Best way to take a sample?

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Dec 2, 2002
Washington St.
What's the best way to take a sample of crankcase oil without draining the sump (and without a sampling pump)?

Clean around the drain plug? (with what solvent?)
Run the engine 'til warm,
Shut the engine off,
Loosen the plug, clean again,
hope for a trickle of oil--not a deluge,
waste a few ounces of oil,
Fill the sample bottle,



[ January 20, 2003, 11:05 PM: Message edited by: Ken2 ]
Yep, without a fumoto valve or similar.


I'm installing a simple valve off my pressure sender next time it warms up. Cheap solution if yours is accessible.

I have one of those drill-operated oil changing pumps (commonly used for boats). Could I get a good sample by running crankcase oil through the pump to flush the old oil out, then filling the sample bottle with the pump? Another option I have is draining the cartridge filter--but I assume there would be the danger of backwashing the particles the filter had caught into the oil sample that drains out (although the particles could be "stuck" to the filter). Any thoughts?
Ken, thinking more typing less...

I'd avoid the drain plug. Makes a mess & you need to drain a bit before you can trust what you're getting is an average.

How about siphoning? Use 1/4" OD 1/8" ID poly tubing. The translucent type used for under-sink plumbing, not the clear flimsy vinyl stuff. Around here it's maybe .20/ft. Get enough to reach to dipstick level and out of the engine bay to your container. Siphon a few ounces to a drain pan and then capture for your sample. You'll waste a little more in the long tubing than with a sample gun but 6' of 1/8" ID is only 1/2oz.

Segfault, my drill pumps are always a mess. I'd worry the pump will have junk in it from previous uses that'll contaminate the sample.

Just bought one of Bob's official sample guns. Sure makes the job simpler. I think it was ~$15.

Problem with siphoning is that even with a warm engine you won't get any flow if the weather is say below 50 degrees outside. Forget the drain plug unless you are draining the whole sump and getting a sample after at least a quart has run through. That plus dirt around the plug threads which you can't get to.

Best may to get a sample kit from but then get the oil analized at one of our site sponsors. They have a squeeze bottle that sucks oil out of the dipstick tube right into a bottle.
If the goal is not to lose much oil, you can use the drain plug, but put a clean container underneath to catch the oil. Then put the oil back in the fill hole.
I do not recommend pouring sample oil into a container and then pouring back into oil filler, I swear the dirt just jumps in the oil under the car. Everytime you move under a car lifted a few feet you bump off dirt without even realizing it.

NO PUMP technique; note I prefer the ease and cleanliness of the pump .

Engine oil at operating temp, protective latex gloves( unless you think your liver is a better filter than your current full flow)
,clean area around plug with isopropyl alcohol and allow to dry (won't take long with hot oil pan). Place a capture pan with low sides to trap initial flow.

Unscrew drain plug, gently and carefully hold in place( if all the nerve endings are burned away like mine it is less painful)
and allow a 20 second stream at least 1/4 in. dia. then fill sample bottle. Reseat plug by hand, being very careful not to contaminate open sample bottle, immediately cap bottle and place out of way.

Retighten the plug and rock on. Did it this way for years and after a while you become quite good at the technique.

The more careful you are the better the sample. Use clean rags to wipe down things, not one that has wiped 100 different surfaces and has residual oils,greases, water,glycol,detergents etc.


A note for those who use any of the myriad valves available, especially bypass ports or valves... DONOT take the first oil that comes out there will be crap in there that will make your oil look worse than it really is. Always allow a stream of clearing oil up to 20 seconds or until the oil looks representative of the sump.

[ January 21, 2003, 05:27 PM: Message edited by: Terry ]
How about draining it into a clean container, then letting the oil settle a bit and scoop some out?
I've just installed a push-button sampling valve on a T-junction with the oil pressure sending unit (and right after the T-junction for the bypass filter, so it's getting crowded down there). It was about $15 for the whole assemblage and there are a few different companies that make them - try searching for "oil sampling valve" on Google.

Also see previous thread on this topic:;f=24;t=000002
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