If you find a puddle under your car like this, chances are you’ve got an oil leak. This can range from a minor dribble to a very serious potentially catastrophic failure, but really the first thing you should do when you notice a leak is check your oil level. If it’s below the minimum line you should top it up before you drive it – and if it’s a massive leak it’s likely worth not driving it at all.
That’s because if it’s leaking out significantly that means either it’s the oil pump literally pumping all the oil out of the engine in which case you won’t have any pressure pushing oil into the bearing faces and lubricating things like the connecting rods spinning around the crankshaft, or it’s a passive leak from say a crack in your oil pan in which case you’ll just have no oil to pump around. Either way running your engine without oil or oil pressure leads to a seized, and mechanically totalled engine.
Assuming it’s not too serious, what should you do to find where it’s coming from? The first thing is to have a look in the engine bay. Pop the bonnet and inspect everything you can see. Look for any signs of oil leaking out, it will likely still look “wet” although do bear in mind if you’ve been driving for a while with that leak it can spread itself quite far. I found this wet spot up around the top of the gearbox, but there weren’t any signs of a leak in that area so this is just oil that has been blown upwards by driving.
If you can’t find anything from the top, it’s time to go under. You’ll want to safely jack up the car and remove any undertrays that block your view of the engine. In our case we removed the driver’s side cover as that covered the engine. You can then look for where the highest concentration of oil is. As you drive the oil will be blown around considerably so you are looking for where the most oil (and possibly dirt) is. If it’s really bad, or if you are sure you know where it’s coming from, you’ll want to clean the area. A can of brake cleaner makes that pretty easy, although a spray bottle with soapy water and a brush will work too.
Clean the area up, then as long as there is enough oil still in the engine you can start it and let it idle for 30 seconds to a minute. You don’t want it to build too much heat, just build enough oil pressure to start leaking out again. You should be able to clearly see where it’s coming from now.
So, what are the common points of failure? I’m going to cover mostly the seals and gaskets that can fail rather than damage as if your engine exploded a chunk out the side or you smashed the oil pan that’s something you’ll likely already know about. So, gaskets, basically any place where two parts are bolted together you have some sort of gasket or seal. The oil pan has a gasket that is squished between it and the engine block, the rocker cover at the top has a gasket around it’s perimeter and around the spark plug holes (or if it’s a diesel possibly around the injectors) and the drain plug as a seal between it and the oil pan. Any and all of those can and do fail over time, although it’s worse on some engines more than others.
If you are working on your own car, it’s a good idea to know what the common failure points are, and ideally do preventative maintenance to fix them. The worst seal to have fail (and yet is pretty common on higher mileage engines) is the rear main seal. That’s the seal that stops oil rushing out the back side of your engine where your gearbox normally mounts. The reason it’s a pain is you have to remove the gearbox and therefore driveshafts, and your clutch and flywheel or torque converter and flexplate, and sometimes also the oil pan. That’s one I’d personally leave to a garage to do for me.
Also of more serious concern is if you have a turbo. They can fail in a few ways, including the seals for the oil in and drain pipes, but also the bearings inside the turbo meaning oil can be pushed into your exhaust or intake. Beyond the oil feed and drain pipes you likely won’t see a leak if the internal seals are failing but if your oil level is dropping and there isn’t a leak check the intake and exhaust ports on the turbo.
Much more commonly though, it’s a relatively simple problem like the one on this 2016 Vauxhall Astra that I’ll actually be fixing. The one I’ve seen the most is the oil drain plug, and this happens for two main reasons. Either, when the last oil change was done it wasn’t tightened to spec properly, or the seal (often a copper or aluminium crush washer) wasn’t replaced. If you have a leak from there you have two options, either try tightening it to the recommended spec, or replace it and the seal and refill your oil.
Luckily for us that one is fine, and our culprit is the oil filter. This one is in a bit of an awkward position and is somewhat unique in that there is a tightening torque value listed for this – 55 nm. That’s pretty crazy as normally you do these hand tight and no more, but as we’ve found out that’s not enough. So to fix it we unscrewed the filter and let any oil still in the passages drop into our drain pan, then we pre-filled the new filter so the engine wouldn’t run dry when we start it, then a gentle lubrication of the rubber seal on top and screw it on. We then used a 76mm oil filter socket and ⅜ torque wrench to tighten it up. We dropped the car so it was level then checked the oil level.
We then started the car and monitored the area to make sure the leak was resolved. Happily for us it was, so then it’s just sticking the under tray back on and removing the jack, and that’s it. Oil leak fixed.
