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Discussion Starter · #1 ·
Please read before replying. I am a bmw tech for years, i've rebuilt multiple S62s, I know these cars inside and out.
This is my personal car that i have rebuilt the engine on(stock rebuild). Everything was down to bare block. Driven the car for 4000kms now. The car pulls hard as [email protected], no noises no issues, runs smooth as it should. Everything on the car is brand new. There is no item that hasn't been replaced during the rebuild. Everything was put on genuine BMW parts, not worldpac. There are no codes.
I have taken the car apart recently to recheck the cooling system, i have removed oil pan and oil pump to check if all is good, no issues found anywhere.

WHY THE [email protected] is my coolant temp at 105 celcius and oil temp 2-3mm to the right of the middle under normal driving when its cold outside. 8deg celcius. On the highway everything goes back to normal, ones i am in abit of traffic or street driving it starts climbing. I've had so many of these cars before, they should not be running this hot unless it's +30 degrees out. The fan clutch comes on i can hear it. The electric fan does not. I tested it and its dead but i don't think it should even come on when its this cold out.

I have no idea what to do. I'm about to sell the car, this is driving me crazy. IF anyone has experienced something like this please let me know. THANKS. PIC of my car.
 

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Um. I think the answer is in your post.
The fan clutch doesn't do the main portion of the cooling. It's the electric aux fan that does the vast majority of the cooling when stationary.
When you are moving, it would be the air blowing to the radiator that cools the car.

Did you pull the codes? Any aux fan codes? Or just test if the aux fan functions by turning on the AC. AC fan should start within some time.
If it doesn't, your aux fan is dead.

Don't have access to ISTA right now, but at the temperature you are reporting right now, the aux fan should be working regardless of ambient temp.

Cheers,
Gabe

--- EDIT ---
Ok. No codes.. that's weird. But the test procedure should still be the same.
 

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Discussion Starter · #3 ·
Um. I think the answer is in your post.
The fan clutch doesn't do the main portion of the cooling. It's the electric aux fan that does the vast majority of the cooling when stationary.
When you are moving, it would be the air blowing to the radiator that cools the car.

Did you pull the codes? Any aux fan codes? Or just test if the aux fan functions by turning on the AC. AC fan should start within some time.
If it doesn't, your aux fan is dead.

Don't have access to ISTA right now, but at the temperature you are reporting right now, the aux fan should be working regardless of ambient temp.

Cheers,
Gabe

--- EDIT ---
Ok. No codes.. that's weird. But the test procedure should still be the same.
thanks, yeah the aux fan doesnt activate with ista. I got a new aux fan coming monday. Last resort.
 

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The fan clutch doesn't do the main portion of the cooling. It's the electric aux fan that does the vast majority of the cooling when stationary.
It's the other way around. The fan clutch is the main fan at idle and low speeds. The aux fan is....auxiliary. Only kicks in when the fan clutch can't keep up and when AC is on.

What coolant are you using? And mix ratio?
Which thermostat did you install? It could possibly be defective. They usually fail open, but I've seen a couple fail closed and raise both temps like in your situation.
Might want to try doing a combustion leak test.
 

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It's the other way around. The fan clutch is the main fan at idle and low speeds. The aux fan is....auxiliary. Only kicks in when the fan clutch can't keep up and when AC is on.

What coolant are you using? And mix ratio?
Which thermostat did you install? It could possibly be defective. They usually fail open, but I've seen a couple fail closed and raise both temps like in your situation.
Might want to try doing a combustion leak test.
Oh I must have mistaken. Sorry for the wrong info.
105 rings a bell to me btw. The M62 thermostat is a 105 degree one. Maybe used the wrong thermostat?

