diagnosing and fixing aux fan... or more?

E28 technical advice asked and given! Troubleshooting, modifications and more.
Mashford
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diagnosing and fixing aux fan... or more?

Post by Mashford »

Hey Folks,

Since I reinstalled recently the instrument cluster with new batteries (probably not related to this problem, just context), I had to replace the clutch main cylinder, (should have taken others' advice to do that when I went to the trouble of removing, replacing broken elbow connector, and reinstalling), and, at the same time as clutch main failed, the engine started overheating. I was "done' with the clutch work, so took it to a reliable shop and asked to check the overheating. They fixed the clutch and said the over-heating was due to disconnected hose. But it's now still overheating. I think the hose "popped" because it was close to red on dash temp gauge (boiling) and I just pulled over in time to cool off and get a tow (because, at that time, the clutch cylinder went bust, too). So, the mechanic reconnected the hose and checked the water pump and said "all good" on overheating. I guess he didn't take a long test drive, because it is still overheating.

So, I read as many threads as I could to start diagnosing further and landed with Bentley's prescription to check the auxiliary fan. To be honest, I didn't want to get a remote thermometer "gun" and check all the temps, which was the start of the most detailed diagnostic process I found on the forum. Bentley's tells me to disconnect and jump the auxiliary fan switches (the white "low temp" and the red "high temp") shown in the photo here, and if they work on jump, it means the switch is broken. I jumped both switches (see photo} and the aux fan worked at both speeds as per connection, so I bought and installed a new "low" switch (the white one) because Bentley's didn't say whether to replace one or both switches, and upon googling around, only the white one popped up as the "radiator temperature switch" for an 87 535is.

I test drove tonight, and it is still overheating and when I opened the hood in driveway with engine hot, the auxiliary fan had not switched on. The gauge was close to red and the coolant overflow tank was close to boiling. I thought perhaps I had the new aux fan switch connectors reversed, so with engine on, I switched the connectors on the replaced "low temp" switch. Still no auxiliary fan.

Does anyone have any suggestions at this stage? Would be most grateful. Seems to me it that somehow the aux fan is not being "told" to switch on, and is the source of the overheating. Should I get a "red" switch, too, the "high temp" switch, to make it work again, because it could be both switches have failed? Something else?

Thank you!!!

Image
Shawn D.
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Re: diagnosing and fixing aux fan... or more?

Post by Shawn D. »

You might not want to get an IR temp gun, but without that (or some other temperature-indicating device), you will not know if the switches are getting hot enough to trigger.

The temp gauge can be in the red and the car boiling over and the switches can still not be triggered. How so? If the radiator is clogged/plugged in the top portion, the coolant can be cool enough at the switches even when the car is overheating. I learned this the long and hard way when my "new" to me '86 had the issue that you're having now, except this was in '92, before most of the internet and of course before MyE28. I never suspected the radiator on a car that was only six years old with 75K on it had a clogged radiator, but it did.

My bet is you have a bad radiator.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Shawn D. wrote: Feb 15, 2023 10:14 PM You might not want to get an IR temp gun, but without that (or some other temperature-indicating device), you will not know if the switches are getting hot enough to trigger.

The temp gauge can be in the red and the car boiling over and the switches can still not be triggered. How so? If the radiator is clogged/plugged in the top portion, the coolant can be cool enough at the switches even when the car is overheating. I learned this the long and hard way when my "new" to me '86 had the issue that you're having now, except this was in '92, before most of the internet and of course before MyE28. I never suspected the radiator on a car that was only six years old with 75K on it had a clogged radiator, but it did.

My bet is you have a bad radiator.
OK, I hear you. But why does Bentley's say that if the main hose to the radiator gets hot as engine warms up, which it did, then the radiator is not clogged? I am ok doing the heat gun test if have to.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Is it because the hot coolant is not getting to the smaller, secondary radiator behind the aux fan?
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Mashford wrote: Feb 15, 2023 11:24 PM Is it because the hot coolant is not getting to the smaller, secondary radiator behind the aux fan?
Or is that “secondary” radiator the transmission fluid cooler?
Mike W.
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Re: diagnosing and fixing aux fan... or more?

Post by Mike W. »

Shawn wrote it out before I saw the post, I concur.

There is no second or aux radiator. I suspect what you're seeing is the A/C condenser which is between the aux fan and the radiator. The switches won't turn the fan on because the coolant is cool at the switches, just not enough flow to cool the engine. Probably. Why doesn't the manual say anything? Because even a good manual knows less than a good mechanic.

Start it up, get it good and hot. Shut it off. Then reach in and feel the radiator, it should feel hot, the core, everywhere you feel it. Cold spots mean low or no flow. Now it's also possible you are getting a faulty reading on the temp gauge, that happens, but since you're blowing a hose off it would suggest not.

