Do you want 5+ MPG back during the cold months? Restrict air flow to the radiator. - Toyota RAV4 Forums
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post #1 of 60 (permalink) Old 01-06-2017, 11:22 PM Thread Starter
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Do you want 5+ MPG back during the cold months? Restrict air flow to the radiator.

Blocking the engine radiator in cold weather is a century old trick. It helps both non-hybrid and hybrid vehicles. But hybrids especially since the engine can be off 50%+ of the time in city driving.

In the RAV4, even in not that cold weather (25-32F), I observed coolant temperature drop below 150F when sitting at long traffic lights or driving down slight hills for a few minutes. That is really cold for an engine that has a 180F thermostat. The engine comes on much more often just to heat up the cabin.

Some newer vehicles made in the last few years have active grille technology that regulates air flow over the radiator depending on the engine cooling needs. But this technology is not available on the RAV4, yet.

So if you trust yourself to remember to take off any grille blocking if it suddenly warms up, you can safely block at least 50% of the grille area if it's below 40F outside.


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post #2 of 60 (permalink) Old 01-06-2017, 11:42 PM
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5MPG is an exaggeration. While its true that radiator blocking helps maintain engine temps, on the Rav it will be more like 1-2MPG than 5. And it doesn't change the severe hit you see from short trips. A Prius might see that amount of increase on longer trips.
Also good to note that active shutters are mechanical, and a failure of that mechanism results in an un-drivable car.

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post #3 of 60 (permalink) Old 01-07-2017, 09:07 AM
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Did you try it out? I'm not gonna do it but I'm curious.


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post #4 of 60 (permalink) Old 01-07-2017, 09:27 AM
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So I lost apx. 1 MPG in mileage this winter but I get 5 MPG back? Dang, where do I sign up for that? After 10 years I should be up to 70 MPG!!
Much of the mileage difference is cooler denser air = more resistance, wet roads = more resistance, winter blend fuels = worse mileage. So IMO, I possibly lost 1/2 mpg due to longer warmup times.

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post #5 of 60 (permalink) Old 01-07-2017, 10:02 AM
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I went from 42mpg to 34mpg. Most is lost because the ICE have to be running very often to produce heat for the cabin.


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post #6 of 60 (permalink) Old 01-07-2017, 10:14 AM
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At most I lose 3 mpg in winter. Grill blocking might get 1 mpg back, if that.

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post #7 of 60 (permalink) Old 01-07-2017, 10:25 AM Thread Starter
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Did you try it out? I'm not gonna do it but I'm curious.
Yes. I used to do many years ago when I was living up north near the Canadian border. In the winter time, it would take 10 miles to warm an engine fully, and at highway speeds the engine would drop 20-30F below the 190F design temperature. This was a pure gasoline large engine 4x4 truck.

And I have tried it 2 weeks ago on the RAV4. So far I blocked only the grille between the headlights, not the lower grille in the bumper. The lower is much larger actually. This helped with MPG greatly.

There is a 20 miles route that I take regularly, with about a 35mph average speed. In the warmer weather I got a consistent 44 to 44.5 MPG. When the temps dropped to around the freezing mark, and I started using cabin heat, MPG dropped to 35 to 35.5 MPG on the same route. With the upper vents blocked I'm back to 40-41 MPG.

But when I look at coolant temperature through OBDII, the engine still does not make enough heat from propelling the vehicle, as coolant sometimes drops into 150-160F range. This is telling me that more grille area can be blocked.

Everyone's mileage will vary, as they say. It depends how much grille area is block, what the outside temps are, the length of trip and type of driving. But you will never know until you try.

I would be very curious to see what improvement you get in the much colder climate than I am. You can Google "vent blocking prius". There is a lot of information about this practice.


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post #8 of 60 (permalink) Old 01-07-2017, 11:10 AM
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Originally Posted by BobVila View Post
Blocking the engine radiator in cold weather is a century old trick. It helps both non-hybrid and hybrid vehicles. But hybrids especially since the engine can be off 50%+ of the time in city driving.

In the RAV4, even in not that cold weather (25-32F), I observed coolant temperature drop below 150F when sitting at long traffic lights or driving down slight hills for a few minutes. That is really cold for an engine that has a 180F thermostat. The engine comes on much more often just to heat up the cabin.

Some newer vehicles made in the last few years have active grille technology that regulates air flow over the radiator depending on the engine cooling needs. But this technology is not available on the RAV4, yet.

So if you trust yourself to remember to take off any grille blocking if it suddenly warms up, you can safely block at least 50% of the grille area if it's below 40F outside.
Can you share some photos and specific materials you used?

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post #9 of 60 (permalink) Old 01-07-2017, 11:46 AM Thread Starter
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Can you share some photos and specific materials you used?
Since my RAV4 is black, I cut a strip of plastic from a heavy duty black trash bag. About 2" x 32". Then I used some black electrical tape to tape it into place. I did this just to see what happens, not expecting to see such large gains.

But now I think I'll keep it as is for the season. The tape seems to be holding up and it looks ok since everything is black. I can take a picture if you are still interested.

I'll try blocking half of the lower grille next.


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post #10 of 60 (permalink) Old 01-07-2017, 11:49 AM
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I would like a picture if possible. Be careful with those cooler fins they are usually fragile.


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