Reving the hell out of a diesel

Submitted: Friday, Jun 24, 2005 at 20:24
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Was in the bush and met a diesel mechanic. He commented on my car and said that diesel engines have a rev limiter (which i kina knew) and so I could floor my car all day and the engine would be fine. He recons you cant ruin a diesel from thrashing the hell out of it. I would like to think this is true but sadly - dont ( i gotta look after my car). However if anyone knows a little on the subject of diesels, reving a diesel and prolonging it's life that would be good to know while out in country side. Thanks.
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Reply By: hl - Friday, Jun 24, 2005 at 21:14

Friday, Jun 24, 2005 at 21:14
He must have been jealous of your nice fourby......
Actually all modern cars (fuel injected) have rev limiting.. that doesn't mean they want to be flogged to the the limit all the time.
Don't let him work on your car!


AnswerID: 117330

Follow Up By: Exploder - Friday, Jun 24, 2005 at 21:46

Friday, Jun 24, 2005 at 21:46
G'day F4

That is not the first time I have herd a recommendation like that on hear or else were, so there may be some truth in it, I not a diesel fitter so can’t comment on that.

As for driving around with the needle perched firmly on 4500rpm all day can’t see it doing much good to the internals or the fuel bill.

It doesn’t do it any harm giving it a workout once in a wile thou,

I know a bloke who is a plant mechanic for CATERPILLAR next time I run into him I will quiz him about it, see if I can’t get some strait answers.

You could always look at it like, if it wasn’t meant to go there why did they put the numbers on the gage :)

FollowupID: 372769

Follow Up By: F4Phantom - Friday, Jun 24, 2005 at 22:16

Friday, Jun 24, 2005 at 22:16
that would be good if you could ask the cat guy, i am sure there is little truth somewhere in this chinese wisper.

If you read the manual it says that under the red line it "normal driving" and over the red line should be for short periods. So next time I drive past at 100km/h in third gear you cant say I dont know what i am doing cause i am in the normal driving zone, if i want to overtake someone i will drop into 2nd, make the diesel rev to 9000rpm for a "short period", none of this of course will in any way harm my engine - the manual says so.
FollowupID: 372778

Follow Up By: Exploder - Friday, Jun 24, 2005 at 22:43

Friday, Jun 24, 2005 at 22:43
Will do; don’t hold yah breath but he does a lot of fly in fly out work and it is wether I happen to bump into him when he’s back in Perth.

He is not really a friend just a person I will have a chat with if I see him.
There must be at least one diesel mechanic, Diesel fitter or Plant mechanic on this site who can give a strait answer.
FollowupID: 372788

Reply By: howesy - Friday, Jun 24, 2005 at 21:26

Friday, Jun 24, 2005 at 21:26
Why don't you ask him if you can try it on his by holding the gas pedal to the floor for twenty minutes. Bet he is not so keen then. Did he have one hand on his appedage when he came out with this wisdom.
AnswerID: 117332

Reply By: KiwiAngler - Friday, Jun 24, 2005 at 21:26

Friday, Jun 24, 2005 at 21:26
I ain't no mechanic but lets look at the scenario.

Dictionary quote:
A mechanic (n) - definition " someone whose job is repairing the engines of vehicles and other machines:"

suggests to you that: He recons you cant ruin a diesel from thrashing the hell out of it.

and that: reving a diesel and prolonging it's life that

I would suggest the answer to your own question may reside right there. :-))

Don't use him :-)

He didnt 'just by chance' also give you his business card and say "If anything SHOULD go wrong give me a call...I will 'see you right'....
AnswerID: 117333

Follow Up By: KiwiAngler - Friday, Jun 24, 2005 at 21:29

Friday, Jun 24, 2005 at 21:29
Hey...just noticed the first sentence in your post "...Was in the bush and met a diesel mechanic"

I think this would make him a "bush mechanic" then :-)))...boom boom
FollowupID: 372757

Reply By: F4Phantom - Friday, Jun 24, 2005 at 21:35

Friday, Jun 24, 2005 at 21:35
i am sure you know how it is when you meet some nice bloke out 4x4ing. He seemed quite honest about this revving thing but did not drive a diesel. He was in a sierra with double diff locks all that goes with em. Basicly I do go with logic but also wanted to know if there was something to this whole diesel rev limiting thing. It came accross as though it was some special diesel trait. I have long been of the opinion that diesels did not need to be revved high cause they generate torque down low.
AnswerID: 117335

