WallyP

Make sure that there is no air recirculation.

If you are missing the small belly pan, hot air will just recirculate thru the radiator - 175 deg air doesn't cool too well.

Check the top and sides as well to minimize recirculation.

Rosesbabe

Thanks for the suggestions thus far. I was on a real downer last night when I got home to find the electric fan wasn't running at all when I pulled up after seeing the engine running hot again. I was thinking this was now an ADDITIONAL problem I had to take care of and would impede my progress on finding the original issue. Did not have a chance to investigate further at the time, but after sleeping on it, I am now thinking that perhaps the in-line relay for the fan may be simply defective. If it switches the fan randomly off and on without consistency, my overheating could be as simple as that. I have just assumed the fan is running the whole time to-date. If I have time, I will check/replace the relay tonight and report back, but anyone think this is likely? Relay is aftermarket generic. It is very exposed to the hottest area under the hood. When I installed it, I had wondered if it should be attached to something solid and shielded from heat.

tveltman

Does the fan run when you turn the car off and leave the key in the ignition, and then turn off as soon as you remove the key (and also not run when the engine is hot like it is supposed to)? That was what my fan did, and that jumper fix solved the problem. Again, IDK if it is particularly useful to you, but presumably your fan must be getting some sort of information on the water temperature, and in that case, it could very well be the same issue. I didn't need to change any relays, and it's running fine and has been for some time. It may be worth investigating if this is the case.

76FJ55

How is the fan controlled? If it is off radiator temp you should verify that the rad is actually getting hot. If the thermostat is failing or the seal in the thermostat the coolant will recirc in the engine and not flow through the radiator. This would explain both the fan not running and the high engine temp. if you have a IR temp gun it would be good to get a few readings off the radiator to know for sure that you have good heat transfer from the engine to the radiator, and then concentrate on the heat trans from the rad to the air.

SharkSkin

Does the 85 even have the "fan runs after shutdown" feature? I didn't think it did.

With the key on, the fan should always run if you short the terminals in the connector at the lower front driver side of the radiator. If it doesn't, leave those terminals shorted while you investigate so the fan will come on when you find the problem.

david928

I had a similar overheating problem on my 87 S4.

There is a cooling control black box located under the carpet next to the passenger side door. I replaced this box and it solved my problem. To test this box, turn on the Air Conditioner and verify the fans come on at the same time. If not, this cooling control unit could be bad (or needs to be reset as described above).

I believe the fans will come on when parked independently of this box, because they use a different sensor.

Good luck.

SharkSkin

No such box on an 85.

Rosesbabe

The 928Motorsport electric fan install info is here:
ftp://70.226.52.38/installpdf/beltdrivefankit.pdf
if you are wondering how it is controlled and configured. It is completely seperate from any other controls (therefore should be a simple operation, and easy to troublewshoot, right?). So why would I have to beef up my fuse and wiring because it would trip on start up? I am in over my head.

Rosesbabe

Oops, link does not work, go here:
http://www.928motorsports.com/install.html
and hit the "Replacing the Belt Driven Fan Installation" near the bottom of page

tveltman

First, check all connections. Clean up the positive cables at the B-terminal and the ground point just behind it where you plugged the cables in. Be sure to clean ALL of those connections to ensure optimum contact, don't just clean one or two. I don't know how electrically experienced you are, so forgive me if this insults your intelligence, but you can clean the contacts simply by getting some sandpaper (I prefer emory paper since it's more durable) and rough up the metal connectors until they shine. Also check your wire tap. Personally I hate those damn things. They are not very resistant to vibration, and that may be your problem. No power to the fan = failure. I guess they used it so that the fan wouldn't come on with the ignition off (anti-lawsuit), but if I was to wire it for my own car, I would skip the vampire clip (the wire tap) and go to radio shack and get a connector that fit the SP plug and a simple ring-type connector and hook it straight up to the jump start terminal. Then your fan would have power all the time, and if your car was overheating and you turned off the engine, the fan would still run until the engine had cooled. Of course, beware that this might slaughter your battery if you have other random drains (which happens in these old cars). It's up to your judgement, but in my experience, that vampire clip is almost certainly your problem. Check the connection on it, or simply wire it differently. You can check continuity by sticking one end of the ohmmeter into the clip and touching the other lead to the terminal post (with the ignition on). If you get 0 resistance, you're golden, if you get a load of resistance, the clip connection is your problem. I don't know how much current the fan draws, but even a hundred or so ohms might be enough to screw up the control circuit.

The next thing I would check is the output of the temperature sender you installed in the upper radiator hose. It's unlikely that it failed, but it could be the culprit. I would guess that it is the same sender that porsche uses for the later model cars (though apparently without the plastic socket), and so if the car is at about 212 F (100 C), IIRC the resistance read off of the sender should be about 680 ohm. Look to see if there is any documentation with the fan that explains the sender specifications, as it may in fact be a different unit.

