Rad blind experiment

[Dieselman]

Having already removed the viscous fan from my car and knowing that most cars are overcooled I decided to try adding a radiator blind, not to make the engine warm up more but to act as an aerodynamic dam.
I read that approximately 30% of aerodynamic drag is caused by air getting trapped in the engine bay, which is why some cars have no or very small grilles.

Just as an experiment I found an old barrel and cut the side out of it, sprayed it black and ty-wrapped it onto the inner grille. It traps up against the outer grill over about 70% of the area.

First impressions are that it causes no overheating problems though must be reducing airflow into the engine bay, the temperature gauge stays just as before, but the car seems more economical at motorway speed and seems more stable when passing large vehicles.
I noticed the other day that snow was building up in the grille slats so it definitely stops the air.

Anyone ever tried any aero mods.?

Sorry about the dark pictures, it was dark.

You can only just see the blind behind the grille.

 

[230K]

Hi

My late father regularly put a "muff" on old cars during the winter. The use of the word always amused me. He did it to keep them running warm in the winter though.

Out in Ukraine they are very common at this time of year they even have proper factory made ones with zipped flaps for lada and other makes.

No puns intended by the way.

230k

 

[jrggino]

will you keep t on and see how you get on in the summer months! Intresting to see how you get on. I think that in the winter months a diesel takes for ever to warm up, I would say its not working afficently. I have blocked the whole gril in my astr 1.7td in the UK and it still takes forever to biuld up to temp.

 

[grober]

Does this not mean your underbonnet air temperature will rise---not the engine you understand since its got a direct coupled means of cooling via the "part rad"--- but the air space and with it all those sensitive little sensors/ECU'S which don't like it hot??? Surely a better solution would be to arrange additional "exits" via louvres under the wings or on the bonnet assuming they didn't screw with the aerodynamics??

 

[stevesey]

I'm tempted to have a bash - would be interesting to take it one stage further make an automatic device.

 

[Dieselman]

I'm tempted to have a bash - would be interesting to take it one stage further make an automatic device.

iirc The old BMW 525TD has such an automated blind.

 

[230K]

iirc The old BMW 525TD has such an automated blind.

124 with the 603 has flaps low down each side of the engine bay that are on springs which i assume are bi-metallic allowing them to open when hot.

230K

 

[stevesey]

Does this not mean your underbonnet air temperature will rise---not the engine you understand since its got a direct coupled means of cooling via the "part rad"--- but the air space and with it all those sensitive little sensors/ECU'S which don't like it hot???

Why an automatic device would be good (just been doing some googling and honda have them and they close at high speeds). In fact it would be interesting to log the underbonnet temp. I suspect at motorway speeds it's lower than when crawling around town, if this is true you can afford to close off a lot of the grill at speed (which is when you get the drag benefits).

 

[Dieselman]

Does this not mean your under bonnet air temperature will rise---

I'll stick a thermometer under there, but from what I can feel the short answer is no, it doesn't seem to make things hotter. I intend to lag the exhaust manifold at some stage, which will cool under bonnet temps.

The ECU compartment is sealed behind the bulkhead so shouldn't really be affected, and this is a diesel so wastes much less heat than a petrol engine.
I also worked on the premise that the grille is large enough for an AMG55 at full chat in the Sahara so much less intake is actually required.

Citroen fitted longer bonnets to diesels than petrols on the BX to assist with aerodynamics as no grille was required for cooling.

This car has an undertray with optimised air exits anyway, though I ought to take some air pressure readings.
Normally there is so much air pressure under the bonnet that cooling can be affected anyway once it builds up.

Warmer under bonnet temps may help some drivers, especially if running on veg oil, as normally the filter is always cold.

Maybe I'll get onto some 'wool tuft testing' as well..

 

[Dieselman]

I suspect at motorway speeds it's lower than when crawling around town,

You an see the temp gauge rise slightly when stationary after a motorway trip, but there seems really to be no difference round town as you're not using much power anyway.

The car still has twin electric fans in front of the rad, but they never come on. it was when fitting this that I checked the fans and found the belt off.