Follow Up By: F4Phantom - Friday, Jun 24, 2005 at 21:57

Friday, Jun 24, 2005 at 21:57
I fotgot, he was revving the absolute freaking hell out of his 1.3L engine (you know the distinct sound an engine makes when it is almost coming alive enough to say "your killing me!" - that kind of revving) to make it pump out some power, it was blowing a fair amount smoke. Also he nearly stuffed his clutch from changing gears while the was but under muddy water in a bog hole and filling the plates. On second thoughts - perhaps this guy was just hard on all machinery and decided i was being a bit soft so told me this story to lighten me up!
FollowupID: 372772

Follow Up By: Exploder - Friday, Jun 24, 2005 at 22:08

Friday, Jun 24, 2005 at 22:08
Maybe it was a customer’s car and he was diagnosing a problem the only way he knows how. MAKE IT PIS* I believe is the commonly use term.

FollowupID: 372776

Reply By: Nick R - Friday, Jun 24, 2005 at 22:13

Friday, Jun 24, 2005 at 22:13
One engine this is the case is with 471 detroit and similar blown engines. Basically they wouldn't pull the skin of a rice pudding unless it is revving it's ring out, this is one case where you should drive it like you hate it. Just wish it had lockers though then it would be unstoppable (commercial front end loader)
By the way, it does like fuel, 20-25 litres per hour at full noise!!!
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AnswerID: 117343

Follow Up By: F4Phantom - Friday, Jun 24, 2005 at 22:25

Friday, Jun 24, 2005 at 22:25
that reminds me of rc car engines which are also diesel engines. they are 1.5cc or a bit more and do around 38,000 rpm. They dont use diesel fuel tho, but have a glow plug so they are called diesel, this raises an intertesting point, diesels dont have to use diesel fuel to be a diesel, its called a diesel by the way it ignites the fuel not by the fuel type.
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Follow Up By: Nick R - Friday, Jun 24, 2005 at 22:32

Friday, Jun 24, 2005 at 22:32
Interesting point, there was a thing about a top fuel dragster which says that they are deiseling part way down the 1/4 mile onwards as they have burnt the spark plugs off.
The loader though does run on diesel, lots of it, it is firing every secong stroke though, not every fourth.
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Follow Up By: F4Phantom - Friday, Jun 24, 2005 at 22:37

Friday, Jun 24, 2005 at 22:37
so the loader is a 2 stroke diesel? i have heard of them but never looked into it - but that explains the no power at low rpm, seems to exhibit the same sort of charateristics as a petrol 4 vs 2 stroke.
FollowupID: 372786

Follow Up By: Nick R - Saturday, Jun 25, 2005 at 21:09

Saturday, Jun 25, 2005 at 21:09
it is a 2 stroke, someone once told me that it should be about 40hp at low revs but peaks around 160-180hp at work, not sure how they worked out the low end power???
A very old but versatile design motor this one, the 2 valve version was used in the American tanks in the 1930s, they went 4 valve in the 60s I think, you can bolt on another block to make an 871 it is already 113 db now so I think that is enough....
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Reply By: garrycol - Friday, Jun 24, 2005 at 22:35

Friday, Jun 24, 2005 at 22:35
my Diesel has a red line at 4500 rpm and the rev limiter cuts in at 5000 rpm - the way I see things is that the red line is the max safe revs for the engine and for the dummies who stuff things up in emergencies or with revs changes the cut out is there to protect the engine - ie do not go above the red line!! - it is there for a reason
AnswerID: 117346

Reply By: Muddy 'doe (SA) - Saturday, Jun 25, 2005 at 01:02

Saturday, Jun 25, 2005 at 01:02
I would think that a big characteristic of a diesel engine is the fact that maximum torque (pulling power) is available at quite low revs when compared with petrol engines where the torque peak occurs quite high in the rev band 5000-6000). This of course varies a bit with displacement (3 litre 4 cylinder versus 7.2 litre V8!).

Several magazine reviews that I have read recently indicate that revving diesels above about 5000rpm is pretty pointless. All the torque is produced in the 2500 to 3500 rpm band. All you get past 5000rpm is smoke and noise!

This is particularly true of the new generation passenger cars hi-tech common rail diesels coming out of Europe (Puegot and co).

My Prado 1KZ-TE Turbo Diesel certainly gets breathless after about 4000rpm and redlines at 5000 I think. performs best at around 3500rpm.

