Smaller radiator for FE?
 

I was looking through the vehicle mods again and I started thinking: given the way most of us drive, would a smaller radiator help FE? A lower overall volume of water and smaller radiator surface area should improve warm-up times. Additionally, a shorter water path should decrease the back pressure on the water pump, meaning less power is required to pump the same volume of water.

The downside is obvious. We could increase the risk of overheating. So I'm not suggesting cutting the radiator size in half. It is also more likely that your fan will kick on more often.

What are your thoughts?

Smallest radiator possible with the highest cooling capacity available.

I think most of the pressure in the system comes from the amount of times the water has to change directions, not necessarily from the radiator. Measure pressure drop across the inlet and outlet of a radiator, at whatever CFM the fluid flows, and then do the same through all the passages of the block/head. I'm sure you'll find that it's much greater in the engine.

I had honestly considered replacing the radiator in my Civic when it started leaking from the end tanks (before I learned how to fix them) with some from a bike, which are much smaller. I never actually did it, but my Civic always ran over-cooled without the thermostat in it, and one of my goals was to be able to remove the t-stat and still have normal warm up times without overheating.

I agree - most of the pressure drop occurs in the engine. But replacing a radiator is much cheaper than the engine :rolleyes:. But the point is to actually lower my available cooling capacity (water volume and surface area) to improve warm up times and SLIGHTLY reduce back pressure (that piece may only be worth 0.1mpg or less).

For the reasons mentioned, I think it would.

Plus a smaller radiator would permit a smaller grille opening, bringing established aero benefits.

That's why I wanted to get a setup that would still allow proper and full warm up without the t-stat installed.

Changing the radiator on a thermostat equipped motor would not decrease warm-up time since that is controlled by the thermostat. The water pump tries to move the same amount of water at a specific RPM no mattter what the size of the radiator and quite possibly a larger radiator would have less flow resistance and reduce the load on the pump. If you want to reduce the load on the pump then look into an underdrive pulley set which would slow both your water pump and alternator and reduce the load of both.

Christ: Why do you run no stat?

It is possible that a smaller radiator would have more flow resistance if the tube diameter were smaller or there were more turns. However, the pressure drop also varies directly by the length of the water path. A smaller radiator is likely to have the same size tubing, fewer turns, and lower length.
I agree that the volume of water pumped will not change. But the overall volume of water contained in the system will decrease, meaning a smaller heat sink and faster warm up times.

People have done "half radiators" and talked about it on GS but I don't recall the details.

...well, here's my "DIM LIT LIGHT BULB" idea submission:

...how about selectively dumping the exhaust through a portion of the radiator to speed-up coolant temperature-rise and thus initial engine warm-up.

...maybe a thermostatic "dump" value (like the old exhaust "rattler" used to 'crossover' the exhaust through the bottom of the carburated intake manifolds).

...sends 'some/most' of the exhaust thru the small radiator when COLD, but once reaching operating temp then sends 'all' exhaust through regular exhaust system as normal.

That's not true at all. The thermostat doesn't just stay open, this is the reason that grille blocks afford a shorter warm up time. The thermostat opens when the water touching it reaches a specific temperature. As the flow rushes past it, it cools down, lower than the temp at which the t-stat would be open, so it closes again. This heats the water up again inside the block. This happens several times before the engine has actually warmed up. A smaller radiator (or a grille block) prevents the water from cooling as much between cycles, so there are less cycles of heating and cooling until complete warm up.

I don't run with no thermostat. It was a goal I had, to be able to run without one and still have normal warm up times and no overheats. T-stats represent a fairly large restriction to flow, even when open fully, which loads the water pump. It's a negligible amount of power, but it's not like it'd be hard to do, and the smaller radiator has obvious aero benefits as well.

A poor man's way of testing this would be to remove your t-stat, blocking off half the radiator via removable aero mods (think cardboard and masking tape), and driving a test loop doing some A-B-A testing. B would be normal. Make sure to monitor coolant temperatures.

Hell, I was just going to remove the T-stat after getting a timed baseline for how long it took to idle up to temp, then start periodically putting in smaller radiators until either I started overheating under my normal driving, or I met the time goal.

In Civics, the half sized radiator works every bit as good as the full sized, but I've seen reports of faster warm-up times, partially due to lowered cooling capacity, but also partially due to less coolant to heat up/cool down for each cycle.

