratio, economy would be incredible. Any engine turning less frequently consumes less of everything: fuel, oil, material, life.

Your fuel consumption at 4 MPG is extreme and a tune-up might be needed. I started noticing MPG decreases at about 55,000 miles and now I have 62,000 with the original spark plugs, wires, cap and rotor. But to achieve the optimal fuel economy, the Diamante's engine must be gently accelerated and not allowed to surpass 2500 RPM. It is difficult and tedious, but possible. The engine must do the lowest amount of work for the highest fuel efficiency. The lower the RPMs the higher the fuel economy.

You might want to measure fuel performance by the odometer and not the fuel gauge since some gauges are inaccurately calibrated making the problem appear to be elsewhere when it is only an instrumentation problem. Also, the curved shape of the tank will cause the fuel sending unit floater measuring device that measures fuel inside the tank to move more rapidly after it passes the top 1/4 portion of the tank. It is just a phenonmenon of geometry and mechanics and not a problem elsewhere. But the gauge should be calibrated to compensate for this, but since it is a mechanical gauge, it is not as reliable as a digital system that uses mechanical parts and computer information to make an estimate about fuel availability.

The Diamante's tank holds about 19 gallons of fuel and at 4 MPG a 76 mile range is near the limit. But there must be something else going on. The Diamante is a 400 miles plus car. I have traveled 185 miles for every quarter tank of fuel with the engine operating no more than 2100 RPM. Still it is impressive for 3.5 liter displacement engine.

How many miles does you car have?

Let us know what is happening and if you have any questions. The Diamante is a gorgeous and very advanced vehicle. It is underrated and unknown.