Finding a stripped oil-pan drain plug is very common. This is expensive to repair, and can result in a ruined engine. Improper service ruins most oil-pan drain plugs and the problem is preventable.
Stripped oil-pan threads
They make most oil-pans today of aluminum. Improper service easily damages these pans. Damaging the threads may render the pan unusable. Many people try to repair the pan, but this is risky and will rarely last. Preventing the problem is easy and far more practical.
People most often damage threads in an oil-pan drain hole by over tightening the drain plug. They design the threads to tolerate a specific amount of torque. This tightness is all that we need to make a good seal. If the plug leaks, another problem exists and we must solve it. Applying additional torque to the drain plug will only damage the threads and plug.
A torque wrench is a necessity when we replace our own oil. The proper torque specification varies widely from one vehicle to another and even on the same vehicle with different engines. Drain plug torque can be found in a service manual for the vehicle. Registered site guests may also access oil-pan drain torque specifications here.
An over tightened oil-drain plug with distorted threads
Over tightening the oil-pan drain plug will not make it seal. Instead it distorts the threads and further crushes the seal. Once we distort the threads on the plug, they quickly tear away the threads in the oil-pan.
They do not design drain-plug threads to seal
Designers always provide a seal on an oil-pan drain plug. This is because they cannot design standard bolt threads to seal. A gap is always present between the plug and the threads of the oil-pan. This is by design and the reason they always provide an additional seal. On some designs the seal bonded to the drain plug.
Crush-washer oil drain seals are also common. We should replace these at each oil change. They design these washers to crush when they seal. Once we crush them, we destroy future sealing ability. Applying more torque destroys the threads in the oil-pan.
Crushed seal and damage oil-pan plug threads
Integral seals also wear out and we need to replace them. Use tears the rubber. It also gets hard or crushes in time. When this happens, additional tightening of the plug will only damage the threads, not increase sealing. Replacing the plug with a new original equipment plug can prevent a very expensive problem.
If you change your own oil, buying an extra plug before needed is wise. Store the extra oil drain plug in the glove box. Here it will be available when we need it. This helps us avoid the temptation of reusing a damaged oil-pan drain plug.
A cross threaded oil drain-plug
The oil-pan drain plug shown above is not loose, in fact we could not remove it with a wrench. The plug is cross-threaded into the pan and has seized. We have to replace both the oil pan and drain-plug. We should thread the oil drain plug in by hand. A good oil-pan drain plug, with undamaged pan threads, screws most of the way in with hand effort. If the plug does not start straight, it will get very tight. At this point replacing the plug and chasing the threads with a die may save the oil-pan.
A rounded drain-plug head
Another problem associated with over tightening is damage to the drain-plug head. Once damaged, the plug is very difficult to remove. Professional mechanics use several methods to remove rounded drain plugs. Sometimes we weld an undamaged nut to the plug. Other times, drilling a hole in the plug allows us to remove it with a special tool.
It is far better to avoid rounding the head, by using the proper tool. They use several designs for drain-plug heads.
Most oil-pan drain plugs use a conventional hex design. A plug with six sides works best with a six-point socket. Some oil-pan plugs have twelve sides. We must use a 12-point socket on this type. Using a 12-point socket with a six-sided plug, does not provide good support. Investing in a good socket, which fits the plug exactly, will prevent problems.
With oil-pan drains, observing a few simple precautions can prevent much grief.
We can prevent Oil-pan drain stripping with a few simple precautions:
Wipe the threads clean before reusing the plug.
Inspect the threads and seal, every time a plug is removed.
Replace any plug with distorted threads or a damaged seal.
Replace washer type seals every time the oil is changed.
Hand tighten the drain plug as far as possible.
Replace any plug that is hard to remove or reinstall.
Always torque the drain plug to the proper specifications.
Always buy an OEM drain plug, aftermarket plugs are sometimes not of the same quality.