revving an engine to "warm it up"

I recently had a discussion on this topic. I have heard that revving
the engine may do harm and does little to "warm" the car up. This is an
older car with an engine that has been modified. This guy revvs the
engine at the house and still seems to have trouble making it down his
driveway (about 1/4 mile steep downhill) without stopping and revving
his engine halfway down and then again at the bottom. Is this type of
"warm up" accomplishing anything or is he just destroying his car?

huts wrote:
> I recently had a discussion on this topic. I have heard that revving
> the engine may do harm and does little to "warm" the car up. This is an
> older car with an engine that has been modified. This guy revvs the
> engine at the house and still seems to have trouble making it down his
> driveway (about 1/4 mile steep downhill) without stopping and revving
> his engine halfway down and then again at the bottom. Is this type of
> "warm up" accomplishing anything or is he just destroying his car?
>

It's probably not good for the car; however, if the engine is "modified"
it may have issues with a cold start, esp. if he has a chokeless
carburetor (sometimes people who don't live in particularly cold
climates will mill the choke housing off the carb for better airflow)
therefore he may have to play with it a little to keep it from stalling.

I know a friend of mine has an old Studebaker with a 383 Chev "crate
motor" in it; he doesn't have the specs on the motor (bought the car
pretty much as it is) but it is pretty hairy (and fun to drive) even
after both of us threw all our tricks at it to get it to start and run
without a long period of sitting still and revving the engine, the "fast
idle" had to be set at about 2000 RPM and it still doesn't always start
on the first crank. (of course, it also has dual AFBs on a low rise
Offy intake, probably not the hot setup for anything but WOT but it
looks cool)

I am guessing the PO didn't ever plan on driving the car in cold
weather; neither carb had a choke on it when he got it. We did install
an electric choke on the rear carb and that did make a lot of
difference, although it's still not the kind of car you'd want to hop in
and drive to work (well, I might, but I'd still probably have to leave
it sit and "idle" - using the term loosely - for a minute or two in the
AM before driving off.)

But yes, your basic premise is correct - the best way to handle a normal
cold start, unless it's bitterly cold, is to simply start the car and
drive off, but drive "easy" until the engine is fully up to operating
temperature.

nate

--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel

huts wrote:
> I recently had a discussion on this topic. I have heard that revving
> the engine may do harm and does little to "warm" the car up. This is an
> older car with an engine that has been modified. This guy revvs the
> engine at the house and still seems to have trouble making it down his
> driveway (about 1/4 mile steep downhill) without stopping and revving
> his engine halfway down and then again at the bottom. Is this type of
> "warm up" accomplishing anything or is he just destroying his car?
>

Both! Yes, that can reduce the time to warm the engine. But, WHY are
we warming the engine? Primarily to ensure proper lubrication from the
oil. If we rev it up before that, we are not getting proper lubrication,
so why do it? This is kind of self defeating.

We ordinarily think of warming the engine before stressing it as
contributing to reduced wear. But if we wear it excessively WHILE
warming, we gain nothing.

Admittedly, if this is an older car with a carburetor, drivability
improves when the car is warmed up. But again, drivability is bad when
he is revving it anyway. Better to ease it along and warm it that way.
If it tends to stall, he should play with fast idle rpm setting.

Not the best for it, but likely it is stalling out so needed.

I have a carb engine that came stock with a 'timer' choke. The sucker
goes open according to how long the engine has been running with no
reference to how 'hot' the engine actually is. These types of chokes
are a pain in the ass up here in Canada. I would stall every time I let
off the gas pedal in the first 1/4- 1/2 mile unless I revved it until
the engine had really warmed up. 3 foot driving style or heel toe on
the gas brake for a while.

I fixed it's case by putting a manual choke in. I now can keep the fast
idle at 1200 until it is actually warmed up and drive away in any
temperature.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

huts wrote:
>
> I recently had a discussion on this topic. I have heard that revving
> the engine may do harm and does little to "warm" the car up. This is an
> older car with an engine that has been modified. This guy revvs the
> engine at the house and still seems to have trouble making it down his
> driveway (about 1/4 mile steep downhill) without stopping and revving
> his engine halfway down and then again at the bottom. Is this type of
> "warm up" accomplishing anything or is he just destroying his car?

huts wrote:
> I recently had a discussion on this topic. I have heard that revving
> the engine may do harm and does little to "warm" the car up. This is an
> older car with an engine that has been modified. This guy revvs the
> engine at the house and still seems to have trouble making it down his
> driveway (about 1/4 mile steep downhill) without stopping and revving
> his engine halfway down and then again at the bottom. Is this type of
> "warm up" accomplishing anything or is he just destroying his car?
>

Exhaust is often shut off, and other things are closed for quick warmup.
shouldn't push the engine under these conditions as you can cause
stuff to wear out more quickly. Probably not as hard on newer cars, but
also even less beneficial.

--
Thank you,



"Then said I, Wisdom [is] better than strength: nevertheless the poor
man's wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

huts wrote:
> I recently had a discussion on this topic. I have heard that revving
> the engine may do harm and does little to "warm" the car up. This is an
> older car with an engine that has been modified. This guy revvs the
> engine at the house and still seems to have trouble making it down his
> driveway (about 1/4 mile steep downhill) without stopping and revving
> his engine halfway down and then again at the bottom. Is this type of
> "warm up" accomplishing anything or is he just destroying his car?

