ybn533

Hi,

I have a problem with my boxster. it's overheating. Read a lot on forums but didn't find the answer. I'm thinking the problem is with the fans.

this is what I can tell:
1. when the car is cold and I start the a/c the 2 fans are working on low speed
2. with a/c not working the car starts the 2 fans at hi speed at 206f.
3. it seems the fans are working at low speed only when the a/c is on.

Today I'm gonna drive it and when it will get hot I will start the a/c and see if it will get it cooler.

what can be the problem that the 2 fan are not working on low speed? (only working when I start the a/c)

Thanks,
Yaron

ybn533

I have changes the thermostat to start working earlyier 2 years ago. until a week ago the car didn't pass the 185f even on worm days.

Macster

How do you know the car is overheating?

Based on my experience with my Boxster the fans should come on when the A/C is switched on, or when the coolant temperature climbs to 212F. The fans switch to high speed when the coolant temperature climbs to 216F.

The fans shut off when the coolant temperature drops below 205F. Let me add that these temperatures were observed using an OBD2 scan tool and monitoring the coolant temperature in real time.

I had one radiator fan on the Boxster fail to come on at least at low speed and had it replaced. There is at least one failure mode, there is some kind of resistor in the wiring harness that fails. (I had another fan in the Turbo stop working. The tech found the shaft had snapped in two, so that's another failure mode. Oh, and more recently he found a Turbo radiator fan not working very well, and found while there were no fan stage errors the suspect radiator motor was drawing way more current than the other fan motor and replaced the suspected bad fan motor, so that's three failure modes.)

The techs tell me often when a car comes in they find the radiator fan wiring has been messed with and the resistor is not in its usual location - held in place with a clip IIRC -- but jammed between some plastic panels where it does not get the cooling air flow it would otherwise get and where it can be exposed to water splash which can damage the resistor if this happens when the thing is hot.

ybn533

Thanks for your reply Macster.
I checked if the car is overheating with the a/c working and the answer is -no!
Without the a/c working the car overheat on stops.

So, I figure that the fan not engaging on the low speed position and that what make it overheat. Now, my question is what is the problem that the low speed works only when I press the a/c.

Thanks
Yaron

Macster

If the fans do not come on when the coolant temperature reaches the trigger point -- and this must be observed and confirmed by something more accurate than the in-dash temperature gage -- my info is the fan resistors are bad.

Sorry, temporarily lost my 'net connection. I wanted to say:

If the fans do not come on when the coolant temperature reaches the trigger point -- and this must be observed and confirmed by something more accurate than the in-dash temperature gage -- my info is the fan resistors are bad. A bit odd is both are bad at the same time based on what you write. Have to mention that I assume the rest of the cooling system is ok, that say the T-stat is opening properly when it should. From under the car as the cold engine idles you should feel the hoses to the radiators get warm as the T-stat opens and routes warm/hot coolant to the radiators. If this does not happen, if the T-stat doesn't open fully, the engine can overheat rather quickly.

I do not have one handy, but check the fuse/relay diagram in the booklet behind the fuses/relay box cover for any fuses related to radiator fan operation. What I'm thinking is there might be two fuses, one for the low speed operation and one for the high speed operation. Admittedly a shot in the dark but it doesn't take much time to check for this compared to replacing the resistors.

Or you can take the car to a shop with a Porsche diagnostics computer and the tech can do a check out of the radiator fans and their operation to pinpoint what is going on. You may pay something for this diagnostics time -- sometimes this is waived if the repairs are done after -- but you can save some money by avoiding throwing parts at the behavior.

ybn533

Thanks Macster.
The fans start working (low speed) when you start the a/c so relay and fuse seems to be out of the question.
So, I need to focus on the resistors or the thermostat.
Now, if the thermostat wasn't good so how come the car working good with the a/c on.

I'm focused on the problem - the fans don't engage at low speed.
Any thing more than the resistors involve here?

