Ram Promaster Forum banner

1 - 20 of 23 Posts

·
Premium Member
Joined
·
815 Posts
Discussion Starter #1 (Edited)
Another one of my crazy thoughts: how much would it cost to idle a gasser PM?

I remember searching the internet a while back and the figure of about $1/hr comes to mind. Maybe a bit more but nowhere as high as $2/hr. I guess it depends on gas prices and engine size.

Maybe someone knows how many litres/hour our 3.6 L Pentastars drink when idling.

Perhaps @GaryBIS still has his flowmeter rigged up to his gas tank and can do an experiment for us. (Sorry for imposing, Gary.)

The background: I was fantasizing about having an electrical system with enough capacity to run an air-conditioner and, further, how to hack a cheap window unit into the van. (I fantasize a lot.) Basically, it came to a lot of money and work. Could be a fun project though and thus it wasn't overly discouraging.

But, for the way I use my van (a few months a year, and only when and where the destination is mild), I was thinking another option is the blunt instrument: idle the engine, have the AC on high.

I'm thinking, cost-wise, it might be effective, i.e., cheaper than more batteries and an AC unit, when I factor in the number of times X the length of time I would actually use it.

Edit: to include note about engine size.
 

·
Super Moderator
Joined
·
8,678 Posts
Actually, Kip has figured this all,out for us several years ago. If he doesn’t jump in it should show up in the forum archives if you search for it.
 

·
Registered
2014 136” HR
Joined
·
4,676 Posts
Given that our temperature gauge is a farce, and the system being stressed by hot/humid conditions without benefit of airflow from driving, what's the chance of the engine overheating without our knowing it? We’ve contemplated running the van's AC a time or two.
 

·
Registered
Joined
·
2,314 Posts
I wanna take a wild guess for the fun of it, before anyone posts the answers and see how close I come without going over.
I'm guessing it will idle for 1:15 on a gallon.
 

·
Premium Member
Joined
·
815 Posts
Discussion Starter #5 (Edited)
Actually, Kip has figured this all,out for us several years ago. If he doesn’t jump in it should show up in the forum archives if you search for it.
Thanks, and yes, I found a number of interesting threads and am reading them now. For example:

One commenter mentioned briefly that idling may not be the best for lubricating the engine. And from personal (and thus anecdotal) experience, I have seen this to some extent:

1) our own minivan Pentastar engine with a worn rocker arm bearing (driven gently)
2) a sporty car that some owners suffered lubrication issues with when driven gently [fortunately, I did NOT drive it gently:p ...and so no issues with mine])

And so while I'm not worried about idling a few hours here and there, maybe my longer-term strategy is to see if I can DIY a small AC into the van when the pricing for LiFePO4 comes down.

Edit: missing a word
 
  • Like
Reactions: frater secessus

·
Registered
Joined
·
3,350 Posts
Eventually I go to the Viper authorized installer and ask if the PM can have the same setup as the Transit. IIRC it works like this, through an app you tell the system when to wake up and check the temperature (both are user input), then it will automatically start and shut off when the temperature is reached.
 

·
Premium Member
Joined
·
815 Posts
Discussion Starter #7
Eventually I go to the Viper authorized installer and ask if the PM can have the same setup as the Transit. IIRC it works like this, through an app you tell the system when to wake up and check the temperature (both are user input), then it will automatically start and shut off when the temperature is reached.
I'll be interested in hearing what you find. Though I suspect that if I need to run the engine for AC, it's going to be fairly roasting hot in the van and thus the engine would need to be run pretty much constantly.
 

·
Premium Member
Joined
·
815 Posts
Discussion Starter #8

·
Registered
Joined
·
356 Posts
I think @jracca has the best AC solution I've seen, if you want to search through his build. He definitely built around it, and it may prove challenging to adapt to after the fact.

On the other topic, I'd definitely suggest a generator over idling if it's going to be a common thing. The return on investment and less stress on engine will pay off quickly, depending on usage, when you can run a quality generator 8+ hours on a gallon or three. Idling every now and then is different than using it as a regular solution.
 