But even there somethings wrong, a hose should not blow off, the radiator cap should vent first, long before the hose blows off. Which hose is it?
Ju@n
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Re: diagnosing and fixing aux fan... or more?

Post by Ju@n »

I agree that a clogged radiator, or a faulty headgasket introducing air in the system could be causing your issue.
But first, I'd say that you don't need an aux fan for the car not to overheat, the viscous clutch fan should be enough, so I'd look that way before.
Shawn D.
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Re: diagnosing and fixing aux fan... or more?

Post by Shawn D. »

Mashford wrote: Feb 15, 2023 11:21 PM OK, I hear you. But why does Bentley's say that if the main hose to the radiator gets hot as engine warms up, which it did, then the radiator is not clogged? I am ok doing the heat gun test if have to.
I didn't think I needed to be this specific, but when I say "clogged," I mean it only has partial flow. Think of a sink that's clogged. Does that mean the water doesn't drain at all? No, the word does not mean that.

Bentley is apparently stating a false dichotomy that radiators are either "not clogged" (100% flow) or "clogged" (0% flow).
Shawn D.
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Re: diagnosing and fixing aux fan... or more?

Post by Shawn D. »

Mashford wrote: Feb 15, 2023 11:32 PM
Mashford wrote: Feb 15, 2023 11:24 PM Is it because the hot coolant is not getting to the smaller, secondary radiator behind the aux fan?
Or is that “secondary” radiator the transmission fluid cooler?
Mike has already explained it, but the order of flow is aux electric fan > condenser > radiator > mechanical fan. There's no "secondary radiator" and the transmission fluid cooler is in the cold side tank of the radiator (not to be too harsh, but it should be obvious by looking at where the transmission fluid lines connect).
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Shawn D. wrote: Feb 16, 2023 10:15 AM
Mashford wrote: Feb 15, 2023 11:32 PM
Or is that “secondary” radiator the transmission fluid cooler?
Mike has already explained it, but the order of flow is aux electric fan > condenser > radiator > mechanical fan. There's no "secondary radiator" and the transmission fluid cooler is in the cold side tank of the radiator (not to be too harsh, but it should be obvious by looking at where the transmission fluid lines connect).
Thanks for your patience all around. As embarrassing as it is to admit, dumbing it down helps me alot. I now understand the nuance of "clogged". :roll:

I ordered a temperature gauge, so I can do a more thorough assessment of the radiator.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Mike W. wrote: Feb 16, 2023 12:03 AM But even there somethings wrong, a hose should not blow off, the radiator cap should vent first, long before the hose blows off. Which hose is it?
Thanks, Mike W. for your patience too. I didn't ask the mechanic which hose "blew", and I tend to hyperbole when tired, like last night in posting. I recall now he said a hose was "loose" and he tightened, and checked the pump, then assumed all was well. The vent hose on the reservoir, close the rad cap, has been taking pressure off (and releasing a lot of fluid), when it has been overheating, so that seems to be working fine.

As noted in response to Shawn D., I will get the temperature gun and do more diagnostics. I don't think I have head gasket leak, but will look for signs / diagnose that, too. My suspicion is the radiator is clogged at this point.

While I am here: do you have any views on trying to chemically clean and flush the radiator if I find clogs? It seems like something that would only buy some time, but it is suggested in Bentleys.

:thanks:
Mike W.
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Re: diagnosing and fixing aux fan... or more?

Post by Mike W. »

Mashford wrote: Feb 16, 2023 1:26 PM I will get the temperature gun and do more diagnostics.
Good. They're inexpensive and I find handy for a variety of things.
While I am here: do you have any views on trying to chemically clean and flush the radiator if I find clogs? It seems like something that would only buy some time, but it is suggested in Bentleys.

:thanks:
Someone was recently saying vinegar works well, I've heard of citric acid also. While I've never used either of them, I have used commercial over the counter stuff over the years which had a grand total of zero success, so I wouldn't get my hopes up too high. I'm a cheapskate, but also paranoid about overheating that big long aluminum head and warping it, so I'd just buy a new radiator. Either the correct one or an E36 one which has been documented some here and can be very inexpensive.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

BTW — just checked my records and radiator is a 2011-build Behr from South Africa and was installed in October 2012. 10+ years old. Suspect it’s time to replace.
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Re: diagnosing and fixing aux fan... or more?

