Effects of using an insect screen

[awill4wd]

A number of members here may know that southern NSW and northern VIC are being hit with Locust swarms.
We went up to Beechworth over the break and only encountered them just before climbing the hills to Beechworth.
The swarms we hit were no where near as bad as seen on the news of other areas but they still made enough mess as it is.
I had made an insect screen up before departure and fitted it up at Beechworth like many other cars travelling the area.
I was a little concerned about the effects on the cars temperature but I recently got a Scangauge for my NS Paj and am able to monitor temps in real time via the ECU.
The only real difference in water temps was an increase of around 3-5 C but I did notice quite a rise in Air inlet temps. This was just in normal driving and not towing the caravan.
It was in towing the van home though with the screen in place that the effects were more pronounced.
Water temps remained the same, the max I saw was 90c with an average of 85c.
The inlet air temps were interesting to watch though, I was seeing average temps of 60ish C and going as high as 92C at one stage climbing a constant hill.
Half way home I removed the screen as the bugs were no longer a problem and the water temps dropped 4 C on average but the inlet air temps dropped considerably averaging low 40's C and maxing out at just under 70C.
I used a fairly open weave fibreglass flyscreen mesh and it certainly served its purpose in keeping the bugs out of the radiator but the temps I monitored certainly confirmed to me that to use them when appropriate and remove them when they aren't necessary.
I found it very interesting just how much they effect inlet air temps and I wonder if the fitting of aftermarket intercooler guards would have similar effects.
Regards Andrew.

[rosahan]

Hi Andrew,
I too have made screens for both the radiator and the inter-cooler. They were made from shade cloth as I found that it results in the bugs hitting it then falling off because it is relatively soft, rather than squishing and staying stuck. I don't have any means of monitoring temperature apart from the car's guage but have kept a close eye on it and observed that it has not risen perceptibly even when towing our van to the Sunshine Coasr and back. I was concerened about the effect it might have on the inter-cooler but the only way I would expect to be able to detect any effect would be through performance and economy, neither of which seemed to be affected. I probably should take them both off now and see if there is any result.
regards
Lindsay

[awill4wd]

Hi Andrew,
I too have made screens for both the radiator and the inter-cooler. They were made from shade cloth as I found that it results in the bugs hitting it then falling off because it is relatively soft, rather than squishing and staying stuck. I don't have any means of monitoring temperature apart from the car's guage but have kept a close eye on it and observed that it has not risen perceptibly even when towing our van to the Sunshine Coasr and back. I was concerened about the effect it might have on the inter-cooler but the only way I would expect to be able to detect any effect would be through performance and economy, neither of which seemed to be affected. I probably should take them both off now and see if there is any result.
regards
Lindsay

Thanks Lindsay, my temp gauge never fluctuated either but it's just that with the Scangauge I can see my normal temps (around home) are around the 78-83C range and with towing it was a bit higher and with the screen slightly higher again.
I could hear the fan cut in a bit more also.
What the Scangauge was showing me is just how quickly the inlet air temps rise under constant load and it's an indicator to me that the intercooler isn't large enough as it heat sinks rapidly. In low range 4x4 work it would be worse as there is very little airflow over the intercooler in those conditions.
I think my next gauge will be an EGT gauge as I'd like the watch the correlation of higher inlet temps and high EGT temps which I suspect may be the case.
Regards Andrew.

[wilyum]

G`day Andrew,
Where did you mount the screen? I made a screen that mounts on the Bull Bar and it has no effect on the temperature of the engine at all. The gap between the grille and the Bull Bar allows a clear path for cooling air to pass.
Cheers,
Wilyum.

[awill4wd]

G`day Andrew,
Where did you mount the screen? I made a screen that mounts on the Bull Bar and it has no effect on the temperature of the engine at all. The gap between the grille and the Bull Bar allows a clear path for cooling air to pass.
Cheers,
Wilyum.

