Changing an oil drain plug without changing the oil

Sometimes our shop has to just change a drain plug when the oil doesn’t need changing. They attach a vacuum to the filler hole to keep the oil from spurting out when the plug is removed. My supervisor is worried about doing this and asked me to get another opinion.

Sorry - but I have no method for you. I think this is the dumbest thing I’ve ever heard. I’ve never worked as a professional in a shop. So I suppose its possible that this could sound more reasonable or maybe even normal (?) to people who have. But I doubt it.

Drain out the oil. Fix the drain plug. Put oil back in it. If its an issue, use a clean container and put the oil that came out right back in the top.

Cig is right, I’ve done it with my tractors several times… otherwise if you are worried and it’s more than half oil change interval…So oil is what…$10 to $15… It’s only occasionally, right ? And, you seldom don’t loose that much because you extend the next change which means the loss could be less then half that on average.

How do you do cooling system repairs? Do you suck out the coolant through the top so it can be returned later?

The normal method in both cases is to drain from the bottom. Make your repair and pour it back in.

I don’t see any problem with your shop’s method of using a vacuum pump. If it works, let it be. It is simply a quirky way of doing a very simple job, one that requires unnecessary equipment.

Isn’t the labor cost greater than the cost of the oil involved? Someone needs to check family trees for a Goldberg leaf.

I don’t understand the reasoning behind this at all. If the plug is damaged then why wasn’t it replaced during the last oil change or why can’t it wait until the next one?

Get out…never heard of this one…LOL. I’m trying to think what if anything could happen by reversing the pressure of the crankcase…as its usually under pressure…Hmmmm

There’s a check valve in the PCV to allow pressure to escape but not flow the other way…so if everything else is copacetic it should just inhale air thru the drain bolt hole till you put the plug back in…and then what?

LOL…in all my days…if anything of this nature had to happen, I would just drain the oil into a clean container do the work and put it back in when done…NOTHING can happen that way, so you don’t need to ponder what might happen by applying a vacuum to the filler…so the issue disappears …right before your eyes


Your supervisor has a right to be worried. This procedure will not be found in any maintenance manual that I’m aware of. Drain the oil, replace the drain plug and refill with fresh oil. I’ve heard of shortcuts before (I don’t like them very much) but this one takes the cake.

I’ve used a shop vac in the manner you speak of to prevent the oil from draining when the plug is removed. The only danger in doing this is, if the oil is contaminated with gasoline and gas fumes are drawn into the vac, the fumes can be ignited by the vac motor and the vac can explode. I always pull the oil dip stick and smell the oil for gas before doing this.


The method of using a canister vac to hold fluid in while the drain plug was out was in a Click & Clack puzzler some years back.

How about flipping the car upside down?

Seriously, is not changing the oil a big problem?

Why drain the oil if all you’re doing is replacing a cracked/missing drain plug gasket washer?


I guess. It just seems like a lot of trouble.

Excuse me for saying this . . . but what kind of automotive repair shop is this? How difficult would it be to just remove the old plug, drain the oil, put in the new plug, and re-fill with the oil you drained? I would probably do an oil and filter change myself, since I was there and dirty anyway, but what kind of shop do you work for? What does your shop do for other repairs? How do you approach day to day repair work (brakes, exhaust, tune-ups, etc)? My advice is simply to drain the oil into a catch pan, do the repair, and then re-fill the crankcase with the oil from the catch pan. Good luck! Rocketman

Right on Rocket! MUCH less trouble than screwing around with a shop-vac…

Yeah. Those shop-vac’s can take up to five minutes to set up. I hate that.


I can see the vac sucking considerable oil out of the valve-cover / crankcase…Who gets to clean the VAC??
Do you raise the car on a lift with the vacuum cleaner screaming away, stuffed under the hood while you work under the car hoping that jury-rig holds together?

I would just drain the oil in a clean pan and reuse it…

Just have the new plug ready and be fast. You should only lose half a quart if you’re careful. It would help if the oil is cold when you attempt this.

My only concern would be if they’re fixing a plug - using one of the replacements that cuts new threads. To my way of thinking, those metal shavings have to go somewhere, and I’d rather have them flow out, than go back in.

If it’s just a gasket (or a gasket/washer and a messed up bolt), I don’t see why a shop vac or other canister vacuum wouldn’t work just fine, providing it’s a quick job. The vacuum will pull more air than the drain hole will let out. Makes perfect sense to me. There should be very little oil drawn out through the calve cover, if the engine isn’t too messed up inside. Heck, even then you can rig up some sort of metal mesh filter to catch it.

The vac will not suck the oil out of the valve cover or the oil pan. Vacuum cleaners are high pressure low flow devices. As far as cleaning the vac? There’s nothing to clean.

You just connect the vac where the oil is poured in, raise the vehicle, turn the vac on, remove the drain plug, install the new gasket washer and reinstall the drain plug. Done!