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Gear versus fan speed
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Bob Brugge
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PostPosted: Tue Jul 19, 2016 2:21 pm    Post subject: Gear versus fan speed Reply with quote

Hi guys,
It is hot! not like Arizona hot, but hot enough for me!
I bring this up as I have a concern about keeping my engine cool. Here is the scenario...:
100 plus degree day, stop and go city traffic, going say...45 ish mph. Engines turning 3800ish RPM. I can keep the Rpm's high for cooling, or I can hit the next gear for economy. I understand from an article I read...somewhere... that the VW fan wont suck any additional air after about 5500RPM and with a 1.7:1 or so ratio 3800 engine rpm = about 6450 fan RPM. Understand too that I am using the ear tach. It is closely related to the butt dyno.
If it was a water cooled engine, I would look at the gas gauge and figure how far I had to go before I could get more gas. Just got paid, already broke and have half a tank, better conserve.
But with my bug, my only concern is keeping the engine as cool as possible. So whats better? 45ish MPH in 3rd or 4th? I know turning the engine too slowly will lug it and cause all kinds of problems, not trying to do that either.
Thanks in advance for advice on my mostly stock 70 beetle. All tin and seals in place, well tuned, etc.
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Bama Dave
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PostPosted: Tue Jul 19, 2016 5:50 pm    Post subject: Re: Gear versus fan speed Reply with quote

Just an observation....gas is cheaper than an engine rebuild. I would hope that driving it for proper cooling is the priority. May need to run 40 in third to keep the balance.
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AlteWagen
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PostPosted: Tue Jul 19, 2016 5:51 pm    Post subject: Re: Gear versus fan speed Reply with quote

First thing to do is have ALL the correct tin and flaps before doing any fan speed mods or you will just be wasting your time (and money). Next is get some gauges to see what your temps really are (CHT and OT), guessing with your butt and ear can be expensive. If indeed you are running hot (CHT > 375, OT >220) then you can proceed to additional cooling mods.

Cheapest way to overdrive the fan is to add a lot of shims on the inside of the pulley and run a smaller belt. Next cheapest is to find an early bus crank pulley with larger diameter (7") followed by the aftermarket aluminum larger crank pulley.

If you want to wait till your next paycheck buy a 356 pulley with the correct porsche shims and nut but this is the most expensive option.

If its a real performer and you spin the engine over 6K regularly invest in a quality welded fan as well.
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porkchop-rob
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PostPosted: Tue Jul 19, 2016 7:09 pm    Post subject: Re: Gear versus fan speed Reply with quote

MY OPINION is that its not that important. in my 65, in the HOT Houston summer.... Evil or Very Mad

If I'm on flat ground cruising at 45mph 3rd feels like its wound up like crazy....4th feels a little boggy.

I have NEVER seen elevated oil temps at 45mph when choosing either gear. Only time my oil temps really get 220+ is when I am on the freeway cruising 60-65 (or more). SO....I say not to sweat it. Drive what feels comfortable. If your driving for EXTENDED amounts of time at 45mph, you may want to install one of those dip stick temp gauges (manual ones not the oil light one, or even a candy thermometer that fits) and check it a few times to see how your driving really effects your oil temp.

If you don't have gauges now....dont get them. They just make you paranoid (at least mine have made me that way - lol). VW only put a speedo and a fuel gauge, its worked pretty good so far.

YMMV, its all up to you, don't believe everything you read on these forums. if you read enough you'll be convinced that these cars are impossible to make reliable, all parts sold are junk, and everything except a 100% stock version of the car will spontaneously combust. LOL Razz Razz Razz
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modok
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PostPosted: Tue Jul 19, 2016 7:16 pm    Post subject: Re: Gear versus fan speed Reply with quote

I think we can say fairly certain that you'll see lower head temps in third, but, oil temp might be the same either gear. I think you will be OK in fourth most of the time at 45mph, but if there is a few % grade or big headwind that you are headed into better to shift down.
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madmike
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PostPosted: Wed Jul 20, 2016 4:39 am    Post subject: Re: Gear versus fan speed Reply with quote

Get a 356/912 Porsche upper pulley and quit !@#$%^ing
worrying Rolling Eyes Laughing Laughing Laughing Laughing Laughing
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mark tucker
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PostPosted: Sat Jul 23, 2016 11:36 am    Post subject: Re: Gear versus fan speed Reply with quote

depending on your carbs and the way there set up it may be too leen at that rpm&load and acctuly be too hot in the chambers.I would be in 4th.unless I was playing. why as us ask the car.
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Eaallred
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PostPosted: Mon Jul 25, 2016 8:13 pm    Post subject: Re: Gear versus fan speed Reply with quote

Rpm's raise oil temp, load raises head temp (for the most part)

When it's 100 degrees out, you just have to find the right balance
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Bob Brugge
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PostPosted: Thu Aug 04, 2016 6:41 am    Post subject: Re: Gear versus fan speed Reply with quote

madmike wrote:
Get a 356/912 Porsche upper pulley and quit !@#$%^ing
worrying Rolling Eyes Laughing Laughing Laughing Laughing Laughing


I think your post proves you are a dumbass, welcome to the ignore list. I am sure you and Deathtrap will be good buddies!
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rockurob
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PostPosted: Thu Aug 04, 2016 7:46 am    Post subject: Re: Gear versus fan speed Reply with quote

Bob Brugge wrote:
madmike wrote:
Get a 356/912 Porsche upper pulley and quit !@#$%^ing
worrying Rolling Eyes Laughing Laughing Laughing Laughing Laughing


I think your post proves you are a dumbass, welcome to the ignore list. I am sure you and Deathtrap will be good buddies!


Actually good advice, but probably an overkill on your application. I have
a 73 Thing, with 235-75-15 rear tires .... 28.8" diameter...with
my 4.125 R&P @65 MPH (4th gear) my RPM is 2,800 which is too slow of a fan speed
for cooling in Oklahoma.... A few days ago, I ordered a complete 356/912 generator/alternator pulley,
which is smaller than a stock VW pulley, which will increase my
fan speed and cooling.....here is a post/thread: 356 pulley on a bus
http://www.thesamba.com/vw/forum/viewtopic.php?t=174252

Here is where I ordered my pulley:
http://www.pelicanparts.com
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madmike
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PostPosted: Fri Aug 05, 2016 2:35 am    Post subject: Re: Gear versus fan speed Reply with quote

Thanks Rob,I Try to help and I get called names Rolling Eyes , Question Question Question WTF go ahead an fry your motor ,,,,,,,,,,,,
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76 Drag/Street bug 2180cc 'Turbo' 11:85 @113 mph"If I go any faster I'll burn up the Hamster" ,gets 28 mpg. also 10/09/22 11.90 @115 mph
"If I'm ever on Life Support,UNPLUG Me, Then Plug me back In see if that Works"
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