Air cooled cylinder head temp

[Roundybout]

What’s a safe maximum temp on a force/fan air cooled small 125cc/232cc all aluminum engine? Currently seeing 311F as a maximum. The max oil temp is 261F. That’s more concerning and being hopefully handled by a small oil cooler and a switch from 0W-40 to 20W-50 Mobil 1. This thing holds 1qt.

[Racer71]

Our Briggs kart motors back in the 90’s on alky ran 425 cyl head temp. Not sure on oil temps we changed oil after heat before feature.

[pcnsd]

What’s a safe maximum temp on a force/fan air cooled small 125cc/232cc all aluminum engine? Currently seeing 311F as a maximum. The max oil temp is 261F. That’s more concerning and being hopefully handled by a small oil cooler and a switch from 0W-40 to 20W-50 Mobil 1. This thing holds 1qt.

How are you measuring cylinder head temp? 311F may be on the cool side or approaching hot depending.
Little motors can experience noticeable pumping loses from oil viscosity changes. What range does the manufacturer recommend for your climate?

[modok]

The strength of aluminum drops rapidly past 300, or 360f for high temp alloys
I think you can get a lot of variation depending on where you place the sensor on what kind of engine.....so some of it will have to be learned by experience, what temp reading corresponds to an actual problem. Spark plug temp can be different from temp under the valve seats, but, I think if the temp under the valve seats gets into the danger zone they will shift or fall out.

[Roundybout]

What’s a safe maximum temp on a force/fan air cooled small 125cc/232cc all aluminum engine? Currently seeing 311F as a maximum. The max oil temp is 261F. That’s more concerning and being hopefully handled by a small oil cooler and a switch from 0W-40 to 20W-50 Mobil 1. This thing holds 1qt.

How are you measuring cylinder head temp? 311F may be on the cool side or approaching hot depending.
Little motors can experience noticeable pumping loses from oil viscosity changes. What range does the manufacturer recommend for your climate?

I’m using the ring terminal sensor that goes under the spark plug. (Trailtech). Also have an oil temp sensor in the sump. I believe cylinder head is on the cool side. I see airplane cylinder head temps of 450F, 2 stroke dirt bikes at 400F and just don’t know what’s safe for these. Recommended oil is straight 40W. I’d suspect if we can get the oil temp down it might help the cylinder head temp too. With only 10-20HP you can definitely feel the effect of oil viscosity changes.

[David Redszus]

For an air cooled engine, Plug Seat Temperature will be affected by:
rpm
fin air speed
spark plug heat range
spark advance.

The most effective way to reduce PST is to retard ignition timing and/or increase air flow.

The head temperature that can be safely run will also depend on the combustion chamber
shape and type of fuel.

[n2omike]

I run Mobil 1 15w50 in my air cooled dirt bike engines, and have had excellent results. It's the only Mobil 1 that has plenty of ZDDP (1300 ppm) for slider/flat tappet cams, and takes the heat well. Sometimes, it's best to not even look at head temp, and just be happy you're not on a water pumper that boils over in tight terrain, gets busted radiators, rad fins plugged with mud, etc.

[Roundybout]

Running Sunoco Optima 95 octane. Max RPM is about 8500. We’ve played with fan diameter and fin angle. Adjusted the shrouds and feel we are getting good air flow. Found a research paper on this particular engine concerning optimizing the cooling. We incorporated a few of the ideas and it helped.

We started out at 340-350F max cylinder head temps and felt that can’t be good for aluminum. The oil temp just keeps climbing under sustained load where the head seems to level out in the low 300’s now.

[Truckedup]

The vintage British bikes can run near 350F or more on a hot day....Heat makes em detonation prone often causing a piston seizure.

[Roundybout]

https://pdfs.semanticscholar.org/cc1d/ ... 60f746.pdf

That’s a link to the study I mentioned. Their goal was a 20C reduction in oil temps. The maximum was 140c which is quite a bit more than I’m seeing. Mind you we did modify the cooling shrouds and fan. They were also seeing head temps of 400F+

So I guess what would be a comfortable oil temp for an air cooled engine? 260F seems high but maybe I’m not trusting enough of today’s oil (using Mobil 1 0W-40). Possibly a 50W would be better? There’s so little of it in the engine (1qt) that adding a cooler along with some capacity is a no brainer?