You got an old engine that hasn’t been started in who knows how long. Maybe it’s an old relic you hauled home, some aging vehicle you haven’t touched for years, or Grandpa’s old farm truck you found stored in a dilapidated barn. You want to see if you can get it running again to determine the state of the engine and whether it’s salvageable. Before you go wire up a battery, slosh some fuel down the intake, and turn the key, it is good practice to do a few other actions. These things may just save you from ruining what may have been a good engine.
First, parked vehicles that sit too long tend to harbor insects and possibly rodents that have taken up residency. Know that these squatting critters could be in the intake, the exhaust, or in the bellhousing.
If you have any doubt how long an engine has been sitting unused, a quick sniff of what’s in the fuel tank may offer a clue. If the gas smells the least bit funky, or old, you will probably want a source of fresh fuel. You don’t want to run old gas into the engine because it could cause valves to stick and other nasty issues due to varnish buildup. Old gas is also a sign that the carburetor could be gummed up as well.
Once you’ve successfully got an old engine to crank over and run for a bit, you will want to consider the needs to make it an engine that can reliably run for sustained periods. Watch for any signs of overheating too. You can determine which parts might need to be replaced for the long term, along with changing whatever oil and coolant is needed. You may experience rough running, which could be caused by simply a worn engine, stuck valve issues, or fuel delivery problem. A compression test is often a good spot-check for stuck valves and lower-end condition.
Amazingly, many old engines can sit for long periods of time yet be brought back to life with a careful approach and a few precautions. Be warned though that seals can age and may start to leak from sitting idle too long. You probably won’t know for sure until the engine is up and running. Good luck bringing that old engine back to life.
You will soon be dealing with electricity and flammable fuel, along with heat. Before hooking any battery to the cables, it is best to do a good exam of the wiring on and around the engine. Look for any bare wire sections or places where the insulation is falling apart. You won’t want the positive side of the battery shorting to metal ground potential, which is almost everywhere. Insulate or repair as needed.
A quick look at the dipstick can at least tell you whether there is still oil in the block and may give some visual clue of condition. A milky appearance usually indicates water in the oil, and combined with a high fill level may indicate that rainwater has entered the engine crankcase. Consider draining and refilling with new oil if in doubt of the condition. Some mechanics like to prelube an engine before startup by manually spinning the oil pump with an electric drill, if possible.
Pulling the spark plugs may also give you some inkling of what things are like inside the cylinders. Unless the plugs are completely caked with carbon or so worn they may not reliably spark, we are not too concerned about their condition for the first startup.
Some mechanics will add a small shot of lubricating oil to each cylinder through the spark plug hole just to ease the piston ring movement when the engine is cranked and restarted. Only a small amount is needed, as we don’t want much liquid in the cylinder. One option is to leave the spark plugs out until the engine is cranked over, blowing the excess oil out of the cylinders.
When the spark plugs are out can be a good time to place a socket on the front crankshaft bolt and attempt to turn over the engine manually. You can tell if the engine has seized, either from some mechanical failure or from rusting in the cylinder walls. Do not overtorque the bolt trying to spin a stuck engine. While doing this, you can also check to see that all the belt-driven components move freely.
Speaking of belt-driven components, the belts themselves should be inspected. Again, at this point we are mostly concerned that all the belts are in place and that they have reasonable tension on them. If equipped, the air conditioning compressor clutch pulley should be unengaged and free to spin.
Sitting engines may experience stuck valves. One way to check is to pull the valve cover(s) and check the position and movement of the valves as the engine is manually rotated.
It is generally a good idea to take a quick look at the distributor components by popping the cap off. Excessive rust or pitted ignition points (if you have them) could mean the engine won’t fire the spark plugs and start. If the distributor hold-down bolt is tight and the distributor body does not turn, you can probably assume the ignition timing is still good from when the engine last ran.
Look for obvious signs of water leaks such as stain trails near hoses and other coolant routes such as the radiator, water pump, and cylinder heads. A quick check of hose condition can confirm that they are still pliable and are likely to still hold hot coolant.
Top off the radiator and coolant system if it’s not already full. Plain water will serve the purpose for the startup. You will want to flush and fill with a fresh and proper coolant mix later. At this point you are close to cranking over the engine to see what you have.
Before trying to turn over the engine you will want to ensure that the vehicle can’t roll forward or backward. Apply the parking brake, if possible. Place a manual transmission in neutral and an auto transmission in Park to disengage the engine from the transmission.
Before trying to crank the engine, make sure all tools and other items are clear of the engine compartment. It is prudent to have a fire extinguisher nearby in case some flame might ignite on your untested engine.
A handy tool for cranking the engine is a remote starter. It is simply a wired switch used to apply 12 volts to the starter solenoid input to engage the starter. This allows you to watch under the hood while you crank the engine. Before adding fuel, you will probably want to simply turn over the engine a few times, listening for any strange noises. You can also purge the cylinders of oil before replacing the spark plugs. This process will also help turn the oil pump and prelube the engine before firing with fuel. In some cases you can watch the oil pressure gauge to see if pressure is building in the engine.
As we mentioned, you will probably want to avoid using the old fuel supply in the vehicle. Bad fuel can cause valve and piston issues if allowed to enter the engine. With a carburetor you can provide a gravity feed of fuel to the inlet, or plumb a temporary external pump to provide fuel to the carb. Be aware that the carb float could be stuck and allow excess fuel to enter the bowl. You can also pour gas down the carb vent tube to fill the bowl. Another option for a quick try at starting the engine is to shoot some starting fluid down the carb throat. However, use it sparingly because it can wash the oil film off cylinder walls if used in excess.
When dealing with fuel injectors in an engine that has been sitting a long time, it’s good practice to remove the fuel injectors and rails and completely flush them to remove any accumulated varnish. A leak-down injector test can ensure that the injectors are neither clogged nor stuck on. If an injector fails, it can fill a cylinder with fuel and cause damage to a piston rod when the engine is cranked over.