cooler carrera

Well, I finally finished installing some auxiliary fans on my 911 and thought I'd update the board. You may recall my ideas from earlier posts.
1) keep the fans running after I turned the car off to prevent the heads from heat soaking (reducing life)
2) help "force feed" the main fan when in rush-hor traffic
3) help the AC condenser cool better

Here is what I ended up doing (please note also that I have the factory whaletail). I was going to install 3-4 5.6" Spal fans between the condenser and tail. Clearance became an issue here as that Spal fan is 3.8" tall and there is about 3" clearance. I now have bought 2 14" ($58 ea)fans from a local auto parts store (2" depth-1200 CFM ea) and mounted them under the tail vents (I had to modify (read cut)the internal louvers). I then hooked up a standard fan control box ($30) (one with the AC switch and temp probe). Finally, I bought an adjustable time-delay relay from Amperite ($28). I now have the fans turn on when the AC is on, or when the ignition is on AND a dash mounted switch is on. If I turn off the ignition (or the dash mounted switch), the fans continue to run for 90 seconds.
Results are not totally in yet as the weather has not gotten hot here in NC. BUT, I can say that is definately cools the motor off after shut-down. I'm going to try to get an infrared temp gun and take readings with them on and off to compare, should give me hard #'s to work with. If anyone would like to know how to do this, I can try to put together some illustrations and instructions.

I must say, I must have missed your earlier post, but I like your idea. Please let us all know how it goes.

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Leland Pate

___79 SC Targa

Scott: I'm interested- here in Palm Springs it will eventually get to 120 deg (only low 90's right now). At the forward end of my turbo tail where the opening for the engine cooling hole starts there appears to be only about 1 1/2 " between the tail and the engine lid. When you say that you modified the internal louvers where did you do the cutting - on the engine lid or the tail louvers?

OK gents, here are the numbers. My wife got home today after a nice long 90 mile drive (highway), so I know the car was warmed up. When she stopped, I immediately took temperature readings with a laser/infrared temperature guage. I read the head cooling fins between the exhaust port and the cam chain cover.

Upon arrival and shut-down, the heads read 265 deg F. They climbed to 275-280 deg F within 1 minute (not as high as I had thought). They did not begin to show a decrease in temperature within the 5 minutes I measured.

Started and ran the car again, again the heads were 265 upon shutdown. Had the fans turn on just at engine shut-off and run for 2 minutes. Within 2 minutes the head temp was down to 240 deg F. re-cycled the fans another 2 minutes and it cooled to about 218. another 2 brought them down to 199.
My feeling here is that 4 minutes is the ideal. I do know that Amperite can make an adjustable timer to handle this. Unfortunately, I bought only one that goes 0-120 secs. (I'll call it research expense) but I am contemplating the extra $30 to upgrade. Each fan draws approx 11 amps, so I'm drawing 22 amps for 4 minutes. That makes 264 watts, not much more than a nice car stereo and headlights. I think that 4 minutes should be no problem for the battery.

There you have it!!! I haven't checked the improvement on the AC side yet, nor have I checked the performance as a fan "booster" as I have not been stuck in rush-hour traffic yet. I do know this though, with the car idling and the fans on, there is a LARGE difference in the amount of heat that is pushed out from underneath the car.

Charlie, as to the installation, you are correct in your measurement. However there is another 1.xx inches between the top of the trunk (hood?) lid and the condenser, so a 2" fan will fit.

What you need to do for the install is
1) Lower the condenser off the trunk lid
2) unbolt the whaletail and remove it from the car.
3) if you look from the underside of the tail, you will see a set of steel internal louvers. there are 2 10 MM bolts on the back and some small (5 each, I think) 7mm on the front. There are also 2 phillips screws in the center section.
4) After the louvers are removed, trace the outline of the fan with a pencil. Cut out fan circle. (tin snips work fine)
5) lay fan on the louvers and drill mounting holes, insert fan mounting ties through louvers.
6) re-mount louvers to tail.
7) attach fans.
8) reassemple tail on trunk lid.
#'s 5 and 6 take some adjustment to get right.

You need to mount the fans to the louvers because the screen is not strong enough to support the fans.

P.S. if your good with sheet metal, you could also just make some new under plates for the tail, rather than cut the louvers.

One note, I'll scan a copy of my wiring diagram and send it to anyone who wants it. just email me at Smatre@telocity.com for a copy.

scott what year is this 911?

scott what year is this 911?

mine is an 87 3.2. I think that this mod would work on any 11 with the factroy whaletail. It'd probably work with modifications on an aftermarket tail. I have not come up with a way for it to work on say, an SC w/o the tail, as there is not enough room for fans on the inside (heater blower vent too close).

Scott,

Rather than chunk the relay you have, you could have a digital logic circuit trigger the relay multiple times, and trigger/control the relay through a 'driver' circuit ... in fact, the actual shutoff of the cycling of the fans could be controlled by a thermal switch, too! If you need ideas/help with circuits, let me know!