He will minimize the wear on the engine during warmup by just getting
in the car and driving it, keeping the engine at a steady and low rpm.
If the engine doesn't idle well when cold it is probably in need of
repair. Much less likely in my experience is that the car is a highly
tuned street racer. The many cars I've driven over the past 15 years
all use an engine computer to make warmup and overall running very
smooth. If taken care of there should be no problem with a modern
engine holding an idle when cold.

dnoyeB wrote:

> huts wrote:
>
>> I recently had a discussion on this topic. I have heard that revving
>> the engine may do harm and does little to "warm" the car up. This is an
>> older car with an engine that has been modified. This guy revvs the
>> engine at the house and still seems to have trouble making it down his
>> driveway (about 1/4 mile steep downhill) without stopping and revving
>> his engine halfway down and then again at the bottom. Is this type of
>> "warm up" accomplishing anything or is he just destroying his car?
>>

It depends on the car. If its an older car that is unmodified or lightly
modified, he's got a PROBLEM that needs fixing (choke flooding the
engine or not applying sufficiently, etc.) Even fairly heavily modified
engines can be made to behave 'tolerably well' when cold if all the
systems are working right.

If its an extremely highly modified car, being horribly cold-natured is
just part and parcel of living with a high-strung engine. Its hard on
it, but its probably not designed with longevity anyway. If its a
question of stopping to rev up and blow the unburned fuel out, versus
stalling and restarting over and over- then revving it a bit is the only
choice.

>
> Exhaust is often shut off,

That is without a doubt one of the sillier things I've ever read on an
automotive tech newsgroup.


The BIGGEST risks for a cold engine a

1) fuel dilution in the engine oil and "washing" down the cylinder walls
with raw fuel. Mostly a problem with carb'd cars, though EFI does this
to s limited degree as well. Prolonged idling to warm the car makes this
much worse than just driving gently.

2) Excessive wear because clearances are larger when cold. This isn't
normally a big deal as long as you give it time to get the oil
circulating before putting a full load on it. Even audible piston slap
doesn't really cause excessive wear most of the time. BUT, the car is
more sensitive to how HARD its driven when cold. Romping on a stone-cold
engine will wear it more than driving it gently for a few minutes until
things come up closer to operating temperature.

dnoyeB wrote:
> huts wrote:
> > I recently had a discussion on this topic. I have heard that revving
> > the engine may do harm and does little to "warm" the car up. This is an
> > older car with an engine that has been modified. This guy revvs the
> > engine at the house and still seems to have trouble making it down his
> > driveway (about 1/4 mile steep downhill) without stopping and revving
> > his engine halfway down and then again at the bottom. Is this type of
> > "warm up" accomplishing anything or is he just destroying his car?
> >
>
> Exhaust is often shut off, and other things are closed for quick warmup.

Do you mean that incoming air is first routed over the exhaust manfold
to warm it and thereby speed engine warmup?


> shouldn't push the engine under these conditions as you can cause
> stuff to wear out more quickly. Probably not as hard on newer cars, but
> also even less beneficial.
>
> --
> Thank you,
>
>
>
> "Then said I, Wisdom [is] better than strength: nevertheless the poor
> man's wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

On 3 Mar 2006 19:13:31 -0800, "John S." > wrote:

>
>dnoyeB wrote:
>> huts wrote:
>> > I recently had a discussion on this topic. I have heard that revving
>> > the engine may do harm and does little to "warm" the car up. This is an
>> > older car with an engine that has been modified. This guy revvs the
>> > engine at the house and still seems to have trouble making it down his
>> > driveway (about 1/4 mile steep downhill) without stopping and revving
>> > his engine halfway down and then again at the bottom. Is this type of
>> > "warm up" accomplishing anything or is he just destroying his car?

================================================== ==========
>> Exhaust is often shut off, and other things are closed for quick warmup.

What really happens in a *modern car* is the thermostat opens
gradually, and in cold weather might take 20 minutes to open fully.
It doesn't *snap open* like a switch. It starts out fully closed, but
as soon as the engine gets to about 170 degrees F, it opens a little,
and as the coolant becomes hotter, it opens more, until at around 200F
it is fully open and oscillates back and forth allowing the water to
become a little warmer, and than a little cooler, producing something
like a sine wave with respect to the temperature signal coming from
the engine heat sensor.

>Do you mean that incoming air is first routed over the exhaust manfold
>to warm it and thereby speed engine warmup?

I don't see how that would make any sense. True that the coolant is
circulated through the heater core according to dashboard settings,
rather than the thermostat.

Lg


>> shouldn't push the engine under these conditions as you can cause
>> stuff to wear out more quickly. Probably not as hard on newer cars, but
>> also even less beneficial.
>>
>> --
>> Thank you,
>>
>>
>>
>> "Then said I, Wisdom [is] better than strength: nevertheless the poor
>> man's wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

"John S." wrote:
>
> dnoyeB wrote:
> > huts wrote:
> > > I recently had a discussion on this topic. I have heard that revving
> > > the engine may do harm and does little to "warm" the car up. This is an
> > > older car with an engine that has been modified. This guy revvs the
> > > engine at the house and still seems to have trouble making it down his
> > > driveway (about 1/4 mile steep downhill) without stopping and revving
> > > his engine halfway down and then again at the bottom. Is this type of
> > > "warm up" accomplishing anything or is he just destroying his car?
> > >
> >
> > Exhaust is often shut off, and other things are closed for quick warmup.
>
> Do you mean that incoming air is first routed over the exhaust manfold
> to warm it and thereby speed engine warmup?
>

He is talking about a heat riser valve that shuts off one bank of a V
engine's exhaust and routes it across the intake for warming the
fuel/air mix.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)