My viscous fan has been off since April last year and it's never got hot. (yes, the thermostat is working).

 

[grober]

It certainly be interesting to monitor variation in air temperature all over the engine compartment. I know certain units have their own cooling fans but I am not sure where they draw their air from?? I assume most heat transfer would be be by localised air convection currents and direct radiation in particular from the exhaust manifold. Don't know the answers just asking questions I know there was a problem with the cooling capacity of the big engined V8 W126's in hotter climates which was rumoured to to associated with a lack of airflow "post radiator" Jim Forgione has details of cooling mods to the viscous fan to increase forced ventilation on his site.

 

[RodgerDodger]

Interesting experiment DM - looking foreward to the results and conclusions

 

[Dieselman]

Something I noticed the other day on the motorway when it was wet, was that there seems to be more air passing over the bonnet, enough for the emblem to make turbulance and spray water droplets backwards.

You can see the effect of the water trails starting right at the lead edge in the picture.

If anyone with a mpg readout could try this it would be interesting to see.

 

[Dieselman]

just asking questions

No problem with that, it's how we learn...

I was also thinking that if there is an areodynamic gain then the engine will be producing less power to drive the car so less wasted heat anyway.

One way to test for drag is to use the 'coast down' method. drive at high speed on a flat road, knock the gearbox into nutural and time how long it takes to slow down.
Repeat in the other direction to average out wind factors.

This guy has reduced his drag from 0.34 to 0.19, but it looks a bit scary...
http://ecomodder.com/forum/showthread.php/aerocivic-how-drop-your-cd-0-34-0-a-290.html

and they are talking about grille dams on there..I'll have a read...

read it..
http://ecomodder.com/forum/showthread.php/what-do-you-guys-think-about-grill-block-6949.html

Don't forget there is always the lower grille as well, and that is in a very high pressure area so will take in lots of air and for the diesels takes in the intercooling air.

Where's mactech when you need him..?

 

[MBManInKen]

I know bugger all about car design, so you should consider these naive questions.

Surely there must be good design reasons for engineers to design grilles and airflows into the engine compartment the way they do? And good reasons why they don't blank the rear side of the grille (partially) off?

If the airflow takes heat away, then what happens to that heat now?

 

[Dieselman]

Surely there must be good design reasons for engineers to design grilles and airflows into the engine compartment the way they do? And good reasons why they don't blank the rear side of the grille (partially) off?

If the airflow takes heat away, then what happens to that heat now?

I think it's one size fits all with most manufacturers and a grille is a design feature as opposed to an engineering one, there are cars with no bonnet grille and they don't overheat.

Consider the same grille is used for a 250kw AMG and a 100kw diesel. The AMG wastes approximately 70% of input energy as heat the diesel approximately 60%. There is about another 5% loss in noise and some of the heat goes down the exhaust so say 50% and 35% wasted as underbonnet heat.
So to achieve outputs of 250kw and 100kw we need a cooling capacity of something like 500kw for the AMG and 120kw for the diesel.

Both have the same size cooling intakes..does that make engineering sense.?

The thermostat is creating a restriction to try to keep the engine warm, the amount of air would overcool it without that.
Maybe a better method would be to restrict the intake air and use electric water pumps, which are already planned for cars in the next few years, and have no thermostat.

 

[MBManInKen]

I think it's one size fits all
[...]
Both have the same size cooling intakes..does that make engineering sense.?

No, it does not and that is a very good point.

 

[DieselE]

I agree that the cooling intakes are the same across the range but does anyone know if the radiators are the same size?

 

[Adam230K]

Diesel, i'm guessing your soul-purpose of doing this is to reduce drag, and to be honest with you, i've thought about blocking up the gaps i have on my bumper under the bonnet to reduce drag... does the 210 have considerably large gaps on the bumper? or would this make no difference?

 

[st13phil]

iirc The old BMW 525TD has such an automated blind.

The latest incarnation of the 3-series with the Efficient Dynamics package certainly has an automatic set of vanes as a rad blind.