Walk down any shelf of the auto parts store and there are dozens of products that claim to solve every engine problem. The problem is finding out the ones that work, and the ones that don't. A friend came by the shop with his Nissan pickup which was leaking oil at a pretty fast rate. I said let's try the engine oil stop leak, but I didn't have much faith, seeing as the oil was really coming out fast. Did it stop the leak?
Real World Testing
My friend stopped by the shop saying that his engine was leaking a lot of oil. We had previously discussed a leak he had at the rear main seal, the seal between the engine and transmission. It has been a small leak for a long time, but was manageable if you checked the oil regularly. I advised changing the seal but he wanted to wait until the truck needed a clutch, so he would only have to drop the transmission once. Makes sense, except the truck has 140,000 miles on the original clutch, so it is becoming clear he might want to do the rear main seal sooner than later, regardless of what the clutch is doing. But he wanted to wait, so I thought we could give the engine oil stop leak a try, it might buy him some time. The product says it, "Restores gaskets and seals to stop and prevent engine leaks." So why not, right? We put the stop leak in and checked the oil, and added the proper amount. The oil was still pouring out, not good news. But something was wrong. I asked him when the last time he did an oil change. His answer was, "It is pouring so much oil out, it is always getting an oil change!" I re-phrased my question, when was the last time he had checked his oil filter. His answer was not as forthcoming this time. Sure enough, his filter was about to fall off, which explains the massive oil loss. The good news came on two fronts. The first was we were able to fix his massive oil leak with a $10 filter. The second was the oil stop leak actually did fix the rear main seal leak. Only time will tell how long the fix holds, but for right now it works well.