I think your Diesel Mechanic "friend" is having a bit of a go - or is seriously misguided!

AnswerID: 117360

Follow Up By: Member - JohnR (Vic)&Moses - Saturday, Jun 25, 2005 at 08:52

Saturday, Jun 25, 2005 at 08:52
Geez Muddy, you get breathless above 100 rpm. Your car keeps going though a bit beyond that.

The newer European diesels really get up and fly with the common rail technology. The developed torque is great on the open road speed of the motorways but I don't know the revs lol. Great for 160 plus there, even a Citroen people mover I drove, heaven forbid.
FollowupID: 372812

Reply By: Bob Y. - Qld - Saturday, Jun 25, 2005 at 08:45

Saturday, Jun 25, 2005 at 08:45

I'm not a mechanic, but have operated, and worked on Caterpillar machinery, since mid -70's. The governor in Cat engines is probably a little different to tojo/nissans, and you can rev them at the max, all day, and they love it! In fact, a few engine tests are done at "High Idle"(max revs-no load) Drove a Cat elevating scraper for 6 years, and it was all pedal to metal work.

My idea of thrashing an engine invariably means thrashing the whole vehicle, not steadying up for bumps, purging through mud at over 4,500rpm, slipping the clutch, and negotiating terrain in high range, when transfer case should be in low.

Diesels do like to loaded, otherwise they glaze the bores, and use heaps of oil.

Seen it all, Done it all.
Can't remember most of it.

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AnswerID: 117371

Reply By: Bob of KAOS - Saturday, Jun 25, 2005 at 09:12

Saturday, Jun 25, 2005 at 09:12
I find that friends who drive my car after driving their own petrol cars tend to over rev the diesel. This occurs even when gently accelerating through the gears. Using the extra torque at lower revs seems to be counter-intuitive. It is rare that I go above 2500 rpm.

Lower engine speed means less friction which means less wear on metal to metal (actually metal/oil/metal) surfaces, and better fuel economy.

The other factor is exhaust gas temperature. At higher revs you are pumping more air and diesel through the same engine. So the mount of energy lost as heat that needs to be dissipated is increased. The extra heat has an adverse effect on lubrication and oil life.

So I wouldn't rev the head off my engine all day.
AnswerID: 117375

Reply By: Member - RockyOne - Saturday, Jun 25, 2005 at 09:51

Saturday, Jun 25, 2005 at 09:51
No-one seems to have mentioned the "glazing" factor,caused,I am told by our mechanic customers, (almost everything is diesel around here) by allowing a diesel to run at low speeds for longer periods of time..Working stationary engines (including plowing tractor engines that run at consistant revs all day/nite) don't have the problem because they are under load,which is what they are built for..Pehaps the new laws that may discourage us softies,from leaving a motor/air-con running while in the shopping centre,are actually doing us ,the motor and the envior a favour..At work we sell to mechanics de-glazers,which are a number of slightly abrasive balls on the ends of wires of "cylinder" brushes..They are spun by a power tool to de-glaze the cylinders that have suffered this condition possibily due to in-correct engine management by the operator..You could almost think I knew what I am talking about..Don't be fooled.! Helps RockyOne!MPG:3!
AnswerID: 117378

Follow Up By: johnsy1 - Monday, Jun 27, 2005 at 22:04

Monday, Jun 27, 2005 at 22:04
Take the air cleaner off and throw a small hand full of bon ami in to the air so the dust is sucked into the engine is a quicker way of de glazing . KIDS DO NOT DO THIS AT HOME .its a bush mechanics method
FollowupID: 373105

Reply By: Kiwi Kia - Saturday, Jun 25, 2005 at 11:00

Saturday, Jun 25, 2005 at 11:00
A red line on a rev counter does not mean never exceed, it just means max normal operating. You should be able to operate up to the red line any time you want and not do any damage. Above the red line the engine is operating out of its 'comfort zone' and all sorts of combinations of temp, lubrication, load etc. may push the engine into a danger zone where a manufacturer does not want you to go or they may have to pay out on an warranty !
AnswerID: 117385

Reply By: Member - Karl - Saturday, Jun 25, 2005 at 13:32

Saturday, Jun 25, 2005 at 13:32
I was told by my diesel mechanic to give mine a 'bit of herbs' every now and then to blow out the cobwebs. He then went onto explain that when doing a lot of city driving the motor starts to glaze up - as explained in an earlier post. He said that by sticking the boot in every now then it can loosen up the glazing and blow it out.

