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Old 08-19-2009, 05:18 AM   #1 (permalink)
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Grill block advice please

Hi all,

A little background first. My turbodiesel car has no less than 4 radiators - an oil cooler, intercooler, air con condenser and the main radiator. The air con is broken so that's left off all the time. Here's an image of how the radiators are arranged. The oil cooler is the sump. I use the car for commuting 800 miles a week, and so I do not want to damage the engine. I will be getting an oil temperature gauge to keep a better eye on engine temperatures - will also be helpful to have a better idea of how quickly the engine warms up as well. An EGT would be useful to keep an eye on how well the intercooler works, but at the moment, I'm too chicken to install one.

There are 2 holes in the factory underpan which I assume is to let in air to cool the oil cooler, so I'll be leaving those alone. Here's an image of the front of the car with the grilles and outlines of the radiators behind it. Here's a poor picture of the front with the bonnet open to get a slighty better idea.

How should I block the grille? Looking at the image, it seems that the upper grille isn't of much use apart from the air inlet, so is it safe to completely block? The lower grille seems to be slightly like a scoop - see the sides where the optional fog lights would have gone. How should I block this, and by how much? The lower grille also contains the environmental temperature sensor which the ECU uses to decide how long to run the glowplugs.

Thanks for advice in advance!

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Old 08-19-2009, 07:18 AM   #2 (permalink)
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Hi,

I think that a full upper grill block is the best place to start.
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Old 08-19-2009, 07:28 AM   #3 (permalink)
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I thought diesels didn't respond well to warmer air. Is that right?
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Old 08-19-2009, 08:28 AM   #4 (permalink)
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Warmer intake air temp? No, that isnt helpful for a diesel. So I would leave a pathway for your air intake, maybe a tube protruding through the rest of your grill block?

Otherwise your top grill looks good to cover. Along the same lines, you don't want to cover your intercooler (much). I think your car is a good candidate for some duct work at the same time as the grill block. Feed the air directly to and ONLy to the areas where you need it.

Pulling the entire A/C system would likely help you out quite a bit.
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Old 08-19-2009, 09:13 AM   #5 (permalink)
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Interesting - I always thought warmer air = better MPG? How come that cooler air is better for a diesel?

How should I block the upper grille, and make a tube to ensure that the inlet get cool air? As the inlet flares out, it seems difficult to make a tube that will fit securely over it?

So would this be a good start, or am I going too far? Sorry for the poor drawing!
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Old 08-19-2009, 10:01 AM   #6 (permalink)
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Hi Eddles,

I tried the warmer intake air by way of a partially blocked intercooler. It didn't work and actually made my FE worse. But then Tasdrouille has it, i think, and it works for him??
Anyway, i'd stick a sheet of cardboard or coroplast (the same size as the aircon radiator) between the aircon radiator and the engine radiator. Then duct fresh air to the intercooler through the lower opening in the bumper, while keeping the opening area the same or more to it.
It'll be tricky but you can ball park the parts and fit them, then mark the final cuts in situ to guarantee a good fit. Then tape it together in situ with duct tape. Should work out easier with the aircon radiator removed.

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Old 08-19-2009, 10:36 AM   #7 (permalink)
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My understanding is as follows:

The reason that a warm air intake works on a gasoline ICE (with fuel injection) is because you actually reduce the density of the air coming in at a given throttle position. The ECU attempts to maintain a given A/F ratio and reduces fueling accordingly. But now you are making less power at a given throttle %. So you dip into the throttle a bit further to get back to the power output you need, and thus match the oxygen intake, fuel consumption, and power level you would have had with a cold air intake at the original throttle %. Only now with the throttle open further in the case of the warm air intake, your pumping losses are reduced because theres less of a stupid restriction in the way. Hence another advantage of the diesel engine (no throttle to arbitrarily reduce engine efficiency).

Increasing the intake air temperature (IAT) has an effect on the quality of combustion. The exact effect is debatable, and multiple papers have been published to investigate the nature of this parameter upon combustion efficiency. My opinion has found that warmer IATs result in less power from my diesel engine. One can logically conclude that this is due to poor(er) combustion. Which means your fuel is not being used to its fullest. So without the benefit of reduced pumping losses, theres no reason to raise the IATs on a diesel.

Your rough grill block sketch looks good to me!

I had the same problem with an upper grill block (engine intake located here) so I solved mine this way:




I'd like to re-route the intake someday and close off the upper grill for good though.
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Old 08-19-2009, 10:54 AM   #8 (permalink)
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Apparently, there are situations (as pointed out by another member here, I think) where warmer intake air on a diesel is desirable, but the results were recorded under less than normal circumstances, testing emulsions of fuel and water or fuel and gasoline.
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Old 08-19-2009, 04:17 PM   #9 (permalink)
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I'm not a diesel expert, so correct me if I am wrong on this:
The reason why a diesel engine will not respond well to a WAI relates to how engine speed and power is regulated. In a diesel engine, there is no throttle per se. You push the pedal, more fuel is added, increasing the downforce, thereby increasing power (whether translated to torque or rpm). The air intake is not throttled, meaning that the engines air is regulated by it's pumping. The AFR is highly variable, but typically run much leaner than stoich (28 - 32:1 rather than 14.7:1). Since the engine is pumping a set volume per revolution (rather than a set mass), a colder (ie denser) air charge means more power as the gases expand. Pumping losses due to increased viscosity are mitigated by the lack of a throttle plate.

In a conventional gasoline engine, you push the pedal and the throttle (air) is opened. Sensors then adjust the amount of fuel injected to acheive the proper ratio. A warm air intake, because of modern MAF sensors, will translate into less fuel injected. Pumping losses due to the throttle plate are slightly offset by the lower viscosity of the air.
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Old 08-20-2009, 11:30 AM   #10 (permalink)
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Wow, I learn a lot every day!

Just a few more questions:

I've forgotten about the environmental temperature sensor which is roughly in the middle of the lower grille. As the ECU use the information from that sensor, and the cabin temperature display use that information as well, I believe it would be better to have accurate information from that sensor. I remember when I used a work's van, a Vauxhall Combo, it had a faulty temperature sensor, it was showing 66.5 degrees C (151.5 degrees F) and the diesel engine (exact same engine as mine but with a common rail injection system) took well over a minute to start each time I used it, I suspect it's because the ECU doesn't use the glowplugs at all. That's certainly not what we want! It could be a different problem, however.

So I guess I should make a tube through the grill block so the temperature sensor would get accurate information? Or end the left block just over the temperature sensor?

Second question - should I edge the block straight, or slope the edge, so the grill block would "funnel" air torwards the intercooler and the air intake pipe? I think I'll be putting the block on top of the grille, and making the block flush with the surface of the bumper.

Finally, how should I attach the block to the lower grille? I need to make it easy to remove in case the engine gets too hot. So something like glue would be out of the question.

So that's 4 jobs:

1) Get rid of air-con
2) Make a duct from the lower grill to the air intake
3) Completely block the upper grill by stuffing something between the slats - someone suggested central heating pipe insulation.
4) If step 3 doesn't heat the engine too much, then make a surface block on the lower grill but making sure the intercooler, air intake duct and temperature sensor is exposed. Make sure that the block will be easy enough to take out. I will leave the bottom-most grill slat alone. I can always stuff that to experiment in the winter.

Sounds good?

Thanks so very much to everyone for your advice, much appreciated!

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