I believe this whole premise to be incorrect.

When you reduce volume pumped by restriction, the load on the pump gets EASIER, not harder.

Example? Take a hairdryer and turn it on. Note the speed. Now block the flow completely. It speeds up! It wouldn't speed up unless the load was reduced.

The thermostat only blocks flow to the radiator. It comes after the pump, and after the flow through the engine block. If the thermostat is closed, the coolant recircs through the block, then back through the water pump.

If the thermostat is open, the coolant proceeds through the water pump, through the block, through the thermostat, then into the radiator, and back to the water pump.

Because the circuit is built the way it is, you're looking at it backwards. The thermostat is a restriction to pressurized hot fluid, and doesn't contact the cooled fluid returning from the radiator to the water pump.

Therefore, instead of choking off the input of the hair dryer, as you suggested, you'd have to test the theory by blocking the output of the dryer (or box fan), which does actually place a load on it, because it's trying to compress a fluid. (Air, in this case.)

An adjustable radiator or grille block that maintained the coolant temperature of the coolant exiting the radiator at the same level it was in summer would help a lot with improving mileage in the winter.

regards
Mech

Yeah, block the output. I didn't specify inlet or outlet. It doesn't matter. Grab that hairdryer and do it. Turn the heat off if you can; it gets damn hot!

I remember Basjoos has a light that tells him the electric cooling fan is running. If it runs often he opens his adjustable air inlet.

With that kind of aero and engine compartment sealing he is getting hot coolant outflow and warm air intake, without anything else.

regards
Mech

K, so without a thermostat, I'd be able to use a smaller radiator, since there would still be more flow, regardless of whether it's loading the water pump or not. Smaller radiator = less fluid to pump, which DOES partially unload the water pump, and less weight (granted, miniscule amount) that the engine has to propel when moving the vehicle, plus another measure of aero benefit.

Granted, all miniscule compared to leaving the t-stat in, but still gains to be had. On top of all that, no worrying about the Tstat failing closed. Not supposed to happen, but it does.

I've no problem with the 1/2 rad concept- a lil lighter, etc.

I don't think the pump will "see" any difference re: volume in the system. Forget about pump loading.

Thermostats regulate temp and improve warm-up times. I am not aware of any data that says they are the limiting factor in cooling system capacity. They rarely fail... or I'm just lucky? Bwaahahahaha!!! I don't see any benefits to disabling them.

I've had two fail in my life. Thinking about it, I'm not really sure why I wanted to go with no Tstat. I don't think it had any premise based on real thought, rather than just going on a whim, saying (yup, I'd like to remove that thing).

I guess goals don't really need a reason, just an end and a means, right?

It's good to think about and investigate stuff even if it doesn't pan out right away. Who knows when down the road the lessons find application?

Frinstance it could be someone comes up with a thermosiphon system that's good enough for hypermilers.

Which would certainly kick ass, but probably would not be using water under pressure. I think it would be using something akin to refrigerant, maybe ammonia or propane? (I've used propane to recharge a car's A/C system... it never gets hot enough in there to reach the auto-ignition temp, and even if it did, other components would fail, causing it to vent to atmosphere long before it was able to ignite.)

When the fan belt broke on my Z car (defective) I drove it ten miles using pulse and eoc.
The air flow across the water pump driven fan was enough to keep the coolant moving with no belt to drive the alt or pump and fan.

It was actually cooler when I finished than it would have been with the belt working.


regards
Mech

The thermostat has a specific range between it's opening and closing. (Probably about 20 degrees) After it opens to a cold radiator it will then close when the temp drops to its closing point keeping the motor temp within the thermostat's range. As long as the motor is in this range it is "warm". A smaller radiator will reduce the number of thermostat cycles but at no time during these cycles does the motor temp get less than the closing temp of the thermostat.

The only way a grille block would speed up warmup is through the reduction of cooling air flow through the engine compartment.

The restriction to water flow provided by the thermostat is necessary for efficient cooling. It slows the flow of the water to give the heat time to be extracted by the radiator. In a race car with no thermostat they put a restrictor in to accomplish this. Keeping up your cooling efficiency is even more important if you are reducing the efficiency of your radiator with a grille block.

And here I was thinking about trying to get a larger radiator in the Insight. Yes, it's got more thermal mass, and that's bad, but if you had a larger radiator, would that allow a smaller grille opening?