·
Registered
Joined
·
1,969 Posts
The Transit with 3.5L V6 goes through 0.36 gallons per hour, according to Ford, while generating 2.4 kW of electricity, and with no air conditioning. Since PM V6 engine is similar in size, and air conditioner should need about the same amount of power, I’d “guess” a PM will use about the same amount of fuel if idling with A/C on. So my wild guess is close to 3 hours of idling per gallon.

If that’s indeed close, idling 9 hours at night would require about 3 gallons of fuel. By comparison, I can run my small window A/C all night (at least 9 hours) on 1.3 gallons of fuel using a 2200/1800 inverter generator.

If it was as safe, I’d idle engine versus running generator just to keep from hassling with portable generator and refueling. The extra fuel would be worth it because we don’t boondock in hot temperatures more than a few nights per year.
 

·
Registered
Joined
·
489 Posts
I think @jracca has the best AC solution I've seen, if you want to search through his build. He definitely built around it, and it may prove challenging to adapt to after the fact.

On the other topic, I'd definitely suggest a generator over idling if it's going to be a common thing. The return on investment and less stress on engine will pay off quickly, depending on usage, when you can run a quality generator 8+ hours on a gallon or three. Idling every now and then is different than using it as a regular solution.
Thank you.

Having some experience in this, I would definitely suggest a generator over idling. My current van is my second, with the first being a 1989 Dodge Xplorer factory built class B with an Onan 3.0 and a 11,500 BTU roof air. My current promaster was built (by me) with climate control in mind around a 5000 BTU window unit.

While I don't mind idling occasionally, it is one of the hardest things on an engine based on everything I have studied. I did it every morning for a while before I got my heater in, but it was just 30 or so nights so I don't feel too bad about it. I just can't justify wearing out my engine to produce 2000-3000 watts of power (about 2.5 - 4 horsepower).

If you really need AC over a longer term (away from shore power) I would suggest you either equip yourself for it in your electrical system or get a generator. If we are talking 10-20 times per year, then I would probably just idle the gasoline engine. But keep in mind you are also putting more wear on the AC system as well. An the cooling system. It isn't all about just the engine.

Being able to cool the promaster takes a total systems engineering approach. You'll need good insulation. You'll need good ventilation, and a cooling system with the right capacity.

My experience is that in all but the hottest climates you can get by with cooling the vehicle down at night and then ventilating it once the outside temps cool off enough. If I was traveling in a very hot climate, my plan would be to sweat a lot until about 8 or 9pm, turn on the AC for an hour or two, take a cold shower (drink 2-3 ounces of whiskey - optional), turn off the AC and go to sleep. my window unit draws about 30 amps from the battery bank while running and can turn the bed area into an icebox or keep the whole van reasonably cool in the late evening or in the shade.

You just should not plan to keep the whole thing cool all day, not a reasonable expectation (besides who wants to sit in the van all day?) but if your use is really limited to 30 or less days a year, I might consider running the engine for an hour or two on those days. But get some true instruments to watch the temperature closely, you don't want to overheat and these vehicles really appear to have limited airflow for the radiator. Anything more than 30 days and a generator will be your cheaper option. I ran the generator to use AC in my prior class B and it was just so noisy I spent quite a bit of money on a huge lithium battery bank on my current vehicle.

If you decide to go with a battery bank and a smaller AC (5000-6000 BTU) you need to consider not just the usage but the ability to recharge the battery bank. I used a 600 AH battery bank, but the problem is that it takes a long time to recharge without shore power. I have a 400W solar system and can get anywhere from 20AH on a cloudy winter day to 150 AH on a bright summer day. So regardless of the bank size I will have to run the engine or use shore power eventually if I use more power than that.

So that is along way to say the answer is quite complicated. If I wanted to run the AC more than a 30-50 hours a year while stationary I would get a generator or plan an electrical system to run it, I chose the latter, but it is not cheap. I just wanted to be able to run the AC a little without the noise of the generator based on the places I used it.
 

·
Registered
Joined
·
908 Posts
It’s been a while since I did the calc, but basically idling the engine costs .4 gallons per hour in summer, and .6 in winter (under 40 degrees F the engine will high idle).
Huge topic, but know that in winter, the $130 chinese espar knockoff is easy to install and pumps out huge heat.
In both winter and summer I have found that you are better off spending your money on insulation. Ceiling foamboard alone makes a huge difference in summer, and wood flooring makes a big difference in winter.
Another huge factor is sleeping height - sleep by the floor in summer and high up in the van in winter. Often, it’s like a 20 degree difference.
 

