One of the most common “shade-tree fixes” we see in the shop is the use of stop-leak products. They make ‘em for lots of different things, like cooling system stop-leak, power-steering system stop-leak, and so on.
Most of these products fall into one of two categories – stuff that clogs things up, and stuff that makes rubber seals swell up. Some products combine the two.
Stuff that clogs things up is what we usually see in cooling systems. The problem with stuff that clogs things up is that it… clogs things up! It doesn’t discriminate between a leak and a coolant passage. Sometimes it clogs things up so well that we have to replace things we wouldn’t have had to replace otherwise. Sometimes it clogs things up so well that we have to flush the system out several times, or take things apart to clean them out. Another type of stuff that clogs things up is a thicker version of whatever fluid is leaking – the thicker, or more viscous, fluid won’t leak out as fast. It also doesn’t do as good a job doing the job it’s supposed to do – if ya follow me. For example, a more viscous engine oil doesn’t do as good a job lubricating the engine because it takes longer to get where it needs to go. This is a big deal, partly because most engine wear occurs on start-up. If the oil takes a few seconds longer to make its way around the engine, the wear will be much worse.
Stuff that makes seals swell is made for engines, power steering systems, transmissions – anything that has oil in it and rubber seals to keep it there. Sometimes these seals wear or harden and leak. Some products sold to solve leakage problems contain a chemical that makes these seals soften and swell. These may be an acceptable short-term solution in a very few cases; by short-term I mean a month or two at the most. I’ve done some experimenting with these products on my own vehicles. The seals can swell so much that they are at risk of tearing out completely, resulting in catastrophic failure – forcing you to either park the vehicle or make the repair immediately. In the best possible outcome, the seals swell to seal, then become so floppy or soft that they fail to seal yet again in short order. It’s probably better just to deal with the leak (protect the driveway and keep the fluid topped up) and save your allowance to have the offending seal replaced. Here’s another big problem - the seal swelling chemical doesn’t know which seals are leaking, and which ones are in good shape – so you end up replacing more seals than you would have if you’d just done the repair in the first place. And here’s a word to the wise – many of the recently popular “high mileage” engine oils have seal swelling chemicals in them.
Thanks for your time! Let me know it there’s a topic you’d like me to write about.