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Old 02-16-2009, 07:50 PM   #1 (permalink)
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Partial grille block - Fully duct tape

I made myself a partial grille block, out of tape. Gorilla Tape to be exact, and I'm pretty pleased.

Ok, it looks pretty bad from up close. But I'm not concerned with my car's appearance anyway. And from more than 15 or 20 feet, you can barely tell it's there. As far as performance, it works well in cold weather, helping my car warm up faster. And the it seems to have a little bit of an aerodynamic effect too. But I didn't do A-B-A testing, so it's tough to entirely verify either of those claims.

The problem is, on semi warm days, around 50 or 60 degrees (10 to 15C) the coolant temps rise what seems to me to be too high. I have seen the scan gauge report as much as 230F (110C) with the grille block while the normal temp without the block was usually 188F (86C)

So, my questions are as follows. Is that an unacceptable increase in coolant temp? The problem is worse at low RPMs and high engine loads (city driving), it usually is fine at medium to high RPMs and low loads (highway). Is is possible that my water pump is going bad or bad to begin with and it can't circulate the coolant fast enough?

Here's a picture of the grille block, I can't get it to embed properly.
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Old 02-16-2009, 08:13 PM   #2 (permalink)
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Hi,

230F seems a bit too high to me, too! Is the fan kicking on? My xA gets up to 204-ish (on hot days, when I'm stuck in traffic for more than 5 minutes) and the fan comes on. 182-184F is where it normally runs, with or without the grill block -- which is about 3/4 coverage.
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Old 02-16-2009, 08:42 PM   #3 (permalink)
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I forgot to mention, I pulled the fuse on the fan so it wouldn't be constantly running when I had the defroster on. I would think that at city speeds of around 30mph the fan wouldn't be needed, right?
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Old 02-16-2009, 09:50 PM   #4 (permalink)
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Oh, yeah, you need to put that fan fuse back in

The reason you're hearing the fan come on with the defroster is because the A/C engages.

But you definitely want it available for cooling. Either that or you have to watch it like a hawk and run the heater blower (on hot, and on high) to bring the coolant temp down. But in either case you're adding electrical load to the engine and cooling system, so you may as well put the fuse back in and let the car handle things automatically.

When the engine gets that hot, the computer is probably retarding timing, so in addition to going "in the red" and the associated risks to the engine/cooling system you're probably also losing efficiency.

Also, for better aero, I'd suggest blocking your upper grille and opening a portion of the lower one instead of vice versa.

I think it's safe to say there's probably nothing wrong with the water pump.
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Old 02-17-2009, 12:38 AM   #5 (permalink)
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Thanks for the advice. I actually did pull the AC compressor fuse first, and the fan would still kick on when the defrost is on. However, I didn't even consider that the timing might be retarded. So yeah, I'll probably pop the fan fuse back in and see what's up. Spring will be here soon anyway, so I'll have to have it figured out by then.

And I did know that it's better to block the upper grille for aero, but this was easier, and I mostly did it for the faster warm up times anyway.
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Old 02-17-2009, 02:47 AM   #6 (permalink)
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Won't hurt to double check that the water pump belt isn't slipping.
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Old 02-17-2009, 02:02 PM   #7 (permalink)
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You disconnected your fan, blocked the grill, so of course it's going to overheat.

Reconnect the fan- cars have them for a reason, and remove at least the center section of the block. That can't possibly do anything good for aerodynamics, because the car now has to push the air down and stuff it underneath.
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Old 02-17-2009, 02:04 PM   #8 (permalink)
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A full grill block will be better than a partial any day. Just because it has to go under the car or around the car means nothing vs hitting tons of stuff going through the cooling system and engine bay.

But, yes you need to reconnect the fan.
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Old 02-17-2009, 03:06 PM   #9 (permalink)
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So I guess the general consensus is reconnect the fan. Ok, can do.

Testdrive: Is it possible the belt is slipping without it making that horrible belt slipping noise?
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Old 02-17-2009, 09:43 PM   #10 (permalink)
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Quote:
Originally Posted by Daox View Post
A full grill block will be better than a partial any day. Just because it has to go under the car or around the car means nothing vs hitting tons of stuff going through the cooling system and engine bay.

But, yes you need to reconnect the fan.
I disagree that a full block is better than partial any day or that grill blocks are universally better than air going through the grill.

The car and the airflow around it don't care whether there is turbulence under the hood. All that matters to the aerodynamics are
1- the resistance that air encounters when trying to enter the radiator. This is a factor of the restrictiveness of the radiator and the hardware behind it.
2- the way air flows over the grill if it doesn't go through.
3- the path of air as it comes out from underneath the car, the back end of the hood, or the wheel wells

If the resistance is high enough, it will be like a virtual grill block that some people attach behind the grill... If it's low enough, the grill would present a nice hole for airflow.

Now, on an angled surface like his upper grill, blocking that off would help, because it's easy to cut through air with a wedge. It would also have the benefit that the air coming up from the bumper would remain smooth, instead of being disturbed by the grill.

But blocking the lower grill under the bumper forces that air to move down or to the sides. The easiest path here is probably downward, especially for the center. That air would compress, go under the car, and be forced out the sides, possibly increasing drag. It could also be forced down and to the sides at an angle, into the tires.

The center of his grill is nearly vertical and flat. The car has to force this air toward the sides and downward. If he removes this, the sides will still help aerodynamics, and the small stream of air flowing through that opening would encounter less resistance proportionally. Also, the fan might be able to suck all the air it needs through the hole even if it is smaller than normal.

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