40 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHCooling Fan Resistor
Reported or suspected cause
cooling fan
Reported cause
No successful repair reported for this finding.
1
Identified cause
0
Suspected cause
0
Reported fixes
Read evidence and context
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that report identifying a cause
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Leading evidence: 'cooling fan' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'cooling fan' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check fan operation first' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
Source reports, not a diagnosis or a success probability. Counts refer to discussions and can overlap.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
The guy in the link provided by phil996cab99 had used the same thing.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that suspect a cause
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suspected cause
I have a driver side fan that works on high speed, the fuses and relays check out, so it's probably the resistor.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
40 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
1 acknowledgements have no verified action link; they do not establish a repair result.
Outcome without a verified action link
We supplied power directly to the fan through the connector and it worked just fine.
So, a couple of weeks ago, I noticed a slightly warmer running temp. The needle was reaching the middle of the 0 in the 180 marker. And usually this would be when driving at low speeds.
My initial instinct was something having to do with the cooling fan. So, I pulled over and listened and as suspected, the passenger side fan was off while the driver side was blasting away. I reached out to one of the RL members and he helped me do some trouble shooting. (Thank you!)
Fuses and relays were OK. So the primary culprit was the cooling fan. However, my brother suggested that we test the resistor and know and behold the fan works but the resistor is bad. So instead of buying a new fan, he is suggesting replacing the resistor if it makes sense. I've attached a picture.
1. Where can I find and buy this?
2. Has anyone done this before rather than replacing the entire cooling fan?
No personal experience but if it's this one, it's $120 (a pure crime if you ask me), may as well get the Bosch fan ($170).
http://www.pelicanparts.com/catalog/...pg5.htm#item12
https://rennlist.com/forums/996-foru...l#post11342583
That guy did it for $5 with a generic resistor from rodeo shack.
I've done the opposite, replacing a bad fan, keeping the good resistor.
Now that's what I'm talking about. The guy in the link provided by phil996cab99 used this same resistor.
Less than $10 vs $170 for a new fan. It kind of makes the decision, doesn't it?
Those regular power resistors with the proper wattage will work. The only concern I have is how to weather proof it properly given the location of the resistors and how they are exposed to the elements, rain, road salt, etc.
Of course the above shouldn't concern us Californians
Considering how often that area gets splashed, you definitely need to protect that resistor.
Definitely check the fan operation first. Run a positive and negative 12V to the fan direct connector and see if it runs. I had a '97 Boxster that had two bad fans, so they can fail.
This one
Amico Aluminum Shell Chassis Mounted 100W Watt 0.33 Ohm 5% Wirewound Resistor: Single Resistors: Amazon.com: Industrial & Scientific
Amico Aluminum Shell Chassis Mounted 100W Watt 0.33 Ohm 5% Wirewound Resistor: Single Resistors: Amazon.com: Industrial & Scientific
says
"can be used in atrocious environment"
... It's an anodized aluminum shell, so it should be ok as long as you make sure the leads are well covered/protected.
As electronics are not my strongest suit I am also interested in adverse effects. For example can one expect adverse affects on other electronic components if not using the factory resistor in this case?
As long as the value is the same and the power rating is sufficient, it makes no difference if it is a Porsche branded resistor or a generic one. It's not a performance part.
The question s is what is the actual resistance value and power rating of the Porsche part
For example if the factory part is 100 w and you put in a 75 watt resistor, it could very likely burn up, if you use a 100w+ part, no problem
If we know the current draw of the fan and the resistor value, we can calculate the needed power size
If the fan shorts and you want the resistor to survive:
Amps = 13.74 V / .33 Ohms = 41 A
Power Dissipated = 13.74 V x 41 A = way more than the 100 Watt rating of the generic part
The much larger Porsche resistor is large for a reason. But if the fan fails and takes down the resistor you could replace the resistor for $7.
If you think a 30 A fuse is going to limit the current to a max of 30 Amps, it will after an hour. A 30 A fuse will typically allow 50% over current for more than five minutes.
That might up the price a bit!
