The ultimate Cessna 206 or 210 Hot Start Procedure

Hello people:)

I have decided to write this post about something that troubles most new 206 or 210 pilots,when they have a very busy day of many flights and engine startups and shutdowns,so common to middle and east african bush flying. The sometimes problematic hot-start of the 206's or 210's big continental engine. When you have the common 35-45 degrees Celsius day and you land,toss your passengers and bags out, jump back in the plane and try and start the now wickedly hot air-cooled, horizontally opposed, 6 cylinder engine,you will become a victim of a Cessna/continental design flaw. The aircraft sometimes refuse's to start using manufacturer recommended procedures or normal start procedures All you bush pilots will know exactly what i am talking about.So i hope this helps some-one new out there or atleast makes for interesting reading.

The design flaw of the continental engine is not entirely a flaw. The manufacturers just never realised that the engine would be subjected to such abuse,high air temperatures and quick turn-around times. Normally the engine would at least get 10-20minutes to cool down after a flight but sometimes with bush flying the time difference between shutdown and start up again can be between 3-10minutes. The continental engine has fuel injection and this is where the problem lie's. The continental IO-540 or similar has a central fuel distribution hub mounted on the top of the engine,in the middle of the two rows of cylinders. This distributes fuel evenly into 6 metal fuel lines,one per cylinder. They run from the fuel control unit over each cylinder to a small injector which vaporises the fuel and delivers the correct flow of fuel into each cylinder for ignition.

Now to explain what sometimes causes the hot-start.The 6 fuel lines are not shrouded between the distribution unit and the injectors and because of the fact that they run so close to the cylinder they are prone to heat-up quickly after shut-down. This is due to the engine being air cooled and as soon as you lose airflow over the engine and cooling oil flow within the engine the engine bakes inside the cowling. This in-turn causes the fuel lines to heat up quickly. So you do your normal start and using the auxiliary pump(yellow section of the two-part fuel pump switch in the cockpit),you prime the cylinders by pumping a bit of fuel in prior to engaging the starter. Little do you know that the fuel you have pumped into the cylinders is still (relatively speaking here)cool but the fuel that has now accumulated in the lines has actually boiled or begun to boil. So you engage the starter and after the second or third propeller turn the engine fires as per normal because it has cool fuel to ignite in the cylinder but it quickly coughs and splutters and then the propeller just spins power-less infront of you. This is because the fuel in the lines has vapourised, so you now have hot aerated fuel and this in simple terms does not allow a stable fuel-air ratio for ignition to occur.

Bush pilots have many different techniques to start the hot engine from pulling mixtures out with throttle all the way in,to putting lots of fuel in and jockying the throttle until you get correct fuel to air ratio etc etc. These all work and i have used and tried them all but usually the engine starts very rough. Normally with a backfire or two aswell as un be known to the pilot,a large flame protruding from the exhaust.The problem with these rough starts is that if you have a backfire while the starter is engaged you can damage your starter motor aswell as damage other related electrical hardware.

After trying them all i have come up with what i believe is the best hot-start procedure. Firstly using the auxiliary fuel pump switch in the cockpit,prime the cylinders with a very short squirt of fuel,basically 1-2 seconds and turn the pump off. Check that your prop area is clear and with the mixture fully rich and the throttle 1/3 of the way in from idle engage the starter. The prop will go through 2-3 revolutions and as always you will get that initial ignition with the "cool"fuel in the cylinder but this is where the trick comes in. Before that vapourised accumulated fuel gets into the cylinder and causes you trouble,what you do is as you get that first ignition using spidey fingers,keep the starter engaged but reach with your middle,ring or pinkey finger and flick on the low volume side of the 2 part auxiliary fuel pump switch(yellow section).What this does is it squirts cool,pressurised and stable fuel into the cylinders at a fairly low volume and this results in a smooth,non-backfiring hot start-up. As soon as you have more than a 1000rpm. Dis-engage the starter and turn off the low volume fuel pump switch. Works every time with minimal fuss and without the large flame out the exhaust.

Hope it was interesting and maybe it will save you from killing the battery and starter motor one day when you cant get the beast started.