I suppose what I want is a carefully designed radiator, don't care what size, where a small amount of air entering the engine room provides as much cooling as possible. Maybe a compact, three row radiator behind a small grille opening would work.

The Insight has the exhaust manifold integrated into the head for better exhaust heat retention and faster warmup. The downside of that, I'd imagine, is the need for more airflow across the radiator once the car is warm.

smaller
 

I think the logic is good and it's smart thinking.Systems are designed for Furnace Creek,Death Valley,California and worst-case-scenario.----------- That's not to say that you couldn't get into trouble with a smaller system.You might rehearse for overheating by sliding or turning temp control to full heat,outside air,and full fan,to create auxiliary cooling in a bad situation.------------------ I my spare time,I would like to explore pressure drops across thermostats at various levels of "open." My HONDA thermostat is a work of art compared to Chevy,Ford,and Dodge units I've encountered.---------------- Also,during development of the Chrysler LH platform and powertrain,it was claimed that the water pump designed by computer for those series of cars,had the lowest hydrodyynamic drag of any ever tested.------------- Racers use "vintage" impeller tech,with cast hydrodynamic vanes rather than bent metal vanes.----------- Additionally,extra-duty towing packages include a "SMALLER" impeller pump to minimize cavitation caused by high tip velocities within the pump volute.-------------- It looks like the cooling system is very fertile ground for modding!

I assume you'll make an external orifice for testing the pressure drop?

Like two thermostat housings bolted together, I mean, w/ the t stat between them, varying pressure/temp?

Could you also try varying mixtures of coolant/water or different types of coolant? I believe there is a viscosity difference, which could change hydrodynamic profile.

It would be great to find out that by varying your coolant mixture by 15-20%, you could get better efficiency from your engine... :rolleyes: (Dreams, right?)

Oops! Apples and oranges. The dryer example is only true because the medium is of variable density. Water can be considered (at least for this discussion) a medium of constant density. Here's the example- nudge your power boat bow-first up against the dock, then go full throttle. Note the max rpms. Then go out into the fishing channel where all the idiots in their row boats are, and go full throttle. Note max rpms. See? :thumbup:

Are there variable vane water pumps?

Interesting point...

but does a prop have comparable properties (pun!!!) to an enclosed impeller pump?

So I just went and got my spare sump pump- axial impeller like a car water pump- put it in the kitchen sink with water and turned it on with my hand over the outlet.

mmmmm... pump motor so powerful it didn't vary much, unlike the hair dryer. I thought it slowed under load ie. pumping water...

Can you vary the input voltage to under-rate the torque?

I don't have anything handy for that.

What I'd like is a tach for that motor.

Edit: What was I thinking? I need an ammeter. Don't have one for AC.

Got a high speed camera? It's a slow, tedious way, but you can gauge max RPM with a high speed camera.

Some water pump stuff:

Inside BMW's Latest Powertrain Technologies

Water Pump Tech

OK here, from a piece regarding sensors for centrifugal water pumps:

http://www.warrender.com/upload/prod...28dab2a7fd.pdf.

So me thinks automobile water pumps could cavitate just like that hair dryer and not like that boat, were flow to be stopped.

But then... the flow isn't ever stopped even when the stat is closed. Circulation is constant through head and block.

Now I think whether t-stat is open or closed likely has very small effect on pump load- too small to matter. For what my opinion on that is worth.

And:

http://www1.eere.energy.gov/industry...pdfs/38949.pdf

Combine that with the SuperChevy dyno stuff, and underdriving the water pump can save HP but don't do it at the expense of low rpm cooling. And they didn't even bother reporting testing below 3000 rpm cuz it was too small.

Just to investigate, I did find that the ECHO does have a smaller radiator (it has the 1.5L engine). As you would expect, the mounts are different and the hoses are in different locations (same diameter heater hose ports though). They both have 5/8" diameter radiator tubing, so the difference in pressure drop will only be due to the shorter tube length. Difference in core size?
Corolla: ~340 sqin
ECHO: ~260 sqin
Or about 25% less area. The height is the same, making the mounting a bit simpler. At a guess, coolant volume would drop by ~10-20%.

EDIT: I'm diggin' what BMW is doing on their water pump tech.

That was my thoughts too. I have a HD cooling system in my cars and blocking the grille is negligible to engine temp. I have to wonder if the light duty system would require me to remove the grille block sometimes.