How can I get better gas mileage from my old Dodge D150?

Short answer: Start with a full tune-up, the right tire pressure and a working thermostat, and drive gently. Don't expect big gains: owners note these trucks were rated about 10 city and 14 highway when new. Dual exhaust barely helps. A self-tuning fuel injection kit (about $1,000) and gearing changes make the biggest difference.

Symptom: The truck gets low-teens mileage or worse, and you want to know what helps.

What to check first

1. Do plugs, wires, cap, rotor and filters.
2. Check that the thermostat opens and coolant is full.
3. Set tire pressure to the door or tire spec.
4. Check for dragging brakes.
5. Look up your axle ratio before buying any upgrades.

Likely causes

1. Engine due for a tune-up. Old plugs, wires, a bad thermostat or low coolant all cost fuel.
2. Tires and driving habits. Low tire pressure, open windows at speed and hauling extra weight cut mileage.
3. Carburetor and gearing. The old carburetor and gearing limit mileage. One member said a self-tuning fuel injection kit costs about $1,000 and helps a lot.

What it usually costs

One member said a self-tuning fuel injection kit costs about $1,000. Owners didn't post tune-up prices.

Is it safe to keep driving?

Yes, low mileage isn't a safety problem. A fuel smell or leak is.

DIY or shop?

Tune-ups are DIY. Injection kits are DIY for capable owners; gearing changes are shop work.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA lists 90V124000 for some 1987-1990 trucks: in a rear-end crash, the pickup box crossmember could hit the fuel pump module's fuel line and cause a leak. It isn't about mileage. Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 0 keyword-matched complaints for Dodge D150 1979–1993 (of 20 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-30; keywords: mileage, mpg, fuel economy) (NHTSA returned no data for 45 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In Better mileage for a 1987 Dodge D150 on Car Talk, a 1987 D150 with the 225 slant six owner wanted better mileage. Members said to do a full tune-up, check tire pressure, make sure the thermostat works and the coolant is full, drive gently and not haul extra weight, but not to expect much from a 31-year-old truck.
• In Will switch to dual exhaust help 1985 Dodge D150 mileage? on Car Talk, a 1985 D150 with a rebuilt 318 was getting about 11 mpg. Members said dual exhaust would barely help, gearing makes the biggest difference, and a self-tuning fuel injection kit for about $1,000 helps a lot and lets you use regular E10 gas. One noted these trucks were only rated about 10 city and 14 highway new.

Quick tip

On these trucks, a good tune-up and fresh tires are the money you'll get back. The rest only pays off if you drive it a lot.

Vehicle focus: Dodge D150 pickups, 1979-1993, slant six and 318 V8.

Safety / mechanic note

If you smell fuel, Verify with a mechanic.