- Gabe
 

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It's the other way around. The fan clutch is the main fan at idle and low speeds. The aux fan is....auxiliary. Only kicks in when the fan clutch can't keep up and when AC is on.
That is so wrong! On the M5 the aux fan is the primary cooler and the mechanical fan is secondary. That is obvious if you just look at the activation temp and compare it to a 540. The M5 activation is a higher temp, and when you consider the operating temps of the two motors, one would say it is considerably higher. That is the OPs most likely problem short of some odd mistake on assembly.
 

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Discussion Starter · #9 ·
Oh I must have mistaken. Sorry for the wrong info.
105 rings a bell to me btw. The M62 thermostat is a 105 degree one. Maybe used the wrong thermostat?

- Gabe
M62 has nothing to do with S62. Two completely different engines. S62 runs a different cooling system lower temp thermostat. Read the everything please. Its a genuine bmw thermostat, very low chances of it being defective. Don't confuse people with your 540 stuff, its irrelevant here.
 

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Discussion Starter · #10 ·
That is so wrong! On the M5 the aux fan is the primary cooler and the mechanical fan is secondary. That is obvious if you just look at the activation temp and compare it to a 540. The M5 activation is a higher temp, and when you consider the operating temps of the two motors, one would say it is considerably higher. That is the OPs most likely problem short of some odd mistake on assembly.
yeah new aux fan coming monday. last chance
 

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This all of a sudden turned into a technical thread and now I'm super confused.
Two very reliable sources of the forum is giving the complete opposite info 🤪

Anyways, I don't think the technicality is super important. To my knowledge, the list of thing that can cause overheating on this engine is not that long.
What's important is that Shafro and Sailor's diagnosis yields the same test procedure.

Cheers,
Gabe
 

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fan clutch does the main cooling especially low speed (its in the puller position on the rad), had both failures and you can definitely cant drive with just electric fan but can with mechanical clutch. the electrical fan kick on iirc 86-88c to assist the clutch fan.
 

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This all of a sudden turned into a technical thread and now I'm super confused.
Two very reliable sources of the forum is giving the complete opposite info 🤪
Yeah, I don't know what happened there. He quoted your username, but with my words. Not sure which he was trying to rebut.

Here's exactly what I said via TIS. It's same thing with any other fan clutch engine



you can definitely cant drive with just electric fan but can with mechanical clutch. the electrical fan kick on iirc 86-88c to assist the clutch fan.
Exactly. Aux fan failure is pretty common on these cars now with age and miles. A lot of cars still run without overheating (E46, E36, etc.)

Its a genuine bmw thermostat, very low chances of it being defective.
It can happen. I've seen it and both oil and coolant needles would start swinging to the right.
 

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I've had a similar issue this year, but my aux fan does work. I can confirm Shady/others are correct in that the aux fan does more. While trying to diagnose, I drove the car for an entire day this fall (mid 60's F) without the mechanical fan installed. I had pretty much the same operating temps in slower speed driving. It gets into the low 90's C. I'm sure it would go higher if I kept idling and moving too slow to move enough air across the radiator.

Turns out my issue is the radiator, which I was suspecting even though it's only 7-8 years old. Not enough flow at low speed and idle in traffic. I had already removed it and cleaned debris at the end of summer. It helped a bit but now I have the smoking gun - the radiator started to distort - it expanded the core. Internal clogging is my guess.

Since you're going to replace the fan, you'll have a chance to review the radiator condition. If you're hitting over 100C, you might suspect more than just the aux fan. As you know, best to replace one thing at a time though.
 

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I've had a similar issue this year, but my aux fan does work. I can confirm Shady/others are correct in that the aux fan does more. While trying to diagnose, I drove the car for an entire day this fall (mid 60's F) without the mechanical fan installed. I had pretty much the same operating temps in slower speed driving. It gets into the low 90's C. I'm sure it would go higher if I kept idling and moving too slow to move enough air across the radiator.

Turns out my issue is the radiator, which I was suspecting even though it's only 7-8 years old. Not enough flow at low speed and idle in traffic. I had already removed it and cleaned debris at the end of summer. It helped a bit but now I have the smoking gun - the radiator started to distort - it expanded the core. Internal clogging is my guess.