Wilyum, I don't have a bullbar so it was fitted direct over the grill and lower inlets in the bumper.
Like I said previously if you don't have a scangauge which can measure temps in real time then you don't know what is happening as the gauge doesn't move. The air inlet temps are one thing no one knows about unless a Scangauge is used.
Regards Andrew.

[road rat]

you know its funny how many people trust that gauge on the dash, we have proved time and again how inacurat they are they have a desine feacher that can allow up to 20-40 deg before they will move and before you now it its on the red, imo the only way you can tell the true temp is with a scangauge or a after market temp gauge

[old Jack]

Rather than start a new thread I thought I would refresh this one as the original post is a clear demonstration of what I have believed for a long time but only have just got around to testing the theory.

I have been of the opinion that running insect screens is worthwhile as it keeps the bugs out of the heat exchangers and I have always run nylon fly wire secured behind the grille as I have never liked the look of external bug screens. Most fly screens have an open area of between 65% to 75% so I was happy to lose airflow to keep the heat exchangers from clogging up with insects. Then a few years ago I replaced the aluminium expanded mesh in the lower section of my Smartbar, as it had fatigued and cracked. I used woven stainless steel mesh like you find on very heavy duty security doors, it has an open area of 62% and once again I was happy to lose airflow for the extra protection it gives the intercooler. This screen has save my intercooler from damage several times as the mesh has some fairly large dents in it.

So apart from not liking the look of bug screens mounted in front of grilles, I was of the opinion that if they were fitted in front of grilles they restricted airflow more than if fitted behind. My argument has been when mounted in front of the grille, the air hitting the screen takes the path of least resistance, so much of the air is deflected out to the sides of the screen and not through it. When the screen was fitted behind the grille then the airflow cannot easily spill sidewards so it was forced though the screen, particularly if the grille openings are funnel shaped or tapered.

So how could I prove this?
I have a handheld Anemometer so it can measure air flow, air speed and air temperatures, I used a cordless leaf blower without the spout fitted and then tested a piece of nylon fly wire and a piece of stainless woven security mesh. I set the leaf blower to an air speed of 60kph and had an airflow of roughly 4000CFM when measured at a distance of 50mm from the air outlet of the blower. I then placed the screens over the inlet of the Anemometer and took a measurement then relocated the screens to behind the Anemometer and took another reading.

The results were very similar for both the nylon fly wire and the stainless security mesh, this surprised me as I thought there would be a significant difference in airflow and air speed between the 2 screens.

I was also surprised at the significant difference in airspeed and airflow between when the screen was in front of the Anemometer compared to when the screen was behind.
Test 1. With air speed at 60kph and airflow of 4000 CFM, when the screens were placed in front of the Anemometer air speed reduced to 48kph and roughly 3100 CFM, so about a 20% loss.
Test 2. With air speed set at 60kph and airflow at 4000CFM, when the screens were placed behind the Anemometer air speed was only reduced to 56kph and roughly 3600 CFM, so about a 10% loss.

Now these experiments where done on the bench but to confirm the results I would need to another experiment with the Anemometer fixed flush to the forward heat exchanger and then do a drive test using cruise control and at varied speeds, with a screen in front of the grille, a screen behind the grille and with no screen at all.

Hopefully I can get a chance to do this over the next few weekends.

OJ.

[erad]

Old Jack:
I too have always fitted flywire behind the grille. This has kept the core of the A/C condenser totally clean over the years. I cannot comment on the radiator core because I cannot see it, but I have no doubt that it is clean too. The main reason for fitting the wire behind the grille rather than in front of the radiator is that you get a much larger are of wire and hence less restriction. I found it interesting your comments about measuring airflow when the anemometer was placed in front of the mesh. I cannot explain this other than the fact that the airflow was affected more by the anemometer body in the 'Clean Air" rather than the turbulent air after the mesh. I will follow your research on this one.

[erad]

Further to my post above, one big advantage of having the screen just behind the grille is that the insects which get splatted against the screen tend to dry out and then simply fall down when you stop. They seem to collect in the bullbar or the sump guard, depending on the particular vehicle being used at the time.