Post by gadget73 »

if its plugged with hard water scale, a mild acid may help. Cleaning vinegar or citric acid, don't really think it matters all that much. Pull the radiator, wash it out as best you can with a hose, lay it flat, fill it with whatever you are using and let it sit for a day. It will fizz a bit if the acid is eating the lime scale. This may still be a complete waste of time depending on how bad it is, or it might dissolve out some paper-thin metal and create a leak.
Mike W.
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Re: diagnosing and fixing aux fan... or more?

Post by Mike W. »

The South African ones do not have a good reputation, people who work them hard seen to find them marginal at best even when new. All the more reason to just buy a new one.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Mashford wrote: Feb 16, 2023 6:08 PM BTW — just checked my records and radiator is a 2011-build Behr from South Africa and was installed in October 2012. 10+ years old. Suspect it’s time to replace.
I bought a remote temp sensor (temp gun) and took readings with engine hot. The gauge was about 3/4 to red zone at the time.

Standing in front of the engine compartment, the temp on the large diameter hose running from engine to the top right corner of radiator was 200 at the engine and 185 near clamp on the radiator. The radiator was 180 -- spotting off of the fins -- at the top right corner where large diameter hose was coming in, and 117 in top left corner. The bottom of the radiator was between 50 and 55 going across across. The (out-take?) hose at the bottom left corner which comes back up to the engine was 75 coming off the radiator. The short large diameter hose connecting from top of engine and curling down to the water pump -- next to the main longer hose where I started this list -- was 190.

Other information:
  • the expansion tank was clearly under pressure, with coolant level close to the top (not boiling though)
  • the auxiliary fan does come on when I push a/c button on dash
  • as mentioned earlier, the aux fan also comes on when jump the low and high temp switches
  • I smell coolant (not too strong) when I run the cabin heater
  • not sure this matters and I just can't remember, but with blower and heat on in the cabin, and the fresh air slider closed, there is no air coming out of the mid-level vents on the dash, only the at the defrost (windshield) and the footwell -- why do I think the mid-level vents should also blow hot when cabin temp is set high and blower is on high? There is no flow in that setting. The mid-level vents <<do>> blow outside air when I move the middle, fresh air, slider to the right
Not sure exactly how to interpret all this, but the temperature readings do seem to indicate that coolant is not flowing from top to bottom of the radiator. Are there any other readings I could get to help inform the process?

Thank you for any suggestions or insights at this stage.
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Re: diagnosing and fixing aux fan... or more?

Post by Mike W. »

Mashford wrote: Feb 18, 2023 4:12 PM
Mashford wrote: Feb 16, 2023 6:08 PM BTW — just checked my records and radiator is a 2011-build Behr from South Africa and was installed in October 2012. 10+ years old. Suspect it’s time to replace.
I bought a remote temp sensor (temp gun) and took readings with engine hot. The gauge was about 3/4 to red zone at the time.

Standing in front of the engine compartment, the temp on the large diameter hose running from engine to the top right corner of radiator was 200 at the engine and 185 near clamp on the radiator. The radiator was 180 -- spotting off of the fins -- at the top right corner where large diameter hose was coming in, and 117 in top left corner. The bottom of the radiator was between 50 and 55 going across across. The (out-take?) hose at the bottom left corner which comes back up to the engine was 75 coming off the radiator. The short large diameter hose connecting from top of engine and curling down to the water pump -- next to the main longer hose where I started this list -- was 190.
I think you have right and left reversed, but yes, it confirms a very restricted radiator, and also tells you why the aux fan isn't coming on, it's nowhere near the 195F of the low speed switch.

Other information:
  • the expansion tank was clearly under pressure, with coolant level close to the top (not boiling though)
  • the auxiliary fan does come on when I push a/c button on dash
  • as mentioned earlier, the aux fan also comes on when jump the low and high temp switches
  • I smell coolant (not too strong) when I run the cabin heater
That suggests a leaky heater core. You shouldn't put any sealant in the coolant, but I limped mine along for 100K by using about a tablespoon of Prestone Super Seal every year or two. NOT the whole bottle, just a little bit. On the other hand, that could be why it's plugged if someone dumped a bunch of stop leak in there. The heater core is of course replaceable, but it's also a PITA. BTDT, it's like the car is built around it.
  • not sure this matters and I just can't remember, but with blower and heat on in the cabin, and the fresh air slider closed, there is no air coming out of the mid-level vents on the dash, only the at the defrost (windshield) and the footwell -- why do I think the mid-level vents should also blow hot when cabin temp is set high and blower is on high? There is no flow in that setting. The mid-level vents <<do>> blow outside air when I move the middle, fresh air, slider to the right
That's as it should be. The idea is so you can stay awake with cool, fresh air, but still comfy warm with heat at your feet and a clear windshield. It's mostly a European car thing, why domestic and Asian makes only provide one temp at all vents is just dumbfounding to me.

