Running a 3.0 liter without a front cooler?

[Tom F.]

Has anyone done it? While it is clearly needed for track use, I wonder how necessary the front cooler is in a car without a/c.

[John Z Goriup]

Tom,

Yes, there are people who run 3 liter 911 engines without external oil coolers, but that certainly doesn't make it the right or the smart thing to do.
It's been my experience that most of those who went the route of no additional external cooling regretted it, and what's more it cost them dearly.

Forgive the long-winded answer, but oil temperatures are too fundamental to longevity and performance in any 911 to dismiss and / or take chances with. It's basic physics. A 3 liter engine makes enough BTUs where the "normal" city traffic oil temp. wihout external cooling will probably hover around 195 to 210 degrees. On a hot day, say 90 F and above, most likely higher. On a prolonged run on the highway you should not be at all surprised to see 225 and even higher temps. regularly......and that's just too damned hot. Your engine won't necessarily expire on the spot under these conditions, but you would be risking cutting your engine's effective lifespan and performance by avoiding the necessary step of cooling the oil. Permit me to remind you, once the factory went past 2.7 liters all 911s received additional, external oil-cooling

I'm sure you've heard the old saying that 911 aren't really entirely air cooled, rather they are air and oil-cooled motors which require premium lubricants at the right temperatures to allow these engines to deliver all aspects of performance designed into them.

I submit that your goal should be a "normal" operating oil temp. of 180 to 190 degrees F and a maximum under any road conditions of 210 F, maybe 215 at the highest..........and that's with a calibrated, accurate oil temp gauge.

My suggestion: start with a set of good, used hard lines which are obtainable from PORSCHE dismantlers, a used, tested oil thermostat, inspect and clean them all out, mount everything properly, use new flex lines to connect to engine and tank, and start out with the basic loop, or "trombone" cooler. That's usually good for 10 -12 dgrees F. See what happens and where your temp. is and then "escalate" to the brass tube cooler or even the fan equipped radiator type if actual oil temps warrant it.

To rebuild a street driven 3-liter properly to get out of it what it's capable of delivering costs anywhere from $ 16,000 to over $ 22,000-25,000 these days at a good, reputable 911 specialist shop. Is that really worth the risk......YES, the front cooler is necessary.

Respectfully,

JZG

[speedo]

Consider the external oil cooler cheap insurance. Ask anyone running a 2.7 (last engine w/o factory external oil cooler) what their temperatures look like on a "warm" day. The price of the lines-thermostat-cooler installation is minimal vs a rebuild. Look at it this way...let the thermostat decide whether the external cooler is necessary...if not, the oil is recirculated back to the engine.

[mikez]

Any engine over a 2.4 that I have played with needed one....and I'm in a rather temperate area.....

[J-P]

Hi John,

I read your post with great interest.

Just today (a moderate 70-ish SoCal day) I saw a peak of 235-240 on the temp gauge while driving on the interstate at a around 65-70 mph in traffic. This on a fresh 2.7 motor.

The temp acutally came down right away to about 220 upon pulling up to the first traffic light after exiting.

Although the oil temperature sender is new, I have not had the gauge calibrated, so I don't know how accurate this reading was.

I did purchase and will install at the next valve adjustment, a factory trombone external cooler.

With your statement of typically getting a 10-12 degree temperature drop with this type of set-up, it seems that I will still be well out of range of your recommended 190 maximum recommended operating temperature.

What would you recommend? Perhaps a custom double-trombone type of set-up? Or, would a multi-row brass cooler make that much of a difference?

I will also be getting my gauge properly calibrated in the near future.

TIA.

[911rips]

I'm dealing with this issue myself. Running a newly built 2.8, mfi, without a cooler on the highway at 80 - 90 , on a seventy degree day, the temp will rise just above 210. runnning at 65 will drop to 195-200 degrees. I've had my fourth discussion with my mechanic, who built the motor, regarding whether to add a cooler. His response don't need it. I'm feeling that I want one, can't understand why he wouldn't want the work.

[John Z Goriup]

Quote: "What would you recommend? Perhaps a custom double-trombone type of set-up? Or, would a multi-row brass cooler make that much of a difference? "

I will also be getting my gauge properly calibrated in the near future.


Tom

I go back to what I stated in my initial reply to your original post. It's all about basic physics. Looking at a loop-style "trombone" oil cooler you'll see a piece of tubing about 20 millimeters or so in diameter ( approx 3/4" or 7/8' inch), with only a relatively small portion of the tubing bent directly into the airstream. There's probably not much heat transfer in the horizontal portion of the oil lines where they are mounted parallel to the direction of travel, only when they are perpendicular to the airflow.

