Geo Metro New Owner's Guide

So I've been wanting to post this online for awhile. It's something I constantly get asked, and I'll probably continue to refine this post into the future as I think of things. Much of what I'm about to say is valid for many cars, but I get a lot of people wanting to know about my Geo Metro which typically gets between 40-50 MPG. I've owned my 1996 3 cylinder Geo Metro Hatchback for about two years, and have come to realize the main difference between many people who own these cars and get good gas mileage, and those who don't, come down to some minor tuning issues, that often are a result of geography (e.g. hotter air in the south, California emissions, etc.). By following the next few guidelines to minimize these difference, almost any Metro can obtain between 40-55 MPG depending on engine condition.

(ALMOST) FREE STUFF (Modifications): 
1- Tire inflation. - Typically most people fill their tires to 35 PSI. Generally that's the recommendation on most vehicle door labels, including the Metro, but some databases show as low as 33 PSI (Discount Tires for one). At that inflation, the car feels like it crawls. I've experienced no negatives to inflating the tires to the maximum rated side-wall pressure of 44 PSI. This vehicle is light, and should never exert enough force to damage the tire at 44 PSI (do not do this to heavier vehicles). In addition some of my Metro peers run 50-55 PSI, though I like to leave a margin of safety. Most vehicles when transported from Japan arrive at the factory with over-inflated (60 PSI) tires to combat flat-spots from sitting up on the barges. MPG increases of anywhere from 3-5 MPG occur generally simply by inflating your tires. This is also my practice when renting sub-compact cars too. If the ride is too harsh, or you live in a pot-hole infested environment you may wish to try a compromise of 40 PSI.

RULE: Set tires at 44 PSI

2- Timing - Timing is everything, and the original Suzuki G10 (The motor inside the Metro) was designed originally to run at 10 degrees. Things change though, including national emission standards, and computerized spark curves (later versions of Metro's list 5 degrees of timing advance +-3, resulting in a possible OE-spec timing of 8). One of the easiest ways for a manufacturer to adjust emissions is by lowering the timing. While this mod is free, I recommend a cooler thermostat (180 F) and adding the CTS mod which I'll post below (a simple resistor). The perfect timing for MPG and performance, after many attempts by multiple people is 12 degrees. If you experience pinging, you may find a 10 degree setting more optimal (for instance if you live is extremely warm climate). Be sure to set it back to 5 at inspection time.

RULE: Ignition timing at 12 degrees.

3- IAT and CTS mods - Metros work with a very strange ECU that seems almost counter-intuitive to other vehicles. The vehicle obtains its best MPG in temperatures exceeding 90 F. Fortunately this can be faked without any compromises in drivability by placing a 2.2K ohm resister in parallel with the IAT (Intake Air Temperature) sensor. Before this mod was invented, many people unhooked their air-intake hose to draw in hot-engine-air, however this method has some severe safety, and engine performance issues and for that reason is no longer recommended. 

There's some confusion over installing these resistor, and certain people have suggested they don't understand what a parallel circuit means, making the modification more difficult than it is for those without minimal electronics comprehension. Parallel simply means one lead (side) of each resistor is connected to one wire (+, and -) of the leads that go to the sensor. For instance, in the case of the IAT, I simple solder on wire to each lead of the resistor then use blue in-line crimp connectors on the sensors two wires to create a parallel connection.

The end result is the car thinks it's warmer than it is. Fuel ratio is still kept in check by the 02 sensor, but it allows us to reach alternate fuel tables for better MPG.

IThe IAT will read between low 100 F to 130 F + (dynamically), and appears to have no detrimental effects based on numerous testers who have tried this mod. Its important to point out that the Ignition retard in our cars has been disabled from the factory which makes this modification very unlike how, and why other vehicle brands utilize this mod.

RULE: 2.2 K Ohm (1/2 watt) resistor in parallel on IAT sensor

Hat-tip to mjspiess, and Geo Glenn of Geo Metro Forum for their aid in this modification.

4- 180 F Thermostat - The middle cylinder on these vehicles tends to suffer from more heat related problems than the two outer cylinders. In addition, rubber seals, oil, and performance are all degraded by heat. More horsepower by a colder intake charge aid in performance. However the most important reason to decrease engine temperature is because of advancing the ignition timing. The two work together to vastly improve MPG, without knock, and being able to use 87 octane fuel.

