Maybe you're right Holy Cow, but I thought I was not aggressive as I see some people block 100%.
By the way: my cooling fan never even came up once. That's why I think I'm still on the safe side. If they don't come up it means the temps are still within the normal range (not over 95?C engine block side).
To be honest I would not dare to drive with 90% block without the diagnostic tool to see the temps. With 60% block there seems to be no risk at all and I'll drive it around like that on long distance if I don't use the tool.

every car is different. you can't see my opening for my car because it is underneath. it was designed that way. the grills on the front of my car did very little and were there mostly for aesthetics (to look good)

for that very reason, I blocked off the entire thing. I did do it in steps similar to yourself. I blocked it off using wing nuts so that it could be removed if it was needed.

also, shouldn't your coolant temp be constant? my T-stat regulates the temp within about 5 degrees all the time. hot, cold, it doesn't matter. I always run around 195 F (~90 C) I think my fan kicks in around 210 or 215 F (not sure the C value)

the big point is that all cars are different. unless you have the same make and model as someone else, they can't say whether it will work or not. even then, you have body style changes from year to year that may affect it.

My 2008 VW Rabbit and my 2002 GMC Sierra both work fine with 100% blocking at the grilles (upper AND lower) or at the radiator. However, I would not do it if the temperature was affected more than a few degrees in normal driving.

Thanks for the replies.
My engine temp is nomally 85?C (by thermostat regulation).
If I want to keep it 100% safe, I guess I will have to stick with the 60% block (behind the grill).
I will only mount the extra block when freezing or short distances (no more than 30 min).
You guys are right: it should be safe. It's not worth the risk of damaging my engine.

why don't you put the 60% on the outside of the grill? you could trace the opening on a piece of plastic/rubber with a silver sharpie and cut it with tin snips. drill a few holes in it and use wire ties to hold it in place. you could even use black ones to blend it better.

you get a slight (very very slight) aerodynamic advantage with having it on the outside of the grill vs the inside. also, if you take your time and make it match the opening, it actually looks better.

that's just my opinion.

I do agree that safety is more important than efficiency. if you can double your mileage but you have to replace the car in 6 months, you have accomplished nothing (you may actually be on the negative side of that equation)

I didn't put it on the outside (yet?) because:
- I do not (yet) have a big enough 100% flat black piece of plastic
- I wanted the car to keep its original look
- I think the difference in aerodynamics will indeed be very (!) slight
- It's a testphase and I need to be sure about two things before wasting a few hours only on cosmetics: proven result and the surface% that can be covered.

About the aerodynamics part: I saw somewhere the flow on an apple (top of the apple) and its aerodynamics are still very good as the hole in it is filled with air (water it was in this case).
For your info: the black plastic I use comes from the aerodynamic undersidecover of another car. These are big, but theye are not flat. I don't want to use this on the outside.
I already used black wire ties for the permanent block. You don't see them, don't you?

:thumbup: Test with cardboard, coroplast, or any material you have available...behind the grille. Then when you're ready, if you think you can do it on the outside, great.

Forgot to tell (with pics)
 

I forgot to tell something. Together with installation of initial block I changed the internal airflow to (...through in fact) the radiator). The stock design lets a lot of air pass over the radiator. I blocked this, in such a way that air entering the car is forced through the radiator or at least will bent of to the air intake. Main reason: improve cooling capacity.
On the picture you also see a yellow wire. This is connected with the internal grill block. In case of emergency I can simply cut the wire ties from the outside of the grill an pull out the block. First picture is original, second with the air forced through the radiator.
https://www.fuelly.com/attachments/fo...ce6f15948c.jpg
https://www.fuelly.com/attachments/fo...65ed9ceee3.jpg

I can't really argue with doing it for experimentation.

when you do get to the point where you want it permanent, a suggestion would be to get a garbage can (large, round, plastic one) and cut it up so you will have a large flat piece. I think they come in a variety of colors too. I want to say the one that I bought was $15 or so. they are relatively inexpensive. I used it for an airdam that I have since taken off. it was easy to use and maybe something to consider for the future.

jay2therescue actually used a broken trash can for his grill block since it was big enough for his purposes. I think he paid a dollar or two for his since it was broken.

Yes, I was at Lowe's and saw 2 cracked black trash cans. Got them for $1/ea after taking them to the service desk and explaining what I wanted to do with them.