rear-mounted radiators and ballast tanks

[aspera]

The cooling system in my MR2 is notorious for trapping air bubbles, and there is a special way to bleed it using bleed screws. Some guys are brought to tears when they have to drop the fuel tank in the middle of the car to get to the stainless steel pipes that transfer coolant from the engine behind the cabin up to the front mounted radiator. These pipes don't trap air, but they can rust or clog. I've been lucky so far, but I think I'd rear-mount a radiator(s) if that happened.

Anyway, that's part of the reason why I like the idea of rear-mounted radiators on front engined cars. I've seen that it is possible to drive a car with the radiator mounted on the opposite end of the car from the engine bay. All you need to worry about is AIR IN and AIR OUT, really. For guys on this forum, you wouldn't need to scoop much air at all.

The benefit of doing all of this is that you could seal up the whole nose.

[Piwoslaw]

Originally Posted by aspera

Land speed racecars also use ballast tanks instead of radiators. Those tanks contain cold coolant. After the end of the run the tanks are hot and are allowed to cool down. The ballast tanks allow the cars to seal up the front grille entirely. Running without a radiator wouldn't work on a street car, but adding a ballast tank *IN ADDITION TO* a radiator would create a buffer so the car wouldn't overheat AS QUICKLY. That might help some of you guys that only have a postage stamp sized hole in your air dams.

Having a balast tank would also slow down the inefficient warm-up stage of the engine. A good idea would be to have large tank of coolant which would be closed at lower temperatures. Only a small amount of coolant would be left in the engine/radiator loop. Once the engine warms up to optimal temperature, the tank would slowly open, letting its cooler contents gradually mix with the warmer coolant in the system. When the car parks and the engine is turned off, the extra amount of coolant in the tank acts as thermal mass, so when the car starts again later it has lost less heat. Also, a slower rate of heating/cooling is better for the engine parts.

[MazdaMatt]

I considered relocating the rad on my track-only del sol, but i realized that 12 feet of rad hose each way, plus the weight of the added coolant that 24 feet of hose would hold was not worth it. Plus it is a high pressure water system, so you can't cheap out. Heavy, expensive and a potential reliability issue. Maybe on my next build-up.

[aspera]

Weight reduction doesn't seem to be the major concern in this small corner of the automotive hobby as it is in racing. Low drag aerodynamics seem to be the #1 concern for highway driving. Not cooling or downforce.

A heavier vehicle smooths out the changes in speed on a hilly road. The mass is like a battery and dampens changes in speed. Racecars use lighter flywheels. I think a hypermileage car might benefit from a heavier one.

I deal with this stuff on my job. I'm a locomotive engineer. Sometimes I drive 16,000 ton coal trains. Sometimes, I drive trains that have more aero drag than hundreds of parachutes. Trains are sort of the ultimate hypermileage vehicles...steel wheels on steel rails, a hundred cars drafting each other, and a TurboDiesel-electric powertrain that keeps engine RPM steady independent of speed.

[aerohead]

Originally Posted by aspera

Why do you say for very light duty vehicles? Almost all of the examples I've been able to find were on race cars.

Good info on the legal problems with production cars heating the surface. There have been some tube-frame drag cars that piped the coolant through the tubing, but a radiator still seem to be better answer. Most cars and trucks stick with the traditional solution of mounting ONE radiator front and center. That works but it isn't the only solution. In my opinion it isn't the best solution either.

Since you guys brought up heating the surface of a car, I've always wondered why some of that waste heat from the radiator wasn't put to good use keeping ice from building up in my front wheel wells in winter. A couple of coolant lines routed inside the front part of the rocker panels or inside the fenders would make winter just a little bit nicer. It only needs to warm up to just over freezing, so lawyers wouldn't have anything to fuss over. Besides, the underside of the car is a hot place anyway. You can put hot bits anywhere you want under there.

road hazard meets rotating tire,tire launches road hazard into coolant line,line breaches,driver on side of road with thumb out?

[aspera]

Yeah, that's why I said inside the rocker panels. If road debris crunches your rocker panels, you shouldn't be driving it anyway.

[aerohead]

Originally Posted by aspera

Yeah, that's why I said inside the rocker panels. If road debris crunches your rocker panels, you shouldn't be driving it anyway.

It was the "inside the fenders" part that gave me the pucker.I've considered the merits of waste heat de-icing,just never thought it out to a point where I thought it was foolproof.------------ I have been stranded.In the winter,the implications of that are really serious.---------------- No doubt,the "impossible" just takes a little longer.--------------------- I like Ford's Probe-IV rear heat-exchanger layout,with coolant running through a finned aluminum extrusion,the full length of the car which itself does some heat rejection and reduces size of radiator.That car had a flat floor so it was easier to pull off.----------------- With radiator in one quarter-panel,and A/C condenser in the other,forced-air fans could push the car to 4-mph!----------------- And with Cd0.15 all these things were adding up to a pretty good fuel-sipper had they produced the car.------------------------------- I think the rear-cooling is a really good idea and hope to one day explore that one.You're on the right path.Just try and avoid some of the stupid pitfalls I've put myself through with my half-baked brainstorms.-------------- Best to you on your mods and keep us apprised of how things shake out.

[MechEngVT]

Originally Posted by aerohead

road hazard meets rotating tire,tire launches road hazard into coolant line,line breaches,driver on side of road with thumb out?

Your best bet is to use a metal tube mounted to the vehicle's chassis. I've actually been in powertrain design on a mid-engine vehicle with a front-mounted radiator that was a 4x4 for off-highway only use (hence my experience with difficult coolant purging). It used a steel tube weldment under the floor of the vehicle that was still up between the frame rails but the finned aluminum extrusion may work as well.

When I was in college I participated in FormulaSAE and weight reduction was a key goal. Just between the mid-engine and the sidepod radiator we found a couple pounds of weight savings by using rubber hoses only for bends and flex couplers, and using steel thin-wall tube for straight runs. The metal tube is lighter AND more durable.

[aspera]

When in doubt, use titanium.

Brad Bedell's Supercharged V6 Toyota MR2 that won SportCompactCar's USSC used titanium tubing for the coolant lines in the tunnel. Awesome or what?

examples

Mech, Were you working on a side-by-side or one of those Honda powered buggies? What's your opinion on the importance of weight reduction compared to aero drag reduction for cars on this forum?

[MechEngVT]

aspera,

I worked on a side-by-side that could get either an air-cooled Honda (at the time) or a liquid-cooled N/A diesel.

As far as weight reduction vs. aero (assuming you mean road cars) it depends largely on your driving cycle. Personally I almost never drive stoplight-to-stoplight and spend large portions of my drive on fairly level controlled access highways. A vehicle's FE on such a cycle is dominated by aerodynamic effects. Any drive cycle where speeds are low (below 35mph) and/or stops and hills are frequent would have its FE dominated by weight/acceleration effects. I'm more of a performance junkie than an all-out eco seeker so I tend to think that all weight is bad, but honestly to do more P&G at highway speeds more mass becomes necessary with a larger CdA or the P&G is less effective.

Just in case you were asking about off-road side by sides or ATVs, unless you're an all-out racer seeking to hold top speed aero doesn't come into play much. That said, you would be surprised how much drag a canvas and plastic canopy illustrates at just under 30mph.