Magnetic Sump Plug

[Wes]

Last night i changed the oil and went to fit the new magnetic sump plug i bought. https://www.morrisminorspares.com/engin ... er-p830179. but it wouldn't screw all the way in? rather then tempt fate I reused the old plug but with the new washer. Any idea why? mines a Nov 1964 engine.

[geoberni]

Well the first thing would be to make a direct comparison between the two, placed side by side.
Then, as it's a fair bit longer, just putting the blunt end of a pencil (or similar) in the hole to the length of the new Plug, to ensure there's nothing obstructing it.
There shouldn't be, but after many decades, who's to know what might be going on with that particular engine; perhaps the Oil Pickup Strainer is mis-positioned a little.
Personally, I wouldn't have proceeded until I knew the answer.
You'll have to wait until next oil change now.

[Bill_qaz]

Or drain into a clean container so you can reuse the new oil and follow Berni's good advice. If its the oil strainer better to know now rather than an oil pick up issue later. Maybe order a sump gasket in preparation.

[svenedin]

I don't have experience of the ESM magnetic drain plug but I can recommend a different type.

I use a "gold plug" AP-01 which is 1/2" 20 tpi. This has a very powerful neodymium magnet and fits perfectly. It is more compact than the ESM plug and does not have a projection on it but it is more expensive.

https://goldplug.co.uk/product/ap-01-1- ... sump-plug/

If you do fit a "gold plug" try not to be as alarmed as I was by all of the iron filings it picks up!

Stephen

[philthehill]

The magnetic sump drain plug purchased from ESM fits without problem into my sump.

[oliver90owner]

Anyone fitting a neodymium magnet should be aware of its temperature rating. Operating above 80 C can irreversibly reduce the magnetic power, for the N series, in double-quick time. Not many people know this.

[svenedin]

Anyone fitting a neodymium magnet should be aware of its temperature rating. Operating above 80 C can irreversibly reduce the magnetic power, for the N series, in double-quick time. Not many people know this.

That's interesting. I fitted my "gold plug" sump plug 3 or 4 years ago and it seems as magnetic as ever judging by how strongly it is attracted to the steel of the sump. Since the engine rebuild there is very little iron filings attached to it at oil change time. Prior to the engine rebuild there was a lot. Plug looked like a Mohican haircut, something out of the days of Punk!

Stephen

[Wes]

The magnetic sump drain plug purchased from ESM fits without problem into my sump.

Hmmm

[Wes]

Well the first thing would be to make a direct comparison between the two, placed side by side.
Then, as it's a fair bit longer, just putting the blunt end of a pencil (or similar) in the hole to the length of the new Plug, to ensure there's nothing obstructing it.
There shouldn't be, but after many decades, who's to know what might be going on with that particular engine; perhaps the Oil Pickup Strainer is mis-positioned a little.
Personally, I wouldn't have proceeded until I knew the answer.
You'll have to wait until next oil change now.

Maybe some thing ins1de has shifted? but looking at drawings i cant see what? oh well old plug is back in and its not leaking so all good.

[svenedin]

Well the first thing would be to make a direct comparison between the two, placed side by side.
Then, as it's a fair bit longer, just putting the blunt end of a pencil (or similar) in the hole to the length of the new Plug, to ensure there's nothing obstructing it.
There shouldn't be, but after many decades, who's to know what might be going on with that particular engine; perhaps the Oil Pickup Strainer is mis-positioned a little.
Personally, I wouldn't have proceeded until I knew the answer.
You'll have to wait until next oil change now.

Maybe some thing ins1de has shifted? but looking at drawings i cant see what? oh well old plug is back in and its not leaking so all good.

I agree. There should be nothing there. Maybe the thread is damaged? Or perhaps the sump has been dented near there? I have had stuff from ESM with bad threads. Send it back.

Stephen

Screenshot 2026-07-29 at 17.01.11.png (1.44 MiB) Viewed 2152 times

[les]

What temperature can the oil in the sump be expected to reach ?

[svenedin]

What temperature can the oil in the sump be expected to reach ?

