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Vegas Heat And My Hybrid


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So today was the first of many 100+ degree days here in Las Vegas. I was curious about how the hybrid would perform in the heat. My (non-highway) observations:

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With the AC going most of the day, the engine ran almost constantly. Just for fun I shut off the AC for as long as I could take it. the motor still never shut down to run on battery power.

I also found it interesting that the monitor sometimes showed no ICE activity at a stop when the engine was running. The engine fan was going at full speed as well until I got moving a little. I took it easy today - felt like the heat was really taxing the whole system.

I stopped for gas as well. After hitting the gas cover button I heard a hiss and had to wait about 30 seconds for it to open. I've heard of this happening before, no big deal.

I'll know more by my next refill, but I have a feeling that I'm going to see a reduction in gas mileage this summer. B)

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With ambient temps like that, I'd make sure to use nothing but premium gas. Otherwise, your RX will be down 50 HP. It was 92 degrees here, yesterday, but I've experienced first-hand the 110+ temps in Vegas. That's why I'm staying as close to the ocean as I can!

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"I'll know more by my next refill, but I have a feeling that I'm going to see a reduction in gas mileage this summer"

There is no question that the mileage goes down with AC usage. It takes energy to cool the car (or house).

My guess would be that you would see a similiar drop in mileage that we see in a cold climate (Wisconsin for me) in the winter with use of the heater (? 2-4 mpg).

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With ambient temps like that, I'd make sure to use nothing but premium gas. Otherwise, your RX will be down 50 HP. It was 92 degrees here, yesterday, but I've experienced first-hand the 110+ temps in Vegas. That's why I'm staying as close to the ocean as I can!

Wow, premium makes that much of a difference?

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So today was the first of many 100+ degree days here in Las Vegas. I was curious about how the hybrid would perform in the heat. My (non-highway) observations:

photo-31.jpg

With the AC going most of the day, the engine ran almost constantly. Just for fun I shut off the AC for as long as I could take it. the motor still never shut down to run on battery power.

I also found it interesting that the monitor sometimes showed no ICE activity at a stop when the engine was running. The engine fan was going at full speed as well until I got moving a little. I took it easy today - felt like the heat was really taxing the whole system.

I stopped for gas as well. After hitting the gas cover button I heard a hiss and had to wait about 30 seconds for it to open. I've heard of this happening before, no big deal.

I'll know more by my next refill, but I have a feeling that I'm going to see a reduction in gas mileage this summer. B)

You can improve your FE pretty significantly by running your A/C without using the reheat/remix mode.

Simply set the system to MAX COOL and RECIRCULATE and then use the blower speed manual control to adjust the cabin temperature to your desired comfort level.

It would also help to buy and install a water shutoff valve from Home Depot to ENTIRELY stop the HOT water flow to the heater core.

Conversely, when cold weather arrives keep the A/C compressor from operating altogether (but NEVER use recirculate) for improved FE. The standard RX has two c-best options for that specific purpose.

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With ambient temps like that, I'd make sure to use nothing but premium gas. Otherwise, your RX will be down 50 HP. It was 92 degrees here, yesterday, but I've experienced first-hand the 110+ temps in Vegas. That's why I'm staying as close to the ocean as I can!

Wow, premium makes that much of a difference?

Of course, I was inflating the number, but I do know that higher intake air temps can easily cause my Corvette's ECU to !Removed! timing enough to reduce RWHP by 10.

Many years ago, My family and I were in Las Vegas in August, driving our Nissan Quest van. It was pinging so badly on regular gas (never a problem in San Diego) that it felt like power was cut in half.

General rule of thumb: If your engine is going to ingest >100F air, use premium fuel.

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With ambient temps like that, I'd make sure to use nothing but premium gas. Otherwise, your RX will be down 50 HP. It was 92 degrees here, yesterday, but I've experienced first-hand the 110+ temps in Vegas. That's why I'm staying as close to the ocean as I can!

Wow, premium makes that much of a difference?

Of course, I was inflating the number, but I do know that higher intake air temps can easily cause my Corvette's ECU to !Removed! timing enough to reduce RWHP by 10.

Many years ago, My family and I were in Las Vegas in August, driving our Nissan Quest van. It was pinging so badly on regular gas (never a problem in San Diego) that it felt like power was cut in half.

General rule of thumb: If your engine is going to ingest >100F air, use premium fuel.

But isn't the engine/ICE in the RX400h so heavily derated already that it would be practically impossible to encounter ping/knock due to low grade fuel...??

Your Corvette, and my Porsche, both have high enough compression ratios that the engine control ECU must somehow automatically "derate" the engine if low grade fuel is used. In my case the factory informed me that the procedure would be that the ECU would first enrich the mixture to prevent, alleviate, knock/ping.

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Strange, somewhat...

The RX400h ICE has a compression ratio of 10.8:1, same as the standard RX engine, and premium fuel, 91 octane or better, is recommended in order to avoid degraded performance.

Yet the RXh ICE only produces 208HP vs 268HP for the RX350.

How is that done...??

Limit the RPM at the upper end or just not ever open the throttle plate fully..??

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Our 94 Nissan had 152 HP out of a V6, so I'd say its compression was very low as well. Yet, it pinged hysterically at 110+ degrees F. I'm sure the lexus wouldn't actually ping long enough for the driver to hear it, but the end result would be a reduction of horsepower. I'll bet if you were to test it on a dyno, the difference would be easily seen.

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Our 94 Nissan had 152 HP out of a V6, so I'd say its compression was very low as well. Yet, it pinged hysterically at 110+ degrees F. I'm sure the lexus wouldn't actually ping long enough for the driver to hear it, but the end result would be a reduction of horsepower. I'll bet if you were to test it on a dyno, the difference would be easily seen.

No knock/ping sensors...??

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The ICE may be on more in that Vegas heat to provide engine cooling (keep the coolant circulating through the radiator). The A/C is electric and not run from a belt off the ICE.

I believe the front electric motor is also water cooled but it is a separate system from the ICE water cooling so I would guess it's also electrically pumped.

Maybe all the above combines to require more power from the ICE to keep the hybrid batteries charged as they are providing the power to cool both the cabin and the front electric motor.

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