Personally if you can't identify the exact specs of the resistor, I would just bite the bullet and buy the correct part. Cooling fans are pretty important. On the bright side, it's way easier to replace the resistor than the fan.
It shouldn't be too difficult to measure the value of a good resistor. If you don't mind paying $130.00 for a $8.00 part that's fine, just not the way I like to do things...
R = E/I Voltage drop across the resistor divided by Amps = resistance.
P = E * R, Voltage times current = power, resistor power rating, 2X for reliability.
I actually ended up ordering a 100W 500mOhm 5% resistor. The guy in the link provided by phil996cab99 had used the same thing. It ended up being $20 + Shipping. Still better than $87 discounted original factory resistor.
If I had known the exact voltage going into low speed, I would have been able to calculate resistor specs. Does anyone know what voltage goes in at low speed?
Right now the assumption is that fuse is 40A so considering overengineering we think the amperage is 16-20A. Therefore a 16-20A X 0.5 Ohms = 8-10V for low speed and the measured amount for high speed is 13.74.
Is my line of reasoning correct?
When all the parts are healthy: Assuming the fuse is 40A and good design limits the circuit to half that or 20A in use, with no resistor in the loop the fan resistance is 14V/20A = .7 Ohms. During low speed operation there will be 1.2 ohms and the current will be 14V/1.2Ohms = 11.7 Amps. At 11.7 Amps a .5 Ohms resistor dissipates 64 Watts which still doesn't leave 100% derating margin but would probably work. If you read the fine print on the resistor it will tell you what temperature you have to keep the outside surface at to maintain its rating at 100 Watts. That temperature is likely to be 25C and which is lower than you would see in typical operation, so that is another hit against the derating margin.
There is more to electrical design than selecting parts that work when the other parts are working properly. If the fan or fan wiring develops a short, that 100 Watt resistor is going to get really, really hot before it blows. The fuse won't blow until the core of the resistor begins to melt and the resistance lowers because the .5 ohm resistor limits the current to 28A. The hot spot inside the resistor isn't the real problem, it is the surface of the resistor that could be a troublemaker. While the fuse will protect the wiring, the outside of that small resistor is likely to get hotter than the plastic parts around it are rated for. If you read the fine print on the resistor it will tell you what temperature you have to keep its outside surface (case temperature) at to maintain its rating at 100 Watts. That temperature is likely to be 25C and that is more than 100C lower than you would see if the fan shorts. The Porsche resistor is big for a reason.
I would try to save $ by sourcing a used Porsche resistor before using that resistor. It may never become a problem, but you may regret it too.
Meanwhile in my driveway, my snowblower engine has lost compression and the driveway is only half cleared and more snow is on its way.
I just wanted to come back and drop a line about an update. After the change, things have been working pretty well - both low and high speed work great. During use, the resistor feels cooler than the stock resistor.
Used zip ties and it sits pretty firm.
I am waiting for the stock resistors to arrive, ended up costing $180.00 for the pair. Was tempted to save a few bucks but in the end decided to continue with keeping things OEM stock with no hacks.
Glad it seems to be working out for you though.
Also, I decided not to drill any holes for the installation because I figured once the fan dies, the new fan will come with a resistor so I'll just plug it in.
I'm wondering if Durametric is going to allow me to lower the temperature setting at which the fans kick in.
the stock value should be .5 ohm 50 watts?
maybe this one?
Uxcell a12050500ux0003 Aluminum Shell 100W 0.5 Ohm Chassis Mounted Wirewound Resistor
Amazon
Amazon
@Rubik
(and anyone else who has done this mod) is this still working for you?
I have a driver side fan that works on high speed, the fuses and relays check out, so it's probably the resistor. I ordered a resistor and will try it out.
I read some past threads where people have worried about heat and failure modes - sounds like yours were good. Any negative experiences with the mod, or would you do it again if needed?
I'm probably too late to reply to this as I don't come to Rennlist regularly anymore. I sold the car. But the current owner has driven it for another 30K miles w/o problem. Take care.