Since you're going to replace the fan, you'll have a chance to review the radiator condition. If you're hitting over 100C, you might suspect more than just the aux fan. As you know, best to replace one thing at a time though.
Hmm. A soft failing radiator. I'll keep this in mind as my cooling system isn't quite as good.
 

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Here's exactly what I said via TIS. It's same thing with any other fan clutch engine
Regardless of what that general statement says, there is a BMW statement that it does not work the same as other BMWs. It might be in the techs introduction manual, not going to waste my time looking. It has been posted here 100s of times. So use your brain and think it through. The M62 operates 25 degrees hotter than the S62. The engagement for mechanical fan for the S62 should be less than the engagement temp on the M62. It is not it is ~15 degrees hotter from bad memory but none the less it is hotter. Albeit the temp of the exhaust air is different than reading the output temp of the coolant. This part seems to be the same on all cars. Clearly with the higher temp engagement on the fan it does not work the same as the other models in that statement which all share the same engagement clutch.
 

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Everything was put on genuine BMW parts, not worldpac.
OP you need to do some other things before you throw your new fan in. Before the recall this was the fan that was catching on fire. It does not catch fire anymore but it still burns up which causes big loads on the electrics. The failure starts by taking out the slow speeds then at the end there is often a large surge which burns the rest. There is a fuse behind the fuse panel in the glove box that has a 50/50 chance of being burned up. Then the wires from that fuse have been heated so badly that the insulation gets hard and can fail.
You might want to take the old fan apart and see how bad it burned up. To give reference this was mine and the fuse was blown and eventually I found a short piece of wire that needed to be replaced but not much. Others have reported much worse where the whole wire needed to be replaced. The fan will still look spotless on the outside.
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This is a thread I started a long time ago and although it is not helpful there are a couple of great linked threads in it. The one thing that you can grasp from it is all the technical writing can't be trusted. From the fan that should have been in the car to the temp of engagement of the mechanical fan. Also the wiring in the WDS. The wiring diagram from this thread should work for all cars delivered to CAN(all CAN car have the cold weather package, might be why they don't follow the standard info), if yours is a US car it maybe different.
The aux fan should be running 100% of the time(except turns off at a specific road speed) when the AC is on and if yours has not that might have helped cause the heat to climb.
It is climate dependent, in my neck of the woods the mechanical fan may never turn on, likely do to colder ambient air temps.
 

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OP you need to do some other things before you throw your new fan in. Before the recall this was the fan that was catching on fire. It does not catch fire anymore but it still burns up which causes big loads on the electrics. The failure starts by taking out the slow speeds then at the end there is often a large surge which burns the rest. There is a fuse behind the fuse panel in the glove box that has a 50/50 chance of being burned up. Then the wires from that fuse have been heated so badly that the insulation gets hard and can fail.
You might want to take the old fan apart and see how bad it burned up. To give reference this was mine and the fuse was blown and eventually I found a short piece of wire that needed to be replaced but not much. Others have reported much worse where the whole wire needed to be replaced. The fan will still look spotless on the outside.
View attachment 956556 View attachment 956557
This is a thread I started a long time ago and although it is not helpful there are a couple of great linked threads in it. The one thing that you can grasp from it is all the technical writing can't be trusted. From the fan that should have been in the car to the temp of engagement of the mechanical fan. Also the wiring in the WDS. The wiring diagram from this thread should work for all cars delivered to CAN(all CAN car have the cold weather package, might be why they don't follow the standard info), if yours is a US car it maybe different.
The aux fan should be running 100% of the time(except turns off at a specific road speed) when the AC is on and if yours has not that might have helped cause the heat to climb.
It is climate dependent, in my neck of the woods the mechanical fan may never turn on, likely do to colder ambient air temps.
Without access to INPA is there a way to test the aux fan direct outside of the care. Example checking a spare used?
 
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