We could find out using an infrared thermometer and aiming it at the sump after a run to full engine temperature.

Stephen

[geoberni]

I believe it's generally 100c, +/-10deg, as the optimum temperature for for things like viscosity of the 'reservoir' of oil in the engine, to burn off any water/condensation that has occurred etc

Whether that figure applied 70 years ago is anyone's guess....
I guess people who hammer their engines and fit Oil Coolers should have an idea...

[oliver90owner]

Anyone fitting a neodymium magnet should be aware of its temperature rating. Operating above 80 C can irreversibly reduce the magnetic power, for the N series, in double-quick time. Not many people know this.

That's interesting. I fitted my "gold plug" sump plug 3 or 4 years ago and it seems as magnetic as ever judging by how strongly it is attracted to the steel of the sump. Since the engine rebuild there is very little iron filings attached to it at oil change time. Prior to the engine rebuild there was a lot. Plug looked like a Mohican haircut, something out of the days of Punk!

Stephen

Likely a higher range series. Not all neodymium magnets are to the N series standard. You need to read my posts more carefully?

[les]

It’s so tempting but I won’t.

[Bill_qaz]

It’s so tempting but I won’t.

+ 1 gritted teeth

[MikeNash]

May I point out that magnetic drain plugs are cheap and easy to make? A 6-7mm rod magnet about 10mm long will do, glued into something like a ¼ inch hole using a 2 part epoxy glue (such as Araldite). Such magnets are usually about a £1 each or less and are widely available across the interweb.
Also, the Minor drain plugs for the engine, gearbox and back axle are (I think) all ½ inch BSPT (British Standard Pipe Tapered) in thread which is obtainable from the more old-fashioned plumber supplier for about a £1 each. (I get my drain plugs from Woodstock Plumbing & Heating Supplies, Andover SP10 5BN who were amused to find that they’re stockists for Morris Minor bits.)
I’ve got my magnets from Guys Magnets at Devizes, Wiltshire (https://www.guysmagnets.com/) who has been helpful in discussion and prompt in supply. Regarding Oliver90owner’s point on temperature limits, Guy recommended a “high temperature“ neodymium material. But I see that there’s now AlNiCo types which can go much higher and are still quite cheap. (And Guy sells his magnets singularly which some of the big suppliers don’t.)
Regarding Les’s query as to the max temp seen in a Minor, I’ve had a sump thermometer fitted for a decade or so on my standard 1098 Trav of 1963 and the max temp I’ve seen was in the upper 90Cs only obtained after an hour and half at 60mph + (GPS read) up the A1(M) towing a trailer in an air temp of some 27/8C. The elderly engine, while quick, was an oil burner and the max oil temp was finally reached as the oil fell to about a half full sump. The problem with the standard Minor engine is getting the oil temp up rather than cooling it down, a feature I suspect required for the expected worldwide sales that were envisaged.
Sven’s idea of using a remote infrared temperature works well (I’ve a cheap Lidl one) and I find the gearbox and back axle after vigorous driving will stabilize at about 50-55C.
Finally, I urge you all to fit these magnets. The engine filter will capture bits down to about 30 microns, perhaps 20 microns as it clogs up but magnets collect bits down to molecular size. And also put them where there’s no filter, the gearbox and back axle. The latter has hypoid gears with sliding action and the wear generated doesn’t sink benignly to the bottom. The axle jumps about too much for that, and first time you remove your magnetic plug to drain the axle you’ll have a cone like a Christmas Tree of bits attached to it.
Regards to all from MikeN.
PS Rod magnets also come in small sizes like 2-3mm dia which I've fitted in compressor and motor mowers drains too.

[Mervin]

That's a very interesting suggestion Mike. However, personally, there's no way I would fit a home made sump plug/glued in magnet. Where is that magnet going to migrate if it becomes detached?
Yes, they are a good idea, never used one myself, but if something goes awry with one bought from a reputable source there could be some kind of comeback with the seller.

[myoldjalopy]

Won't it just stick to the sump if it detaches?

[les]

My thought too