The next step to test is to test the logic of the control unit. I would suggest that you disconnect the wires from the temperature sender and jumper them together. This would make the sender "see" an extremely high temperature and automatically turn the fan on. If the fan doesn't turn on, then you probably need a new relay. It looks like from the instructions the relay is the only control unit you have, so at least replacement is straighforward. As for heat-sensitivity, you may be right. It is positioned right at the radiator inlet near the hose. Those hoses can get damn hot. You can go to radio shack (or some similar place) and get connector plugs that will mate with both the fan connector (FC) and the Switched Power (SP) plugs. Then just make longer jumper wires and run the sender out in front of the whole unit and zip tie it to something else, like maybe the AC unit (IDK if you have AC or even if the filling point is out in front like on the 88, so maybe that's crappy advice), or you could just run it into the fan shroud or behind the black plastic cover for the B-terminal jumping post.

Rosesbabe

Thanks tveltman, good suggestions - on my install I could not find a live wire from the ignition system to tap, (I had a previous post on this question) so did exactly what you suggested and connected with a ring connector directly to the terminal, which is why the fan continues to run on when I shut her down (see first description of problem). I am certain the power is there. I will jump the temp sensor to test the relay, but is a simple relay likely to "fail" by switching randomly and be the issue, or is this a possible red herring?

tveltman

Well, if you have wired it to have constant power, and the fan does come on, I would guess it would have to be the (unlikely) failure of the temperature sender. Since it works off of resistance, you might want to make sure the connections are good to the sender, and do try jumpering those two wires together. Whether the temp sender is defective or not, if the relay is functioning the way I think it should, the fans should come on, and in your case, the ignition won't even have to be on (the way to go, IMO). If you can make the fans turn on and off at will by jumpering those two sender wires together and then breaking the connection, then I would say that your problem must be at the sender. I'm sorry that you are nowhere near me, because I happen to have a spare temp sender that I thought was defective, but ended up testing good. The way I would test the sender is to remove it from the mounting sleeve and drop it in boiling water with the multimeter hooked up to the leads. If the resistance drops precipitously (like from 22kohm at room temperature down to about 700 in the boiling water), I'd say that the sender is probably good, and that the problem must be in the relay, although since I don't know anything about the relay's construction, I couldn't tell you what that problem might be. Fortunately, if it's an aftermarket relay, they should be pretty cheap at the local electronics/auto parts store. I will say that there is a small chance that the circuit is designed such that hooking it up to constant power will prevent proper operation. I am no electronics whiz, Alan is your guy there, but if I can get a wiring diagram and an ohmmeter I can figure out what is going on and fix it. If someone who knows more about circuitry in general wants to chime in, that would be helpful, because I am at the limit of my general knowledge here.

There is one other possibility. Are you certain that your thermostat is opening properly? The way the thermostat works is that it opens at the appropriate temperature and hits a rubber seal which diverts the water from circulating between the heads and out to the radiator. If your thermostat isn't opening, the water will continue to get pumped between the heads and won't ever get to the radiator, and thus won't trip the sender. You can test the thermostat the same way you can test the sender. Drop it in water on a stovetop. Use a meat thermometer to gauge when the water has reached 180 degrees F (83 C I believe), and a that point you should see the thermostat opening up. If it gets much past 180 and it isnt opening at all, you've got a defective thermostat. I think you mentioned that you already were satisfied with the thermostat and the seal in the water manifold, but it's worth repeating just in case, because you definitely don't want warped heads.

To answer the last bit about likelihood of failing relays, all electronics are designed with a max operating temperature. If the temperature is exceeded for a certain length of time (depends on how the max temp test was done), the electronic device is likely to fail owing to heat build-up. If the relay in question is not rated to withstand that sort of temperature it might encounter by being so close to the water hose, then I'd not be surprised if it failed. As to whether it is a red herring or not, if you are certain that the thermostat is opening, then I can't see what else it could be. The hot water heats up the temp sender, the current passing through the sender increases with the temperature, and presumably at some point is enough to trip the circuit and kick on the fans. What this means is that you have to be certain of the wires and connections as well as the sender and relay itself. If for some reason there is a load of internal resistance within the wires (probably a bad connection at the plug if this is the case, it's unlikely for the wires to be broken within the insulation), then that could DEFINITELY screw up the circuit functionality. I'm afraid it's going to be you and a multimeter getting real friendly with the fan wiring. If there is no discontinuity in the wires and the sender is working and the relay is switching properly, then I'll have to come up with a more exotic explanation, but at that point, I'd be making it up moreso than I am already!