So every now and then I give it a bit of stick through the gears. So far so good.
AnswerID: 117400

Reply By: cmilton54 - Saturday, Jun 25, 2005 at 17:03

Saturday, Jun 25, 2005 at 17:03
The detroit must be same as v8 190hp cummins short stroke , so it needs to be flat rev`s to get max power. Would not flat strap my own triton`s or toyota`s any more than needed.
AnswerID: 117421

Reply By: Member - Jeff M (WA) - Saturday, Jun 25, 2005 at 17:06

Saturday, Jun 25, 2005 at 17:06
What an absolute spanker!

Diesel's don't particulary like reving at the best of times. Ever notice your diesel's Tacho, how it only goes to 4 instead of 6 or 7 like your average petrol powered vehicle??

Conventional diesels are running at around 21:1 compression ratio, the new euro diesels are running at about 17:1, your petrols would be lucky to see 10:1.

Think of it like this:
It's good for you to go for a fadt paced walk or even a jog for 20minutes a day. It's not good for you to have a rope tied around your waste and told to keep up while you mate drives from Perth to Adelaide!

It's not so much rev's that diesels like, it's having some load. That means being able to put your foot down 3/4 on the pedal at 2000 or 3000 rpms. Towing is a good exaple, beach dirving, going up long hills, or even just cruising on the highway with all ya camping gear. Thrashing any engine will kill it eventually.

As for rev limiters, what is this guy? a total knob licker? Any car with an ECU petrol or diesel has a rev limiter. Mechanically controlled diesels would not have rev limiters and would keep reving until you see bit of the engine protuding through the bonnet.
My work car (a small 4cyl petrol) hit's the rev limiter every day... Why? Cos it's a work car and it's a POS. ;-)

Look after your diesel, baby it till it's warmed up then drive it normally, don't thrash it and don't drive like grandma and you will be fine.
AnswerID: 117423

Follow Up By: snowman - Sunday, Jun 26, 2005 at 13:45

Sunday, Jun 26, 2005 at 13:45
Hi Jeff,

I dont know of any mechancically control diesel fuel pumps that DONT have a govenor fitted to them. I repaired cummins mechanical fuel pumps for 6 years.
Cheers Dave
FollowupID: 372914

Follow Up By: Member - Matt Mu (Perth-WA) - Monday, Jun 27, 2005 at 11:21

Monday, Jun 27, 2005 at 11:21
Yep, sorry Jeff, never worked on a mechanical diesel FIP that didnt have a governor, usually just a fly-weight setup that will push against the fuel rack (or swash plate) if the set RPM is reached. Its got nothing directly related to the tacho, but I think the manufacturer would have to have the tacho resemble the FIP (fuel injection pump) set max rpm.
Max RPM can still be exceeded though, but usually in trucks not cars. If the weight of the vehicle (trailer, load etc ) is large enough then on down hill runs the vehicle can be pushed over the engines max RPM and damage the engine.
Hence why trucking companies like the fact they can look up a new diesel engine computer to see if the engine has been over-sped. ie damage is the drivers responability!!!

FollowupID: 372992

Follow Up By: Member - Jeff M (WA) - Monday, Jun 27, 2005 at 14:41

Monday, Jun 27, 2005 at 14:41
Yeah I would have thought a fuel pump governer wouldn't have been directly related to REVS and that you could'nt assume it would protect the engine from over reving.

As far as going down hill even EFI rev limiters can't stop you hitting the limiter then goning down a steep hill. Hell I used to do it in my feroza all the time up the alkimos. Hit 6.5k (rev limiter activates), shoot down one side with the tacho bouncing off the edge of the guage (7) then zoom up the other side with just enough steam to make it over the top.
FollowupID: 373027

Reply By: Beddo - Saturday, Jun 25, 2005 at 17:21

Saturday, Jun 25, 2005 at 17:21
I lived out western NSW at Tibooburra for a few years and the locals said flog the diesels - a comparison between 2 vehicles I drove both 78 series cruisers 4.2 diesels - one was run in slowly and not reved much, the other was - the one that was reved harder was quicker - did 12Km faster flat out approx if I remember. they said it was all to do with glazing aswell. Top speed was around 135Km - that is above the speed limit I know - but out at Tibooburra it takes you 3 & half hours to get to the nearest major town Broken Hill.
AnswerID: 117428