·
Registered
Joined
·
1,400 Posts
My thoughts are similar to @jracca

The fuel burn is just part of the true or total costs.

I gambled on a Honda gas generator as backup power when shore-power is not available. Time will tell if this was the right bet for us.

I have read lots on here about the pros of solar & I believe in those pros, but what I do not read much here are the cons about solar & contrary to popular belief I thing there is a wind drag fuel burn cost to roof mount solar panels along with an interior van temperature gain (not a wintertime problem, but neither is air conditioning).

I think Gary is a pretty smart dude & read lots of his stuff. A while back he posted what I believe to be a very objective note about “not” installing solar. I would like to hear more from him regarding his current thoughts on the topic.

I also think jracca is “dialed in” & understands these things, & think get his reasoning of installing solar (my summary of his reasoning; benefits out-way the costs in his case & use, but it is no magic solution). His designs are seemingly goal oriented & engineered towards the goal.

I note the big brand commercial camper vans I have looked at with air conditioners on the roof all have 120v generators underneath & under-mount propane tanks. They are also 3 to 4 times the total cost of a our PM & DIY conversion.
 

·
Premium Member
Joined
·
1,663 Posts
Hi RV8R,
I'm still planning to the MPG test on my solar panel using the same scheme as I used for the vortex generators. Just need to work it into the schedule and get a good day for it.

I guess one of the flexible solar panels adhered directly to the roof is a good low drag solution -- but, as you say, not going to work if you need AC with no shore power.

I'm not a fan of generators at all, but have noticed several youtube videos on noise reducing measures or enclosures. I wonder if there is a way to incorporate one of these on a PM? A technical/design challlenge for you!!
I do realize the smaller Hondas are about the best of the bunch on noise when in good shape, but still room for improvement.

Best -- Gary
 

·
Registered
Joined
·
2,314 Posts
Wasn't your guess 0.80 gallons per hour?
Yes. I guessed a gal would last 1:15.
You guessed 3:00.
The answer is 2:00.
I'm the closest without going over.
Now, I want my dam prize!
Don't I get like a jet ski or dining room set or something?
 

·
Registered
Joined
·
1,400 Posts
Hi RV8R,
I'm still planning to the MPG test on my solar panel using the same scheme as I used for the vortex generators. Just need to work it into the schedule and get a good day for it.

I guess one of the flexible solar panels adhered directly to the roof is a good low drag solution -- but, as you say, not going to work if you need AC with no shore power.

I'm not a fan of generators at all, but have noticed several youtube videos on noise reducing measures or enclosures. I wonder if there is a way to incorporate one of these on a PM? A technical/design challlenge for you!!
I do realize the smaller Hondas are about the best of the bunch on noise when in good shape, but still room for improvement.

Best -- Gary
Hi Gary - Thanks !!

I am not a fan of Gas/Diesel burning generators either (Noise & Environment). It is kinda like pick your poison. We rarely have a need for the Honda generator & if space is tight I would leave it at home. The majority of our camping has been one day stays - not boon-docking. If we boon-docked, then solar panels IMO are a must & we would pay the solar cons price.

Regarding flexible solar panel mileage test; IMO the leading edge needs to seal off airflow from the underside of those panels (leading edge ramp ups from the valley of the roof corrugation). @bensoloart is “printing” plastic “flute fillers” that I would assume could be fabricated to incorporate a leading edge ramp from the bottom of the roof valleys ( believe MsNomer is buying another one of his products ).

If I were to design a mount for the Honda, I would look at a hitch mount or swing away hitch mount (theft is then the issue). We plan on trailering a couple of motorcycles (amongst other things) & if that is the case the generator could go in the trailer.

