Shock Cooling

[Yenn]

I thought that one of the touted advantages of water cooling was that it reduced the rapid changes of temperature.

 

Cold seizure is caused by the piston rapidly heating in a slowly heating cylinder. Does the Rotax cooling system, water cool the cylinders. from what I can see it is the heads that are water cooled and the cylinders are air cooled.

 

One way to prevent a cold seizure was to start the engine and run it foe a short while, stop it and let it sit for a few minutes, then start and prepare for flight in the normal way. That ensures that the cylinders heat soak for a while when the engine is not running.

 

 

[pudestcon]

Close cowl flaps, apply carby heat.

A bit hard to do on the ol' T500 Thruster:wink:

This time of year though, I cover part of my radiator elements to ensure sufficient engine temps.

 

Pud

 

 

[Dafydd Llewellyn]

Erhm - the 582 has water-cooled barrels and heads, so the original question of the thread is apposite. Apart from cold start-up, will the thermostat not prevent a sudden circulation of cold water from the radiators?

 

 

[facthunter]

We shouldn't confuse two strokes with 4 strokes. When you cut the throttle on a two stroke is gets cooled from outside and a bit on the inside. I am not sure about putting a thermostat on a 912 as it has water pipes everywhere and they are hooked up in parallel. Only the heads are water cooled and they are supposed to be a very UN critical motor in this regard. The heads tend to run too cool (unless using Evans waterless). Be carefull where you get information from. There are more and more crackpot theories out there that seem to be reinventing the wheel and rubbishing older techniques. Gypsy Major engines used to be extremely reliable. Today they are just average because of all the "experts" playing with them, who all seem to know more than the next guy. Say Hoo roo to the guru, and just find someone who knows his stuff. Nev

 

 

[Dafydd Llewellyn]

Well, the man didn't say it was a four stroke - and as I've just purchased a 582, I'm interested in what might emerge on this thread. I'd assumed that the thermostat would suffice - and I'm looking at air restarts after periods of gliding. Yes, I'll be closing cowl intakes & outlets when the engine is shut down, and the restart procedure will have to include a warm-up at idle, to the thermostat cracking temperature.

 

The early Gypsies, with bronze cylinder heads, were fairly immune to shock cooling - but you had to be a bit more careful with the later versions, which had aluminium alloy heads.

 

I put a thermostat on a 912 in one of the first Murphy Renegades, because the heads were experiencing what I considered far to great a variation in temperature between climb and descent. The thermostat improved that greatly. However, I also included a manual thermostat bypass valve, in case the thermostat failed shut - and in fact that saved the engine (and possibly the aircraft) a couple of hundred hours later.

 

 

[bushcaddy105]

All of the above highlights one big advantage of a fully liquid cooled engine - hence the great track record of the Subaru EA81. The stock car thermostat (83 C) keeps the coolant between 80 and 100 under all conditions (with correspondingly low cylinder head temperatures) so thermal shock isn't an issue.

 

 

[facthunter]

There can be thermal shock when the thermostat opens initially and allows totally cool coolant into the motor. Depending where you fit the thermostat and how much of the coolant is bypass circulated when the thermostat is shut. Nev

 

 

[Dafydd Llewellyn]

No, because the thermostat always opens gradually; have you never tested one in a saucepan of water, on the stove?

 

 

[facthunter]

Well they DON'T in a motor Dafydd. When it reaches the opening setting the temperature of the water behind in the top part of the engine, it is very hot, and it opens fully in most cases. It's only when the cold water from the radiator goes right through the motor that it modulates.. Sometimes they will "hunt". A far from satisfactory set-up is the normal placement of the thermostat at the outlet from the engine, particularly IF there is no recirculating bypass. Nev

 

 

[Dafydd Llewellyn]

Sounds like a reason to put a temperature sender in the engine water intake hose & see what's going on, then. I do prefer the bypass style of installation. I doubt what Rotax put on the 582 is that style, which means I'll be modifying it and adding a manual override valve to it.

 

 

[facthunter]

Good idea, but consider adjustable shuttering of the radiator in a way that reduces drag. You have the least temp drop across the engine that way as your intake coolant temp is raised. This effect is achieved by having a radiator that is just adequate, but a hot day is your enemy. Nev

 

 

[Dafydd Llewellyn]

Yes, I'm familiar with the principle. But I'm not dealing with a standard installation, here; the motor is in a pod at the top of a streamlined pylon, and the radiators are inside the pylon, with doors that are opened by the process of turning on the fuel. There's a limit to the number of control cables I can run up the pylon. I'll be testing the whole installation in an instrumented test cell, so I'll find out whether the thermostat will do the job.

 

 

[facthunter]

You have to keep your set-up compact .I often just drill a 3-4 mm hole in the thermostat so it never completely blocks anything right off. Nev

 

 

[Dafydd Llewellyn]

Yep, I know that trick too. However it's not really necessary with a bypass-type setup, I suspect.

 

 

[bushcaddy105]

EA81's have a small bypass hose from the thermo housing (right alongside the thermostat body) back to the water pump inlet, thus ensuring a gradual warmup of the thermostat and preventing sudden opening or closing. It works well.

 

 

[blueline]

Shock cooling doesn't seem to have much effect on engine life in the Lycoming 360 used in Seminoles

 

I was cross hiring one that had 2800 hours on one engine (never had a top overhaul), and looked at another one to buy that had one engine at 2400 hrs and it had never been touched (according to the log books).

 

Certainly not going to hurt making progressive temperature changes but it seems that the big killer of aircraft engines is high temperatures and rust!

 

 

[ben87r]

Non turboed engines with normal use (GA) shouldn't have an issue if used with reasonable care. With a power on descent, the temp difference is marginal. Highest being in cruise after the cowl flaps are closed. It takes a long time for the CHT to come down and a gradual reduction of power throughout descent will be enough all old wife's tales aside. And by that I mean if you reduce power by say 2-3 " per thousand the world won't implode. Just have some consideration of the engine and care that any pilot worth his name should.

 

 

[Dafydd Llewellyn]

It does if you are using them - e.g. in a Bellanca Scout - for glider towing.

 

 

[ben87r]

Ild argue that gilder towing isn't in the above and that the old wives tale (or one of them) being an " per k are on the extreme ends of the argument. Also I would think the amount of time spent at climb power per hr flown would be more of a consideration for TBO

 

 

[frank marriott]

I guess in your own aircraft you can do whatever you like.

 

With most Chief Pilots I have known shallow power on descents (higher TAS as well) V steep power off would mean the difference between regular flying and a DCM - whether you agree or not.

 

 

[ben87r]

DCM Frank?

 

 

[frank marriott]

Don't come Monday

 

 

[ben87r]

Oh! That's a new one!

 

 

[frank marriott]

Ben ,

 

More like a very old one then a new one - maybe not used much now.

 

 

[ben87r]

Well hopefully I don't hear it too often... I don't think it helps pay the mortgage