Follow Up By: Member - Davoe (Widgiemooltha) - Sunday, Jun 26, 2005 at 02:36

Sunday, Jun 26, 2005 at 02:36
yea but I am yet to see 2 78s that go the same yet some will do 120kph while others run to nearly 140 and I am talking underground vehicles that hit 4500 rpm at least a dozen times a shift
FollowupID: 372889

Follow Up By: bundyman - Monday, Jun 27, 2005 at 08:22

Monday, Jun 27, 2005 at 08:22

As Davoe says in the underground minng industry the work cruiser utes spend 75% of their time doing over 3500rpm typically around the 4000rpm mark. This is because the we only have low range and up to 3rd gear. Now these utes will cop that for the 2-4 years of their short lifes underground will no ill effect. I have never seen a motor replaced (that hasn't been cooked). I personally wouldn't drive mine like that but you do need to watch for glazing of the bores. I always drive mine in 4th for the first 40 odd kms when I do a highway run.

Yes the big medium speed diesels in trucks and machinary spend probably 80% of their lives sitting on the rev limiter. I've operated underground loaders on remotes and have had the exhaust glowing red hot from the exhaust manifold thru to the exhaust tip (looks awesome in the dark), from sitting on full revs and putting out max horespower under full load for hours on end. But these engines are designed to do that. Vehicle motors are not.

Anyway thats my 2 cents worth.

FollowupID: 372979

Reply By: viz - Saturday, Jun 25, 2005 at 18:44

Saturday, Jun 25, 2005 at 18:44
I think I was born on a diesel engine... :)

Old injection pump type diesels, slow reving and low revving could go all day at full revs - redline might be 2700 rpm or even 1500 rpm for the big Gardners. So redlineing all day would never harm it.

Modern *light* diesels are high revving 4000+ rpm. This is due to things like high pressure common rail injection, electronic timing, variable valve timing, pulsed injection etc. Sure they produce heaps of power (eg. Nissan 3.0 diesel), but do so at high revs, with often a loss of low down torque - and the jury is still out on engine longevity. In balance, a petrol may even be cheaper in the long term than some diesels on the market at the moment, if one includes service and a rebuild.

I have a Mercedes diesel, 2150 cc in s Sprinter van. Once the revs are up (4000 redline) it pulls like a schoolboy. Power to weight ratio is amazing and even loaded will easily keep up with the traffic (check out the ambos in NSW - all diesels and they are not slow...). However one of the reasons one might buy a diesel is a little lost on the Mercedes - it is a *very* expensive motor to maintain - e.g. injectors are $1200 each (non servicable) and I look like replacing a second set in the very near future (under warranty).


AnswerID: 117440

Reply By: angler - Sunday, Jun 26, 2005 at 20:12

Sunday, Jun 26, 2005 at 20:12
I used to drive a few game boats with twin diesels, standard procedure was to go to full noise then drop the slowest engine to about 100revs below full noise then slow the other to match and synchronise.
Newer boats have auto sync and can have single control for both engines, Same procedure for setting cruise speed.
AnswerID: 117585

Reply By: Redback - Monday, Jun 27, 2005 at 12:16

Monday, Jun 27, 2005 at 12:16
Here ya go guys a diesel revving it's ring out, mine in fact.

the Disco is mine.

A trip to the Watagans

AnswerID: 117674

Reply By: Big Woody - Tuesday, Jun 28, 2005 at 07:06

Tuesday, Jun 28, 2005 at 07:06
Hi all,

I am a diesel driver and tend to keep my revs lower than most but I have a brother that screams his diesel to the redline in every gear and has done so for as long as I can remember.
My other brother and I cringe whenever we are in the car when he is driving. It sounds horribly destructive and I am waiting for a piston to shoot out through the bonnet.
The thing that is amazing though is that this same brother brought a 60 series cruiser in 1982 from the showroom and sold it in 1993 with 650,000 km on the clock and the motor had never been touched.
Then in 1993 he brought an 80 series diesel GXL cruiser and he still has it. It now has 680,000 on the clock and it is still going strong.
I am still not convinced and could never bring myself to drive like this but who knows? There may be some merit in what this mechanic was saying.


T/D 75 Series Ute
AnswerID: 117837

Reply By: F4Phantom - Tuesday, Jun 28, 2005 at 08:39

Tuesday, Jun 28, 2005 at 08:39
i think i have a solution to give your diesel everything it needs, give your car an easy ride onroad & service it properly, then off road give it hell.
AnswerID: 117851

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