Happy Easter all –
I've got a few questions about auxiliary fans, auxiliary water pumps and cooling systems in general. I’ve spent the last hour or so on the search, but that’s led me to more questions as usual.
First off, the car is an 87 SDL with ~210000 miles. I’ve changed out the coolant about two months ago after doing a rather extensive drain and purge and burping the system – water pump went south, so that’s new too. My problem is that now the car seems to run hotter than normal. Granted, I live in the high desert part of CA which means that there are lots of steep grades and in a few months the average daily temp will be about 110F (which is still hot even though it’s a “dry heat”). What I notice is that on uphills the temp goes up quick and stays at around 100C, I generally slow down and don’t push the engine too much. Last year the temperatures were much lower for the same hills at a higher speed. I get a pretty substantial rise in temp just going up small inclines these days.
While searching I came across some info on the auxiliary fan sensor and I’m thinking that this may be the culprit as that fan does not come on these days at all from what I can see. I stopped at the top of a hill today and checked, no fan, temp around 100C+. Drove home with a/c same hot temps and no fan operation.
So, where is the sensor for this fan? Can it be tested? I’m assuming that if I unplug the Aux fan and connect direct to battery I can test to see if it works; please let me know if that’s a bad assumption these fans appear to go for around $300. How much cooling does the aux fan supply anyway? Could this be an aux water pump issue? Thanks in advance and I hope this isn’t too simple a question for everyone. BTW, the wildflowers in Death Valley and this region are pretty spectacular this year.

Cheers,

Matt

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-livin' in the terminally flippant zone

The question is whether you have the a/c on or not.

If not, the electric fan won't come on until the engine gets to 105°F.

If yes, there is a pressure switch on the dryer that controls the fan to lower the pressure in the condenser when it climbs too high. You need to check to see if the fan will run if you provide 12V directly to the fan. Sometimes the fan itself is the issue.

100°F. is nothing to be concerned with. This one will climb up to 100°F. in 80° ambients with the a/c on when I hit the slightest upgrade. It won't go above that, however. To get it to hit 105°F. requires a five mile 6% upgrade at 80°F.

I probably have issues with the thermostatic fan clutch after all these years, But, I'm not concerned with it.

There are better things to worry about.

Today I replaced my fan clutch, actually, it's not really clutch mechanism, but gel filled fan hub thermostatically engaged. I replaced it because summer is coming and with a 603, I don't want to worry about overheating. All other cooling system components are recent, so it made sense.

Took it into town this afternoon and the temp gauge barely climbed above 80c, down a few degrees from what had been normal. So replacing that fan clutch did make a difference. .....BB

BB, I'd be very curious to see if you suffer from a drop in fuel economy now that you only run 80°C. Mine generally runs hotter than most others with the SDL, but, it also gets the best fuel economy when compared others.

If you have prior data, it would be interesting to compare to the new fuel economy numbers.

BTW, the difference won't be much. Maybe 1 mpg or so. You would need several tanks to notice it.

Brian, I was running without a/c. I'll connect the two leads off the fan tomorrow to see if I can get it to run at all.

It makes me nervous though since it seems to run hotter this year than it did last on the same grades, and we havn't even gotten to the hot part of the year yet here. it also heats up quicker (to the 100C mark) on very shallow grades. Granted I wouldn't have called them that shallow when I lived back east before I moved here. I guess I'm pretty paranoid about heat and this engine, but if the consensus is that 100C is no big deal I'll go with that.

BB, what were your symptoms prior to changing out your fan clutch? You mean the viscous fan clutch right behind the radiator, right? what temps were you running prior to the change?

thanks to both of you for your quick response,

Matt.

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-livin' in the terminally flippant zone

If you're taking these hills at speed then neither the clutch fan nor the auxiliary fan will do much to lower engine temps even if they're working properly. I believe the clutch fan has an rpm clutch, besides the thermostatic clutch, that freewheels it above 2500 rpm or something like that. The auxiliary fan is strictly driven by the AC pressure switch and engine temp switch.

Sixto
95 S420
87 300SDL

sixto, nope I'm actually taking the hills really slow cause I'm paranoid about the heat gain. RPMs never get over 3K.

__________________
-livin' in the terminally flippant zone

I'll tell you one thing that I guarantee will lower your temperatures by 5 degrees or so, provided it has not been done in the last five years:

The radiator on these vehicles has some very fine air passages and they get clogged with dust and fine debris. Most folks just brush off the debris from the front of the fins and call it a day.

You need to remove the radiator from the vehicle and hold it up to the sun. Take a look at all the crap that blocks the airflow. Now, you have the task to remove all the crap. It's a slow two hour process with compressed air, cleaning agents, and water. I'm still looking for a proper industrial condenser cleaner when I do it for the next time.

Yep, I found your suggestion on the search when I did the water pump a couple of months ago and spent some time doing that. I really was amazed at all the stuff that came out from between the fins. I used water and an air compressor as well. Don't know of any commercial stuff that would do the trick.

__________________
-livin' in the terminally flippant zone

I was just blowing out my radiator this weekend and was amazed at the amount of dirt that came out of it. I cleaned it with 100psi air blown out from the fan side. I kept blowing it out and blowing it out it seemed like it would never stop. It has to make a huge differance in the effectiveness of the radiator.

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82 Rabbit diesel (first d), 84 Jetta turbo d (300k when sold), 83 240d (305k when sold), 84 F250 6.9d w/Banks turbo(parts truck), 86 F250 6 cyl.gasser(waiting for 6.9d), 84 300d ( 347k Sold 8/04), Y2k New Bettle TDI (185k miles), 95 740IL (wifes), 87 300TD (206k Sold 7/05), 05 Passat TDI Wagon

My thoughts, exactly. And, when you get finished, hold it up to the sun. It's still not completely clean! But, a 65% improvement, for sure.