Engine Temps - Let's be Reasonable

[Superman]

Someone said they avoided redline because it was cool in Montana and oil temp achieved only 165. I say that when an engine reaches equilibrium temp, it is ready for redline, regardless of whether the magic 180 number is reached.

Also, JW has told us that engines need to be cooled for valve adjust, but not necessarily ICE COLD. I agree with this too, as long as it has had time to truly cool down.

Anybody want to disagree?

[CamB]

Super - you crack me up.

Every month or so you post a debate like this - always a well thought out issue, always with two good arguments.

Alright, I'll take the bait. Non-engineer's viewpoint.

I agree on the engine temp before running to redline - if it has reached equilibrium then why not. Maybe a couple of brief forays up that way will "fix" the low temp problem.

My BMW has a 70 deg C thermostat and upgraded radiator and it won't achieve anything higher unless it is running in traffic with no airflow (fan turns on at 80-85 deg). I figure I am safe gettin on it once it has run at 70 deg for a while.

Valve clearances? Well I understand the reason you set them cold is because the gap closes to basically nothing when the engine is hot. I suspect the spec could also be "gap equals bugger-all when hot" but how the hell do you set that? So they have a specification for when the engine is cold.

Thus as long as the engine is cold enough for the gap to be as wide as it will ever be (stone cold, cool, whatever?), then it is fine. So we need one of the guys who can give a discussion on the thermal expansion rate of the valve train and can tell us how much the gap would be closed on a cool engine vs a cold engine.

Cam's essay is complete.

[Superman]

I was hoping for a more vicious argument, Cam.

Knowing that I am one of this site's most colorful troublemakers, I occasionally have checked with Wayne as to whether I am in bounds or OB. He has not deleted my registration, so I guess I am good to go. I appreciate his patience with me. So yeah, I get bored some times and deliberately try to stir things up. Guilty.

[5axis]

A quick search and ...

Metals have a thermal expansion coefficient. This means the metal will expand a certain amount with every increase in temperature. For example, a typical 304 stainless steel has a linear thermal expansion coefficient of 9.500e-06 or 0.0000095 in / in * F. The steel will expand 0.0000095 inches for every inch in diameter and every Fahrenheit degree increase in temperature.



nuff said.
david 89 turbo cab

[RoninLB]

[QUOTE]Originally posted by Superman
[B]. I say that when an engine reaches equilibrium temp, it is ready for redline, regardless of whether the magic 180 number is reached.

Well Super, how do you define "equilibrium"? When oil temp is in "equilibrium"?? .............Ron

[724doorE]

And I can remember a few instances of you suggesting my comments or intentions were less than appropriate....


Doing it cold is just for sissys that are afraid of getting their fingers burned...once you do it a few times, it don't hurt no more!!! OK happy.

Frankly I don't see why if your are sure that your valves have reached there maximum expansion, (ie hot), you wouldn't be able to set them the same way you set valves in a V-8,(ie hot and with no clearence). The difficulty would concern your super powers of determining exactly when the rocker adjustment screw just touches the valve stem tip. And maybe at that point one would even go so far as to back the screw off some minor amount. So how well do you see back deep inside with both hands and a wrench in there under the car or on top at elevated temps trying to get it right twelve times when you could just do it cold and actually measure the clearence without stickiing your head or a mirror down inside!!!

This is what you were looking for isn't it....

[Jim Sims]

If I had to live in Montana again (I remember the tank heaters, battery heaters, oil dipstick heaters and pieces of cardboard in front of the radiator) and run a Porsche there during the cold season (Aug 15th to June 15th) I think I'd just rig up an adjustable metal shutter on the bottom of the engine mounted oil cooler to make it a little less effective or recirculate some of the heater box air back into the shroud. I wonder what to do about a heater for the transmission oil though? Perhaps a mix of kereosene, Marvel Mystery oil and Swepco like they do in Alaska Jim

[cary]

I'm after the hook...............Super

I'm the one that didn't redline it at 165 degrees. My problem is the oil pressure is sitting at 8 on the gauge. 3500 rpms.
With cold oil, my oil pressure is pretty high. And I have NO / 0 leaks after switching to Mobil 1 mid stream.
So I always wait till the aux oil cooler opens to really run it hard.

Mine wasn't a matter of not red lineing it. I said "stretch it out". That means 5 -10 MINUTES at over 100 mph.
No traffic Saturday AM. And a Big Blue Sky.

Cheez......I can't get on the freeway with out red lineing. I always have to hit the brakes to get on the freeway.

Cary's House Rules :
Based on 14 years of 911 ownership. ( no scientific data )

I don't go over 3000 rpm's till the temp needle moves.
And no exercising until the front oil cooler is up and running.

Works for Me ............ I hate oil leaks.

[island911]

Originally posted by Superman
. . ..I say that when an engine reaches equilibrium temp, it is ready for redline, .. .
. . .
Anybody want to disagree?