RULE: 180 F Thermostat

5- Brake Calipers - Metros suffer from brake caliper failure (and/or

sometimes the hoses). Typically you won't even notice it, but it will suck MPG very slowly from you as they begin to fail, and the calipers only partially disengage, leaving them partially pressed against the discs. Symptoms may include above-average brake-dust on the wheels, pulling to one-side while driving or braking, or un-even tire wear. In my case, I have one disc that has glazed (rippled), with severe brake dust and poor tire wear despite two alignments. If it's the hoses, they will show no physical signs of failure generally themselves. Calipers and brake hoses life-span is about 15 years, meaning most Metros are now due for these. Hoses can be purchased as little as $7.50 a piece, Calipers about $40, and ensure proper operating brakes. It's typical to still get 40+ MPG with bad brake hoses, but replacement may improve gas mileage even more, if indeed they're failing acutely or intermittently while driving. Replace both at the same time if you suspect any of the above symptoms.

RULE: Replace brake calipers, hoses (and wheel cylinders) if more than 15 years.

6- Transmission Fluid - It's important to realize that regular maintenance issues such as changing the oil, and filters can have a huge effect on the longevity and performance of your vehicle, but often people forget about their transmission fluid, especially in a manual transmission. Metros tend to suffer from bad synchros in second gear, and failure in fifth. Both can be improved upon, even in a semi-failed state (if they have completely failed, it's unlikely to improve it). A factory bulletin changed the original transmission fluid to a thinner type despite most databases still today indicating the opposite. This new thinner combination of fluid and additive improves performance, fuel mileage, and longevity of those weak links within the transmission. I recommend Tufoil engine additive, and Penzoil Syncromesh in the transmission case (yes the engine additive, it works amazing). It is a night and day difference between the factory recommended oil and this combination.

RULE: In Manual Transmission: Tufoil Engine Additive 
RULE: In Manual Transmission: Syncromesh by Penzoil fluid.

7- Oil - As mentioned prior, this is free, because, you're going to have to change your oil at some point (let's hope). Factory recommendation is 5W-30 via TSB, but that was before the existence of the super-oils of today. My recommendation is 0w-20 synthetic. Considering this car only takes 3.5 quarts, it's not expensive and can makes a huge effect on mileage. Best part of it all, is you can just drive to the oil change place and ask for it. Be sure not to place a Fram oil filter on the vehicle. Why? See here.

RULE: Oil 0W-20

8- GAS - Use only Top Tier gasoline, as outlined here. Create a new habit of using only BP, Shell, or Chevron gasoline. In addition I highly recommend using Techron Chevron Plus fuel additive at every oil change, as these engines are known for their carbon, and this cleaner is absolutely fantastic at dealing with it. For a few cents more on every fill up, it's worth it to have my engine performing at its best.

RULE: Fill up only at BP, Chevron, or Shell
RULE: Use Techron Chevron Concentrate Plus every oil change.


Not Free, but Highly Recommended:

7- Lowering Springs - People ask what the single greatest (best) modification you can make to a Metro is, and hands down this is it. My MPG increased almost 3 MPG (which pays for the suspension), the car looks great, and it changes the suspension geometry in such away that will really blow your mind. It reduces surface area drag on tires, control arms and under-body. It handles unlike any vehicle I've ever known, and considering it does this on 155 mm wide tires, I'd say that's a safety measure in itself.

Some have a hard time believing that vehicle height has an effect on mileage, but here's a couple things to keep in mind:

When Eibach (a company who produces lowering springs) modified the two most popular vehicles in production, they both increased their MPG drastically (note this modification is more relevant to those who drive at high-way speeds):

Eibach has two vehicles they did testing on and gained up to 13% more MPG:

Civic 7.5%: ... g_test.pdf

Mustang 4.8% / Camaro 13% ... ce_testing

And when Ford & GM attempted to improve mileage on their vehicles, in the past and current models, many times it included lowering vehicles. The best example was the Lincoln Mark VIII with its active suspension that lowered at highway speed to achieve better gas mileage. 


Also not free, but recommended if you have money and time.

8- Underdrive Pulley and Timing Gear Pulley - Underdrive pulley is available from Suzukird for $99, and Timing Gear pulley available is available from 3-Tech performance. Both serve to improve drivability and performance.

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