Electric motors running in oil?

Does anyone know what type of oil is used to lubricate an electric motor?
The motor is submerged in oil and is part of a pump.

What liquid is being pumped—is it freon such as used in a compressor?

The oil has to be compatible with the process fluid.

No, it’s just water, but it’s not mixed with the oil. The pistons, shaft and motor are running in oil. Water passes through some manifold and is compressed by the piston heads.
I spilled some oil out and now I don’t know what kind of oil do I need to buy to add. It’s thick and golden

The manufacturer said I could use standard 15W40 motor oil, but wouldn’t this type of oil affect the motor?
It’s the first time I see an electric motor submerged in oil.

It’s fairly common to run a motor submerged, for example the fuel pump on most cars is cooled by the gasoline in the tank—it runs submerged.

Also the compressor motor in air conditioners.

The manufacturer should know so i would trust what they said.

Why are you not simply trusting what the manufacturer is telling you to do?

Because the pump is 40 years old, and the manufacturer doesn’t even have the datasheet for it anymore. The employees who were involved in the development are probably dead by now.
It’s not that I am not trusting them. I thought it was weird that an electric motor could run in regular motor oil. So I thought about asking here too, maybe there are users experienced in these stuff.

I would go with the oil they recommend. I have a couple of sumps that are large and run in oil, I use Rotella diesel engine oil in mine. My compressors for HVAC use an oil that is in the freon lines, many are polyester based oils now.

In my experience, searching for the owner's/operator's manual for an old product isn't always successful until hitting upon the perfect set of search parameters. This was the case for me just last week in searching for the owner's manual for a 35 y.o. dehumidifier. It took several attempts, but I was ultimately able to match my unit with online photos, then onto a .pdf download of the manual.

So, in an effort to help out, if you provide the specific type of pump it is, along with the manufacturer & model number, and preferably a photo(s), maybe one of us will get lucky.

Curiously, has this pump been in service for the past 40 years, or has it been out of operation for a long period?

Anyway, if you would like some assistance in searching, I'm willing.

It’s a very old pressure washer pump that I found at the flea market, there is no online manual, I still have the tag with model number and all. I don’t think it has been in service for all this time because the condition is quite good. Piston seals are gone I think because water leaks from below the pistons, but still gives out decent pressure, more than enough for a misting application. I`ll just add the oil and use it to turn my garden into a jungle

A quick google search tells me that ‘normal engine oil’ is non conductive. So I would guess that you can trust the manufacture with his advice.
(A lot of text but this is one of the search results: Is Engine Oil Conductive? A Comprehensive Guide – Oil Genesis)

Another search got me to this forum where they are talking about a different version of a Hanning pressure washer. However, as far as I understand it, the selling point of Henning is that they use a submerged motor en pump that is the same to many of there models.
In this post the person says it uses just “Einfaches Motoröl” which translates to “Simple motor oil”. (but you’re probably German so you can read and understand that topic better than me)

That looks like a great find! Best wishes for getting it up and running and hopefully to help you with your garden jungle! Let us know how it works out.

Thanks. It will probably be next year, because weather is getting colder so there’s no point in refitting all the tubes and connectors/nozzles now.
Very helpful links thijsco19, thanks!

Don’t know if this helps but I know a sump pump motor I had used vegetable oil.

i;d maybe try 5w, thinner is probably ok

wle

The only concern I have would be over the long term if the metal shavings from running the motor can conduct electricity. There is nothing wrong with running electrical equipment in oil, almost all electrical transformer run in oil bath but they also blow up because over time oil degrades and conducts. I would change that oil every year or every half year.

So I filled it up with 15w40 mineral oil and couldn’t contain my curiosity and tested it on my existing installation.

Seems to be working fine and it produces a decent mist. Normally the tubes should be lifted up, but it requires many changes and I do not have the time to do it now. I used these tubes for low pressure misting with a normal water pump, that’s why I left them down.