Cold Starting Issues...

Reply Subscribe

Thread Tools

Search this Thread

Jan 12, 2010 | 05:10 PM

#31

lobuxracer

Tech Resource

iTrader: (2)

Joined: Jul 2006

Posts: 23,066

Likes: 4,727

From: Georgia

Quote:

Originally Posted by Och

Well, but when you start a cold car, your idle is about 1500 rpm until the engine warms up, which is about the same speed as normal driving, doesn't that take care of most of the problems you described?

Not any more. Back in the carburetor days fast idle was really fast - 1200 to 1500 rpm and it was adjustable with a screw usually over two steps. With modern engine management, I've seen much lower cold cycle rpm increases - usually about 200 or 300 rpm over idle - and the engine management is intentionally running rich to fire up the catalysts. Oil pressure on initial start is always good, but as soon as you get some heat in the oil it thins out and idle oil pressure drops like a rock. The theory is, you're not moving the car at idle so the rod bearings aren't under any significant load. Oil pressure doesn't need to be high if there's no load. It also saves horsepower because pumping oil takes energy just as any other accessory drive does. So we see low oil pressure at idle after a few minutes of operation. Letting the engine idle to full operating temperature has got to be about the most wasteful thing you can do.

Jan 12, 2010 | 10:37 PM

#32

mmarshall

Lexus Fanatic

Joined: Oct 2003

Posts: 94,226

Likes: 222

From: Virginia/D.C. suburbs

Quote:

Originally Posted by lobuxracer

It depends on the ambient temperature....the colder the engine, generally the faster the initial-start idle RPM is. On most of the EFI computer-controlled cars I've owned, initial RPM, from cold-start enrichment, runs from about 1800 in below-freezing temps to about 1500 PRM when it's warmer. When the shift lever comes out of park, it drops to about 1200. If you blip the lever into a driving-gear range momentarily and back into neutral before the gear engages, it will drop to about 1000 RPM....that saves a little gas and holds off on some cold-RPM friction. Most engines are considered fully warm at 140 degrees on the coolant temperatrure......by which time the idle speed should be normal (around 800-900 for most cars)

I'm with you, BTW on carburators......for MANY reasons, they were a PITA. EFI, without a doubt, is one of the best automotive inventions of all time.

Last edited by mmarshall; Jan 13, 2010 at 08:14 AM.

Jan 13, 2010 | 12:18 AM

#33

lobuxracer

Tech Resource

iTrader: (2)

Joined: Jul 2006

Posts: 23,066

Likes: 4,727

From: Georgia

My current F and previous 350 both peak at about 1200 rpm in neutral on a sub-freezing morning (we've had an unfortunately large number of these in the last couple weeks). If it's anything above freezing its 100 rpm. Idle is 700 - 800 according to the book and the tach.

Every once in awhile I miss the old Stromberg. Then I wake up from the nightmare and thank God for EFI!

Jan 13, 2010 | 06:01 PM

#34

Stage3

Thread Starter

Lexus Fanatic

iTrader: (3)

Joined: Sep 2003

Posts: 7,379

Likes: 0

From: Tampa, FL

Quote:

Originally Posted by DASHOCKER

32 degrees is a heat wave for us here in NYC

I don't belive you guys in Florida get the winter blend fuel as we do here in the North East. Non winter blend fuel can freeze up with temps 32 & below. You should purchase a bottle gas line anti-freeze for those cold days & pour it into your gas tank. Let us know how this pans out. I bet you will notice quicker starts.

Good luck.

I'm gonna get a bottle of this and try it. It's supposed to get warm again this weekend, but it's not looking good for next weekend. I'll report back to see what's up! Thanks!