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Engine Specific Info and Questions => IDI Engine => Topic started by: The Mad Hatter on May 06, 2008, 04:42:16 pm

Title: Concerned about RPM's
Post by: The Mad Hatter on May 06, 2008, 04:42:16 pm
I may have put this in the wrong section.  Sorry!  But, i wanted to ask the experts!   I'm hoping to use my diesel Golf for commuter duty, but the hwy is 75mph, and thats 3600-3700 according to my tach.  Is that too much for sustained trips?  I don't know much about these little diesels, and i don't want to burn her up!   What kinda RPM's do you guys get on your commutes?  Thanks!
Title: Concerned about RPM's
Post by: jtanguay on May 06, 2008, 04:57:01 pm
i wouldn't be worried... as long as the cooling system is working good all you'll be doing is burning some extra fuel.  at or around 2800 rpm seems to be a sweet spot on these motors.  50mpg range.. at 3600 rpm lookout for crap fuel economy...
Title: Concerned about RPM's
Post by: The Mad Hatter on May 06, 2008, 05:07:14 pm
Well there isnt much i can do about that, speed limit is the speed limit.  Anything under 70 and i'm a small tasty meal for a tractor trailer!  Anyway to bring down the ratio so its not running so high at high speed?
Title: Concerned about RPM's
Post by: Vincent Waldon on May 06, 2008, 06:06:31 pm
Diesel gensets run at 3600 RPM for days and days and days and days...

In terms of lowering your highway rpms... best bet is to figure out what tranny you have (the model is listed on a flat spot at the bottom of the bell housing) and then see what you can find at the local wreckers:

http://www.scirocco.org/gears/
Title: Concerned about RPM's
Post by: The Mad Hatter on May 06, 2008, 06:17:15 pm
I haven't crawled under it to look, but i'm pretty sure its a ACH.
Title: Concerned about RPM's
Post by: burn_your_money on May 06, 2008, 06:19:04 pm
larger tires will also help lower the RPMs. If I drive highway speeds at 3300 RPM I get 40 MPG with my NA
Title: Concerned about RPM's
Post by: The Mad Hatter on May 06, 2008, 06:26:19 pm
I'm running 195 50 R15's.  HOPEFULLY she gets 40mpg.  I'm driving an 130 miles a day!
Title: Concerned about RPM's
Post by: theman53 on May 06, 2008, 06:56:38 pm
I don't know if I should admit this...
I had an 81 rabbit stock na. I got it stuck in the driveway( it is 3/4 of a mile dirt) about 2:30 am comming home from a late late night. I was so not in the mood to try to get it out in the morning and thought it would be better to blow it up than to try to do that in the morn. I held it to the floor for about 4.5 minutes and just rocked it from 1st to reverse NEVER letting up on the fuel until it finally came out. During this time the engine made noises that the only thing that I could say it sounded like was when valves float on a small block chevy and it wouldn't rev past a certain point, but it screamed right along the whole time. I drove it for 30,000 more miles with no problems and sold it. It is still going...I think.
 I don't do that anymore as I am older and don't have a roomate that parks in the way so I don't have to go around and get stuck, but I know that RPM's and these motors get along well. From my experience and IMHO.
P.S. I always got 45MPG with that one as well.
Title: Concerned about RPM's
Post by: jtanguay on May 06, 2008, 07:04:15 pm
forgot to mention as well... the higher the rpm's, the more oil these motors consume.  that might be different if the engine is good and tight though.  hard acceleration seems to burn oil too.  i've been able to not burn a drop by smooth acceleration and keeping rpm's low.  having fun is where the oil level starts dropping  :oops:  :lol:
Title: Concerned about RPM's
Post by: shegel on May 06, 2008, 10:10:26 pm
i drive my 86 na 100 miles a day at 70+ speeds and i average 46 mpg's
Title: Concerned about RPM's
Post by: The Mad Hatter on May 14, 2008, 05:27:49 pm
Well 3 days trips into the week, and here's what i've got:

-I'll calculate the mileage when i fill it up, but its sitting around a half a tank with about 340 miles on the trip od.   That's a least 40mpg, if not better.  That's running between 70 and 75 and around 3800rpm according to the tach.
-The new problem, she's using oil rather quickly  :( .  I know jtanguay said it would at higher rpms.  I checked it tonite after i got home, and its down halfway of the marked area on the dipstick (i'm assuming that's a half a quart low), over a 3 day period.   Engine has 139K miles on it, and just had a new timing belt, if any of that matters.  

The long term solution is for me to move closer to my job, BUT, that could take months.  Anything i can do to try and stop the oil burnage?  Probably nothing besides drive at a lower rpm right?
Title: Concerned about RPM's
Post by: burn_your_money on May 14, 2008, 05:53:03 pm
I have never had a diesel that would hold oil above half on the dipstick. It always disappears within a few hundred kms. The bottom half last a lot longer though, just keep an eye on it.
Title: Concerned about RPM's
Post by: gigaz2 on May 15, 2008, 05:03:47 am
new valve oil seals and guides help, but they won't last long till they start leaking again.

I once drove a Fiat Panda 1.3D on a 200Km trip it used 4L of diesel, and 3L of oil... ;)
Title: Concerned about RPM's
Post by: Dr. Diesel on May 17, 2008, 04:07:20 pm
if it's normally aspirated, you're probably better off with those rpm's. It might have trouble holding that speed in a headwind with a taller gear ratio.
Title: Concerned about RPM's
Post by: theman53 on May 17, 2008, 05:23:09 pm
I fitted a baffle from a later hydraulic head on my mechanical head 84 rabbit and that cut the oil consumption in half. I have heard that you can lose a quart in 300 miles without that baffle on the hydro models. It might be a stretch but maybe that is your problem. It is really easy to forget to put that back on if your messing around under the valve cover :oops: like when you do head gasket or timing belt.
Title: Concerned about RPM's
Post by: James8485 on May 17, 2008, 06:19:55 pm
i drive approx 200k's per day the motor was rebuilt but i dont use a drop of oil in between oil changes, thats driveing 115-120KM/H at 2900-3200RPM

if the motor is in good shape you shouldn burn any oil, mine burned a crap load untill i had the rebuild done. ppl kept telling me theres supost to burn oil! well a motor thats in good shape and all seals are good shoulnt as mine doesnt! and i do alot! i mean alot of highway miles!
Title: Concerned about RPM's
Post by: The Mad Hatter on May 17, 2008, 06:44:21 pm
well, i've switched routes to work to a smaller highway with a 55mph speed limit.  HOPEFULLY, running at 3k rpm will be better that 4k.  I'll keep an eye on it.

I had the timing belt and valve cover gasket done by a shop, perhaps its missing that baffle?
Title: Concerned about RPM's
Post by: hamradio on May 17, 2008, 09:06:12 pm
Huh.  Before I tore apart my engine, I got 32 mpg consistently, running 3rd gear up to about 60 often, flooring it everywhere, and dropping into 3rd or 4th on the highway quite often, and using higher revs a lot. :D
Title: Concerned about RPM's
Post by: The Mad Hatter on May 18, 2008, 05:03:36 am
well, running at 4k rpm and 75mph, i got 37mpg, but it was burning oil too fast for my comfort.