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Warren Hall
1973 911S Targa

Warren,
Thanks for the ideas about digital cycling. I am still debating whether or not to change the relay. Either way, it was only about $30 so it wouldn't be a crisis if I replaced it. I'm also sure that I could find another use for the original if I do, so I wouldn't be chucking it.

2nd item, I have tought about temperature control, and no doubt that would be the preferred way. Problem is that I could not figure a reasonable way to attach a temp probe to that area of the engine. If I attached it to the metal air deflectors (around the cylinders), I was afraid that the fans would cycle too much. In fact, I tried to take readings earlier with a contact pyrometer, but got wildly varying results.
If you have any thoughts, I'm always open to improving the design.

is the heat buildup such a problem that it causes serious problems with longevity? I don't usually get to drive my 88 911 more than 5 miles before I shut it down for a couple of hours. The alternative , not drive it.I don't take it to work because of that reason. I don't have a whale tail, would it be cool to raise the deck lid when I put it back in the garage to increase heat escape? Thats easy enuf and easy to close next time out.

Don't want to alarm anyone regarding heat effects on reliability. To be sure, the 3.0 SC's are probably some of the world's most durable engines. On the otherhand, my 3.2 needed a valve job at 120K. There has been alot of talk about what the reasons for this are. I can't say that it is heat related, but I remember an old rule of thumb for trannys. that is a 10 deg drop in fluid temp will double tranny life. I am just extrapolating to think that lower head temperatures can only help the longetity of my 3.2. If I think about how the engine operates, the heads dissipate heat from 1300m deg in the combustion chamber to 265 head temp. If you then stop the car, airflow stops, but the combustion chamber is still 1300. Seems logical that cooling shoud continue after ****down. Me thinks the reason we do not see this on water cooled cars is because water is a far superior heat transfer medium versus air. I also have some concerns with a fan that is designed to go from 900-7000 rpm providing enough air flow at 900 rpm.
I may in-fact be solving a problem that is not there, but I also figure that it is cheap insurance.

I really must appologize for the typo in my last post. It was unintentional.

Scott - overkill never hurts. I built a V8 S10 a few years back (and still drive it daily) and totally overkilled the cooling system. What I ended up with was a vehicle that could tow 4000lb on a 95F day in heavy traffic and never get over 195F. Your fans might not do anything significant for you 99% of the time, but that last 1% might save you in a jam on a 100+F day.

Scott,

Earlier you stated you were not sure how to attach a temp probe to that area of the engine. Have you looked into the aircraft industry?

For the aircooled aircraft engines, Lycoming and Continental, several avionics manufactures offer Cylinder Head Temperature gauges (CHT) and use a bi-metal probe that replaces the spark plug gasket. I checked into this a while back and was told that they can make probes for the 14mm spark plugs.

Check out: http://www.ksavionics.com

Let us know what you do.

Alvin

Here is the earlier post!!!!!!!!
this is post 1

Scott,
Great idea, ane one I have been contemplating for some time after recently buying my first 911. Can you tell me where you sourced your parts?? (control box, time delay relay, fans etc)
Thanks

I got the fans from Autozone actually, you can buy them from most any autoparts store. Just look for the most shallow unit (2" or less). I used a 14" dia. it is the largest that will fit.

The control box came from PepBoys. It is a Hayden brand, but I know that others sell a similar unit. It houses the relay, provisions for a temp sensor (non adjustable probe) and AC switch. You just cut the tmp probe wires and that is where the manual switch and delay realy wire into.

The time delay realy came from Amperite. They have a web page and you can order via phone. I used the 0-120 second adjustable.

Wiring is not complicated, but can be tricky. The AC switch is straight forward, just tap into your compressor wire by the fuse box. Wiring the relay and manual switch is more complicated. If you email me with your time frame, I can try to make a wiring diagram. The key here is that the delay relay and manual switch need to go on the switching (low power) side of the main control unit/relay. The delay relay is only rated for .5 amps, which is plenty to pull in the main 25 amp fan relay on the control box.

by the way, my email has changed to Scott_matre@yahoo.com

[Wayne 962]

Those are some good thoughts, except for the fact that the engine is no longer running. You want to be concerned when the engine is running and creating wear patterns on the metal. You can stick the engine in an oven and heat it up well beyond it's normal temp (might hurt the rubber seals), but the mechanical components should suffer because they aren't moving.

The concern happens when the parts heat up and clearances close when the engine is moving. Also the viscosity of the oil changes, and that affects the way that the bearings turn inside. The crank actually floats on a pocket of oil in the engine - not the bearing itself. The only time when the bearing itself is contacted is when the engine is started.

That in mind, the worst thing you could probably do is start the engine when the temperature spikes after just shutting it off. I'm not sure what would be worse, but I think that cold starting takes the cake...

Just some thoughts...

-Wayne