How to remove (spilled) oil from the engine compartment

A pump sprayer full of avgas. That’s the best and cheapest degreaser you’ll find.

After oil spillage or leakage there will be some oozing out from various places for the next few hours, so give it a clean after each flight and eventually it’ll be ok.

Alternatively, you could just leave it. The oil won’t do any harm, just make a mess, and the airflow in the cowl exits underneath so you’re unlikely to get it on the windshield.

An aquaintance had some kind of oil leak issue a few weeks ago, where the oil burned up and he got comatose, meandering through controlled airspace with the controller telling him later “he watched him die”. Luckily he came to and landed at the nearest airport he could find.
I’d make sure to get most of the oil if it has gotten anywhere near the hot parts.

@TB_flyer wrote:

Thanks for the hint regarding the pump sprayer.

Vaporized fuel is pretty flammable, so take care. One spark could ruin your whole day.

The classic spray-on evaporating solvent to clean aircraft engines is mineral spirits or white spirits, otherwise used as a paint thinner. Link

A lot of people use avgas. It’s good clean stuff; dries without any trace. Just make sure no “environmental types” are watching

Obviously you need to make sure it’s all dried off before running the engine. The exhaust will otherwise ignite it instantly.

Same with engine oil; that will also ignite from the exhaust system contact.

I would use brake cleaner (auto parts shop), but 0,5L of oil is a lot.
All mechanics use avgas.

Diesel and related stuff (kerosene, jet fuel, white spirits etc) is a better solvent/cleaner. It’s also much gentler on paint, rubber, plastics and not remotely as flammable as avgas. People use avgas because it’s available there and then and works well enough, not because it’s “the best”. To clean it properly, break cleaner is of course the way to go, but it also could remove stuff you don’t want to be removed. A spray can of WD40 or similar that you can get everywhere will also do miracles (need some wiping though, but you have to do that anyway). The safest and best is white spirits. This is what it’s made for (more or less).

Another thing. If there’s a lot of dirt there collected through the years, then water and soap is the right thing to use. Well, WD40 kind of works well on that also, but gasoline (avgas) does not, and neither does kerosine related stuff (white spirits).

This happened to me many years ago – I inserted the funnel incorrectly and poured a quart of oil all over the engine. It was a rental plane in the club I belonged to at the time. They steam cleaned the engine compartment and charged me accordingly. The idea of spraying avgas over a potentially hot engine sounds terrifying.