[old Jack]

Further to my post above, one big advantage of having the screen just behind the grille is that the insects which get splatted against the screen tend to dry out and then simply fall down when you stop. They seem to collect in the bullbar or the sump guard, depending on the particular vehicle being used at the time.

Hi Erad,

When I say behind the grille I mean attached , stretched tight on to the back face of the grille. I think there will be a point that as soon as the screen is placed away from the back of the grille the airflow could decrease down to a level even lower than when the screen is attached to the outside of the grille.

OJ.

[old Jack]

I have been thinking of a way to do further testing in real life conditions but my problem is the wiring length between the wind vane and the digital display unit of my anemometer is only about 600mm long and I need about 3 metres!

I had another thought on what bench test I could carry out to see the effects of insect screens and their placement in regard to restricting airflow. I have the factory grille insert out of the lower section of the front bumper cover that was left over from when I fitted the Smartbar. So I set up the leaf blower and the anemometer 300mm from each other, I then measured the airflow with no restriction, then again with the factory grille in between, then with the factory grille with fly wire attached on the rear side of the grille and finally the fly wire attached across the front of the factory grille. The results below really surprised me but also reinforced what I believed was happening.

Test 1. No restriction between the leaf blower and the anemometer, 60kph, 100% airflow.
Test 2. The factory grille between the leaf blower and the anemometer, 56kph, 97% airflow.
Test 3. The factory grille, with fly wire attached to the rear side of the grille, and located in the same position between the leaf blower and the anemometer, 46kph, 77% airflow.
Test 4. The factory grille, with fly wire attached to the front side of the grille,and located in the same position between the leaf blower and the anemometer, 32kph, 53% airflow.

This is a closer test to real life than the first test I did the other day and the results indicate that the loss in airflow are much more than I indicated in the first test.

So based on these test having a fly wire bug screen fitted externally to the grille will reduce your airflow by 47% whereas the same fly wire fitted to the rear of the grille you only reduce your airflow by 23%.

Fitting shade cloth will surely be much worse even if it is the 50% shade grade.

OJ.

[erad]

Although not 100% scientific testing, your tests certainly are better than anything I have seen so far. Well done. I guess that 23% seems about what I would expect because flywire has a fairly large blockage ratio, and having the bars of the grille to catch incoming air and help to ram it through, I would expect better airflow than with the wire in front of the grille. By having the wire directly behind the grille, you have probably double the area of the radiator core, so overall, the net loss of airflow will be minimal, certainly compared to having the cores of the A/C and radiator blocked up by locusts etc. I would never use shadecloth because the blockage ratio is fr too high. The quoted figures for shadecloth are talking about sunlight transmission, not airflows.

[alanymarce]

Here's how we fitted our mesh screen. As you can see, it's not intended to trap small insects, but will stop flies, locusts, etc. No impact on running temperature at all. We blow out the mesh from behind every so often.

[TC.Barky]

This is my setup (picture taken pre winch). Not particularly fine, just for the bigger bugs and objects that will bend fins, didn't want anything too fine as I thought it would cause issues with mud caking on it. It's aluminium (quite stiff, not very flexible). 110,000kms nothing looks obviously bent. Just attached directly to the back of the grille. You can buy it in a sheet from supercheap.

Be interested to see if you'd note a big drop in airflow from this style rather than flywire OJ.

[Dicko1]

This is my setup (picture taken pre winch). Not particularly fine, just for the bigger bugs and objects that will bend fins, didn't want anything too fine as I thought it would cause issues with mud caking on it. It's aluminium (quite stiff, not very flexible). 110,000kms nothing looks obviously bent. Just attached directly to the back of the grille. You can buy it in a sheet from supercheap.

Be interested to see if you'd note a big drop in airflow from this style rather than flywire OJ.

Same setup as mine. No effect on cooling whatsoever. Actually I think I stole the idea from you several years ago......