Whats the running temp of an air cooled engine?

[Chris142]

I bought a new air cooled ATV. I know the fins help disapate heat and that I need to keep them clean but regardless the things gotta run way hot.

Maybe not so bad moving @ 40 mph but I got into a gully and had to jog it around to get out which took about 5 mins.

It never pinged or rattled but it had to be real hot w/o airflow across the fins.

I work at a radiator shop and see overheated cars all day so I know how bad it can get. It just blows my mind that these engines can run for years at extreemly high temps.

 

[Al]

Thanks for helping me waste my time.

The short answer is that your maximum head temperature (away from the cooling coils) would be 500 degrees max (probably). Barrel temperatures would be about 100 degrees less. Exhaust temperatures would be less than 600F. So you can figure that fin temperatures are at least 100 degreees below the temp of the average head temperature. Here are a couple of references that will give you some insight. Note that aircraft engines run hotter bc they have a pretty high specific power and they are much better finned. Hope this helps.


http://naca.larc.nasa.gov/reports/1939/naca-report-645/index.cgi?page0001.gif

http://luscombesilvaire.info/endowment/_disc1/000000ca.htm

http://me.engin.umich.edu/autolab/Publications/Adobe/P2002_04.PDF

 

[k1xv]

It all depends on the engine, its load and conditions. That's why a lot of them have fans.

For example, on a Harley, the rear cylinder runs hotter than the front, because it is out of the air flow, and the exhaust port on the rear cylinder is on the rear of the engine.

On the other hand, in the BMW opposed boxer twin, the cylinders and heads are right out there in the air flow. I have a 30 year old BMW twin, and when you ride down the road, you can put your hand right on the valve cover and it only feels warm.

 

[Jimbo]

500F is way too high for an aluminum cylinder head temp. 425F is the redline CHT for some aircooled aircraft engines and it is best to keep them below 375F. Corvairs had an "idiot light" sensor set for about 450F CHT. The problem is that aluminum casting alloys rapidly loose strength above about 180C. This information is based on some old Pratt and Whitney radial aircraft engine manuals.

Aircraft engines can last over 2000 hours of operation before overhaul. The old fan-cooled VW's typically went 60-80,000 miles before the heads needed work.

 

[PandaBear]

Sounds like a candidate to use synthetic oil