RVing is relatively new to us (15 months experience now). When we started our build at the tail end of 2018, our design was fully electric hahahaha, that was before we knew anything. I would still like a fully electric (other than gas PM engine) van, but I do not consider it cost efficient. It seems to me the world is making leaps & bounds in this technology, but I do not think we have hit “the sweet spot” yet & I am hoping when we have mile‘d out our 2018 & it is time for Van #2 we can go full electric & solar. Til then I’m staying away from the “bleeding egde” of this technology.

If you are able to produce favorable test results with solar panels & drag mileage increase data then I will install solar on my roof (the roof top heat gain is secondary to the drag increase & mileage).

Drag increase is not just about fuel for me, but a theoretical economy of the entire drivetrain right up to more wear on the tires (just like idling the PM engine to charge my house bank costs us more than fuel).
 

·
Registered
Joined
·
489 Posts
I wanted to add something before anyone looks at my design (or any other design) and thinks that it is a solution to their issues. My circumstances are very unique to me.

Those are: I work in the Northeast and fly back and forth every week from Mid July though early December, and about every other week from Mid - Jan through early May. The van was created for to stay in during the week to function both as my only transportation and to save me from either renting an apartment (or room in one or a house) or hotel. In either case it would cost me about 800 a month from July - December and 400 a month from Jan through May.
Part of the equation in my build is that I only stay in the van for 3-4 days most weeks (occasionally I don't travel anywhere on a weekend maybe 2-3 times a year so those stays are 9-11 days).

When you only use the vehicle for about half the week it allows time for the solar system to charge the batteries back up. It also means I have a 40 minute drive to the airport and from the airport every week which is more juice into the batteries. (at first I did not have solar and these drives were important because they charge my batteries) I don't want to spend money on campgrounds and only park in 'free' places most of the time with the occasional 1 day stay in a campground during the July, Aug months so I can top off the battery bank.

Having a monster of a battery bank is only a partial solution to running air conditioning. I have a 600 AH battery and a 3000 VA victron inverter, so I can run pretty much any load at least for a while. In my case I can draw that battery down for 2-3 days and then I park the rig and it can charge back up (plus it charges on the 80 minute round trip to the airport). If I was using it continuous the big battery bank would buy me almost nothing because it would gradually drain and without shore power I couldn't get it charged back up without shore power or a long drive.

I feel like in a situation where you are staying the vehicle continuously a large battery bank is overrated. If you have a the ability to charge the thing quickly you don't really need the capacity, if you don't have the power sources to charge it, then the extra capacity will do you no good. If you use it one the weekends only, or a few days a week like I do, then it can be very beneficial but your use case really determines the utility of a large battery bank.

I considered putting in an outlet and charger that could charge from electric vehicle chargers (we have those at my office at work) so that I could charge my battery easier. It would be a pretty easy task to complete, but Covid19 came along and the rig is sitting in my driveway for the next 13 months or so until I return to work. After than maybe?

If I was full time I would have designed differently, probably with a generator (though my experience in my 1989 Xplorer really turned me off generators as it was load and right under my bed). As it is, it is a place to sleep, shower, and get ready to go back to work the next morning without paying. If I was full time my 600 AH battery bank would probably be a 200-300 ah bank. (the difference could easily pay for a generator).

Step 1 in any design is to really understand your use. I had the advantage of staying in the old class b for 4 years before building the new rig. I really understood what I wanted and what I didn't. Conventional wisdom in the past was that it was better to idle engines than stop and start them. Modern engines often have technology that stops them at stoplights and restarts when ready to drive (I hate this, but there is a reason). The emissions control systems don't do well at idling, and are more fragile than the engine, and can be just as costly to repair. The propulsion system is more than the moving parts of the engine (which are probably not the most damaged part if you are idling). I would worry more about the emissions system, overheating, and whether this would tax the HVAC system.
 

·
Registered
Joined
·
1,969 Posts
Yes. I guessed a gal would last 1:15.
You guessed 3:00.
The answer is 2:00.
I'm the closest without going over.
Now, I want my dam prize!
Don't I get like a jet ski or dining room set or something?
Question was gallons per hour, wasn’t it? You guessed 0.80 GPH. I guessed 0.36 GPH, the same as Transit Pro Power — not that I care about a prize.

Ford 6.8L V10 is around 0.80 GPH with air conditioner running, so smaller engines should do much better.
 
1 - 20 of 23 Posts
Top