Thanks
Yaron

JJF3

A couple of other thoughts,
The coolant temp sensor can be faulty, not telling the fans to kick in.
Also have you checked your coolant level and condition? These engines need extended life antifreeze, not plain old "Green stuff". I have also experienced water pump problems where they can be losing impeller blades, creating uneven circulation causing all kinds of crazy problems.
I don't know what you have attempted so far, just suggesting some basics
JJF3

Macster

To add to what JJF3 covered and to reinforce what I covered earlier is you have to be sure the coolant temperature is reaching the trigger point.

This confirms that the fans are not coming on when they should. It also confirms the coolant temperature is real. That is the sensor is reporting something reasonable in analog and the DME is able to convert this to something digital. It also helps to confirm the T-stat and water pump are working.

If you intend to tackle this job yourself you are going to have to get your hands dirty at some point. Checking the fuse/relays is fairly easy and would be the place to start.

If you find the fuses/relays ok then there is the resistor which has come up before in these situations. One bad one was keeping one of my Boxster's radiator fans from coming on when the trigger temperature was reached. (The other fan came on just fine.) I do not recall know if just the resistor was replaced or if the fan motor with the resistor as part of the wiring lead was replaced. As I touched upon in a previous post these can be at risk if they have been disturbed and improperly left exposed to water splash. In my car's case it was the passenger side resistor but the resistor was not disturbed. Given the number of miles I believe the thing just failed due to old age.

But how to ID the resistor is bad (or good)? A tech with the proper diagnostics computer can exercise the fans to confirm that at least from the DME to the fan motor the wiring is ok and that the fan works.

ybn533

But can it be that both resistors broke at the same time? weird
Fuse=ok relays=ok

ybn533

If I do the hack at the relays the fans will work at low speed all the time?
For now, I drive with the a/c on all the time to trigger the fans.

Macster

My philosophy is I do not like to operate a car that has a compromised cooling system.

In the case at hand, the radiator fans do not come on when they should. This is a failure. If you wire the fans so they run all the time that's one thing, but if another failure occurs one or both fans may not work at all, and that's entirely another thing. It has the characteristics of a hack job.

The car will not overheat with the fans not working at low speed as long as they work at high speed. Granted in traffic or in conditions which have the coolant temperature elevated the coolant will range from a high of 216F (the point at which the fans as supposed to switch to high speed), to a low of 205F (at which point the fans should be switched off). (As an aside I've seen the coolant temperature in my Boxster climb to 226F even with perfectly healthy fans with no harm done to the engine at all.)

But even so, the cooling system is compromised and as I mentioned I do not like to operate a car with a compromised cooling system.

So I would track down what is going on and fix it. That both fans do not work at low speed doesn't read like a resistor problem in that the two fans at the resistor level are quite separate so the failure to work at low speed suggests a common failure and one before the resistors.

So, is it a coolant temperature sensor that is not working part of the time but does work at other times, at elevated temperatures? That is not a sensor failure mode I'm familiar with. But I'm not a professional mechanic.

It could help the situation to know what the temperature sensor behavior is as all time this is going on. If one observes the temperature reading remaining low (at least below 212F) then suddenly reading above 216F that pretty much pinpoints the coolant temperature sensor.

OTOH, if the temperature reading rises up to 212F and no fans then climbs to 216F and the fans come on that points to a possible problem with the DME in that its signal to the fans to begin low speed operation is not making it to the fans. I'd have to look at a wiring diagram though to be sure there are two signals to the fans, one for low speed operation and another for high speed operation. I think there is but I'd like to be sure.

ybn533

Thanks Macster. I'll try taking it to a pro mechanic

Macster

There is a Fan Stage 1 signal which comes from the DME and is routed to the Relay Step 1 for Cooling Water Blower 1. This input is also routed to the Relay Step 1 for Cooling Water Blower 2.

From the diagram it does not look like the Relay Step 1 for Cooling Water Blower 1 can interfere with the signal to the Relay Step 1 for Cooling Water Blower 2.

But a problem with the line that carries the Fan State 1 signal from the DME to the Relay Step 1 for Cooling Water Blower 1 can have both fans not working at low speed.

There is a separate Fan Stage 2 signal. It comes from the DME and is routed to the Relay Step 2 of the Cooling Water Blower 1. A line then carries this signal over to the Relay Step 2 of the Cooling Water Blower 2.