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Bob Brugge Samba Member
Joined: April 09, 2015 Posts: 721 Location: Missoula, MT
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Posted: Tue Jul 19, 2016 2:21 pm Post subject: Gear versus fan speed |
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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. _________________ Keep on Dubbin'! |
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Bama Dave Samba Member
Joined: April 19, 2015 Posts: 963 Location: Alabama
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Posted: Tue Jul 19, 2016 5:50 pm Post subject: Re: Gear versus fan speed |
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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. _________________ David Richerson
1970 Beetle
1971 Super
1972 Baja
hellthorne wrote: |
First off, I know i made stupid decisions that led to my predicament, so while you are welcome to tell me that I am an idiot for doing the things I did, please know that I am already aware of this. |
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AlteWagen Troll
Joined: February 23, 2007 Posts: 8498 Location: PNW
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Posted: Tue Jul 19, 2016 5:51 pm Post subject: Re: Gear versus fan speed |
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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. _________________ Grapes of Wrath $200 Engine Rebuild
Official Dual Carb Thread
Cylinder Head Quick Reference Sheet |
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porkchop-rob Samba Member
Joined: April 28, 2015 Posts: 440
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Posted: Tue Jul 19, 2016 7:09 pm Post subject: Re: Gear versus fan speed |
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MY OPINION is that its not that important. in my 65, in the HOT Houston summer....
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 _________________ 1965 Beetle
1968 Beetle Baja (Son's First Car)
1976 Bus with Subaru (Wife's Riviera Camper) |
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modok Samba Member
Joined: October 30, 2009 Posts: 26743 Location: Colorado Springs
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Posted: Tue Jul 19, 2016 7:16 pm Post subject: Re: Gear versus fan speed |
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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 Samba Member
Joined: July 11, 2005 Posts: 5291 Location: Atlanta,Michigan
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Posted: Wed Jul 20, 2016 4:39 am Post subject: Re: Gear versus fan speed |
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Get a 356/912 Porsche upper pulley and quit !@#$%^ing
worrying _________________ 'Black Ice'Drag Buggy 'Turbo'
Rail Buggy 1915 turbo
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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mark tucker Samba Member
Joined: April 08, 2009 Posts: 23937 Location: SHALIMAR ,FLORIDA
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Posted: Sat Jul 23, 2016 11:36 am Post subject: Re: Gear versus fan speed |
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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 Samba Member
Joined: May 18, 2003 Posts: 5756 Location: West Valley City, Utah
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Posted: Mon Jul 25, 2016 8:13 pm Post subject: Re: Gear versus fan speed |
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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 _________________ Eric Allred
You have to remember something: Everybody pities the weak; Jealousy you have to earn. |
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Bob Brugge Samba Member
Joined: April 09, 2015 Posts: 721 Location: Missoula, MT
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Posted: Thu Aug 04, 2016 6:41 am Post subject: Re: Gear versus fan speed |
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madmike wrote: |
Get a 356/912 Porsche upper pulley and quit !@#$%^ing
worrying |
I think your post proves you are a dumbass, welcome to the ignore list. I am sure you and Deathtrap will be good buddies! _________________ Keep on Dubbin'! |
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rockurob Samba Member
Joined: August 23, 2009 Posts: 358 Location: Okla City, Oklahoma
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madmike Samba Member
Joined: July 11, 2005 Posts: 5291 Location: Atlanta,Michigan
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Posted: Fri Aug 05, 2016 2:35 am Post subject: Re: Gear versus fan speed |
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Thanks Rob,I Try to help and I get called names , WTF go ahead an fry your motor ,,,,,,,,,,,, _________________ 'Black Ice'Drag Buggy 'Turbo'
Rail Buggy 1915 turbo
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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