Good luck and keep at it. I think the smart money is on the relay overheating, as those temperature senders are virtually bulletproof (I think they are just standard thermocouples, so there are no mechanical parts to fail, and they are sealed to prevent degradation. It's possible you got a bad one straight out of the box (electronics in general tend to fail either right out of the factory or not at all for many years), but if it's working now, then odds are it will work for the next fifty years.

Oh of course the relay failing out of the box is also a possibility, so if/when you get one, buy a spare if they aren't too expensive. It's extremely unlikely that you'll get a second or third bad one right out of the box, and if the second fails, it was probably the heat doing it. Plus, if it ever fails again, youll have an emergency spare you can keep in the glovebox so you won't be stranded on the side of the road. Personally, I'd relocate the relay just to be safe.


I re-read the thread and noticed that you had a fuse blowing problem. Did 928motorsports say anything about how much amperage the fan is supposed to draw? You may have an intermittent short that was blowing the fuse and preventing the fan from operating. Check to see if your 30A fuse has blown. It isn't particularly safe to put a higher-amp fuse in a location that specifies a lower rating since the wiring isn't necessarily designed to pass that much current and you can end up with a fire. Roasted shark ≠ fun.

Rosesbabe

tveltman,
This whole overheating thing has plagued me from the time I first purchased the car. I will go back further in time to give you a more complete picture + if you are interested, you can check my previous postings.
The PO installed an electric 928Motorsport fan poorly. My fix was to tie it more securely to the rad and on I went. Original fan did not have a relay in the circuit. Fan wires fried in a puff of smoke one day (phew, no fire) and I immediately contacted 928M to enquire what the issue may be + ordered another fan. No other problems reported by owners. I suspect now, that fuse installed was too high amperage and a large draw melted the wire. I assumed at that point that this large draw was due to the old fan having a worn bearing from a small wobble in it resulting from the fan hitting the rad due to the sloppy install.
I install the new fan (different make this time) complete with new temp sensor and harness, now with a relay in it and I found that I went through fuses like matches. Measured instantaneous draw on fan start and found it to be huge, but once running, the draw was small and ran great. Fixed by increasing wire size (didn’t want to fry them again!) and upped fuse from 25A to 30A. Damaged the original relay removing it from the harness, so bought a new generic one, with bayonet, from Napa with the same specs. Seemed to run fine for the longest time, until the system was recently tested by the traffic jam where the start of this thread began. I seriously doubt the temp sensor, like you say, no moving parts, and it is now the 2nd one in there. I will also check there is no air in this portion of the line that may have tricked it by filling reservoir+running heater. I will check the relay by tripping it and replace – almost certain this is the reason why the fan is not running now, since the fuse is good. The thermostat is an easy one - may just replace if I get it out, but will test old one also. I suspect I will get the fan going with a new relay and all will appear well again for a while. I would prefer to find the cause and fix it for good. Thanks for the great feedback.

Mrmerlin

did you ever replace the oil cooler thermostat and springs??

tveltman

I would move the relay for sure then. When the car is running, there may be enough air circulating in the engine compartment to keep the relay cool, but when it is standing still, as it is now it isn't held in the path of any moving air and is right near the hot hose.

Did you try jumpering the sender anyway? I know it isn't likely, but it could be the problem and its a 10-second test to save yourself from pulling your hair out. Also, Mrmerlin is always spot-on in my experience. TBH I didn't even know there was an oil cooler thermostat.

I think someone suggested getting an IR temp sensor and pointing it at various areas to check the temperature locally. If your radiator isn't heating up, it's the thermostat. If it is heating unevenly, it's probably a blockage in your radiator. If the water is circulating fine, and the fan is running as it should, and the oil thermostat isn't bad, I'd say you've got ghosts.

The other fix, if it is a problem with the fan control, is to wire up a secondary circuit to a switch. Use a two-position switch that can pass plenty of current, and wire one position into the normal relay-controlled circuit and the other directly from power to the fan. It's ghetto as all hell, and it ain't pretty, and I'd try to avoid doing it at all costs, but it will keep you safe. If you see the temp start to climb, throw the switch and kick on the fan. You should probably put a fuse in the direct line to be safe.

I guess the obvious has been checked already, but did you run the heater at all? I've had air trapped in the heater core get into the system and play havoc with the engine cooling. My money is still on the fan, because when you drive in normal traffic the engine is cool enough, but stopped it heats up. I'm also going to guess that you don't have a belly pan of any sort on the car. I don't on mine, so as far as I can tell it isn't that critical, and it allows you to run with your alternator uncovered/unducted, although there may be reduced amperage concerns in that setup. Seems like you're getting plenty of air across the radiator at speed but crappy air flow standing still. That's a classic bad fan symptom in my experience. Good luck, I know from my shark that overheating problems can be a real pain to fix, but you'll get there, probably when you replace and relocate that relay. Incidentally, does the fan come on when you turn the ignition to "on" but don't start the car?