David L. Lutz

Recently completed the install of a Murf Stage III and eventhough its not overheating it is running hotter that I would like.

Before the install of the supercharger, my guage would barly read over the 1st white line even in traffic on a hot day here in Florida.

After the install of the Stage III here are my experiences;

1) Connecting the 4 8inch fans to the orginal primary fan circuit and the 16" fan in front of the A/C condensor to the secondary wiring, the gauge would read almost to the upper white mark all the time. With A/C on it would cross the upper white line (way too hot for my comfort) and I just did not push it any further.

2) I changed the wiring on the 4 8" fans using a relay running full out all the time. I first tried hooking up the relay to the primary fan lead and it would not engage the relay all the time and some times the relay would just flutter. I guess that's when the fan controller is sending less that 12 v. So I change using a hot 12v lead to engage the relay when the switch is on. NOW with this set up the guage reads exactly where it did before (just above the 1st white line) as long as the AC is off. But when the AC is on the needle creeps up to about midpoint or higher if you are getting on it hard. (all these test runs are on 95 degree sunny days)

AnyOne else had similar problems?

Also one more comment, I notice the 16" fan (left using the secondary fan circuit) does not run at full rpm even when the guage is past midpoint!
I'm thinking about changing out the wiring on this fan also.

Thanks for any input.

PS: By the way Bill, I have triple checked the direction of all the fans and all blades are installed in the correct direction.

aggravation

Mine doesn't change with the AC on or off. It stays just barely above the 1st white line (of the two lines that are between the top and bottom marks) on the highway and freeway and can go to just under the second white line if I'm doing a lot of WOT runs. It only went above the second white line once or twice when I was in bumper to bumper crawl right after having done some WOT stuff.
My radiator was rebuilt with aluminum end caps welded on and it was cleaned out before the caps were welded on. Hacker had Todd do it and he said it was really bad, it took him a lot of time to get it clean. I was kind of surprised too because before the repair the radiator never over heated it was just that it had a pinhole on one end cap....of course I was barely making 4 psi of boost before with the old supercharger so that's probably why.

hacker-pschorr

IMO, not only do 928's come with too hot of a spark plug from the factory, so is the thermostat. Both are higher in temp for emissions reasons, nothing more.

At stock 928 with a Murf Stage III (even with the stock thermostat) should run at the same temp as a stock 928, assuming all parts of the cooling system are 100%. My 81 with a 17psi system runs right at the lowest white marker an all but the hottest days (95+ ) then it might move up to the middle.

I would suspect the radiator is tired above everything else. I’m not sure where Todd is at offering the service he provided for aggravation to more people (in-between other projects) but that is one option.

EMan 928

My car runs pretty much close to the last white line all the time. Never beyond it. Should this be something I take a look at, or is this normal.

I am also toying with the idea of installing a stage III. How is it?

dr bob

David--

Assuming you still have the original temp sensor in the bottom of the radiator, take a look at the WSM section on cooling fans. The sensor is looking at radiator coolant temps after it has cooled off, again assuming you have good radiator flow at the bottom on the cold side. Fan speeds are adjusted based on that temp. Meanwhile, your gauge is looking at temps at the coolant bridge, top of the motor by the outlet nozzle that sends hot coolant to the radiator. So you look at a temp reading on the gauge that the fans don't directly know about. The WSM section includes the fan speed vs radiator temp chart, so you can see what the fans should be doing. The temp (and other...) signals are used to calculate which of the three available fan speeds is needed to keep the bottom of the radiator cold. You have bypassed that function for your rear fans but maintained it only for the front, so you are now much more likely to see swings in coolant temp directly related to heat input from the engine.

You can use three relays, tied to the original controller, with a small circuit (a couple diodes, two resistors, a capacitor and a transistor) on each to set the trigger point for each relay, and mimic the original fan operation some by sequencing the fans on and off based on demand from the temp sensor in the radiator.


Oh--

My somewhat-educated guess is that you need a new radiator. You've added heat loading with the SC, and now strain the transfer capability of the old radiator. It was marginally OK before, now it's marginally not OK with the extra heat from the SC engine coupled with the higher August ambient temps you are currently enjoying.

David L. Lutz

If you are speaking of the 2nd white line from the bottom and your guage/sensors are giving you a correct reading IMO you are running too hot and will have problems with the Stage III.

David L. Lutz

Dr Bob,

Both temp sensors are brand new. The one on botttom of the rad and the one on the water bridge.

Maybe you didn't notice that before the install which was just 2 weeks ago, my current rad. kept my temp. guage right at the 1st white line. (Not the middle or at 2nd line, which I felt was good) However I am not saying I don't need a new one with my current situation.


In reference to your comment on water temps. at the bottom of the rad. vs. top of the engine where the hot water flows back to the radatior. Are you saying that for example the temp sensor at the bottom is seeing cool enough water and therefore not running my secondary fan at top speed?

I will check the WSM for additional info.

Thanks Bob

AO

Stop toying around with it... and do it already. I'll help!

hacker-pschorr

Sweet - another build weekend!!

AO

The 85-88 cars temp gauge is quite different than the 89+ car with the digital dash. In the 89+ cars, they seem to want to run right around the 2nd white line.

In Eric's case, he may need a cooler thermostat and the rear seal replaced. No biggie.

My GT routinely runs past the 2nd white line. This winter I will replace the thermostat with a cooler one to help bring this down a bit. BTW, the radiator is brand new!

AO

I know... but who's gonna bring the crab legs this time?

Damn those were tasty!

hacker-pschorr

We can tell Shane they never arrived so he needs to send another batch. Yea, that will work. Good thing they don't have the internet in Alaska.

Bill Ball

My 89 has always run up to and just over the second white line (which is said to be 195F) on HOT days and under a load (going uphill, or pushing hard on a fun-ride or open road race). On cool days it will run down near the first white line (170F) which is where the low temp T-stat opens, but once the load conditions rise, here comes the second white line. If that is 195F, it doesn't bother me, but add the AC and it will creep over that. A needle width or two is about all I will accept before I kill the AC until we crest the hill and the temp falls back down. The radiator has been rodded and otherwise cleaned twice. Your experience with a new radiator not making much difference has been a common one.

My belief, as stupid as this sounds, is that over the years as the output of the motor rose, not much changed with the cooling system but the fan setup. You see pictures of desert tests with the early cars, but none with the later cars, so I believe Porsche thought the cooling system was more than adequate and left it alone as the HP rose from 222 to 340 or whatever. It's the same radiator capacity, same water pump design, etc. The only thing they did was move the oil cooler out of the radiator in 90. If you have AC there's not a lot you can do, as the rigid mounted AC condenser limits the thickness of the radiator. I don't think even the nicely done all aluminum radiators our 928 vendors sell make much difference if your current radiator is clean and leak-free.

hacker-pschorr

The S4 radiator is an upgrade for an OB. The core is tighter with more cooling lines. Reason why I have an S4 radiator going into my 81.

IMO having the oil and transmission coolers in the radiator is not ideal.
Especially in a track car....

Shane E.

What crab legs?? We don't have any stinking crab here...nothin' to see here...move along now!

It is like strapping on a big friggen rocket and hitting the launch button!!