The brass tube cooler is a soldered assembly with 28 ( I'm going by memory) 1/2" dia. approx. 11" long brass tubes arraigned in staggered rows so all of them are equally exposed to the airflow. I think you would find that the brass tubing affair offers several times the radiating surface of the loop cooler and Yes, would therefore be significantly more efficient.

For what it's worth, my car is a '70 with a mildly modified 3 liter (225 HP) with a brass tubing cooler and Elephant ribbed lines, and without exception so far has resolutely stayed in the desired (by me) temp. range of 180 to 190 F under normal operation at sea level. Last year, on a 100 degree day on the Grapevine, two people aboard ( no A/C ) at about 80ish mph it crept up to 210, but promptly got back to where I like to see it once past the summit (in both directions).

There are a couple of relatively minor things I did on my car to help oil cooling. I'd be happy to take some photos tomorrow and post if you'd like to see them.

1. I cut the majority of the passenger side battery box away just to the point inboard where the through-the-grill light brackets mount, and re-attached the end of the battery box, which is now only about 1-1/2" deep. That opened things up a lot.

2. In building my car I chose to utilize a steel S front bumper which has no openings what so ever, and in fact channels air to the side of the car and under it. After the Grapevine episode, I reconditioned and repainted my original stock bumper and modified it by cutting away the cover-bracket behind the fog-light opening on the passenger side. I feel this will create an even more effective flow of cooling air straight into the cooler. I will mount the bumper in the next few days and will be happy to report if things have changed (if anyone is interested). Depending on results , I may remove the through-the-grill lights and mount my Cibie hood mounted units.

Tom, please do not misinterpret this as talking down to anyone, but as long as we're talking basic physics, permit me to point out that there are only three possible ways to transfer heat:

1. Radiation
2. Conduction
3. Convection

Looking at our 911s and their physical layouts, (efficient aerodynamically, no front openings, no coolant radiators) I think it's a given that concentrating on maximum heat transfer to ambient air through convection will have the most dramatic and best results.

Lastly, theres always the radiator type cooler with fan ($$$, weight, wiring the blower motor) if the above doesn't get you into the ballpark, but I honestly think that's only a last resort.

PS: from your description your gauge seems plenty accuarate and sensitive. I don't think you need to go to any more trouble. A lot of mechanics have no-contact laser thermometers which can be astoundingly precise. Prehaps your guy will let you use his to check your temp.....if he has one.

Cheers,

JZG

[Tom F.]

John,

How did you run the lines in the rear wheel well, to the thermostat?

Tom

[a911s]

My experience (having battled high oil temperature for ten years with increasingly hot motors):

Until you have your gauge and sender calibrated to each other (or at least checked with boiling water at 212F) you really cannot be sure what the oil temperature is. Laser pyrometers checked at the sender are about ten degrees below actual engine oil temperature at best. Once you are sure your gauge is accurate, then you can start to go to work. Here are the steps you can take to lower temperature:

1. Clean your engine cooler of all grime
2. Make sure your fan/belt is correct for the engine
3. Make sure your oil thermostat is opening early and fully
4. Add factory, or better yet, Elephant Racing oil lines and a loop cooler, multi-tube cooler or better yet Carrera cooler (and push fan) with -16 connections and lines
5. Duct air to cooler
6. Enclose sides of air flow to and through cooler completely with sealed ducting with at least 2X greater outflow area compared to inflow area - bigger is better
7. Add a second cooler (and push fan) to the other fender with -16 lines/connections and repeat 5. and 6.
8. Add a nose (RS type) cooler with -16 lines/connections - bigger is better - and repeat 5. and 6.
9. Any screen used to protect the cooler should be SS quarter inch (not corrugated).

With a track 2.0 to 2.4L motor, or street 2.7 to 3.2L you need to perform steps 1-4 at least IME.

With a track 2.7L or street 3.4L, or larger, you will need to add steps 5-9, depending on track configuration, humidity, air temperature and how hard you drive (revs used).

[John Z Goriup]

Tom,

as mentioned, I bought Elephant ribbed brass hard lines instead of the factory hardlines ( 1st photo). They are dimensionally identical, use the same factory mounting hardware and locations (welded studs and clamps) but have much more surface area for increased heat-dissipation. In the front corner of the right rear wheelwell I mounted a new OEM oil thermostat in the stock location. (2nd photo) From there to engine and tank stock, new OEM lines.( 3rd photo)

My car has steel RS flares and is equipped with Fuchs 8" wheels with 225 /60 x 15 tires and 12 millimeter spacers. I have not experienced any tire / oil-line interference. If that's your concern you may have to modify your right rear wheel well to allow recessing the lines somewhat into the inner fender wall.