Your all wrong Super. . .it is ready for redline within seconds. And to see how many seconds it takes to get to that "tootsie roll center" called redline; start the motor and plant your foot in the gas pedal (and count).
Remember, as mechanical engineers will tell you, anything is possible with enough force and the proper lubrication

Besides, there *is* an oil pressure relief valve.

[RoninLB]

[QUOTE]Originally posted by Jim Sims
[B]If I had to live in Montana again (I remember the tank heaters, battery heaters, oil dipstick heaters and pieces of cardboard in front of the radiator) and run a Porsche there during the cold season (Aug 15th to June 15th)

strange but true about the cold season in Montana..I was heading south on I-15 leaving Montana.............Ron

[pwd72s]

Ronnie...I'll never tire of seeing that pic posted. It's one of those "thousand words" shots!

[A Quiet Boom]

About valve adjustment, I think it has to do with the engine design. On my solid lifter V8 engines the pushrods expand when hot and the valves get tighter, if they are loose you only hear them when cold (unless they're really loose) but on my 3.0 P-car I misadjusted a valve on the loose side and guess what, it only makes noise when hot! I think the thermal expansion of the aluminum cam towers being greater than the steel rockers and cam cause the rockers to move farther away from the valves but that's just a theory. As for warming the oil, I'm not that retentive about it, I just let it warm up for a block or two then it's up to 3/4 throttle and about 5000 rpms until it reaches 160 or more. Maybe I'm causing longterm damage maybe not but I have yet to see anything more than advice on the subject, I'd like to see scientific tests. I concede though that I did run a oil heater on my drag car when it's cool outside to keep the temp high enough between runs for consistency yet not heat up the intake and heads.

My .02, correct me if I'm wrong but give me something more than opinion, like facts.

[Superman]

Dennis, I sure hope I have offended no one. Who didn't deserve it I mean.

By equilibrium I mean as warm as it's gonna get. In the winter time here our temps are fairly mild (just occasionally in the 20s on a few mornings), and my exterior thermostat does not open between October and April. For most of the trip to Doug's and back Saturday, the needle stayed below the first line. I say "big deal." I don't really care how cool the oil is, but even at these times the oil is decidedly "hot." I think the temperatures of the engine parts, and how they fit together is the major issue. I think they get hot enough for flogging any time they are warmed up for 10 or 20 minutes. That was my point. After 20 minutes, cruise at 130 if you want. Even after five minutes, I believe those engine parts are fitting together nicely. I think the engine heats up before the oil, but that the main engine parts that need heating (case, bearings) are not hot enough for the whip in just a block. MHO.

I don't think the valve lash closes at operating temp. I believe there is still a gap.

[jluetjen]

As far as the oil temperature required to red-line, I don't think the issue is in the engine so much as in the external oil accessories such as the cooler. Once the engine has run for a few thousand rev's (1 or 2 minutes) I'm pretty sure that the oil pressures are adequate to keep everything lubed. They may even be a bit high because of the potentially increased thickness of the relatively "cool" oil. At the same time I suspect that the drag from the oil pump will be higher due to the higher pressures and thickness of the oil. Of course the spec's of the particular oil that you are using will have an affect on all of this.

The external things such as the oil cooler would be my concern. Let's say that the oil thermostat is closed. The oil in the lines to the front cooler is lets say -- 20 degrees and fairly thick, while the motor is being spun up to redline. As soon as that thermostat opens, a lot of hot oil at "high" pressure will be rushing it's way to the front cooler with a slug of cold oil sitting in front of it that doesn't want to go so fast. The weakest link in the system will be at risk of failing -- that could be a weak joint in the cooler, maybe a area which has had some slight corrosion, or maybe just an area where the aluminum is a little thinner in the cooler. After enough abuse, that weak joint will just give up and then you have a real problem: oil spewing on the tires, a sudden drop in oil pressure, etc. etc.

Once or twice may not do it -- but are you feeling lucky? Avoiding issues like this is known as "mechanical sympothy" and all of the truely great drivers had it.
That being said, I'd agree that once the engine temperatures have stabilized and all of the circuits have opened, I'm not convinced that it's an issue to red-line the motor.

[Wil Ferch]

Guys:
Valve gap opens more as (911) engine gets hotter....

Teoretically....if you target .004" at 60 degF..you should be able to find some much lower temp that predicts "zero" lash as being correct.

Just close em up at minus 10 degF ambient ( or whatever)..and forget about those pesky feeler gauges !!

--Wil Ferch

[Chuck Moreland]

Originally posted by jluetjen


The external things such as the oil cooler would be my concern. Let's say that the oil thermostat is closed. The oil in the lines to the front cooler is lets say -- 20 degrees and fairly thick, while the motor is being spun up to redline. As soon as that thermostat opens, a lot of hot oil at "high" pressure will be rushing it's way to the front cooler with a slug of cold oil sitting in front of it that doesn't want to go so fast.

Not to worry. The thermostat doesn't work that way, it opens slowly over a range of about 10F. It's not an on-off switch, so there is no cold slug of oil racing into the engine.