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Crusing RPMs
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dgsaz
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Location: Phoenix / San Diego
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PostPosted: Fri Mar 24, 2017 4:57 pm    Post subject: Crusing RPMs Reply with quote

Hello all,

Is it safe to say that when cruising on the highway, the optimal RPM for extended driving (350 Miles a day)and mileage is between 3300 and 3600 RPMs?

I have a temporary tach in place and I'm going to calibrate my speed/RPM using my GPS for speed.

3300 for hotter temps and headwinds.
3600 for cooler temps and tailwinds, down hills.

I've got a plan to drive out to Austin, Texas in April from San Diego. It should still be cool enough to stay out of trouble if I get a early start in the AM.

I'll post from the road if all works out. Thanks

dgsaz
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Eric&Barb
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PostPosted: Fri Mar 24, 2017 8:43 pm    Post subject: Re: Crusing RPMs Reply with quote

From what we have found these engines cool best at 3,000 RPM to keep below 230F oil temp, and even then you might need to drop down to as low as 2,500 RPM if really loaded up and climbing a steep hill. The latter we improved on with cooling upgrades.
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Lind
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PostPosted: Fri Mar 24, 2017 11:12 pm    Post subject: Re: Crusing RPMs Reply with quote

I find that a stock engine/transmission/tire size scenario cruises just fine. Don't bother overthinking it with a tach or a temp gauge, you will just end up worrying instead of enjoying the drive. Pay attention to how your bus feels, and drive in the sweet spot where it feels comfortable. Climb hills in third gear. If you shit ain't built right, or don't run right, or you don't know how to drive, then your bus will let you know by cooking your engine. I am totally serious. I drive buses for many thousands of miles every year through the summer in the desert, and I have an engine go south on me about once a decade.
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AS350driver
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PostPosted: Fri Mar 24, 2017 11:36 pm    Post subject: Re: Crusing RPMs Reply with quote

^^^^^ Agree. I have several thousand hours flying behind Lycoming and Continental air cooled engines, thousands of those hours flying at low altitude in the desert heat. A Continental aircraft engine looks almost identical to a VW one. The concepts are all very similar. A newer engine in good tune with good baffling will run cool at various RPM/Manifold Pressure/mixture settings..... a tired engine will run warm no matter how you adjust everything. Our VWs don't have mixture controls like planes but that's about the only difference. All FAA or its forerunner required planes to have for engine monitoring were a tachometer, oil pressure, and oil temp gauge. MP gauges were required with constant speed/variable pitch props. Just like VWs, your typical 60's 70's etc general aviation planes will have all sorts of cylinder head temp gauges, exhaust gas gauges, etc etc added over the years, which are notoriously innacurate and unreliable. I've watched several aircraft owners burn up their engines using aforementioned , not required by FAA, aftermarket instrumentation to lean and monitor their engines instead of using the FAA recommended way, which is by sound and watching the tach and oil gauges. Kinda like Lind mentioned, except the plane needs the tach. I think over revving a VW motor would be harder to do than over revving a plane engine(steep dives, etc).
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Clara Premium Member
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PostPosted: Sat Mar 25, 2017 7:21 am    Post subject: Re: Crusing RPMs Reply with quote

I found that the engine runs coolest at ~3,000K on the flat.
(I did not test on hills, so no info there.)
I generally drive about 3,500 - 4K. My VW don't tend to run hot even in summer, so I am not paranoid about it running the coolest possible.

If it is over 100F out, I might slow down a bit.

VW says the engine is most efficient at 3/4 top speed; top speed is about 4K rpms for a 1600. Top speed isn't the fastest it can go, but the fastest VW recommends driving . They call it something like 'top and cruising speed' check the owners manual.
VW did their mileage ratings at 3/4 speed and half load.
Putting a roof rack on the bus increase drag, but I have to have a hat. sometimes there is big stuff on the rack, which increases drag and works the engine more.

The most important thing is

1) Is your engine dressed properly? Show us a pic of it.
2) Have you driven your bus enough to feel comfortable driving a trip like this?
3) Always check your oil every gas stop. Do a quick visual engine check. Check fan belt tension.
How hot is it? I spit at the base of the gen stand and see if it boils instantly (over 210) or just gently sizzles (170-210 is ideal) or not sizzle at all ( not really warmed up yet)
You can use a laser pointer thermometer (cheap at harbor freight) if you have dry mouth.

I've put a bunch of miles on the engine in my April 61 bus and it is getting a little tired. It does not run hot. It just has less oomph than in 1997.

I've heard some people say gauges make them paranoid. I don't get that. It just gives me more info, which is nice. Obviously, if you don't know what to make of the information, it can be confusing.
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dgsaz
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PostPosted: Sat Mar 25, 2017 9:14 am    Post subject: Re: Crusing RPMs Reply with quote

OK, thanks everyone.

I'll stick with a 3300-3600 range. Dependant on the variables of the day.

dgsaz
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