Herman and Operation 30MPG

[June]

Not really June.

It takes about 20HP to cruise at 65 mph, and and a 10 amp , 12 volt load is about 120 Watts or 1/6 HP

You might see a 1% dip at most, hard to measure

Homework...you can measure your required HP at 65 yourself without anything more than a stop watch.

Hint...you need to vary the speed of the car.

Does the fan actually run say at 65? Or does the computer shut it off due to the force of air naturally occurring at 65? I understand sitting still or at slow speeds the electric fan would be needed to maintain air flow, but at higher speed would the fan still need to run to maintain flow? This question ran through my mind if the extra draw effects mpg? I know it is a silly question, but if the electric fan died out on the interstate would my car overheat leaving me stranded between exits? I do like to understand how my car functions. June

[mrbrian200]

Compressor/radiator fans running while cruising 65mph? ..generally no. However, some vehicles run this fan when the AC mode is active regardless of speed. I have not paid attention to how the S60 handles this while on the highway.

When I add the the radiator fan (around 100 watts), HVAC passenger compartment fan at a higher speed (probably another 100) and the AC compressor clutch (fuse is either 10A or 15A so I'll guess another 100w) I get a current draw that would draw down econ at 65mph by around 1-1.5 mpg. At lower speeds it's more like 3mpg. I'm sticking with my initial 'assessment' - combination of AC load and heavier traffic.

A side note. I think I'm noticing the S60 gets slightly higher highway econ when all 4 windows are cracked about an 2 inches down (not fully closed). I might be imagining this.

[abscate]

When you add that compressor into the picture the math gets worse. The compressor is pulling more like 2-3 HP mechanical power net, so there is your 2-3 mpg mileage penalty from cruise. The electrical draw is still pretty low in comparison.

Auto AC units are surprisingly high capacity..they can run from 10-50,000 BTU/ hr in a big SUV. Much bigger than your house unit, where a 5000 BTU/ hr will chill a 10x10 room nicely.

The extra load on auto AC is caused by

Large solar load
Application..you can take an hour to chill the car from 120F parked in mall, driver wants it cold in a minute or two
Large air influx into vehicle
Variable compressor speed
Small exchanger volumes required by compact climate units and radiators

[mrbrian200]

I was so focused on the electrical loads I forgot about the mechanical compressor load. And in heavier slower/stop and go traffic this load would be constant with no correlation to speed. You would normally expect to see decreasing econ as vehicle speed increases due to wind loading. The flat, non speed dependent drag on the engine from the compressor would have the opposite net effect on fuel consumption. You would get lower econ at lower speeds as the amount of extra fuel you burned running the AC becomes a function of 'how long did it take you to get there'.

[callahanoffroad]

I was so focused on the electrical loads I forgot about the mechanical compressor load. And in heavier slower/stop and go traffic this load would be constant with no correlation to speed. You would normally expect to see decreasing econ as vehicle speed increases due to wind loading. The flat, non speed dependent drag on the engine from the compressor would have the opposite net effect on fuel consumption. You would get lower econ at lower speeds as the amount of extra fuel you burned running the AC becomes a function of 'how long did it take you to get there'.

When you add that compressor into the picture the math gets worse. The compressor is pulling more like 2-3 HP mechanical power net, so there is your 2-3 mpg mileage penalty from cruise. The electrical draw is still pretty low in comparison.

Auto AC units are surprisingly high capacity..they can run from 10-50,000 BTU/ hr in a big SUV. Much bigger than your house unit, where a 5000 BTU/ hr will chill a 10x10 room nicely.

The extra load on auto AC is caused by

Large solar load
Application..you can take an hour to chill the car from 120F parked in mall, driver wants it cold in a minute or two
Large air influx into vehicle
Variable compressor speed
Small exchanger volumes required by compact climate units and radiators

Both of these.

I totally forgot how much it takes to run an automotive ac. Well that explains my 3-4 mpg loss. I have to run the AC non stop on full blower during the day. It was cooler the last few days so I ran w/o the AC so we will see what it looks like when I fill up tomorrow.

Strange question, has anyone else ever noticed that 850's feel a little jittery around 65 mph? Light in the steering and like it gets blown around a lot? But once you hit 85 - 90 it feels really planted and smooth? Both my wagon and sedan are like that. My wagon liked to cruise at 105 and my sedan is really happy around 95... Not that I would ever drive at such reckless speeds mind you... Never...

[mrbrian200]

Strange question, has anyone else ever noticed that 850's feel a little jittery around 65 mph? Light in the steering and like it gets blown around a lot? But once you hit 85 - 90 it feels really planted and smooth? Both my wagon and sedan are like that. My wagon liked to cruise at 105 and my sedan is really happy around 95... Not that I would ever drive at such reckless speeds mind you... Never...

My '06 S60 is the same way. It really smooths out and drives like it's on rails at speeds over ~85mph.

I suspect it has something to do with the standard strut/shock damper tuning and the ride height. These cars are designed to be stable at autobahn speeds with 1-2 adult passengers. If you want stable ultra high speed capability generally you trade away some ride quality at lower speeds. Hence with higher trim packages Volvo started utilizing the 4C suspension setup so you can have it both ways.

When it's just me with no junk in the trunk the ride quality is a bit harsher than I might prefer at the speeds I normally drive.

Euro luxury makes are somewhat known for favoring high speed capability.

[Rattnalle]

Volvo didn't count among the euro luxury makers in the 90s though. Not in Europe at least

They've tried hard to get in among them since.

I've never noticed any of my Volvos being less planted at 65 than any other speed.

[June]

Volvo didn't count among the euro luxury makers in the 90s though. Not in Europe at least

They've tried hard to get in among them since.

I've never noticed any of my Volvos being less planted at 65 than any other speed.

They did attempt to compete in the luxury market with the 960/S90 EXECUTIVE. But in my opinion finally succeeded with the 1998 release of the S80 T6 EXECUTIVE.

I also agree I never noticed any of my Volvo cars feeling less secure at 65 than 95. I will say the P80 cars I've had felt lighter (clunky) compared to the P2 models. I have noticed that 3000 rpm seems to be the sweet spot for the white engine cars. 3000 rpm in the 98 XC was like 70 ish mph where as the 02 T6 120 mph and my 04 T6 100 mph. June

[mrbrian200]

Thinking about it, I did put on Sachs blue label struts. A previous car behaved in a similar way when I put Sachs struts on it: harsh/stiffer ride than I really prefer at slower speeds, drove really nice at excessive speeds. After that previous experience I probably wouldn't have used Sachs on the Volvo except they were listed as 'OEM'. In retrospect I wish I had used the Billsteins or maybe even the Monroes.

[callahanoffroad]

Thinking about it, I did put on Sachs blue label struts. A previous car behaved in a similar way when I put Sachs struts on it: harsh/stiffer ride than I really prefer at slower speeds, drove really nice at excessive speeds. After that previous experience I probably wouldn't have used Sachs on the Volvo except they were listed as 'OEM'. In retrospect I wish I had used the Billsteins or maybe even the Monroes.

That's funny I actually have Monroe front shocks and I wish they were more sporty! Lol

So I have to conceede to those with the ability to calculate engine load. Ran 300 miles with out AC and mpg popped back up to 24mpg from 20 mpg. So yes I can confirm that AC costs 4mpg.