Not sure exactly how to interpret all this, but the temperature readings do seem to indicate that coolant is not flowing from top to bottom of the radiator. Are there any other readings I could get to help inform the process?

Thank you for any suggestions or insights at this stage.
Terminology. It's a crossflow radiator, coolant moves from the drivers side across to the passenger side, so you're looking at right and left temps, not up and down.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Thanks, Mike W. Seems pretty clear I need a new radiator and will order one. Meanwhile, When I say “right” I mean driver side and the radiator was in fact hotter at the top than the bottom, not moving right to left, reading off the fins. I am not sure it matters, but will do again tomorrow for good measure and send some photos.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Here are pictures with temp gauge and laser reading. I think they are self-explanatory.

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If you, Mike W., or others have any further certainty about the current diagnosis -- that I need a new radiator -- or other thoughts, please let me know.

Thank you!
Shawn D.
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Re: diagnosing and fixing aux fan... or more?

Post by Shawn D. »

Yep, looks as if a new radiator is in order. Your temp readings confirm why the switches aren't triggering the aux fan.

BTW, read this from the Tech FAQ: No Heat From Dash Vents.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Shawn D. wrote: Feb 20, 2023 9:58 AM Yep, looks as if a new radiator is in order. Your temp readings confirm why the switches aren't triggering the aux fan.

BTW, read this from the Tech FAQ: No Heat From Dash Vents.
Thank you, Shawn D. Nice schematic, too! I have been pondering whether or not I should try to repair / rebuild the a/c. The priorities shift when things like clutch main failure and radiator clog pop up! 😅

But the engine is running like a top, as always, and my interior is looking nice due to recent deep clean. 😁

Labors of love.
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Got the new radiator:

Image

Question/advice: Bentleys says to open the engine block coolant drain plug, too, when replacing the radiator. It says the plug is under cylinder 6 on the driver's side. I cannot get a visual on this plug from above or below and wonder how critical it is. It look like I would have to remove some things to get to it, air intake?

Thanks for any tips.
Aldo525
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Re: diagnosing and fixing aux fan... or more?

Post by Aldo525 »

Mashford wrote: Mar 02, 2023 9:06 AM Got the new radiator:


Question/advice: Bentleys says to open the engine block coolant drain plug, too, when replacing the radiator. It says the plug is under cylinder 6 on the driver's side. I cannot get a visual on this plug from above or below and wonder how critical it is. It look like I would have to remove some things to get to it, air intake?

Thanks for any tips.
Block drain plug is located on right side, not driver's side, under cylinder 5 or 6 in M30 engines. It is the same kind of plug as maybe you have at thermostat housing. When I remove and replace that plug a lot of rust and "things" came out from that drain. But if you remove the plug be sure on have a new one (with washer) as in my case had just one thread left because the corrosion....
Mashford
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Re: diagnosing and fixing aux fan... or more?

Post by Mashford »

Aldo525 wrote: Mar 02, 2023 9:51 AM Block drain plug is located on right side, not driver's side, under cylinder 5 or 6 in M30 engines. It is the same kind of plug as maybe you have at thermostat housing. When I remove and replace that plug a lot of rust and "things" came out from that drain. But if you remove the plug be sure on have a new one (with washer) as in my case had just one thread left because the corrosion....
Thanks! Was wondering if it was an M30 thing.
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Re: diagnosing and fixing aux fan... or more?

Post by vinceg101 »

Finding this thread now:
-Nissens over the S.A. Behr. I had erratic behavior with my engine temps over several long road trips with a S.A. unit before changing it out with a Nissens early last year. Night and day performance for the better. Many discussions about Behr's change in the internal design which makes them poorer than even before (round vs. flat internal circulation tubes). So I would say you chose correctly in your purchase.

-Block Flushing: Normal cooling system maintenance is a cooling fluid replacement every 12-24 months depending on usage (although you can probably stretch that to 30 months). Flushing the block is the most thorough way to accomplish this. 'Flushing' doesn't necessarily mean a mechanical method (e.g. pressure hose), but just repeated filling, running the engine, and draining with distilled water, then wash-rinse-repeat 2 or 3 times until there is no evidence of coolant anywhere. Run the heater and A/C during this process to circulate any coolant residing in the heating system.
The block drain is a bit tough to find at first and is not terribly convenient to access as it sits up above the passenger side front axle system and front subframe. It's also just below the exhaust manifold and downpipes. As such it's a bit of a hot mess when you open it as all that hot coolant will spill out over everything (including yourself).
You can see it here in this photo: notice the brass valve (Fumoto Valve) I installed on mine to make the whole flush process much easier. It's just in front of the transmission bellhousing:
Image
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