Too goofy?

1. Of course it could.

1. It's not worth it (little benefit, more cost, less reliability)

2. I'm sure there's at least one vehicle driving around with one already.

There are a couple of good reasons against it. Economics and reliability are probably the best. Also a pump is usually a _big_ flow restrictor when it's not turning, so you might even need to add a bypass valve to it.

Main one though is that cooling needs are matched fairly well to rpm, so having an engine driven pump is already a reasonable first approximation to what you need. Couple this with the airspeed-sensitive cooling efficiency of typical radiators and an electrically driven radiator fan that only puts in an appearance when stationary, and things are already quite well matched.

If you're after a few HP back at top speed, why not switch from hydraulic power steering to electric ? Now there's a system that works well and saves wasted power (if it's Japanese rather than American, at least).

As to the thermostat, then so what ? You don't need thermostats or restrictors by some divine law, you just need them in systems designed around having them. I've got car engines that run cold with no thermostat, are infamous for running hot with no thermostat, and even that form an outside 3-way pipe junction (try removing that!) I used to have one where the thermostat was known for having no effect at all, but the radiator blind had to be adjusted according to the weather forecast.

Thermosyphons, and pump-assisted thermosyphons were used in cars for _years_, well into the '80s. Peak combustion temperatures have also dropped, if anything.

If there's a single reason why thermosyphons no longer cut it for car engines, it's to do with mechanical density of cylinders in smaller blocks with smaller passageways. Flow velocities are increased, and on many systems the pressure is too. 15psi used to be fairly standard, now it's often around 30psi.

Who mentioned either enthalpy or entropy ?

Besides which, what does it matter ? We're not changing coolant characteristics or temperature here, just regulating the simplest mass flow of it and wondering whether that's best done with a valve or a controlled-speed pump.

snipped-for-privacy@codesmiths.com wrote in news: snipped-for-privacy@b28g2000cwb.googlegroups.com:

"Pump assisted thermosyphon"? Isn't that contradictory?

They have. From about 2,700F to about 2,000F. Nitric oxide emissions are the reason. NO emissions become significant at about 2,500F.

As I said...

I'm wondering about your examples. I see 13psi (0.9bar) and 16psi (1.1bar). 30psi would be 2.0bar. Personally, I've never seen a road- going automotive cooling system running under that kind of pressure.

Because you NEVER want to slow down the water flow through the engine. Modern cooling systems (and even ancient ones, but to a lesser degree) do not SLOW the flow of coolant when little cooling is needed, they DIVERT it away from the radiator and circulate it back through the engine. What this does is make the temperature through the engine more uniform, because without recirculation some parts of the engine would overheat and others would be running too cold for maximum efficiency and minimum wear. Even when maximum cooling IS needed, a lot of heavy-duty cooling systems still recirculate up to 50% of the total flow volume to mix with the cool water returning from the radiator so that the engine isn't cold around the cylinder skirts and boiling in the heads. Reverse-flow cooling systems achieve similar results, but still use some blending.

Why? You have a large bore, slow flow system, and it gains a pump too. Think of all those '50s Brit engines that stayed in production until the '80s.

Depends on the engine - some of the leaner burn engines still have pretty high temperatures (NOx is indeed a major problem with their adoption).

Look at modern mainland Europe. 2 bar is almost commonplace on recent designs.

snipped-for-privacy@codesmiths.com wrote in news: snipped-for-privacy@i3g2000cwc.googlegroups.com:

Didn't those things overheat all the time? And in any case, we're talking modern engines designed by people who hadn't had two gallons of best bitter at the pub the night before.

Like I said...

It does not depend on the engine. If combustion temperatures approach

Really? I wonder how their rad hoses are built.

No. Unless people took the thermostats out, as the BL A & B series engines were one of those where removing the stat completely would disrupt the waterflow.

Are we? Like much of Usenet, this group is somewhat US-centric. You can lecture Europe on engine design when you lose your obsession with huge low-compression OHV V8s.

Of course combustion temperature depends on the engine! Look at the trouble Porsche had with the 911 engine, where they had to start watercooling the heads to get emissions under control. It's not just the peak temperature that matters here, for volumes of NOx, it's an integral over the whole volume of the combustion chamber and duration of combustion.

Look at modern Japanese small engines, like the Honda Jazz. Tiny engine with high compression, lean mixtures, high specific outputs and every sign of peak combustion temperatures being set to go high -- yet they keep the emissions down somewhow. I don't know how they do it, but I guess it's by avoiding localised high temperatures (we're back to cooling system density again, and the problems of small waterspaces and making them reach absolutely everywhere).

Same as ever. The limit is in hoses are attached to spigots. If you see a failure it's nearly always because a hose has blown off, not because it has split. If you do see a car boiled up by the side of the road today, it's usually full of teenage chavs wondering why their silicone dress-up hoses have blown off from their Subaru, when they didn't fit them carefully enough.